June 2025

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Oceanography | Vol. 38, No. 2

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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

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