June 2025

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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

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