June 2025

Oceanography

THE OFFICIAL MAGAZINE OF THE OCEANOGRAPHY SOCIETY

VOL. 38, NO. 2, JUNE 2025

Video of a thin black smoker chimney spire, part of the Godzilla/Bambi complex in the northern part of the

High Rise Vent Field on Endeavour Ridge, Northeast Pacific Ocean. Jump to page 10 to read the full article

by Mihály et al. Video courtesy of Ocean Networks Canada

June 2025 | Oceanography

10

40

24

36

3 QUARTERDECK. What Do Cuts to US Science Mean for Oceanography

By E.S. Kappel

5 PERSPECTIVE. Setting a Course for Research on Offshore Wind

Development Impacts Near Nantucket Shoals

By G. Gawarkiewicz

7 PERSPECTIVE. Zooplankton and Offshore Wind: Drifters in a Sea

of Uncertainty

By G.K. Saba

10 FEATURE ARTICLE. Scientific Research and Marine Protected

Area Monitoring Using a Deep-Sea Observatory: The Endeavour

Hydrothermal Vents

By S.F. Mihály, F.C. De Leo, E. Minicola, L. Muzi, M. Heesemann, K. Moran,

and J. Hutchinson

24 FEATURE ARTICLE. How Do Tides Affect Underwater Acoustic Propagation?

A Collaborative Approach to Improve Internal Wave Modeling at Basin to

Global Scales

By M.C. Schönau, L. Hiron, J. Ragland, K.J. Raja, J. Skitka, M.S. Solano, X. Xu,

B.K. Arbic, M.C. Buijsman, E.P. Chassignet, E. Coelho, R.W. Helber, W. Peria, J.F. Shriver,

J.E. Summers, K.L. Verlinden, and A.J. Wallcraft

36 FEATURE ARTICLE. From Wind to Whales: Potential Hydrodynamic Impacts

of Offshore Wind Energy on Nantucket Shoals Regional Ecology

By E.E. Hofmann, J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-Gutbrod,

D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig

40 FEATURE ARTICLE. Overview of the Atlantic Deepwater Ecosystem

Observatory Network

By J.L. Miksis-Olds, M.A. Ainslie, H.B. Blair, T. Butkiewicz, E.L. Hazen, K.D. Heaney,

A.P. Lyons, B.S. Martin, and J.D. Warren

52 FEATURE ARTICLE. Exploring Climate Change, Geopolitics, Marine

Archeology, and Ecology in the Arctic Ocean Through Wood-Boring Bivalves

By J. Berge, T. Bakken, K. Heggland, J.-A. Sneli, Ø. Ødegård, M. Ingulstad, T. Thun,

and G. Johnsen

contents VOL. 38, NO. 2, JUNE 2025

June 2025 | Oceanography

Oceanography | Vol. 38, No. 2

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58 MEETING REPORT. Community Recommendations on Belonging,

Accessibility, Justice, Equity, Diversity, and Inclusion Initiatives in Ocean

Sciences: A Town Hall Discussion

By J.T. Middleton, S. Clem, K.L. Gallagher, E. Meyer-Gutbrod, A.A. Sefah-Twerefour,

M.H. Serres, M. Behl, and J. Pierson

66 DIY OCEANOGRAPHY. The PIXIE: A Low-Cost, Open-Source, Multichannel

In Situ Fluorometer Applied To Dye-Tracing in Halifax Harbor

By K. Park, D. Atamanchuk, A. MacNeil, and V. Sieben

73 OCEAN EDUCATION. Hands-On Post-Calibration of In Vivo Fluorescence

Using Open Access Data: A Guided Journey from Fluorescence to

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83 THE OCEANOGRAPHY CLASSROOM. TAP: Teaching Analysis Poll for

Student Feedback

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86 BOOK REVIEW. A Philosophical View of the Ocean and Humanity, Second

Edition, by Anders Omstedt

Reviewed by E. Coleman

88 CAREER PROFILES. Lilian (Lica) Krug, Scientific Coordinator, Partnership

for Observation of the Global Ocean • Flávia M. Guebert, Director, Coral

Vivo Project

66

73

ON THE COVER

A thin black smoker chimney spire,

part of the Godzilla/Bambi complex in

the northern part of the High Rise Vent

Field on Endeavour Ridge, Northeast

Pacific Ocean. Video courtesy of

Ocean Networks Canada

Oceanography | Vol. 38, No. 2

June 2025 | Oceanography

A lot has already been published about the how the current and

anticipated steep reductions in US federal funding for science,

along with reductions in staffing at federal agencies, will affect

the scientific enterprise, though not all the collateral damage has

been picked up in news stories nor assessed (e.g., Flannery, 2025;

Garisto, 2025; Harvey, 2025; Wadman, 2025). From my perch,

as editor of Oceanography, I’ve been thinking about what fed­

eral funding cuts might mean for scientific publishing, and for

this journal in particular. For decades, US federal agency sup­

port has been vital to the long-term health of Oceanography

and our ability to openly share critical research on a wide vari­

ety of ocean science related topics. Many special issues and indi­

vidual articles have been used as a basis for undergraduate and

graduate classroom instruction and discussions as well as to

inform policymakers.

Federal support has also enabled us to publish two special

issues on Women in Oceanography and more recently a special

issue on Building Diversity, Equity, and Inclusion in the Ocean

Sciences. Three federal agencies supported this year’s special

issue on A Vision for Capacity Sharing in the Ocean Sciences.

These landmark special issues are contributing in various ways

to inspiring the careers of our next generation of ocean scientists,

who are vital to the continued health of our field. Importantly,

special issue sponsorship means that no authors pay publication

fees, allowing scientists from under-resourced nations or others

who may not have large research grants to fully participate. This

sponsorship also enabled The Oceanography Society (TOS), the

publisher of Oceanography and a nonprofit organization, to pro­

vide full open access to articles long before it was fashionable, or

even required, for scientific journals.

From the beginning, Oceanography’s mission has been to

communicate across disciplines in the ocean sciences—a dif­

ferent but complementary objective from other, more techni­

cal journals in our field. The aspiration is that special issues and

individual articles that are accessible to all ocean scientists, and

contributed by the global community, may spur new collabora­

tions or provide new insights that will advance the field. While

Oceanography will continue to pursue its mission by publish­

ing special issues as the situation permits, there will likely be

fewer in the future unless sponsorship opportunities with other

US-based organizations as well as groups outside of the United

States arise. Instead, we will publish more “regular” (unspon­

sored) issues that are based on unsolicited manuscripts (e.g., this

June 2025 issue; see also the September 2024 issue).

I highly encourage TOS members to check out our Author

Guidelines for instructions on how to submit a manuscript

to Oceanography and to share those guidelines with your col­

leagues. If you are unsure whether a topic might be of interest to

us, please contact one of the associate editors and discuss your

idea. Your articles, whether published in a regular or special

issue, are vital to communication among ocean scientists and

the continued health of Oceanography.

WHAT DO CUTS TO US SCIENCE

MEAN FOR OCEANOGRAPHY?

Ellen S. Kappel, Editor

REFERENCES

Flannery, M.E. 2025. “Scientific Research is Getting Cut—And That Should Scare All Americans.” neaToday, March 5, 2025, https://www.nea.org/nea-today/all-news-articles/

scientific-research-getting-cut-and-should-scare-all-americans.

Garisto, D. 2025. “Trump Moves To Slash NSF: Why Are the Proposed Budget Cuts So Big?” Nature, June 5, 2025, https://doi.org/10.1038/d41586-025-01749-x.

Harvey, C., 2025. “Trump Takes a Giant ‘Wrecking Ball’ to US Research.” E&E News, February 18, 2025, https://www.eenews.net/articles/trump-​takes-​giant-​wrecking-​

ball-​to-​us-​research/.

Wadman, M. 2025. “National Academies, Staggering From Trump Cuts, on Brink of Dramatic Downsizing.” Science, June 2, 2025, https://doi.org/10.1126/science.z4wjf7q.

ARTICLE DOI. https://doi.org/10.5670/oceanog.2025.313

QUARTERDECK

Oceanography | Vol. 38, No. 2

September 2024 | Oceanography

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informs the public about ocean research, innovative tech­

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June 2025 | Oceanography

PERSPECTIVE

The National Academies Consensus Study Report, Potential

Hydrodynamic Impacts of Offshore Wind Energy on Nantucket

Shoals Regional Ecology: An Evaluation from Wind to Whales

(NASEM, 2024), is important, timely, and succinct. During this

time of political and financial uncertainty regarding the devel­

opment of offshore wind, this report, summarized by Hofmann

et al. (2025, in this issue), offers clear directions for the research

needed to resolve significant scientific and engineering questions

during a time of rapid change in the Northwest Atlantic Ocean.

The report highlights the difficulty of unraveling the impacts

of offshore wind development from oceanographic variabil­

ity. The Northwest Atlantic is one of the most rapidly warm­

ing regions in the world ocean (e.g., Pershing et al., 2015; Chen

et al., 2020; Seidov et al., 2021), resulting in a trend of increas­

ing stratification in the region (Harden et  al., 2020). While

there is a longer-term warming trend, in part relating to vari­

ability upstream (e.g.,  Gonçalves Neto et  al., 2021), extreme

events, such as marine heatwaves in the region, have resulted

in large temperature anomalies over time periods from days

to months. Further complicating the matter, the spatial scales

of the marine heatwaves depend on whether they result from

atmospheric forcing or ocean advection (e.g., Chen et al., 2014;

Großelindemann et al., 2022).

Another factor that makes attributing impacts in the region

complex is the manner in which Gulf Stream variability has influ­

enced continental shelf stratification and water mass properties

via increases in shelf break exchange processes. Gulf Stream

meanders have increased in peak-to-trough size, and their first

downstream appearance from the Cape Hatteras destabilization

point first shifted west over an extended period of time (Andres,

2016) and then shifted eastward over the last several years

(Sánchez-Roman et al., 2024). This increased Gulf Stream vari­

ability is likely related to a regime shift in the annual formation

rate of warm core rings in the year 2000 (Gangopadhyay et al.,

2019). An indication of the growing influence of Gulf Stream

rings and water masses on the continental shelf in this region

is the remarkable increase in frequency of mid-depth salinity

maximum intrusions (Gawarkiewicz et al., 2022). These intru­

sions commonly occur in proximity to warm core rings (Silver

et al., 2023) and bring warm salty water tens of kilometers shore­

ward of the shelf break and potentially into the offshore wind

lease areas off Nantucket Shoals. Significantly for northern right

whale prey fields, salinity profiles reveal there may be several dif­

ferent intrusions at different depths in the water column over the

continental shelf, thus possibly diminishing the concentration

within an individual intrusion layer.

The flow around offshore wind turbines is affected by pre-​

existing continental shelf processes and in turn alters those pro­

cesses. A key contribution of the Consensus Study Report is to

clearly delineate the three major scales over which the effects

on hydrodynamics must be considered and assessed: the indi­

vidual turbine scale, the wind farm scale including all turbines

in the region, and the larger regional scale over which the wind

farm scale exerts an impact via advection and changes in stratifi­

cation. This delineation is important as both the computational

approaches and the observational tools differ among the differ­

ent spatial scales. Prioritization is important, as is the linkage in

understanding among the scales.

A key portion of the report is the careful evaluation and sum­

mary of numerical modeling studies that highlight the wide

uncertainties regarding the impacts of turbine wakes on strati­

fication. Most of these studies have been directed toward infra­

structure in the North Sea, which exhibits considerable dif­

ferences in stratification, tidal velocities, and wind forcing

relative to the Nantucket Shoals region. Validation of mod­

els with careful observations is stressed and will be crucial to

reducing uncertainties.

Several challenges inhibit progress over these three spatial

scales. Large Eddy Simulations are needed at the individual tur­

bine scale to parameterize mixing and the downstream evo­

lution of turbulent wakes from the turbines. On larger scales,

much of the small-scale turbulence will need to be parameter­

ized. Progress in this specific area has been achieved by numer­

ical modelers in Europe, and parallel efforts are needed for the

Nantucket Shoals region.

A significant gap that is not addressed directly in the report is

the manner in which internal waves and tides have been chang­

ing over the past decade as stratification has changed. In addition

SETTING A COURSE

FOR RESEARCH ON OFFSHORE WIND DEVELOPMENT

IMPACTS NEAR NANTUCKET SHOALS

By Glen Gawarkiewicz

Oceanography | Vol. 38, No. 2

to ambient mesoscale and submesoscale processes, the charac­

teristics of the high frequency processes have likely changed

even in the absence of the wind farms. Again, it will be a chal­

lenge to differentiate changes resulting from the offshore wind

development and those that may have occurred as a result of

changing ocean currents and stratification. There is a clear need

for observations focused on high frequency processes to support

the numerical modeling.

All of the knowledge generated in understanding hydro­

dynamic effects will also need to be applied to further under­

standing regional marine ecology, as the prey fields, including

prey aggregation, and the roles of convergences and localized

upwelling in generating observed prey concentrations must be

better understood.

There are many challenges ahead, but the Consensus Study

Report produced by this NASEM committee is the clearest state­

ment possible of the path forward. This is particularly import­

ant, as the varied funding entities include federal agencies, off­

shore wind developers, and foundations for all of which this

report provides clear guidance on research needs and directions.

Given the dire need for alternative energy sources, there is an

urgent need for progress. The committee should be commended

for producing a clear, eminently readable report with strong rec­

ommendations. Let us hope that the resources become available

to meet the challenges that they so eloquently describe.

REFERENCES

Andres, M. 2016. On the recent destabilization of the Gulf Stream path down­

stream of Cape Hatteras. Geophysical Research Letters 43(18):9,836–9,842,

https://doi.org/​10.1002/2016GL069966.

Chen, K., G.G. Gawarkiewicz, S.J. Lentz, and J.M. Bane. 2014. Diagnosing the

warming of the Northeastern US Coastal Ocean in 2012: A linkage between the

atmospheric jet stream variability and ocean response. Journal of Geophysical

Research: Oceans 119(1):218–227, https://doi.org/10.1002/2013JC009393.

Chen, Z., Y.O. Kwon, K. Chen, P. Fratantoni, G. Gawarkiewicz, and T.M. Joyce.

2020. Long-term SST variability on the Northwest Atlantic continental shelf and

slope. Geophysical Research Letters 47(1):e2019GL085455, https://doi.org/​

10.1029/2019GL085455.

Gangopadhyay, A., G. Gawarkiewicz, E.N.S. Silva, M. Monim, and J. Clark. 2019. An

observed regime shift in the formation of warm core rings from the Gulf Stream.

Scientific Reports 9(1):12319, https://doi.org/10.1038/s41598-019-48661-9.

Gawarkiewicz, G., P. Fratantoni, F. Bahr, and A. Ellertson. 2022. Increasing fre­

quency of mid depth salinity maximum intrusions in the Middle Atlantic Bight.

Journal of Geophysical Research: Oceans 127:e2021JC018233, https://doi.org/​

10.1029/2021JC018233.

Gonçalves Neto, A., J.A. Langan, and J.B. Palter. 2021. Changes in the Gulf Stream

preceded rapid warming of the Northwest Atlantic Shelf. Communications Earth

& Environment 2(1):74, https://doi.org/10.1038/s43247-021-00143-5.

Großelindemann, H., S. Ryan, C.C. Ummenhofer, T. Martin, and A. Biastoch. 2022.

Marine heatwaves and their depth structures on the northeast US continental

shelf. Frontiers in Climate 4:857937, https://doi.org/10.3389/fclim.2022.857937.

Harden, B.E., G.G. Gawarkiewicz, and M. Infante. 2020. Trends in physical proper­

ties at the southern New England shelf break. Journal of Geophysical Research:

Oceans 125(2):e2019JC015784, https://doi.org/10.1029/2019JC015784.

Hofmann, E.E., J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-

Gutbrod, D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig. 2025. From

wind to whales: Potential hydrodynamic impacts of offshore wind energy on

Nantucket Shoals regional ecology. Oceanography 38(2):36–39, https://doi.org/​

10.5670/​oceanog.2025.304.

NASEM (National Academies of Sciences, Engineering, and Medicine). 2024.

Potential Hydrodynamic Impacts of Offshore Wind Energy on Nantucket Shoals

Regional Ecology: An Evaluation from Wind to Whales. The National Academies

Press, Washington, DC, https://doi.org/10.17226/27154.

Pershing, A.J., M.A. Alexander, C.M. Hernandez, L.A. Kerr, A. Le Bris, K.E. Mills,

J.A. Nye, N.R. Record, H.A. Scannell, J.D. Scott, and G.D. Sherwood. 2015. Slow

adaptation in the face of rapid warming leads to collapse of the Gulf of Maine

cod fishery. Science 350(6262):809–812, https://doi.org/10.1126/science.aac9819.

Sánchez-Román, A., F. Gues, R. Bourdalle-Badie, M.I. Pujol, A. Pascual, and

M. Drévillon. 2024. Changes in the Gulf Stream path over the last 3 decades.

In Copernicus Ocean State Report, 8th ed. K. von Schuckmann, L. Moreira,

M. Grégoire, M. Marcos, J. Staneva, P. Brasseur, G. Garric, P. Lionello,

J. Karstensen, and G. Neukermans, eds, Copernicus Publications, 4-osr8,

https://doi.org/​10.5194/sp-4-osr8-4-2024.

Seidov, D., A. Mishonov, and R. Parsons. 2021. Recent warming and

decadal variability of Gulf of Maine and Slope Water. Limnology and

Oceanography 66(9):3,472–3,488, https://doi.org/10.1002/lno.11892.

Silver, A., A. Gangopadhyay, G. Gawarkiewicz, P. Fratantoni, and J. Clark. 2023.

Increased gulf stream warm core ring formations contributes to an observed

increase in salinity maximum intrusions on the Northeast Shelf. Scientific

Reports 13(1):7538, https://doi.org/10.1038/s41598-023-34494-0.

AUTHOR

Glen Gawarkiewicz (ggawarkiewicz@whoi.edu), Woods Hole Oceanographic

Institution, Woods Hole, MA, USA.

ARTICLE CITATION

Gawarkiewicz, G. 2025. Setting a course for research on offshore wind develop­

ment impacts near Nantucket Shoals. Oceanography 38(2):5–6, https://doi.org/​

10.5670/oceanog.2025.303.

COPYRIGHT & USAGE

This is an open access article made available under the terms of the Creative

Commons Attribution 4.0 International License (https://creativecommons.org/

licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and repro­

duction in any medium or format as long as users cite the materials appropriately,

provide a link to the Creative Commons license, and indicate the changes that

were made to the original content.

June 2025 | Oceanography

ZOOPLANKTON AND OFFSHORE WIND

DRIFTERS IN A SEA OF UNCERTAINTY

By Grace K. Saba

Scientists are often tasked with addressing challenging, seem­

ingly impossible questions. An example is the recent Consensus

Study Report (NASEM, 2024a)—summarized by Hoffman

et al. (2025, in this issue)—asking: “How will potential offshore

wind-induced changes in ocean physical dynamics affect the

North Atlantic right whale in the Nantucket Shoals region?”

Most concerns about potential direct impacts of offshore wind

farms (OSW) on the North Atlantic right whale (NARW) focus

on noise interference and higher vessel activity increasing the

risk of vessel strikes. The impact of OSW on ocean physics or

hydrodynamics and subsequently NARWs is more difficult to

gauge because the effects are indirect and likely highly vari­

able. We do not yet know enough to accurately predict when

and where zooplankton will aggregate at concentrations that

support NARW foraging and success. Additionally, the under­

lying confounding challenge is how to decipher turbine-induced

hydro­dynamic changes relative to the background of extremely

high spatiotemporal variability in oceanographic conditions and

zooplankton dynamics in the Nantucket Shoals region. When

posed as a modified question—“How will potential OSW-

induced changes in ocean physical dynamics affect zooplankton

in the Nantucket Shoals region?”—a variety of scenarios come

to mind along with three questions that need to be addressed in

order to move closer to understanding whether and how OSW

may impact zooplankton.

WHAT CONTROLS ZOOPLANKTON SUPPLY AND

THE FORMATION OF AGGREGATIONS AT LEVELS

SUFFICIENT FOR NARW FEEDING?

The number of NARWs in the Nantucket Shoals region has

increased over the past decade, and although their peak for­

aging occurs during the winter and spring seasons, their pres­

ence has been observed year-round (Quintana-Rizzo et  al.,

2021). Successful NARW foraging requires an adequate sup­

ply and concentration of zooplankton (103–104 individuals m–3;

Baumgartner and Mate, 2003) as well as mechanisms that pro­

duce high-density aggregations at 100–1,000 m spatial scales

(Sorochan et  al., 2021), which coincidentally match those of

potential single turbine impacts. Coastal currents from the

Gulf of Maine and the Great South Channel control the supply

of NARWs’ primary prey, late stages of Calanus finmarchicus,

to Nantucket Shoals, while alternative copepod prey species

(Centropages spp., Pseudocalanus spp. Paracalanus spp., Oithona

similis) occur year-round with relatively different times of peak

abundance (Sorochan et al., 2021). We do not yet fully under­

stand the specific mechanism(s) that facilitate the production of

high-density zooplankton layers and aggregations in and around

Nantucket Shoals, as simultaneous NARW sightings and cope­

pod aggregations have not been observed at either tidal mixing

fronts or in a locally persistent wintertime upwelling gyre (Leiter

et  al., 2017; Sorochan et  al., 2021). The interactions between

source and advective supply, behavior (e.g., vertical migration),

ontogenetic cycles, food availability and distribution, and ocean

physical conditions that regulate these variables likely influence

zooplankton aggregation in the Nantucket Shoals region. These

dynamics are likely species-specific. Therefore, observational

studies in this region need to focus on determining which prey

species NARWs are targeting and on collecting high-​resolution

spatiotemporal observations of concurrent physical oceano­

graphic properties, copepod species distributions and aggrega­

tion dynamics, and NARW presence.

HOW MIGHT OSW AFFECT ZOOPLANKTON

ABUNDANCE AND AGGREGATION POTENTIAL?

A severe lack of observational data means that we do not know

the potential turbine-induced downstream and surrounding

increased turbulence and wake effects at scales of 0.1–1.0 km.

This could lead to, or alternate between, different scenarios of

OSW acting on zooplankton that are dependent on seasonal

ocean physical structure, circulation patterns, biological pro­

cesses, and highly variable wind, current, mixing, and tidal

dynamics. An added layer of complexity is that different zoo­

plankton species may respond differently to hydrodynamic

changes due to variable behaviors, preferred food resources,

and seasonal cycles.

Five possible scenarios are outlined here. One scenario is

that there is no overall effect; Figure 1 depicts the remaining

four. Scenario A would act to disperse surface zooplankton

aggregations and potentially those in diapause at depth (Incze

et  al., 2001). Whether this scenario could negatively change

PERSPECTIVE

Oceanography | Vol. 38, No. 2

Flow direction

Higher wind speed

Flow direction

Lower wind speed

Wind wake

Higher turbulence & ocean wake

Physical dispersion of zooplankton

(Late fall – Early spring; Unstratified)

*Seasonally

high wind

speeds

Low turbulence & ocean wake

Nutrient injection

Phytoplankton

Flow direction

Higher wind speed

Flow direction

Lower wind speed

Wind wake

Zooplankton

aggregation

Bottom-up support of zooplankton aggregation

(Late spring – Early fall; Strongly stratified)

*Seasonally

low wind

speeds

Flow direction

Higher wind speed

Flow direction

Lower wind speed

Wind wake

Higher turbulence & ocean wake

Physical dispersion of zooplankton

(Mid-spring, Mid-fall; Weakly stratified)

*Seasonally

moderate

wind speeds

Flow direction

Higher wind speed

Flow direction

Lower wind speed

Wind wake

Top-down predation on zooplankton

(All seasons)

*Seasonally

variable

wind speeds

Scenario A

Scenario B

Scenario C

Scenario D

FIGURE 1. Four potential scenarios of offshore wind turbulence and wake effects on

zooplankton in Nantucket Shoals waters.

zooplankton availability and aggregations at a level

that would impact NARW foraging is an open ques­

tion. This scenario may be of most relevance to

NARW ecology because it encompasses the time­

frame when NARW are most abundant and actively

foraging in Nantucket Shoals waters. In Scenario B,

OSW effects are strong enough to slightly disrupt

stratification, permitting nutrient injection upward

into the surface layer, but not strong enough to

break down stratification and disperse aggregat­

ing zooplankton. These higher nutrient conditions

could enhance primary production and therefore

zooplankton (Carpenter et al., 2016; Floeter et al.,

2017). Scenario C would destabilize stratification

(Carpenter et  al., 2016; Miles et  al., 2017), which

could potentially disperse zooplankton aggrega­

tions similarly to Scenario A. However, current

velocities would need to be high enough, and strat­

ification weak enough, for OSW-induced turbu­

lence to break down stratification (Carpenter et al.,

2016) and negatively impact zooplankton aggrega­

tions. Scenario D involves a more biological mecha­

nism whereby high colonization and abundances of

filter feeding invertebrates (e.g., mussels) on turbine

structures facilitate a top-down decrease in zoo­

plankton abundance (Perry and Heyman, 2020).

Although this scenario is independent of season,

different physical conditions and levels of turbu­

lence will create variable encounter rates and inter­

action times between sessile predators and zoo­

plankton prey (Prairie et al., 2012).

At the wind farm scale (10–100 km), cumula­

tive impacts of multiple turbines may act to reduce

surface current speeds and stratification and cre­

ate horizontal shear-induced upwelling and down­

welling dipoles that could differentially aggregate

or disaggregate zooplankton (Carpenter et al., 2016;

Sorochan et  al., 2021; Christiansen et  al., 2023).

Evaluating wind farm-scale impacts on oceano­

graphic and zooplankton dynamics will be more

difficult to isolate from regional high natural envi­

ronmental variability.

ARE THESE POTENTIAL OSW IMPACTS

ON ZOOPLANKTON GREATER

THAN NATURAL PROCESSES

THAT DRIVE A RANGE OF SCALES

OF SPATIOTEMPORAL VARIABILITY?

Oceanographic conditions on Nantucket Shoals

and on the broader US Northeast shelf are sub­

ject to high daily to decadal variability, driven

by local wind conditions, tidal forcing, storm

June 2025 | Oceanography

activity, and fluctuations in large-scale circulation (summa­

rized in NASEM, 2024a). Furthermore, increased frequency

of mid-water salt intrusions into shelf waters has been associ­

ated with recent warming, an inshore movement of the shelf-

break front, and changes in water column structure (Harden

et  al., 2020; Gawarkiewicz et  al., 2022). Zooplankton abun­

dance and distribution follow similar trends of variability, lead­

ing to spatiotemporal fluctuations in NARW foraging habitat,

including warming-associated declines in C. finmarchicus and

Pseudocalanus spp. (Record et al., 2019).

Given the significant uncertainty outlined here, the initial

question really should be how do we determine if OSW will

affect zooplankton and NARW in the Nantucket Shoals region?

Luckily, as Hoffman et al. (2025, in this issue) indicate, the com­

munity now has some guidance through the recently released

workshop proceedings, Nantucket Shoals Wind Farm Field

Monitoring Program (NASEM, 2024b). Isolating OSW impacts

from natural variability will require monitoring and model­

ing studies designed to target specific impacts at relevant scales

with sufficient resolution. Localized field efforts should sam­

ple along a gradient inside and outside OSW fields or include

“control” areas outside of OSW areas, before, during, and

after construction. Monitoring should also include simultane­

ous physical and biological observations at both the turbine

and wind farm area scale as well as repetition during variable

oceanographic conditions.

REFERENCES

Baumgartner, M.F., and B.R. Mate. 2003. Summertime foraging ecology of

North Atlantic right whales. Marine Ecology Progress Series 264:123–135,

https://doi.org/​10.3354/meps264123.

Carpenter, J.R., L. Merckelbach, U. Callies, S. Clark, L. Gaslikova, and B. Baschek.

2016. Potential impacts of offshore wind farms on North Sea stratification.

PLoS ONE 11(8):e0160830, https://doi.org/10.1371/journal.pone.0160830.

Christiansen, N., J.R. Carpenter, U. Daewel, N. Suzuki, and C. Schrum. 2023. The

large-scale impact of anthropogenic mixing by offshore wind turbine foundations

in the shallow North Sea. Frontiers in Marine Science 10:1178330, https://doi.org/​

10.3389/fmars.2023.1178330.

Floeter, J., J.E.E. van Beusekom, D. Auch, U. Callies, J. Carpenter, T. Dudeck,

S. Eberle, A. Eckhardt, D. Gloe, K. Hänselmann, and others. 2017. Pelagic effects

of offshore wind farm foundations in the stratified North Sea. Progress in

Oceanography 156:154–173, https://doi.org/10.1016/j.pocean.2017.07.003.

Gawarkiewicz, G., P. Fratantoni, F. Bahr, and A. Ellertson. 2022. Increasing fre­

quency of mid-depth salinity maximum intrusions in the Middle Atlantic Bight.

Journal of Geophysical Research: Oceans 127(7):e2021JC018233, https://doi.org/​

10.1029/2021JC018233.

Harden, B., G.G. Gawarkiewicz, and M. Infante. 2020. Trends in physical proper­

ties at the southern New England shelf break. Journal of Geophysical Research:

Oceans 125(2):e2019JC015784, https://doi.org/10.1029/2019JC015784.

Hofmann, E.E., J.R. Carpenter, Q.J. Chen, J.T. Kohut, R.L. Merrick, E.L. Meyer-

Gutbrod, D.P. Nowacek, K. Raghukumar, N.R. Record, and K. Oskvig. 2025. From

wind to whales: Potential hydrodynamic impacts of offshore wind energy on

Nantucket Shoals regional ecology. Oceanography 38(2):36–39, https://doi.org/​

10.5670/​oceanog.2025.304.

Incze, L.S., D. Hebert, N. Wolff, N. Oakey, and D. Dye. 2001. Changes in copepod

distributions associated with increased turbulence from wind stress. Marine

Ecology Progress Series 213:229–240, https://doi.org/10.3354/meps213229.

Leiter, S.M., K.M. Stone, J.L. Thompson, C.M. Accardo, B.C. Wikgren, M.A. Zani,

T. Cole, R.D. Kenney, C.A. Mayo, and S.D. Kraus. 2017. North Atlantic

right whale Eubalaena glacialis occurrence in offshore wind energy

areas near Massachusetts and Rhode Island, USA. Endangered Species

Research 34:45–59, https://doi.org/10.3354/esr00827.

Miles, J., T. Martin, and L. Goddard. 2017. Current and wave effects around wind­

farm monopile foundations. Coastal Engineering 121:167–178, https://doi.org/​

10.1016/​j.coastaleng.2017.01.003.

NASEM (National Academies of Science, Engineering, and Medicine). 2024a.

Potential Hydrodynamic Impacts of Offshore Wind Development on Nantucket

Region Ecology: An Evaluation from Wind to Whales. The National Academies

Press, Washington DC, 120 pp., https://doi.org/10.17226/27154.

NASEM. 2024b. Nantucket Shoals Wind Farm Field Monitoring Program.

The National Academies Press, Washington, DC, 64 pp., https://doi.org/​

10.17226/28021.

Perry, R.L., and W.D. Heyman. 2020. Considerations for offshore wind

energy development effects on fish and fisheries in the United States:

A review of existing studies, new efforts, and opportunities for innovation.

Oceanography 33(4):28–37, https://doi.org/10.5670/oceanog.2020.403.

Prairie, J.C., K.R. Sutherland, K.J. Nickols, and A.M. Kaltenberg. 2012.

Biophysical interactions in the plankton: A cross-scale review. Limnology

and Oceanography: Fluids and Environments 2(1):121–145, https://doi.org/​

10.1215/21573689-1964713.

Quintana-Rizzo, E., S. Leiter, T.V.N. Cole, M.N. Hagbloom, A.R. Knowlton,

P. Nagelkirk, O. O’Brien, C.B. Khan, A.G. Henry, P.A. Duley, and others. 2021.

Residency, demographics, and movement patterns of North Atlantic right whales

Eubalaena glacialis in an offshore wind energy development area in southern

New England, USA. Endangered Species Research 45:251–268, https://doi.org/​

10.3354/esr01137.

Record, N.R., J.A. Runge, D.E. Pendleton, W.M. Balch, K.T.A. Davies, A.J. Pershing,

C.L. Johnson, K. Stamieszkin, R. Ji, Z. Feng, and others. 2019. Rapid climate-​

driven circulation changes threaten conservation of endangered North

Atlantic right whales. Oceanography 32(2):162–169, https://doi.org/10.5670/

oceanog.2019.201.

Sorochan, K.A., S. Plourde, M.F. Baumgartner, and C.L. Johnson. 2021. Availability,

supply, and aggregation of prey (Calanus spp.) in foraging areas of the

North Atlantic right whale (Eubalaena glacialis). ICES Journal of Marine

Science 78(10):3,498–3,520, https://doi.org/10.1093/icesjms/fsab200.

AUTHOR

Grace K. Saba (saba@marine.rutgers.edu), Department of Marine and Coastal

Sciences and Center for Ocean Observing Leadership, Rutgers University,

New Brunswick, NJ, USA.

ARTICLE CITATION

Saba, G.K. 2025. Zooplankton and offshore wind: Drifters in a sea of uncertainty.

Oceanography 38(2):7–9, https://doi.org/10.5670/oceanog.2025.302.

COPYRIGHT & USAGE

This is an open access article made available under the terms of the Creative

Commons Attribution 4.0 International License (https://creativecommons.org/

licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and repro­

duction in any medium or format as long as users cite the materials appropriately,

provide a link to the Creative Commons license, and indicate the changes that

were made to the original content.

Oceanography | Vol. 38, No. 2

10

SCIENTIFIC RESEARCH AND

MARINE PROTECTED AREA MONITORING

USING A DEEP-SEA OBSERVATORY

THE ENDEAVOUR HYDROTHERMAL VENTS

By Steven F. Mihály, Fabio C. De Leo, Ella Minicola, Lanfranco Muzi, Martin Heesemann, Kate Moran, and Jesse Hutchinson

FEATURE ARTICLE

The cabled TEMPO-Mini ecological observatory module at

Main Endeavour Field. Image credit: Ocean Networks Canada

and Canadian Scientific Submersible Facility – Remotely

Operated Platform for Ocean Sciences (CSSF–ROPOS)

Oceanography | Vol. 38, No. 2

10

June 2025 | Oceanography

11

INTRODUCTION

Marine protected areas (MPAs) are designated regions set aside

to manage conservation efforts, with the primary aim of pre­

serving and protecting marine life. Effective conservation con­

siders the overall ecosystem functions, encompassing the physi­

cal, geological, and geochemical aspects of the habitat, and their

relationships with biological communities, as well as the func­

tional relationship among the ecosystems within the MPA and

the neighboring undesignated marine areas (e.g.,  Hays et  al.,

2020). Preservation efforts also extend to the cultural signifi­

cance of the marine area and the sustainable use of its resources

(Gomez et al., 2021).

Managing an MPA involves balancing multiple—often com­

peting—concerns, such as habitat protection and sustainable

use. Effective management must be informed by a strong sci­

entific understanding of an evolving ecosystem, which requires

continuous collection of key observations. For MPAs situated

in the deep sea, this can be facilitated remotely through sensors

delivering time-series observations and recurrent collection of

physical samples that help to interpret the continuous sensor

data. However, the impacts on the protected area from sensor

deployment and data collection as well as of recurring scientific

and maintenance expeditions also need to be considered in the

MPA management plan (e.g., Cuvelier et al., 2022).

In 1984, the human-occupied vehicle Alvin confirmed the

existence of “unusually large” sulfide structures and biological

communities supported by hydrothermal venting off the west

coast of Canada (Tivey and Delaney, 1986). These structures and

communities were localized to the Endeavour Segment of the

Juan de Fuca Ridge within Canada’s exclusive economic zone.

Upon discovery, and with its fortuitous proximity to coastal

ports, the Endeavour Segment became a mecca for scientific

research, enabling the dissemination of what some describe as

its magical nature and broad recognition in Canadian society of

Endeavour’s unique features and their environmental and socio­

economic significance (Tunnicliffe and Thomson, 1999).

Although the size of hydrothermal vent fields is relatively small

globally, their ecological significance is high; and even though

they are generally located in the remote deep sea, they are threat­

ened by human disturbance (Van Dover, 2012). The process of

hydrothermal venting concentrates minerals at the discharge

sites, making them ideal candidates for deep-sea mining. The

scientific interest they generate can also raise threats of overzeal­

ous sampling and other disturbances (Turner et al., 2019).

As a signatory to the Convention on Biological Diversity

(1993), Canada resolved to protect 30% of its oceans by 2030.

In 2003, Canada began this process by establishing the 97 km2

Endeavour Hydrothermal Vents (EHV) MPA as Canada’s first

MPA and the world’s first protected hydrothermal vent site

(Figure 1). Established under Canada’s Oceans Act, the primary

conservation objectives were to ensure that human activities in

the area contributed “to the conservation, protection, and under­

standing of the natural diversity, productivity, and dynamism of

ABSTRACT. Designating marine protected areas (MPAs) is an increasingly utilized policy instrument for preserving marine eco­

systems and biological diversity while also allowing for sustainable use. However, designation is only the first step and cannot

be successful without monitoring mechanisms to drive an effective and adaptive management plan. This article discusses the use

of the NEPTUNE real-time seafloor observatory—originally designed to understand the complex interdisciplinary nature of the

Endeavour mid-ocean ridge spreading center—as a tool to inform MPA management. We describe the ways in which geophysical

and geological forces control biological habitat and water column biogeochemistry, and highlight research enabled by the observa­

tory that increased our understanding of Endeavour’s hydrothermal vent ecology and these dynamic processes. Endeavour is natu­

rally undergoing change, so an understanding of the multidisciplinary mechanisms and factors controlling its environment provides

key management information.

FIGURE 1. The boundaries (white-lined box) and the five main active vent

clusters (shaded boxes) of the Endeavour Marine Protected Area are

delineated here on a bathymetric map. Coordinate system: WGS 1984

UTM Zone 9N. Image credit: Ocean Networks Canada

Oceanography | Vol. 38, No. 2

12

the ecosystem” and that these activities were “managed appro­

priately such that impacts remained less significant than natural

perturbations” (Fisheries and Oceans Canada, 2010).

The EHV MPA is on the Endeavour Segment of the Juan de

Fuca Ridge, a section of the global mid-ocean ridge (MOR) sys­

tem located in the Northeast Pacific Ocean off the west coast

of British Columbia. The MOR extends for 70,000 km through­

out the global ocean and is where tectonic plates diverge and

new oceanic crust is formed. This spreading process results

in a permeable seafloor, allowing cold seawater to percolate

downward where it is heated by rising magma from the upper

mantle. During its subseafloor circulation, the seawater reacts

chemically with the surrounding crust and is eventually ejected

back into the ocean as mineral-laden, oxygen-depleted, and

superheated fluid. The process of mixing with cold, oxygen­

ated seawater leads to a succession of rapid chemical reactions,

which form precipitates and creates the chimney-like hydrother­

mal vents that are the hallmark of the Segment (Figure 2). As the

buoyant vent plume rises, the hot metal- and sulfide-rich hydro­

thermal vent fluid continually reacts with the seawater to cre­

ate dark, smoke-like, emissions highly enriched in Fe, S, Cu, Ca,

and Zn (Feely et al., 1987). The plume rises 200–300 m above the

seafloor, at which point it reaches a neutrally buoyant state and

spreads with the local oceanic currents as the chemical processes

continue (Coogan et al., 2017). This flux of vent fluids plays a

major role in maintaining the ocean’s chemical balance. Nearer

to the seafloor, chemosynthesis-based biological communities

utilize both the energy exchange occurring when these chemical

species mix with the oxygenated seawater and the chemical spe­

cies themselves to form the basis of the hydrothermal vent eco­

systems on the seafloor and in the water column (Van Dover,

2000; Burd and Thomson, 2015).

This paper provides an overview of the main geological, bio­

geochemical, and physical processes at the Endeavour Segment

and their roles in regulating the biological communities and

habitat structures that host ecosystems at the vents and near the

seafloor. We describe highlights of the past 16 years of scien­

tific research and monitoring enabled by the NEPTUNE sea­

floor cabled observatory that support management decisions for

the MPA. Recently, the EHV MPA’s boundaries were repealed

and subsumed into the 133,017 km² Tang.ɢ̱ wan – ḥačxʷiqak –

Tsig̱ is (TḥT) MPA. This significantly expanded area is of cul­

tural and economic significance to coastal Indigenous peoples

of the west coast of North America and is cooperatively man­

aged by the Council of the Haida Nation, the Nuu-chah-nulth

Tribal Council, the Pacheedaht First Nation, and the Quatsino

First Nation, together with Fisheries and Oceans Canada

(Government of Canada, 2024).

THE NEPTUNE OBSERVATORY

In addition to its designation as an MPA, the Endeavour Segment

was also selected as one of the three Integrated Studies Sites for

the US National Science Foundation-funded Ridge 2000 pro­

gram (Fornari et al., 2012) that attracted significant global sci­

entific attention. Highlighting Endeavour’s scientific value, the

proposal for a NEPTUNE cabled observatory was successfully

funded, with the primary purposes to understand the spread­

ing, subduction, and faulting of the Juan de Fuca plate, as well as

the ecosystems and oceanography off the west coast of Canada.

For the purposes of MPA management, the deep-sea observa­

tory enhances observation and monitoring in the area.

FIGURE 2. This close-up view shows a black smoker chimney at the Main

Endeavour Field. Image credit: ONC and CSSF–ROPOS

June 2025 | Oceanography

13

Operated by Ocean Networks Canada (ONC), the NEPTUNE

observatory comprises an 840 km fiber-optic cable extend­

ing from Vancouver Island across the North American and

Juan de Fuca tectonic plates to connect five major node sites

to power and the internet (Barnes et al., 2007). The western­

most Endeavour node supports the scientific sensors in the

heavily instrumented Endeavour Hydrothermal Vents MPA

(Table 1, Figures 3 and 4). Real-time data, archived data, and

data products from sensors in the axial valley and on the flanks

of the Endeavour Segment of the Juan de Fuca Ridge have been

available since 2010 through ONC’s digital infrastructure,

Oceans 3.0 (Owens et al., 2022). Regular expeditions using ships

and remotely operated vehicles (ROVs) to maintain infrastruc­

ture also collect observations and physical samples to ground

truth and complement the sensor data. Internet connectivity

from the ships allows the Canadian and international science

community to participate from shore to conduct experiments

and sampling strategies to aid in developing a more complete

understanding of the physical, geological, and biological pro­

cesses of this protected environment (Table 1).

TABLE 1. Summary of major disciplines, sensor technology, and geological, physical, chemical, and biological properties monitored and their scientific

and MPA monitoring impacts. MEF = Main Endeavour Field. RCM = Regional Circulation Mooring North and South.

MONITORING

EQUIPMENT

PROPERTIES

MEASURED

VENT FIELD/

SITES

(See Figure 3)

SIGNIFICANCE

(Value in MPA management)

KEY PUBLICATIONS

DISCIPLINE: GEOPHYSICS AND GEOCHEMISTRY

1. Seismometers and

accelerometers

Seismic ground

motions and

low-frequency

hydroacoustic signals

• RCM-N

• MEF

• Mothra

• Ridge Flank

• Node

Identify periods of seismic unrest driven by

tectonic spreading events that are linked

to changes in venting and/or eruptions.

Also, detect chimney collapses and activity

from baleen whales.

• Krauss et al., 2023

• Bohnenstiehl et al., 2004

• Smith and Barclay, 2023

2. Bottom pressure

recorders (BPR)

Vertical seafloor

movements and sea

level changes

• RCM-N

• MEF

• Ridge Flank

• RCM-S

• Node

• Mothra

Inflation/deflation can indicate changes

in the underlying magma chamber that

affects the hydrothermal system and can

precede spreading events.

• Barreyre and Sohn, 2016

3. Benthic and

Resistivity Sensors

(BARS), paired with

vent fluid samples

Temperature,

resistivity, and redox

potential

• MEF

• Mothra

Changes in chemical composition of

vent fluids over time, and the influence

of chemical and heat fluxes on the

composition and diversity of benthic vent

biological communities.

• Xu et al., 2017a

4. Vent imaging sonar

3D vent plume and

heat flux mapping

• MEF

Hydrothermal heat and chemical flux

variability is a fundamental control on the

ecosystem.

• Bemis et al., 2015

• Xu et al., 2014, 2017b

5. Serial gas tight

sampler

Fluid geochemistry

• MEF

Changes in chemical composition of vent

fluids over time, and the influence of

chemical and heat fluxes on the makeup

and diversity of benthic vent biological

communities.

• Seyfried et al., 2022

• Evans et al., 2023

6. Water samplers

(RAS-PPS)

Water geochemistry

and biology

• MEF

Diffuse venting and its effects on the

benthic ecosystem.

• Lelièvre et al., 2017

7. Sediment traps

Particulates from

vent plumes

• MEF

• West Flank

• South Axial

Hydrothermal venting and its effects on

the water column.

• Coogan et al., 2017

• Mills et al., 2024

• Beaupre-Olsen et al., 2025

DISCIPLINE: PHYSICAL OCEANOGRAPHY

1. Regional Circulation

Moorings

Ocean circulation

and water properties

(temperature, salinity,

and density)

• RCM-N

• NW Mooring

• RCM-S

• SW Mooring

Proxy measurement of the overall heat flux

variability to the ocean from hydrothermal

venting. Current circulation in and above

the axial valley controlling larval and vent

plume chemistry dispersal.

• Thomson et al., 2003

• Xu et al. 2014, 2017b

2. Conductivity,

temperature, and

depth (CTD)

Temperature, salinity

and density, dissolved

oxygen

• Node

Near seafloor water properties.

Continued on next page…

Oceanography | Vol. 38, No. 2

14

GEOLOGY AND SEAFLOOR HABITAT

The Endeavour MPA hosts hydrothermal vent ecosystems

whose formation and persistence are directly linked to the

dynamic geological and tectonic processes of the Juan de

Fuca Ridge. Understanding this interplay through continu­

ous, multidisciplinary monitoring is foundational to effective

MPA management.

The Endeavour Segment is an intermediate-rate spreading

center (full rate: ~52 mm yr–1) (DeMets et al., 2010; Krauss et al.,

2023) characterized by a 10 km long and 1 km wide axial val­

ley flanked by rift crests rising 100–150 m above the valley floor.

Extensive and vigorous hydrothermal venting occurs within the

axial valley focused at five main active vent clusters spaced about

2–3 km apart (Figure 1; Kelley et al., 2012). The Main Endeavour

(MEF) and Mothra fields have received significant scientific

attention and are currently being monitored by sensors con­

nected to the NEPTUNE observatory. The High Rise and Salty

Dawg fields (see Figure 1) are designated for minimally intru­

sive studies and outreach opportunities (Fisheries and Oceans

Canada, 2010) and have no cabled sensors.

The uniqueness of hydrothermal venting regions, with respect

to other deep-sea benthic habitats, stems from the chemical flux

and exchange of heat between the ocean and the seafloor and

the geologically rapid change of the seafloor morphology due

to local tectonic dynamics. This leads to a chemically and phys­

ically extreme environment that hosts the specialized life that

has physiologically and biologically adapted to the geologically

controlled environment. Although vent ecosystems are rare and

their global extent is small, their contribution to the understand­

ing of life and their ecosystem functions and services are sig­

nificant and are considered ideal candidates for designation as

Vulnerable Marine Ecosystems and recommended for Area-

Based Management Tools (e.g., Menini and Van Dover, 2019).

The Endeavour Segment features a combination of active and

inactive chimneys, edifices, and mounds along its axial valley.

The active structures cluster into the five major vent fields with

more than 400 inactive structures as well as the diffuse venting

sites interspersed among them. Conceptually, they are geolog­

ically connected, and the entire ridge segment can be consid­

ered a single temporally and spatially varying vent field driven

MONITORING

EQUIPMENT

PROPERTIES

MEASURED

VENT FIELD/

SITES

(See Figure 3)

SIGNIFICANCE

(Value in MPA management)

KEY PUBLICATIONS

DISCIPLINE: BIOLOGY

1. Video cameras

Video, paired with

other sensors

(i.e., temperature)

• MEF

• Mothra

Track biological community structure and

responses to venting physico-chemistry

dynamics.

• Cuvelier et al., 2014, 2017

• Lelièvre et al., 2017

• Carter, 2025

• Robert et al., 2012

• Lee et al., 2015

2. Biological samples

Whole specimens,

tissue, assemblages

and e-DNA

• High Rise

• MEF

• Mothra

Characterization of vent and vent-

periphery communities (from microbes to

megafauna).

• Perez and Juniper, 2016, 2017

• Perez et al., 2023

• Lelièvre et al., 2018

• Georgieva et al., 2020

3. Colonization

experiments

Community

recolonization/

ecological succession

• MEF

Investigate faunal colonization (from

microbes to macrobenthos) simulating

recovery from natural perturbations

(e.g., eruptions).

• Ongoing studies

4. Passive larval

trap collectors

Benthic invertebrate

larvae

• MEF

Larval ecology and genetic connectivity

among different vent, vent periphery,

and background deep-sea benthic

communities.

• Ongoing study

5. ROV video

surveys, including

photogrammetry

Habitat and benthic

community dynamics

• MEF

• Mothra

• High Rise

Track, at larger spatial scales, temporal

changes of vent community composition

and responses to natural perturbations.

• Neufeld et al., 2022

DISCIPLINE: SOUNDSCAPES

1. Cabled hydrophone

arrays

Intensity and direction

of broadband sound

• MEF

Vent activity monitoring, earthquake

detection (near and distal), marine-mammal

detection and monitoring.

• Smith and Barclay, 2023

2. Deep acoustic

lander (autonomous,

Dalhousie University)

Sound velocity,

pressure, conductivity,

temperature, salinity;

intensity and direction

of broadband sound

• MEF

Water-column properties affecting sound

propagation, vent activity monitoring.

• Smith and Barclay, 2023

TABLE 1. Continued…

June 2025 | Oceanography

15

by heat from a continuous axial magma chamber (Jamieson and

Gartman, 2020). Over at least the last 2,000 years, there have

been no large-scale eruptions with significant lava flows that

could bury these vent fields (Jamieson et al., 2013; Clague et al.,

2014, 2020). Krauss et al. (2023) attribute this to the degassing

of the axial magma chamber, which limits extrusive magmatism

and results in the mature chimneys, edifices, and mounds, both

active and inactive, that define the Segment. Concurrently, the

underlying shallow magma chamber ensures sufficient heat and

chemical flux to sustain regular hydrothermal circulation and

consistent sulfide structure growth.

Long, continuous time series of physical parameters provide

opportunities to reveal complex dynamics and ongoing evolu­

tion of the vent system. For example, Barreyre and Sohn (2016)

correlated vent fluid temperatures with bottom pressure fluc­

tuations and estimated the permeability of the shallow upflow

zones near hydrothermal venting using poroelasticity theory.

The study revealed that the Main Endeavour Field (MEF) pos­

sesses geospatially distinct shallow upflow zones characterized

by different effective permeabilities, which sets it apart from

Lucky Strike and the East Pacific Rise, sites with different geo­

logical characteristics and spreading rates.

At Smoke and Mirrors, located near the southern Benthic and

Resistivity Sensors (BARS; shown in the MEF inset in Figure 3),

Barreyre and Sohn (2016) modeled higher effective permea­

bilities characteristic of a slow spreading center, such as Lucky

Strike, with lower heat flux and a thicker extrusive layer that has

ample permeable pathways. Just 150 m apart at Grotto (located

near the northern BARS shown in the MEF inset in Figure 3),

they modeled higher effective permeabilities that are character­

istic of a fast spreading center, such as the East Pacific Rise, with

higher heat flux and a thinner extrusive layer more frequently

paved by volcanic activity.

Rather than attributing these differences to spreading rate, the

effective permeability likely varies due to output from the irreg­

ular distribution of the underlying magma body. This is corrob­

orated by anecdotal visual evidence from repeated visits show­

ing the southern part of the MEF waning in black smoker output

(e.g.,  Smoke and Mirrors edifice), while the northern part of

the field (Grotto edifice) is growing and gaining in vigor. These

results and visual observations also imply that the magma sup­

ply within intermediate spreading centers can vary in space and

time (possibly rapidly) and therefore regionally modify the ben­

thic environment to host biological communities that are more

suited to fast or slow spreading centers.

Continuous geophysical monitoring, primarily using cabled

seismometers and bottom pressure recorders (BPRs, Table 1),

tracks the tectonic activity that can drive these changes in the

FIGURE 3. ONC infrastructure within the area of the Endeavour vent fields and adjacent ridge flanks. The node (orange square) powers the instru­

ment platforms (white circles) that host scientific sensors connected to the internet via fiber-optic cables (white lines). Moorings—both autonomous and

cabled—are shown as yellow circles. Image credit: ONC

Oceanography | Vol. 38, No. 2

16

environment. The real-time data streams permit continuous

monitoring of seismic events and seafloor deformation, pro­

viding insights into processes influencing environmental sta­

bility and enabling timely responses to significant events. Since

2018, heightened seismicity has been observed by Krauss et al.

(2023), mirroring precursors to past diking events (1999–2005).

This culminated in a notable increase in activity in March 2024,

including an M4.1 earthquake and periods with up to 200 events

per hour, suggesting the segment may be approaching the next

diking event, prompting the scientific community to meet in

November 2024 to prepare for a rapid response to a major per­

turbation of the system.

Understanding the chemical environment driving these eco­

systems is critical. Due to the harsh environment of hydrother­

mal venting regions, geochemical sensors for measuring the

continuous temporal variability of the chemistry of fluid emis­

sions are very limited, and scientific research has relied predom­

inantly on laboratory analysis of discrete samples obtained on

scientific expeditions. To obtain a continuous time series at high

temperature vents, ONC employed a cable-connected BARS

to measure temperature, resistivity, and redox potential (eH)

of the vent fluids in situ (Table 1). With discrete samples taken

at the beginning of the deployment and at the time of recov­

ery, the continuous time series of the sensors’ measurements are

used to infer changes in fluid chemistry. However, these sensors

reside in black smoker vents with 300°–350°C fluid emission

and often do not last a full year between maintenance expedi­

tions. Another method to improve time resolution of the vari­

ability of chemical fluxes is to remotely collect discrete sam­

ples. Currently, a serial gas tight sampler is deployed alongside a

BARS. Its containers can be remotely triggered to collect a time

series of 12 vent fluid samples (Seyfried et al., 2022). The timing

of the sampling is adapted to changes in seismicity or vent fluid

temperatures, allowing correlation between specific geological

events and vent fluid chemistry.

The current period of heightened seismicity marks a critical

phase for the evolution of the Endeavour Segment. It presents a

rare opportunity to observe a potential dike intrusion or spread­

ing event that would offer valuable data for refining models of

mid-ocean ridge processes. Studying the Endeavour Segment,

with its intermediate spreading rate characteristics, provides a

key comparison point between fast- and slow-spreading sys­

tems across the globe and other intermediate spreading cen­

ters (e.g., the Galápagos Spreading Center). An impending tec­

tonic event may cause significant shifts in hydrothermal output

(heat and chemistry), providing a natural experiment to study

the resilience and adaptive responses of the specialized vent

communities within the MPA. To better capture such an event,

Dalhousie University and the University of Washington, in part­

nership with ONC, enhanced observatory capabilities by deploy­

ing five autonomous ocean bottom seismometers in summer

2024; an additional 20 ocean bottom seismometers (including

replacements for the 2024 units) are scheduled for deployment in

summer 2025. This denser network will improve detection and

location of seismicity, providing crucial data for understanding

geological and tectonic processes and their impacts on hydro­

thermal vent ecosystems. It will inform future MPA management

strategies regarding natural and anthropogenic disturbances.

OCEANIC ENVIRONMENT

Changes in and redistribution of heat and chemical fluxes from

the vent fields along Endeavour’s axial valley alter seafloor char­

acteristics, affecting benthic ecosystems as well as the overlying

water column and the pelagic ecosystem it hosts. Not only is

the seawater chemistry directly altered, but changes in the heat

flux from hydrothermal venting affects the local ocean circula­

tion through changes in buoyancy input from the rising hydro­

thermal plumes. On an axial valley scale, the rising plume gen­

erates inflow near the seafloor toward the hydrothermal vents,

which facilitates the retention of vent field larvae and plankton.

Conversely, the rising plume can also entrain planktonic organ­

isms, moving them up into the water column where along-axis

currents can relocate them to vent sites with more retentive cir­

culation, or higher up in the water column where they can be

swept away by ambient ocean currents to less hospitable ocean

environments (Thomson et al., 2003). If the organisms have the

ability to swim vertically or alter their buoyancy, they can use

this circulation to move to a preferred location. There is obser­

vational evidence of larvae exhibiting this type of behavior at

other vents sites (Mullineaux et al., 2013). On the segment scale,

the off-axis propagation of the plume alters the chemistry of the

ocean (Coogan et al., 2017; Beaupre-Olsen et al., 2025) and has

a marked impact on the overlying pelagic ecosystem, enhancing

secondary productivity (Burd and Thomson, 2015).

Estimating the flux of hydrothermal fluid and heat along the

Endeavour Segment has generally been conducted by observing

water property anomalies, either by dense shipborne or autono­

mous underwater vehicle (AUV) sampling. These observations

are inverted to estimate flux using the known temperature of the

vent fluid as it leaves the seafloor (Kellogg, 2011), resulting in an

overall value of heat flux over the time window of the repeated

surveys. With yearly AUV surveys (2004, 2005, 2006), Kellogg

and McDuff (2010) identified a transient anomaly over the Salty

Dawg vent field, suggesting that there is spatial and temporal vari­

ability in hydrothermal flux; however, their temporal resolution

made it difficult to determine both the subseafloor causes and the

water column effects. As an alternative to annual AUV surveys

with their inherent coarse time resolution, four moorings of cur­

rent meters and water property sensors (CTDs) were installed in

the axial valley of the Endeavour Segment. The array is designed

to utilize the “sea breeze effect” caused by the rising buoyant

plume. This effect relates horizontal currents to the intensity of

heat flux from the hydrothermal venting (Thomson et al., 2003);

therefore, variability in hydrothermal heat flux is continuously

June 2025 | Oceanography

17

estimated in real time. This four-mooring array also monitors

the background bathymetrically modified circulation that con­

trols the mixing and dispersal of the chemical-laden hydrother­

mal plume (Xu et al., 2013; Coogan et al., 2017; Figure 3), and

enables researchers to relate circulation dynamics to ecosystem

dynamics (Cuvelier et al., 2014; Lelièvre et al., 2017).

A specialized sonar was developed to image rising plumes

in real time after researchers observed that avoidance sonar on

submersibles could detect reflections from these plumes (Bemis

et al., 2015). The deployment of the Cabled Observatory Vent

Imaging System (COVIS; Figure 4) marked a significant tech­

nological milestone. COVIS allows for direct tidal-frequency

resolution of the total flux from the multiple hot vent orifices

that makes up the rising buoyant plume. Utilizing the imagery

of the acoustic backscatter off the turbulent fluctuations of the

buoyant plume and the Doppler shift of the backscattered sig­

nal, researchers were able to estimate the rising plume veloc­

ity and the expansion rate and heat flux to the ocean from the

hydrothermal venting and its variability through time, and to

gain insights into the diffuse low temperature flow (Bemis et al.,

2012; Xu et al., 2013, 2014).

Chemical analysis of hot vent fluid samples collected by a

remotely controlled, internet-connected serial gas tight sampler

revealed details of the input of nutrient transition metals (e.g., V,

Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo) from the oceanic crust to the

water column (Evans et al., 2023). These metals play an import­

ant role in nutrient-related biological processes. They are essen­

tial for the growth of organisms and can be rapidly utilized in

near-surface waters and therefore limit growth. Determining

the dynamics of chemical flux across the seafloor interface using

these types of cabled seafloor samplers informs understanding of

the benthic-pelagic coupling that regulates the trophodynamics

over regional scales and offers insights into the global role of

hydrothermal venting in primary and secondary productivity in

the ocean (e.g., Burd and Thomson, 2015; Cathalot et al., 2021).

SOUNDSCAPE

A significant challenge when monitoring a site like Endeavour

is posed by the aggressive environment that can deteriorate

instrumentation quickly, especially when placed in the vicinity

of the plume. Passive acoustic monitoring (PAM) from hydro­

phones positioned at a safe distance from the hot and chemically

FIGURE 4. Artist’s rendering

of a selection of ONC’s cabled

and autonomous instruments

monitoring Endeavour. Image

credit: ONC

a. Regional circulation

mooring

b. Junction box

c. Bottom pressure recorder

d. Hydrophone array

e. Broadband seismometer

f. Cabled Observatory Vent

Imaging Sonar

g. Passive larval trap collector

h. Sediment trap

i. Deep Acoustic Lander

j. Remotely operated vehicle

k. Water sampler

l. TEMPO-Mini ecological

module

m. Benthic and Resistivity

Sensors

June 2025 | Oceanography

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Oceanography | Vol. 38, No. 2

18

corrosive fluids is used to monitor, in real time, the soundscape

at the site for extended periods of time. For example, PAM was

applied successfully to the detection and classification of explo­

sive events at volcanically active sites (Chadwick et al., 2008).

Different features of the sounds produced by venting are

related to the physical mechanisms producing the sounds.

These, in turn, are influenced by physical parameters such as

flow rate, chimney height, sound speed, and cavity size (Little

et al., 1990; Crone et al., 2006; Smith and Barclay, 2023). Studies

aimed at establishing the connection between these parameters

and the sounds produced can, in principle, enable the contin­

uous, remote, long-term monitoring and investigation of flow

rates, growth, and other aspects of the vents via PAM.

To explore the potential of PAM, ONC deployed a hydro­

phone at MEF in 2018, and then upgraded the installation to a

four-element array in 2023. Additionally, Dalhousie University’s

Deep Acoustic Lander (Figure 4) was deployed and recovered

in 2021 and 2023, further augmenting the time series (Smith

and Barclay, 2023). Though still in its infancy, this study has

already detected a large number of transient (i.e., of duration

measurable in seconds or less), often impulsive, sounds char­

acterizing the soundscape at MEF. These include chimney col­

lapses, waterborne signals associated with earthquakes, and a

number of other sounds whose origins are being investigated.

A recent study reports that numerous such signals were cap­

tured by ONC’s hydrophones during the major seismic event of

March 5–6, 2024. Through the investigation of power spectral

density, ambient-noise coherence, and cross-correlation with

other sensors at MEF, the same study highlighted other, longer-​

term changes in the MEF soundscape that may be associated

with changes to the venting activity resulting from the increased

seismicity in the region (Smith and Barclay, 2024).

Finally, PAM is also being explored as a tool for environmen­

tal impact assessment. Some marine organisms may use acoustic

cues to select settlement locations around hydrothermal vents

(Eggleston et al., 2016). Industrial activities, such as shipping

and deep-sea mining, can potentially interfere with the local eco­

system by introducing changes in the soundscape, even though

they may be located at significant distances (Chen et al., 2021).

Understanding of the local soundscape relevant to the biological

activity of a site is an important component of an effective envi­

ronmental impact mitigation strategy (Lin et al., 2019).

VENT BIOLOGY

Numerous biological studies utilizing video imagery and sam­

ples collected from ROVs and submersibles have been con­

ducted at Endeavour. They focused on describing the benthic

assemblages inhabiting a range of hydrothermal vent condi­

tions, from those on high-temperature black smoker chimneys

to those sustained by broadly spread diffusive flows (Sarrazin

et al., 1997; Tunnicliffe et al., 1997; Lelièvre et al., 2018; Murdock

et  al., 2021). The early studies of hydrothermal vent systems

described a specialized fauna characterized by low species diver­

sity, high biomass, and high levels of endemicity (i.e., species

only occurring at vent environments; Tunnicliffe and Fowler,

1996; reviewed in Van Dover, 2000).

A key characteristic of typical vent fauna is successful asso­

ciations between chemoautotrophic, symbiotic microorganisms

and their macroinvertebrate hosts (Lonsdale, 1977; Corliss et al.,

1979). Utilizing the chemical energy from sulfur, hydrogen,

iron, and methane, vent microorganisms fix carbon not only in

symbiont associations with host species but also as free-living

cells or in extensive bacterial mats (Dick, 2019). Host-symbiont

associations often achieve high densities and biomass surround­

ing the areas of hydrothermal fluid flow. At the Endeavour

vents, the most conspicuous and abundant vent fauna assem­

blages are comprised of the siboglinid polychaete tubeworm

Ridgeia piscesae, alvinelid polychaetes Paralvinella sulfincola

(sulfide worm) and Paralvinella palmiiformis (palm worm), the

limpet Lepetodrilus fucensis, and many other species of snails

(Figure 5a-d, Sarrazin et al., 1997). Studies to date have inven­

toried close to 60 vent-associated species at Endeavour, with

12 endemic species not occurring anywhere else in the world

(Fisheries and Oceans Canada, 2010). Sampling of macrofauna

associated with tubeworm bushes near the Grotto edifice alone

revealed up to 31 species occurring in substrate patches of less

than 0.1 m2, and it highlighted the importance of keystone

species such as R. piscesae in creating habitat complexity that

enhances local biodiversity (Lelièvre et al., 2018).

The roles of microbial diversity and production in con­

trolling large-scale nutrient elemental cycling and ecosystem

function have also been topics of studies based on the frequent

sampling at Endeavour. Samples of diffusive sulfidic vent fluids

helped to quantify microbial production pathways (denitrifica­

tion, anammox, and dissimilatory nitrate reduction to ammo­

nium), aiding global estimates of nitrogen (N) removal rates

to the subsurface biosphere that represent 2.5%–3.5% of total

marine N loss (Bourbonnais et al., 2012). Microbes were also

the focus of a number of studies examining vent fauna host-​

symbiont relationships and population structure. The tubeworm

Ridgeia piscesae, a keystone species, was found to have the same

phylotype Gammaproteobacteria symbiont (Ca. Endorifitia

persephone) as six other tubeworm species in the Eastern Pacific,

revealing high levels of interconnectivity between the Northeast

Pacific and the East Pacific Rise vents (Perez and Juniper, 2016).

However, the same authors later uncovered multiple genotypes

within E. persephone making up the symbiont assemblages

of R. piscesae and argued that this genetic diversity could be

an important predictor of resilience to environmental change

(Perez and Juniper, 2017).

Since the installation of seafloor cables and platforms in the

axial valley of the Endeavour Segment in 2010, in situ instru­

ments and sensors, including time-lapse video imagery, have

been providing new insights into the environmental controls

June 2025 | Oceanography

19

FIGURE 5. A sample of habitat heterogeneity and biological diversity of vent-associated and vent periphery fauna at Endeavour. (a,b) Black smoker

chimneys colonized by dense assemblages of R. piscesae tubeworms. (c,d) Typical assemblages that occur near diffusive hydrothermal flow, includ­

ing alvinelid polychaetes (Paralvinella sulfincola, Paralvinella palmiiformis), polynoid scale worms (Branchinotogluma tunnicliffae), limpets (Lepetodrilus

fucensis), and snails (Buccinum thermophilum). (e) Field of view of the Mothra vent field observatory camera showing the seafloor partially covered

by white bacterial mats, Ridgeia piscesae tubeworms, Buccinum thermophilum gastropods, and the deep-sea spider crab, Macroregonia macrochira.

(f) Vent periphery sulfide and (g,h) basalt structured seafloor that provide habitat for corals, sponges, and mobile macro- and megafauna. Image credits:

ONC and CSSF–ROPOS

over vent species community composition and biorhythms. At

Main Endeavour Field, a video camera platform (TEMPO-Mini;

Auffret et al., 2009), installed in collaboration with the French

national institute for ocean science and technology (IFREMER),

provided nearly 10 years of continuous data. The length of the

video time series enabled analyses that, for the first time, estab­

lished astronomical (tidal) and atmospheric (storm passages)

forcing as a control on vent macrofauna behavior (Cuvelier et al.,

2014, 2017; Lelièvre et al., 2017). The data revealed that mobile

macrofauna, such as sea spiders (pycnogonids) and polychaete

scale worms (polynoids), responded to the passage of win­

ter storms 2.2 km above by regulating their biorhythms to the

storm-​triggered cyclical oscillations in the diffusive vent flow

dynamics (Lelièvre et al., 2017). Video observations of picno­

gonids and scale worms living in association with R. piscesae

tubeworm bushes that are supported by low-temperature dif­

fuse venting also indicated that the animals respond to the cur­

rents generated by these storms. At the latitude of Endeavour,

storm-induced currents have a four-day cycle due to the pas­

sage of the storms and a 16-hour cycle resulting from the iner­

tial oscillations generated by the storm winds that can propa­

gate to the seafloor as inertial internal waves. As the currents

cyclically increase, they dilute the warm, low-oxygen vent fluids,

and the animals can be observed moving deeper into the bush,

disappearing from camera view. A study performed in waters

1,688 m deep at the EMSO-Azores Mid-Atlantic Ridge obser­

vatory (EMSO = European Multidisciplinary Seafloor and water

column Observatory) corroborates these findings, as biologi­

cal rhythms and circadian clock gene expression of the hydro­

thermal vent mussel Bathymodiolus azoricus were found to be

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