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