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The lipid-rich calanoid copepod, Calanus finmarchicus, plays a critical role in the Gulf of Maine pelagic food web. Despite numerous studies over the last several decades, a clear picture of variability patterns and links with key environmental drivers remains elusive. This study applies model-based scaling and sensitivity analyses to a regional plankton dataset collected over the last four decades (1977–2017). The focus is to describe the gulf-wide spatio-temporal patterns across three major basins, and to assess the relative roles of internal population dynamics and external exchanges. For the spring stock, there is strong synchrony of interannual variability among three basins. This variability is largely driven by internal population dynamics rather than external exchanges, and the internal population dynamics are more sensitive to the change of top-down mortality regime than the bottom-up forcings. For the fall stock, the synchrony among basins weakens, and the variability is influenced by both internal mortality and external dilution loss. There appears to be no direct connection between the spring stock with either the preceding or subsequent fall stock, suggesting seasonal or sub-seasonal scales of population variability and associated drivers. The results highlight seasonally varying drivers responsible for population variability, including previously less recognized top-down control.

The signal of phytoplankton responses to climate-related forcing can be obscured by the heterogeneity of shelf seascapes, making them difficult to detect from fragmented observations. In this study, a physical–biological model was applied to the Northwest Atlantic Shelf to capture the seasonality of phytoplankton. The difference in phytoplankton seasonality between the Mid-Atlantic Bight (MAB) and the Gulf of Maine (GoM) is a result of the interplay between nutrients and temperature: In the MAB, relatively high temperature in the cold season and longer oligotrophic environment in the warm season contribute to an earlier winter bloom and a later fall bloom; in the GoM, low temperature and strong mixing limit phytoplankton growth from late fall to early spring, resulting in a later spring bloom and an earlier fall bloom. Although the temperature difference between the GoM and the MAB might decrease in the future, stratification and surface nutrient regimes in these two regions will remain different owing to distinct thermohaline structures and deep-water intrusion. The spatial heterogeneity of phytoplankton dynamics affects pelagic and benthic production through connections with zooplankton and benthic–pelagic coupling.

Sea scallops (Placopecten magellanicus) are a highly fecund species that supports one of the most commercially valuable fisheries in the northeast U.S. continental shelf region. Scallop landings exhibit significant interannual variability, with abundances widely varied due to a combination of anthropogenic and natural factors. By coupling a pelagic-stage Individual-Based scallop population dynamics Model (hereafter referred to as Scallop-IBM) with the Northeast Coastal Ocean Forecast System (NECOFS) and considering the persistent aggregations over Georges Bank (GB)/Great South Channel (GSC) as source beds, we have examined the dispersion and settlement of scallop larvae over 1978–2016. The results demonstrated that the significant interannual variability of larval dispersal was driven by biophysical interactions associated with scallop larval swimming behaviors in their early stages. The duration, frequency, and stimulus of larval vertical migration in the ocean mixed layer (OML) affected the residence time of larvae in the water column over GB. It thus sustained the persistent aggregations of scallops in the GB/GSC and Southern New England region. In addition to larval behavior in the OML, the larval transport to the Middle Atlantic Bight (MAB) was also closely related to the intensity and duration of northeasterly wind in autumn. There was no conspicuous connectivity of scallop larvae between GB/GSC and MAB in the past 39 years except in the autumn of 2009. In 2009, the significant larval transport to the MAB was produced by unusually strong northeasterly winds. Ignoring larval behavior in the OML could overestimate the scallop population’s connectivity between GB and the MAB and thus provide an unrealistic prediction of scallop larval recruitment in the region. Both satellite-derived SST and NECOFS show that the northeast U.S. shelf experienced climate change-induced warming. The extreme warming at the shelfbreak off GB tends to intensify the cross-isobath water temperature gradient and enhance the clockwise subtidal gyre over GB. This change can increase the larval retention rate over GB/GSC, facilitating enhanced productivity on GB.

The cryptic copepod species, Pseudocalanus moultoni and P. newmani, co-occur on Georges Bank and in the Gulf of Maine (Northwest Atlantic); even recent studies have reported results and conclusions based on examination of the combined species. Species-specific PCR (SS-PCR) based on mitochondrial cytochrome oxidase I (COI) sequence divergence was used in this study to discriminate the species. Species-specific descriptions of habitat usage and predicted patterns of transport and retention on Georges Bank were made by mapping distributions and calculating abundances of each species from January to June, 1999 for four vertical strata (0–15 m, 15–40 m, 40–100 m, and 0–100 m) and five regions (Northern Flank, Bank Crest, Northeast Peak, Southern Flank, and Slope Water) identified on the basis of bathymetry and circulation. Patterns of distribution and abundance for the two species during January to June, 1999 were largely consistent with those described based on vertically integrating mapping and analysis for the same period in 1997 by McGillicuddy and Bucklin (2002) . The region-specific and depth-stratified analyses allowed further discrimination in habitat usage by the species and confirmed the distinctive patterns for the two species. The observed differences between the species in abundances among the five regions and three depth strata over Georges Bank impact their transport trajectories. The concentration of P. moultoni in deep layers likely explains the higher rates of retention and lower rates of advective loss of this species from the Bank, compared to P. newmani, which may be more subject to wind-driven transport in the surface layer. Accurate identification and discrimination of even closely-related and cryptic species is needed to ensure full understanding and realistic predictions of changes in diversity of zooplankton and the functioning of pelagic ecosystems.

Nitrogen fixation is an important yet still incompletely constrained component of the marine nitrogen cycle, particularly in the subsurface. A Video Plankton Recorder (VPR) survey in the subtropical North Atlantic found higher than expected Trichodesmium colony abundances at depth, leading to the hypothesis that deep nitrogen fixation in the North Atlantic may have been previously underestimated. Here, Trichodesmium colony abundances and modeled nitrogen fixation from VPR transects completed on two cruises in the tropical and subtropical North Atlantic in fall 2010 and spring 2011 were used to evaluate that hypothesis. A bio-optical model was developed based on carbon-normalized nitrogen fixation rates measured on those cruises. Estimates of colony abundance and nitrogen fixation were similar in magnitude and vertical and geographical distribution to conventional estimates in a recently compiled climatology. Thus, in the mean, VPR-based estimates of volume-specific nitrogen fixation rates at depth in the tropical North Atlantic were not inconsistent with estimates derived from conventional sampling methods. Based on this analysis, if Trichodesmium nitrogen fixation by colonies is underestimated, it is unlikely that it is due to underestimation of deep abundances by conventional sampling methods.

The ultimate goal of early life studies of fish over the past century has been to better understand recruitment variability. As evident in the Georges Bank haddock (Melanogrammus aeglefinus) population, there is a strong relationship between recruitment success and processes occurring during the planktonic larval stage. This research sought new insights into the mechanisms controlling the recruitment process in fish populations using biological–physical modeling methods together with laboratory and field data sets. We created the first three-dimensional model of larval haddock on Georges Bank by coupling models of hydrodynamics, lower trophic levels, a single copepod species, and larval haddock. Interactions between feeding, metabolism, growth, vertical behavior, advection, predation, and the physical environment of larval haddock were quantitatively investigated using the coupled models. Particularly, the model was used to compare survival over the larval period and the sources of mortality in 1995 and 1998, 2 years of disparate haddock recruitment. The results of model simulations suggest that the increased egg hatching rates and higher food availability, which reduced starvation and predation, in 1998 contributed to its larger year-class. Additionally, the inclusion of temperature-dependent predation rates produced model results that better agreed with observations of the mean hatch date of survivors. The results from this biophysical model imply that food limitation and its related losses to starvation and predation, especially from hatch to 7 mm, may be responsible for interannual variability in recruitment and larval survival outside of the years studied.

Coupled physical–biological modelling experiments were made for the period of 1995–2009 to analyse the spatial and interannual variability of nutrients and phytoplankton production in the Gulf of Maine (GOM). The physical model was the Finite-Volume Community Ocean Model (FVCOM) and the biological model was a Nitrogen, Phytoplankton, Zooplankton, and Detritus (NPZD) model. The simulation was carried out with realistic meteorological surface forcing, five major tidal constituents, river discharge, and observation-based open boundary conditions. The results were robust with comparison to SeaWiFS chlorophyll data and historical data of nitrogen. An Empirical Orthogonal Function analysis clearly identified two dominant modes in nutrient and phytoplankton dynamics: (1) sustained nutrient supply and phytoplankton production from spring through autumn, and (2) a dominating phytoplankton bloom in spring, relatively low production in summer, and a noticeable bloom in autumn. Mode 1 was a dominant feature in strong tidal energy dissipation regions such as the southwestern shelf of Nova Scotia, Georges Bank, Nantucket Shoals, the Bay of Fundy, and the coastal regions of GOM, where tidal pumping and mixing were the major drivers for the sustained nutrient supply, and primary production showed certain resilience with less interannual variability. Mode 2 was a characteristic in the deep Gulf, the offshore region of the Scotian Shelf, and in the open sea area, where the timing and amplitude of the spring phytoplankton bloom is essentially controlled by the salinity regime, and its interannual variability was significantly influenced by freshening events controlled by local and remote forcing.

In this study, we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the Northwest Atlantic shelf, with a focus on the Nova Scotian Shelf (NSS)-Gulf of Maine (GoM) region. Long-term observational data of alongshore wind stress, sea level slope, and along-shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales. Additionally, a simplified momentum balance model is used to examine the underlying mechanisms. Our results show significant correlation among the observed interannual variability of sea level slope, along-shelf flow, and alongshore wind stress in the NSS-GoM region. A mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along-shelf flow: stronger southwesterly (northeastward) winds tend to weaken the prevailing southwestward flow over the shelf, building sea level in the upstream Newfoundland Shelf region, whereas weaker southwesterly winds allow stronger southwestward flow to develop, raising sea level in the GoM region. The wind-induced flow variability can influence the transport of low-salinity water from the Gulf of St. Lawrence to the GoM, explaining interannual variations in surface salinity distributions within the region. Hence, our results offer a viable mechanism, besides the freshening of remote upstream sources, to explain interannual patterns of freshening in the GoM.

Author(s): Batchelder, HP; Daly, KL; Davis, CS; Ji, R; Ohman, MD; Peterson, WT; Runge, JA | Abstract: The 20-year US GLOBEC (Global Ocean Ecosystem Dynamics) program examined zooplankton populations and their predators in four coastal marine ecosystems. Program scientists learned that environmental controls on zooplankton vital rates, especially the timing and magnitude of reproduction, growth, life-cycle progression, and mortality, determine species population dynamics, seasonal and spatial distributions, and abundances. Improved knowledge of spatialtemporal abundance and distribution of individual zooplankton taxa coupled with new information linking higher trophic level predators (salmon, cod, haddock, penguins, seals) to their prey yielded mechanistic descriptions of how climate variation impacts regionally important marine resources. Coupled ecological models driven by improved regional-scale climate scenario models developed during GLOBEC enable forecasts of plausible future conditions in coastal ecosystems, and will aid and inform decision makers and communities as they assess, respond, and adapt to the effects of environmental change. Multi-region synthesis revealed that conditions in winter, before upwelling, or seasonal stratification, or ice melt (depending on region) had significant and important effects that primed the systems for greater zooplankton population abundance and productivity the following spring summer, with effects that propagated to higher trophic levels. © 2013 by The Oceanography Society. All rights reserved.

The spatio-temporal variability of marine copepods, like other aquatic and terrestrial organisms, is controlled by both bottom-up (through changes in food resource) and top-down (through changes in predation) forcing. Canonically, climate-related changes in hydrography, nutrient chemistry and circulation can modulate phytoplankton production, thus imposing a bottom-up control on marine copepods, whereas human activities such as fishing may affect the predation mortality of copepods through food-web re-organization such as trophic cascading. Evaluating the sensitivity of copepod populations to bottom-up and topdown forcing is an essential step toward the prediction of future marine planktonic ecosystem changes. In this study, we used a coupled hydrodynamics/food-web/ population-dynamics model to identify the key processes controlling the observed seasonality and distributional patterns of two copepod groups in the Gulf of Maine (GoM) region, including Pseudocalanus spp. and Centropages typicus. Numerical experiments were conducted to assess the sensitivity of the modeled species to changes in phytoplankton biomass and bloom timing, as well as the changes in mortality regime. The results show that both copepod groups are more sensitive to changes in mortality rates than to food availability and peak timing. Bottom-up processes alone cannot explain the observed variability in Pseudocalanus and Centropages population sizes, while top-down controls play a critical role in copepod population dynamics in the GoM region.

Calanus spp. copepods play a key role in the Arctic pelagic ecosystem. Among four congeneric species of Calanus found in the Arctic Ocean and its marginal seas, two are expatriates in the Arctic ( Calanus finmarchicus and Calanus marshallae ) and two are endemic ( Calanus glacialis and Calanus hyperboreus ). The biogeography of these species likely is controlled by the interactions of their life history traits and physical environment. A mechanistic understanding of these interactions is critical to predicting their future responses to a warming environment. Using a 3-D individual-based model that incorporates temperature-dependent and, for some cases, food-dependent development rates, we show that (1) C. finmarchicus and C. marshallae are unable to penetrate, survive, and colonize the Arctic Ocean under present conditions of temperature, food availability, and length of the growth season, mainly due to insufficient time to reach their diapausing stage and slow transport of the copepods into the Arctic Ocean during the growing season or even during the following winter at the depths the copepods are believed to diapause. (2) For the two endemic species, the model suggests that their capability of diapausing at earlier copepodite stages and utilizing ice-algae as a food source (thus prolonging the growth season length) contribute to the population sustainability in the Arctic Ocean. (3) The inability of C. hyperboreus to attain their first diapause stage in the central Arctic, as demonstrated by the model, suggests that the central Arctic population may be advected from the surrounding shelf regions along with multi-year successive development and diapausing, and/or our current estimation of the growth parameters and the growth season length (based on empirical assessment or literature) needs to be further evaluated. Increasing the length of the growth season or increasing water temperature by 2 °C, and therefore increasing development rates, greatly increased the area of the central Arctic in which the Arctic endemics could reach diapause but had little effect on the regions of successful diapause for the expatriate species.

Copepod populations in the Gulf of Maine/Georges Bank region are dominated by warm water species in late summer/autumn, which are specifically adapted to lower food conditions and higher temperatures and metabolic costs. Better knowledge of their physiological processes and behavior is needed to estimate the impact of changes in environmental conditions on their seasonality and spatial distribution. We investigated the population dynamics of the warm water species Centropages typicus in this region using a copepod population model coupled with a three-dimensional ecosystem model. Although growth and development of copepods are well-investigated processes and well represented in population models, the importance of other life-history traits (e.g. cannibalism, feeding and migration strategies) and their impact on seasonal dynamics and spatial distributions are recognized but difficult to quantify. In this study, species-specific life-history traits were included to investigate their influence on the spatio-temporal patterns. The results confirmed our assumption that cannibalism is a possible constraint controlling the abundances on Georges Bank. Omnivorous feeding by C. typicus on both phytoplankton and microzooplankton is important for maintaining the population in the deeper basins, while vertical aggregation in zones of high-food concentration is a secondary mechanism sustaining the population in low-food seasons. Finally, advective influx from the upstream region on the Scotian Shelf is critical in sustaining the Gulf of Maine population.

SeaWiFS (Sea-viewing Wide Field-of-view Sensor) chlorophyll data revealed strong interannual variability in fall phytoplankton dynamics in the Gulf of Maine, with 3 general features in any one year: (1) rapid chlorophyll increases in response to storm events in fall; (2) gradual chloro- phyll increases in response to seasonal wind- and cooling-induced mixing that gradually deepens the mixed layer; and (3) the absence of any observable fall bloom. We applied a mixed-layer box model and a 1-dimensional physical-biological numerical model to examine the influence of physical forc- ing (surface wind, heat flux, and freshening) on the mixed-layer dynamics and its impact on the entrainment of deep-water nutrients and thus on the appearance of fall bloom. The model results suggest that during early fall, the surface mixed-layer depth is controlled by both wind- and cooling- induced mixing. Strong interannual variability in mixed-layer depth has a direct impact on short- and long-term vertical nutrient fluxes and thus the fall bloom. Phytoplankton concentrations over time are sensitive to initial pre-bloom profiles of nutrients. The strength of the initial stratification can affect the modeled phytoplankton concentration, while the timing of intermittent freshening events is related to the significant interannual variability of fall blooms.

Copepods of the genera Pseudocalanus and Centropages play an important role in the North Atlantic ecosystems and have distinctive spatial and temporal patterns depending on physiological adaptation to different environmental conditions. To examine the possible impact of climate change on these biogeographic patterns, potential population growth rate was computed for each species using IPCC projections of sea surface temperature together with chlorophyll distributions from SeaWiFS climatology and published laboratory data on temperature and food-dependent life-history parameters. The results indicate that the predicted temperature increase throughout the North Atlantic will cause temporal and spatial shifts in copepod species population growth potential. The Centropages population is projected to increase in mid-latitudinal shelf areas, e.g. the Gulf of Maine and the North Sea, due to shorter generation times and a longer growing season, while Pseudocalanus is predicted to be less abundant in these regions after 2050. These shifts potentially have a significant impact on the future demographics of pelagic fish species for which the copepods are the major food source.

We put forward a combined observing and modeling strategy for evaluating effects of environmental forcing on the dynamics of spatially structured cod populations spawning in the western Gulf of Maine. Recent work indicates at least two genetically differentiated complexes in this region: a late spring spawning, coastal population centered in Ipswich Bay, and a population that spawns in winter inshore and on nearshore banks in the Gulf of Maine and off southern New England. The two populations likely differ in trophic interactions and in physiological and behavioral responses to different winter and spring environments. Coupled physical–biological modeling has advanced to the point where within-decade forecasting of environmental conditions for recruitment to each of the two populations is feasible. However, the modeling needs to be supported by hydrographic, primary production and zooplankton data collected by buoys, and by data from remote sensing and fixed station sampling. Forecasts of environmentally driven dispersal and growth of planktonic early life stages, combined with an understanding of possible population-specific predator fields, usage of coastal habitat by juveniles and adult resident and migratory patterns, can be used to develop scenarios for spatially explicit population responses to multiple forcings, including climate change, anthropogenic impacts on nearshore juvenile habitat, connectivity among populations and management interventions such as regional fisheries closures.

A major problem in biological oceanography is sparseness of data. Ocean observing systems are being developed to fill this need. Design of these systems can benefit from optimal sampling analysis applied to output of biological–physical models. This study describes a method for optimizing plankton surveys through the use of Observing System Simulation Experiments (OSSEs). Using a coupled physical–biological hindcast simulation for 1999 as “truth”, we applied the variance quadtree (VQT) algorithm to determine the locations of a fixed number of samples to reduce error. The optimized sampling process derived by the VQT algorithm is significantly better (at 95% confidence level) than simple random sampling. The relationship between root mean square error (RMSE) and number of samples allows one to balance the number of samples and the expected error, aiding the design of ocean observing systems. Compared with an existing sampling strategy used in the Gulf of Maine region, a fixed VQT-derived sampling strategy for Pseudocalanus alone can reduce expected errors by 20% on the annual average (range from 15% to 23%). While sampling for combination of two variables (adult Pseudocalanus and phytoplankton), the errors are modestly reduced by an annual average of 7% (range from −4% to 14%), suggesting that the ongoing operational observing strategy is close to optimal for multi-constituent sampling. The VQT-derived sampling stations are more densely (sparsely) spaced in areas having larger (lower) variance in the quantity of interest. Sampling strategies differ for Pseudocalanus and phytoplankton, reflecting differences in the statistics of their distributions. This kind of information can be used for directed sampling in the real ocean, which must grapple with multiple physical and biological properties that vary on different scales. This methodology can contribute to optimal sampling of biological–physical properties by ocean observing systems.

Previous analyses of SeaWiFS ocean color and hydrographic data [fi, R., Davis, C. S., Chen, C. et al. (2007) Influence of ocean freshening on shelf phytoplankton dynamics. Geophys. Res. Lett., 34, L24607. doi: 10.1029/2007GL032010] have suggested that changes in the intensity of low-salinity Scotian Shelf Water (SSW) inflow can significantly influence the winter-spring phytoplankton dynamics in the Scotian Shelf and Gulf of Maine region. In the present study, a 3-D coupled biological-physical model was applied to examine underlying mechanisms through a quantitative comparison of circulation pattern, water column stability, nutrient/ phytoplankton concentrations and net primary productivity between low and high freshening scenarios. The model results revealed that observed levels of surface freshening can significantly change water column stability and therefore control the winter-spring phytoplankton bloom dynamics in different regions. Freshening caused earlier blooms both on the Scotian Shelf and in the eastern Gulf of Maine, agreeing with inferences drawn from prior empirical analyses. Earlier phytoplankton blooms in the low surface salinity case were followed by earlier depletion of nutrients at the surface along with earlier decline of blooms compared with the high surface salinity case. The model results also suggested that surface water freshening can impede vertical nutrient exchange between surface and deep waters, thus reducing the overall spring primary productivity throughout the region. The coupled model described in this study provides a unique tool to quantify the response of lower trophic level production to climate-scale environmental disturbances in a complex but ecologically important shelf ecosystem that has a history of such alternations in surface salinity.

Georges Bank is one of the world's most highly productive marine areas, but the mechanisms of nutrient supply to support such high productivity remain poorly understood. Intrusions of nutrient-poor Labrador Slope Water (LSW) into the Gulf of Maine (NAO-dependent) potentially can reduce nutrient delivery to the bank, but this mechanism has not been quantitatively examined. In this paper, we present the first whole-year continuous model simulation results using a biological–physical model developed for the Gulf of Maine/Georges Bank region. This high-resolution three-dimensional coupled model consists of the Finite Volume Coastal Ocean Model (FVCOM) and a Nitrogen–Phytoplankton–Zooplankton–Detritus (NPZD) model, and was used to examine the influences of local and external processes on nitrogen and phytoplankton dynamics on Georges Bank. The model captured the general pattern of spatial-temporal distributions of nitrogen and phytoplankton and provided a diagnostic analysis of different processes that control nitrogen fluxes on Georges Bank. Specifically, numerical experiments were conducted to examine seasonal variation in nitrogen transport into the central bank (new nitrogen supply) versus nitrogen regenerated internally in this region. Compared with previous observation-based studies, the model provided a quantitative estimate of nitrogen flux by integrating the transport over a longer time period and a complete spatial domain. The results suggest that, during summer months, internal nitrogen regeneration is the major nitrogen source for primary production on the central bank, while nitrogen supply through physical transport (e.g. tidal pumping) contributes about 1/5 of the total nitrogen demand, with an estimated on-bank nitrogen transport at least 50% less than previous estimates. By comparing the model runs using different nitrogen concentrations in deep Slope Water, the potential influence of NAO-dependent intrusions of LSW was examined. The results suggest that the change of nitrogen concentration in the deep Slope Water may not have a significant impact on nitrogen and phytoplankton dynamics on the well-mixed central bank, largely due to limited nutrient exchange across the tidal mixing front and enhanced near-frontal nutrient uptake. However, relatively more significant impact was observed in the model simulations if both well-mixed and seasonallystratified areas (inside 100 m isobath of the bank) were considered in flux calculations. © 2007 Elsevier B.V. All rights reserved.

The Western Antarctic Peninsula is a critical locus of Antarctic krill Euphausia superba abundance and thought to be a site of successful overwintering, particularly for the larval stages. A primary goal of the Southern Ocean GLOBEC program was to describe factors that contribute to the overwintering success of krill in this region. As part of this effort we conducted Video Plankton Recorder (VPR) surveys during austral fall and winter, 2001. The VPR survey yielded high-resolution distributions of larval krill, other plankton, and marine snow in relation to hydrography from a series of transect lines orthogonal to the coast on the continental shelf of the Western Antarctic Peninsula. Four taxa (larval krill, copepods, polychaetes, pteropods) and marine snow were numerous during fall; much lower abundances of all categories were present during winter, with only larval krill, copepods, and polychaetes present in any abundance. Distributions of plankton and marine snow were associated with water-mass types and the vertical structure of the environment, particularly for larval krill that were primarily associated with the pycnocline. During fall, larval krill were present across the entire shelf, with high abundances at the shelf break. Copepods were most numerous at depth during fall, consistent with ontogenetic migration to depth at the onset of winter.

Communicating editor: K.J. Flynn Molting rate is a key life history parameter in copepods. Since copepod population growth is an inherently exponential process, accurate formulation of molting rate is of critical importance. Many experiments have been conducted to culture different copepod species under varying temperatures and food concentrations. Probability density functions (PDFs) then were used to estimate the median development time (MDT) of different copepod stages from the experimental data. These MDTs are used in copepod population models. Asymmetrical PDFs are widely used to model molting rate, because the shapes of these curves are similar to laboratory data on cohort development. In this paper, we developed an individual stochastic model (ISM) to simulate the molting rate with different PDFs. We showed that there was no connection between the asymmetry of cohorts and the asymmetry of the molting PDF. Although age-within-stage models have been widely used to simulate copepod population dynamics, we found that none had used the correct formulation of molting rate. The population model requires the probability of molting at each time step, whereas the laboratory-derived PDF is the frequency distribution of stage duration. Therefore, the PDF cannot be applied directly to the population model. We present here a corrected formula based on the PDF for use in copepod population models, termed the probability of molting for remaining individuals (PMR). Despite emphasis on use of the gamma function for copepod molting, we found simpler functions work equally well, but that prior use of incorrect molting rate functions in copepod models can seriously overestimate generation time.

Episodic eddy-driven upwelling may supply a significant fraction of the nutrients required to sustain primary productivity of the subtropical ocean. New observations in the northwest Atlantic reveal that, although plankton blooms occur in both cyclones and mode-water eddies, the biological responses differ. Mode-water eddies can generate extraordinary diatom biomass and primary production at depth, relative to the time series near Bermuda. These blooms are sustained by eddy/wind interactions, which amplify the eddy-induced upwelling. In contrast, eddy/wind interactions dampen eddy-induced upwelling in cyclones. Carbon export inferred from oxygen anomalies in eddy cores is one to three times as much as annual new production for the region.

Correlations of Trichodesmium colony abundance with the eddy field emerged in two segments of Video Plankton Recorder observations made in the southwestern North Atlantic during fall 2010 and spring 2011. In fall 2010, local maxima in abundance were observed in cyclones. We hypothesized surface Ekman transport convergence as a mechanism for trapping buoyant colonies in cyclones. Idealized models supported the potential of this process to influence the distribution of buoyant colonies over time scales of several months. In spring 2011, the highest vertically integrated colony abundances were observed in anticyclones. These peaks in abundance correlated with anomalously fresh water, suggesting riverine input as a driver of the relationship. These contrasting results in cyclones and anticyclones highlight distinct mechanisms by which mesoscale eddies can influence the abundance and distribution of Trichodesmium populations of the southwestern North Atlantic., Key Points: Trichodesmium abundance was elevated in certain cyclonic and anticyclonic eddiesEnhancement in cyclonic eddies could be driven by Ekman convergenceAnticyclonic eddies with elevated abundance were anomalously fresh

Correlations of Trichodesmium colony abundance with the eddy field emerged in two segments of Video Plankton Recorder observations made in the southwestern North Atlantic during fall 2010 and spring 2011. In fall 2010, local maxima in abundance were observed in cyclones. We hypothesized surface Ekman transport convergence as a mechanism for trapping buoyant colonies in cyclones. Idealized models supported the potential of this process to influence the distribution of buoyant colonies over time scales of several months. In spring 2011, the highest vertically integrated colony abundances were observed in anticyclones. These peaks in abundance correlated with anomalously fresh water, suggesting riverine input as a driver of the relationship. These contrasting results in cyclones and anticyclones highlight distinct mechanisms by which mesoscale eddies can influence the abundance and distribution of Trichodesmium populations of the southwestern North Atlantic., National Science Foundation (U.S.), United States. National Aeronautics and Space Administration

The Japan/East Sea (JES) contains several oceanic regions separated by dynamic boundaries. These distinct regions and the physicals feature that establish and maintain the boundaries between the regions have significant impacts on its ocean biology. Until recently, most studies of the biology of the JES have focused on nearshore regions, with few detailed studies of the interior of the JES or the dynamic features that define the different regions. In addition, the classic sampling methods used in previous work have not allowed high-resolution studies of biological-physical interactions associated with key dynamic mesoscale frontal zones, quasi-synoptic surveys of water column and biological structure in three dimensions, or broad-scale description of the seasonal cycles in the different biogeographic regions of the JES.

Optical imaging samplers are becoming widely used in plankton ecology, but image analysis methods have lagged behind image acquisition rates. Automated methods for analysis and recognition of plankton images have been developed, which are capable of real-time processing of incoming image data into major taxonomic groups. The limited accuracy of these methods can require significant manual post-processing to correct the automatically generated results, in order to obtain accurate estimates of plankton abundance patterns. We present here a dual-classification method in which each plankton image is first identified using a shaped-based feature set and a neural network classifier, and then a second time using a texture-based feature set and a support vector machine classifier. The plankton image is considered to belong to a given taxon only if the 2 identifications agree; otherwise it is labeled as unknown. This dual-classification method greatly reduces the false positive rate, and thus gives better abundance estimation in regions of low relative abundance. A confusion matrix is computed from a set of training images in order to determine the detection and false positives rates. These rates are used to correct abundances estimated from the automatic classification results. Aside from the manual sorting required to generate the initial training set of images, this dual-classification method is fully automatic and does not require sub- sequent manual correction of automatically sorted images. The resulting abundances agree closely with those obtained using manually sorted results. A set of images from a Video Plankton Recorder was used to evaluate this method and compare it with previously reported single-classifier results for major taxa.

The Japan/East Sea (JES) may be thought of as a model or microcosm of larger oceanic systems where biogeographic boundaries juxtapose at highly dynamic boundaries. The northern and southern portions of the JES are hydrographically and biologically distinct, with the southern portion being more tropical/oligotrophic and the northern portion being more boreal/eutrophic. Regional zooplankton taxonomic and size compositions and abundance and the high-resolution vertical distribution of plankton, fluorescence, and coincident hydrography were described using the Video Plankton Recorder (VPR), equipped with high- and low-magnification cameras and environmental sensors and mounted on a vertically profiling towed vehicle, in the upper 80 m of the JES during the summer of 1999. A survey was conducted over both the northern and southern regions, including the Subpolar Front (SPF), that spanned 10–12° of latitude and longitude and covered an along track distance of 7000 km. Plankton also were collected at 15 selected stations using a ring net for silhouette analysis of taxa and size. Distributional patterns in abundance (#/liter) of plankton taxa from the VPR were quantified at sea in real time, identifying plankton automatically using a neural network classifier. The most abundant taxa identified were copepods, Oithona spp., Calanus spp., copepod nauplii, protozoa, and diatoms, with copepods the dominant taxon. The northern JES, southern JES, and North Korean Cold Current were distinct based on based on temperature-salinity properties. The hydrography was complex and characterized by multiple mesoscale features including currents and the meandering of the SPF. Different taxonomic and size compositions were observed in the three hydrographic regions. The vertical distributions of copepods and fluorescence were associated with hydrographic structure, especially at fronts. Plankton abundances varied with regional hydrographic region and environmental conditions, although strong associations were not always observed. The extremely dynamic nature of the JES may effectively mix the plankton and obscure strong gradients or differences between regions.

A long-standing problem in plankton ecology is sparseness of taxa-specific data. New optical imaging systems are becoming available which can acquire high-resolution data on the abun- dance and biomass of plankton taxa. The Video Plankton Recorder (VPR) has been designed and used for automatic sampling and visualization of major planktonic taxa at sea in real time, providing high-resolution data over a broad range of scales. Although these optical systems produce digital images of plankton that can be automatically identified by computer, the limited accuracy of auto- matic classification methods can reduce confidence in subsequent abundance estimates, especially in areas where a taxon is in low relative abundance. This paper describes an improved classification system for automatic identification of plankton taxa from digital images. Classifiers are trained from a set of images that were classified by human experts. The data set used to verify the classification system contains over 20 000 planktonic images manually sorted into 7 different categories. The new method uses co-occurrence matrices (COM) as the feature, and a Support Vector Machine (SVM) as the classifier. This new method is compared against a previous plankton recognition system, which used moment invariants, Fourier descriptors and granulometry as features and a learning vector quantization neural network as a classifier. The new method reduced the classification error rate from 39 to 28%. Subsequent plankton abundance estimates are improved by more than 50% in regions of low relative abundance. In general, the reduction in classification error was due to a combination of the use of COM and SVM.

The relationship between the distribution of zooplankton, especially euphausiids (Euphausia and Thysanoessa spp.), and hydrographic regimes of the Western Antarctic Peninsula continental shelf in and around Marguerite Bay was studied as part of the Southern Ocean GLOBEC program. Surveys were conducted from the RVIB N.B. Palmer in austral fall (April–June) and winter (July–August) of 2001. Acoustic, video, and environmental data were collected along 13 transect lines running across the shelf and perpendicular to the Western Antarctic Peninsula coastline, between 65°S and 70°S. Depth-stratified net tows conducted at selected locations provided ground-truthing for acoustic observations. In fall, acoustic volume backscattering strength at 120 kHz was greatest in the southern reaches of the survey area and inside Marguerite Bay, suggestive of high zooplankton and micronekton biomass in these regions. Vertically, highest backscattering was in the 150–450 m depth range, associated with modified Circumpolar Deep Water (CDW). The two deep troughs that intersect the shelf break were characterized by reduced backscattering, similar to levels observed off-shelf and indicative of lower zooplankton biomass in recent intrusions of CDW onto the continental shelf. Estimates of dynamic height suggested that geostrophic circulation likely caused both along- and across-shelf transport of zooplankton. By winter, scattering had decreased by an order of magnitude (10 dB) in the upper 300 m of the water column in most areas, and high backscattering levels were found primarily in a deep (>300 m) scattering layer present close to the bottom. The seasonal decrease is potentially explained by advection of zooplankton, vertical and horizontal movements, and mortality. Predictions of expected backscattering levels based on net samples suggested that large euphausiids were the dominant source of backscattering only at very particular locations and depths, and that copepods, siphonophores, and pteropods were more important in many locations.

The Marguerite Bay region of the Western Antarctic Peninsula is known to support a large population of krill during the summer and is hypothesized to be a site of successful overwintering of krill. The distributions of zooplankton biomass, abundance, and taxonomic composition at six locations on or near the continental shelf at Marguerite Bay were determined for fall and winter, 2001, as a part of the Southern Ocean GLOBEC program. Water column zooplankton were sampled using a 1-m 2 MOCNESS. Samples were analyzed for taxonomic composition, size, and estimated biomass using silhouette analysis. Characteristics of four categories (small and large copepods, small and large krill) were described in detail. Total biomass and abundance were markedly reduced in winter relative to fall. The vertical distributions of total abundance and biomass, and of taxonomic composition, were associated with the hydrographic structure of the water column. Larger larval krill were observed at all locations during winter than during fall. Krill were relatively unimportant to total biomass and abundance at most locations, while copepods frequently dominated both biomass and abundance. In fall, greatest abundance and biomass of larval krill were observed on the continental shelf in association with a persistent clockwise gyre located to the west of Adelaide Island. During winter, much lower abundances of larval krill were present in the water column throughout the study region. High abundance and biomass of juvenile and adult krill were observed only in Laubeuf Fjord (Marguerite Bay) during fall.

Adult euphausiids are difficult to capture with the nets typically used by oceanographers due in part to avoidance of the net. A cruise of the Southern Ocean GLOBEC program (NBP0103) in April/May 2001 permitted an evaluation of the efficacy of a high-powered strobe light (150 W) mounted on a 1-m2 multiple opening/closing net and environmental sampling system (MOCNESS) in reducing net avoidance. Three horizontal tows were made in Laubeuf Fjord, Marguerite Bay (western Antarctic Peninsula, 67.89°S; 68.30 W) on 28–29 May in an area that had a high abundance of adult krill (mostly Euphausia superba, Dana and a few E. crystallorophias, Holt and Tattersall). Each tow consisted of a series of paired down and up casts through a set depth interval (e.g. 50–90 m), with each successive net (335 µm mesh) sampling both a down and up cast. The strobe light was either “on” or “off” while each net was open, and when on, the light flashed at 4-s intervals. During a tow, four of the eight nets sampled with the strobe flashing and four sampled with the strobe off, in a random sequence. Total zooplankton displacement volume was significantly higher (P

The roles of plankton behavior, stratification, and microstructure in the formation of fine-scale plankton layers were examined using a 3-dimensional video plankton recorder mounted on a remotely operated vehicle. Vertically compressed plankton patches were observed in associa- tion with a cold pool over the Southern Flank of Georges Bank, extending from the tidal mixing front to the shelf-slope break during the months of May and June, 1994, 1995, 1997. In June 1995, 3 major plankton layers were present: a 10 m thick layer above the thermocline, a 1 m thick layer within the thermocline, and a third, 2 to 5 m thick layer immediately below the thermocline. Energy dissipation rate was lowest in the central layer and increased in both top and bottom layers. Some passive organ- isms and particles, e.g. the colonial diatom Chaetoceros socialis and rod-shaped diatoms, were con- centrated in all 3 layers, while marine snow particles were found only in transitional regions. All stages of Calanus spp. were present in high numbers on the fringes of all 3 layers, while Oithona sp. was found only in the thin, central layer. Plankton were significantly aggregated only when the motility number, Mn (i.e. ratio of plankton swimming speed/rms turbulent velocity) was greater than 3, suggesting dominance of plankton behavior over physical structure. Under both quiescent and turbulent conditions, the Lagrangian frequency spectra (f ) for swimming plankton and passive particles decreased with a slope of f -2 . However, in quiescent conditions, the magnitude of the spec- trum for swimming plankton was 10-fold greater than for passive particles, illustrating a decoupling of plankton swimming from turbulent eddies. The air/water interface, the pycnocline, and multiple shear interfaces at density discontinuities act as boundaries to vertical zones where plankton be- havior may succumb to or dominate background microstructure, thus providing a mechanism for formation of plankton and particulate layers.

A fundamental problem in limnology and oceanography is the inability to measure the taxonomic composition of plankton quickly over a broad range of scales. Traditional sampling with bottles and nets provides critical data at the species-level, but has limited spatio-temporal coverage and can destroy ubiquitous delicate forms. To augment traditional sampling, recent advances in bio- acoustics and non-imaging optics provide real-time high-resolution data on biomass abundance and size composition. New optical imaging approaches provide coarse taxonomic composition but require manual image identification, preventing real-time observation. Here, we describe a method of opti- cal sampling and analysis, using the Video Plankton Recorder, to automatically identify plankton to major taxa (and to species in some cases) and observe their distributions at sea in real time. We pre- sent a detailed assessment of classifier accuracy, including a comparison of machine- and hand- classification of images. The automated classification method was found to be sufficiently accurate for estimating abundance patterns of dominant taxa but not for less abundant taxa. The range in overall accuracy was 60 to 70% for 7 taxa and 79 to 82% for 2 taxa, with accuracies for individual taxa rang- ing between 45 and 91%. Classification error was small relative to natural variability in abundance of dominant taxa. For a given taxon, the error in the abundance estimate was low in regions of high relative abundance. A manual correction step can be used in areas of low relative abundance to obtain accurate abundance estimates. Example data from 2 cruises are presented to illustrate the util- ity of real-time taxa-specific data collection. These data represent the first real-time automatic iden- tification and mapping of plankton taxa at sea. This methodology represents an intermediate step towards the ultimate goal of real-time identification of plankton to the level of species and life stage. At present, optical imaging methods cannot replace net and bottle surveys, but can be used to obtain coarse taxonomic composition of plankton (including fragile forms) with an identification accuracy that is high enough to produce quantitative high-resolution maps of abundant taxa in real time.

Colonial spumellarian Radiolaria are heterotrophic protists that form large (up to several meters in length), gelatinous structures in the surface waters of all tropical and subtropical oceanic ecosystems. These species are morphologically and trophically complex and some, but not all, produce silica skeletal structures of considerable paleontological significance. Skeletonless species of Radiolaria are poorly sampled by plankton nets, which can severely damage these delicate organisms. Therefore, abundances of colonial Radiolaria typically have been underestimated in quantitative studies of zooplankton abundance and biomass. Here we document the abundances of colonial Radiolaria in the central North Pacific based on analysis of video images from a miniaturized video plankton recorder. We observed abundances of radiolarian cells in colonies that exceeded previous reports of total Radiolaria by more than ten-fold, and counts of skeleton-bearing Radiolaria by more than two to three orders of magnitude. Biomass (carbon) within these colonies was similar to or greater than the total radiolarian biomass (i.e. including all solitary species) previously reported for the Pacific. Symbiont productivity within colonial Radiolaria was estimated to constitute a modest but significant fraction of total primary productivity (up to 9%) in the upper 150 m. These findings indicate an important contribution of skeletonless spumellaria to food webs and biogeochemical cycles of these communities.

It is well known that plankton abundance is highly variable over a broad range of scales. Conventional sampling with nets, pumps, and bottles is discrete and covers only a small portion of the total variance spectrum. Development of the Video Plankton Recorder (VPR) has enabled us to quantify the abundance of seston and plankton, including delicate taxa, over a range of scales from centimeters to hundreds of kilometers. During the 1994–1995 GLOBEC Georges Bank field years, three VPR surveys were conducted across the bank from the Slope Water in the south to the Gulf of Maine in the north, a distance of ∼200 km. The surveys, conducted in June 1994, January 1995, and March 1995, intersected at least four distinct water types (Slope Water, stratified bank water, well-mixed bank water, Gulf of Maine water) and crossed several frontal boundaries (shelf break front, tidal front, Gulf of Maine front). The Video Plankton Recorder was equipped with temperature, conductivity, fluorescence, and transmissivity probes in addition to two video cameras, permitting comparison of the plankton and particle distributions with the physical fields. Only data collected using the low-magnification camera are considered here. A combination of analytical methods including temperature–salinity–plankton plots and statistical analyses (spatial variance spectra, principle component analysis, and correlation analysis) revealed that the distribution of taxa and particles were associated with particular water mass types but that smaller-scale variability in plankton abundance did not appear to be tightly coupled to or correlated with hydrography. The distributions and seasonal progression in abundance of Calanus finmarchicus , the most abundant plankton taxon, revealed a deep dwelling population in the Slope Water and shallower populations on the bank and in the Gulf of Maine in January with abundance becoming increasingly greater on the bank in March and June. The data indicate that physical advection of water mass types and intrinsic plankton was important to the establishment of Calanus populations on Georges Bank.

A set of observational system simulation experiments (OSSEs) have been designed to assess quantitatively the synopticity of the broad-scale surveys of Georges Bank carried out as part of the US GLOBEC program. The approach uses model simulations that contain realistic spatial and temporal fluctuations of adult females of the planktonic copepod Calanus finmarchicus observed during February and March 1995. Simulations are constructed with two types of assimilation procedures (nudging and the adjoint method), which are used to dynamically interpolate between the two broad-scale surveys taken one month apart. Using these simulations as representations of the real ocean, the model fields are subsampled in space and time along a typical cruise track. These simulated data are then objectively analyzed and the resulting maps compared with “reality” as represented in the original simulation. Results indicate a total error of approximately 50%, which is comprised mostly of simple mapping error (incomplete spatial sampling) and a smaller contribution from space/time smearing. Adjustment of the station positions for displacement by the mean flow reduces the latter error by about half.

A detailed physical model of Georges Bank, including M2 tidal rectification, realistic topography, Mellor-Yamada 2.5 mixed-layer dynamics, and time-varying wind forcing, was used to simulate plankton transport. Wind records from January 1 through March 4 of each year from 1968 through 1993 were selected to force the model. For each year, two model runs were made, one time-variant and the other using the mean wind stress for the entire period. Simulations using no wind and a 26-year climatological mean (1968–1998) also were conducted. Differences in net transport and 2-month mean currents between the vector-averaged and time-varying runs for a given year were slight. Plankton distribution in time-varying winds moved in response to transient wind events, but distributions at the end of the 60-day simulation period were remarkably similar to those from model runs using vector-averages of the same winds. Interannual differences were significant; depending on the direction of the mean wind stress, tracers were transported to several different regions on and off the bank. The use of wind-stress averages over a 2-month period is supported for models addressing transport on that time scale. Interannual variability in winter wind stress may play a major role in determining transport and subsequent recruitment of plankton on the bank.

The underlying scientific objective here is to determine the mechanisms that control seasonal variations in the abundance of Pseudocalanus spp. in the Georges Bank–Gulf of Maine region. It is postulated that the observed distributions result from the interaction of the population dynamics with the climatological circulation. The problem is posed mathematically as a 2-D advection–diffusion–reaction equation for a scalar variable. Given an initial distribution of animals, we seek the population dynamics source term R(x,y) such that integration of the forward model will result in predictions3 that minimize the sum of squares of differences with observed concentrations at a later time. An adjoint data assimilation technique has been designed for these purposes. This approach has been used to invert for the population dynamics associated with the transition between bimonthly (i.e. for 2 months) climatological Pseudocalanus spp. distributions derived from MARMAP data. Vertically averaged velocity and diffusivity fields diagnosed from hydrodynamical simulations of the climatological flow are specified. Solutions converge rapidly, and the procedure reduces the cost function by an order of magnitude within 50 iterations. The resulting population dynamics vary considerably in space and time, as does the balance between local tendency, physical transport and biological source terms. Generally speaking, the patterns in population dynamics are not inconsistent with current knowledge concerning potential controls such as predation and food limitation. Analysis of the solutions indicates that the Pseudocalanus spp. population centres located in the western Gulf of Maine and on Georges Bank may be self-sustaining, in contrast to prior studies which characterize the former as a source region for the latter.

Estimation of zooplankton biological parameters such as biomass distributions from single-frequency acoustic surveys of zooplankton is generally not possible because of the diversity of taxa present in assemblages and resultant ambiguities in acoustic analysis. We present an approach that assumes that at a given, fixed depth, the relative proportions of sizes across species remains constant. Using this assumption, along with independently sampled Video Plankton Recorder (VPR) data on the species and size composition of the sound scattering assemblage, single-frequency acoustic data have been used to estimate the spatial distribution of zooplankton taxa and their biomass within a region of ocean without the use of acoustic scattering models. The data from a joint-ship study of the fine-scale physical and biological structure of a 3.5 km×4.5 km×75 m deep region of Georges Bank were used to demonstrate the utility of this approach. The spatial distributions of zooplankton biomass were estimated for pteropods, copepods, amphipods, euphausiids, chaetognaths and fish. Within each of the six parallel cruise legs that constituted the joint-ship survey, we estimated the relationship between mean zooplankton concentration from the VPR and mean acoustic volume backscatter within each 2 m depth bin. These relationships were used to scale the volume backscatter data throughout the transect into estimates of total zooplankton concentrations. The relative proportion of each taxon was estimated from the VPR for each 2 m depth bin within each leg and used to convert total zooplankton concentrations to taxon-specific concentrations. We then estimated biomass for each taxon using VPR estimates of mean sizes along the transect in conjunction with length-wet mass morphometric relationships. Several large acoustic patches were detected within the surveyed volume of water. Volume backscattering within the 10–20 m depth strata was largely associated with copepod biomass, while deeper scattering appeared to be a consequence of pteropod biomass. Amphipods contributed to scattering in the upper 10 m of the sixth leg of the grid. Euphausiids made minor contributions to the observed volume backscattering, while scattering due to chaetognaths and fish appeared to be negligible. Our results suggest that these patches were primarily due to the presence of copepods and pteropods. Our biomass estimates were highly correlated with data from a 1 m2 MOCNESS tow in leg 6; however, they predicted only 19–29% of the measured silhouette biomass from the net tow. This discrepancy was explained by a systematic underestimation of zooplankton concentrations by the semi-automatic image analysis system used to process VPR data. The results described herein suggest that the combination of independent data from optical samplers, nets or pumps and single frequency acoustic surveys may provide a viable method for generating near real-time estimates of zooplankton biomass distributions.

Plankton form the base of the food chain in the ocean and are fundamental to marine ecosystem dynamics. The rapid mapping of plankton abundance together with taxonomic and size composition is very important for ocean environmental research, but difficult or impossible to accomplish using traditional techniques. In this paper, we present a new pattern recognition system to classify large numbers of plankton images detected in real time by the Video Plankton Recorder (VPR), a towed underwater video microscope system. The difficulty of such classification is compounded because: 1) underwater images are typically very noisy, 2) many plankton objects are in partial occlusion, 3) the objects are deformable and 4) images are projection variant, i.e., the images are video records of three-dimensional objects in arbitrary positions and orientations. Our approach combines traditional invariant moment features and Fourier boundary descriptors with gray-scale morphological granulometries to form a feature vector capturing both shape and texture information of plankton images. With an improved learning vector quantization network classifier, we achieve 95% classification accuracy on six plankton taxa taken from nearly 2,000 images. This result is comparable with what a trained biologist can achieve by using conventional manual techniques, making possible for the first time a fully automated, at sea-approach to real-time mapping of plankton populations.

T H E PRESENCE OF PATCHES and layers in marine pelagic ecosystems may play an important role in providing food for higher trophic levels at concentrations high enough to support the metabolism, growth, and reproduction of the consumers. There has been a persistent enigma of average bulk water prey concentrations frequently being below that necessary for consumer growth, yet the consumer populations are observed to grow and persist (Lasker, 1975: Mullin, 1988). Concentrated patches or layers of prey organisms are not accurately sampled by traditional means such as net tows, bottle sampling, and even standard CTD and in situ fluorescence profiling. The formation of a subsurface chlorophyll maximum (SCM) during the late spring and early summer in temperate waters is well established (Steele and Yentsch, 1960). This maximum is most likely caused by the combination of sinking of larger phytoplankton cells from surface waters following nutrient depletion, and the establishment of a seasonal pycnocline within the euphotic zone (Jamart et al., 1977). This combination of biological and physical factors probably controls the composition of the SCM and its vertical extent. In some cases the SCM could be vertically compressed enough to lbrm a thin layer, on the order of several meters thick. It is likely that if such layers are common in the marine environment, consumers have adapted to

Traditional methods for determining spatial distributions of planktonic taxa involve net, pump, and bottle collections followed by the tedious and time-consuming task of plankton sample analysis. Thus, plankton ecologists often require months or even years to process samples from a single study. In this paper, we present a method that allows rapid visualization of the distribution of planktonic taxa while at sea. Rapid characterization of plankton distributions is essential in the dynamic physical environment, where biological and physical patterns can change quickly. Such a “sample-and-observe” capability is necessary for mapping ephemeral features (such as patches, eddies, jets, plumes) and determining appropriate locations to conduct more localized sampling, including in situ observational studies. We describe the techniques used in imaging the plankton, analyzing the video, and visualizing the data. We present an example of at-sea data analysis conducted aboard R.V. Columbus Iselin on Georges Bank in May 1994 and visualizations of the 3-dimensional distribution of selected planktonic taxa in a 2 × 2 km × 90 m volume of seawater.