US Continental Shelf Research Articles

Changing source waters on the Northeast US Continental Shelf: Variation in nutrient supply and phytoplankton biomass

The Northeast US Continental Shelf (NES) is a highly productive marine ecosystem that has experienced wide swings in phytoplankton chlorophyll concentration (CHL). To better understand this variability, we examined changes in CHL over the period 1998–2022, while also considering three indicators of the potential supply of nutrient source waters including cross-shelf advection via deep channels, transport from beyond the shelf edge via Gulf Stream warm core rings (WCR), and input from river and estuarine discharge. Traditionally, deep channel advection of water across the NES was assumed to be derived from Labrador Slope Water (LSW) and Warm Slope Water (WSW). These designations do not fully capture the range of water types contributing to cross-shelf advection. The contribution of LSW and WSW was reciprocal over time, with the presence of WSW at an increased level in recent years. There has been an increase in the number of WCRs off the NES represented by indices of ring occupancy. Precipitation increased over the study period as well, generally over the NES region and in particular in the Mid-Atlantic Bight drainage. We see evidence of the effect of increased precipitation on the NES proper through a change in the area of the ocean surface having 555 nm reflectance with sr−1 > 0.004. Using a canonical analysis, CHL correlated positively with the proportion of LSW and negatively with WSW. These correlations suggest there are aspects of the nutrient content associated with these water masses that are key to phytoplankton growth. WCR frequency negatively correlated with CHL, which was expected since the nutrient loadings of WCRs tends to be low. Finally, CHL negatively correlated with precipitation rate, which suggests terrestrial origin nutrient inputs to the NES are minor. We suggest that in order to understand future CHL dynamics in the NES, careful consideration of advective sources of nutrients in the Northwest Atlantic is necessary.

Quantifying predation on benthos and its overlap with bottom fishing in the NW Atlantic

AbstractContinental shelves experience many human pressures with demersal fisheries central to disturbing the ocean floor. However, ecological processes such as predation rates of benthos and their relationship with bottom fishing are often unknown for large marine ecosystems. We examined the amount of benthos consumed by 14 benthivorous fishes, the overlap between benthos predation and bottom fishing (dredge and trawl gear), and temporal trends in benthivorous fish abundance and the number of fishing trips on the northeast US continental shelf. Mean annual predation (biomass of prey removed) and 95% confidence intervals ranged from .0002 (.0001–.0003) to 3967 (1761–7112) t per 10‐min area squared grid cell and prey taxa for these benthivorous fishes. Predation and bottom fishing had overlapping footprints of activity, which were slightly stronger for dredge gear. Trophic success (ratio of prey biomass eaten to the biomass of the benthivore community per grid cell) revealed more Bivalvia, Gammaridea, and Polychaeta eaten in areas targeted by trawling with more fish biomass. In contrast, dredging did not target fish biomass, but these areas had increased (Echinoidea, Gammaridea, and other benthos) or decreased (Ophiuroidea) trophic success relative to dredging footprint, suggesting habitat preferences for benthic prey and demersal fisheries have converged rather than diverged. Despite declines in bottom fishing, recent increases in benthivorous fish abundance and growing interest in ocean floor use suggest that fisheries managers should ensure benthivores have sufficient prey resources relative to their community size and human pressures to promote long‐term sustainability of demersal fisheries and healthy ecosystems.

Anticipating the winds of change: A baseline assessment of Northeastern US continental shelf surficial substrates

AbstractThe introduction of thousands of wind turbines along the North American Atlantic continental shelf over the next decade will constitute the largest regional change in marine substrates since the retreat of the Laurentide Ice Sheet over 14,000 years ago. Here, two large data sets, SMAST drop camera survey (242,949 samples, 2003 to 2019) and the US Geological Survey databases (27,784 samples, 1966 to 2011), are combined to derive sea floor surficial substrate probability maps for the Northeastern US continental shelf from Virginia Beach to the Gulf of Maine to 300 m depth (218,571 km2). Geostatistical models were used to estimate the probability of five geologic and one biogenic substrate types being present at a 250 m resolution, and the proportional contribution of each substrate type to the seabed composition at a 500 m resolution. By providing the first synoptic maps depicting the probability of a particular substrate or combination of substrates occurring at any location on the Northeastern US continental shelf, including planned wind energy sites, we aim to (1) provide insights regarding how substrates in the areas selected for wind energy development compare with other locations, (2) motivate the development of a priori expectations for ecosystem changes to inform monitoring and research efforts going forward, and (3) to provide a baseline characterization of the Northeastern US continental shelf surficial substrates to support robust examination of the future changes observed in areas impacted by wind energy installations.

Multispecies population-scale emergence of climate change signals in an ocean warming hotspot

Abstract Ocean waters of the Northeast US continental shelf have warmed rapidly in recent years, with sea surface temperatures rising 2.5 times faster than those of the global oceans. With this strong warming trend, the frequency and duration of marine heatwaves have increased. These temperature changes stood out as a distinct warm temperature regime during the 2010s. During this decade, fish population characteristics also differed from the past. Species distribution shifts were detected for many species, demonstrating one way species could adapt to warming conditions. However, for most species, distribution shifts were insufficient to avoid warmer surface or bottom temperatures. As species occupied warmer habitats, growth patterns aligned with expectations for warming temperatures. Consistent with the temperature-size rule, some species exhibited faster growth at early life stages but plateaued at smaller body sizes; other species, however, experienced reduced growth across all ages, indicating thermal stress. Finally, population productivity indexed by the recruit-to-spawner ratio declined significantly during the 2010s for some populations. Changes in these three processes—distribution, growth, and productivity—indicate the emergence of climate change signals across multiple Northeast US fish populations. These effects create new challenges for fishery managers and industry participants operating in the context of non-stationarity and uncertainty.

Regional growth rates and growth synchronicity between two populations of Arctica islandica in the western Mid-Atlantic (US)

Arctica islandica supports an important fishery in the US Mid-Atlantic. This species is extremely slow growing and long-lived, characteristics that may make this species particularly vulnerable to fishing pressure and climate change. Understanding regional growth dynamics over time and growth responses to changing environments will improve current fishery assessments to maintain the sustainability of this stock. Two populations of A. islandica from Georges Bank and off Long Island on the US continental shelf with observed ages between 17 and 310 y were evaluated for age-at-length relationships and growth trends over time. Growth rates have been increasing at Georges Bank and Long Island since the 1700s. Growth rates at Long Island have been accelerating and have exceeded those at Georges Bank since the 1980s. Growth rates from this study support previous research that this species is sexually dimorphic, and females grow faster than males within a population post-maturation. Positive growth index periods at both sites may be synchronous with 32-y harmonics of the Atlantic Multi-Decadal Oscillation. A modification to the traditional Tanaka growth model that included a growth term to further increase growth at old age proved the best-fit growth model to not only each population, but also to birth-year cohorts. Both the classic and modified Tanaka models used in this study are vast improvements over the von Bertalanffy models currently applied to this species in assessment models and population dynamics models. Increasing growth rates over time resulted in fewer years of reproduction prior to recruiting to the fishery as A. islandica are reaching fishery size in an increasingly short period of time. The impact that reduced years of reproduction has on A. islandica population resiliency is yet unknown.

Shelf break exchange processes influence the availability of the northern shortfin squid, Illex illecebrosus, in the Northwest Atlantic

AbstractThe United States Northern Shortfin squid fishery is known for its large fluctuations in catch at annual scales. In the last 5 years, this fishery has experienced increased availability of Illex illecebrosus along the Northeast US continental shelf (NES), resulting in high catch per unit effort (CPUE) and early fishery closures due to quota exceedance. The fishery occurs within the Northwest Atlantic, whose complex dynamics are set up by the interplay between the large‐scale Gulf Stream, mesoscale eddies, Shelfbreak Jet, and shelf‐slope exchange processes. Our ability to understand and quantify this regional variability is requisite for understanding the availability patterns of Illex, which are largely influenced by oceanographic conditions. In an effort to advance our current understanding of the seasonal and interannual variability in this species' relative abundance on the NES, we used generalized additive models to examine the relationships between the physical environment and hotspots of productivity to changes in CPUE of I. illecebrosus in the Southern stock component, which comprises the US fishery. Specifically, we derived oceanographic indicators by pairing high‐resolution remote sensing data and global ocean reanalysis physical data to high‐resolution fishery catch data. We identified a suite of environmental covariates that were strongly related to instances of higher catch rates. In particular, bottom temperature, warm core rings, subsurface features, and frontal dynamics together serve as indicators of habitat condition and primary productivity hotspots, providing great utility for understanding the distribution of Illex with the potential for forecasting seasonal and interannual availability.

Broadband measurements and modeling of low-grazing angle bottom reflections from muddy marine sediments

In 2017 and 2022, a series of experiments using explosive sound sources were conducted on the New England Mud Patch (NEMP), an area of the Eastern US Continental shelf defined by its thick muddy seafloor sediments. Broadband measurements from the near-bottom Intensity Vector Acoustic Recorders (IVARs) reveal resonant frequencies in the bottom reflected signals, which are excited at very low-grazing angles. A signal model based on a layered-bottom reflection coefficient is used to examine the geoacoustic properties of the marine mud, which leads to the conclusion that the sound-speed contrast across the water-mud interface (i.e. index of refraction, n) is less than one (n < 1), and also an increase in sound-speed occurs within the deeper mud-sediments (n > 1). Measurements in May 2022, replicating the same source and receiver locations from March 2017, also show resonances in the bottom-reflected signal. Differences between the two data sets (2017 and 2022) are primarily caused by the complex oceanography encountered during the spring-time measurements, absent during the isothermal winter conditions. Comparison of the two datasets examines the stability of the sound-speed contrast, including the effect of time-varying temperature at the water-mud interface.

Using Geographical Overlaps to Track Temporal Changes in Species Interactions and Community Coexistence Instability

Environmental and climatic changes are expected to redistribute species, altering the strengths of species interaction networks; however, long-term and large-scale evaluations remain elusive. One way to infer species interaction networks is by analyzing their geographical overlaps, which provides indices of species interdependence, such as mean spatial robustness (MSR), which represents the geographical impact of a species on other species, and mean spatial sensitivity (MSS), which indicates how a species is influenced by other species. Integrating MSR and MSS further allows us to assess community coexistence stability and structure, with a stronger negative relationship between MSR and MSS (i.e., species are unequally dependent on each other) within a community at a given time suggesting a more stable community. Here, we assessed multidecadal changes in adult marine fish communities using bottom trawl datasets across latitudes from 1982 to 2011 in the Eastern US Continental Shelf, North Sea, and Eastern Bering Sea. Consistent, significant long-term increasing temporal trends of MSR and MSS were found in all three large marine communities. MSR exhibited strong correlations with species’ range sizes, especially in high-latitude communities, while MSS was strongly positively correlated with species’ median proportion of overlap with interacting species. The relationships between MSR and MSS were generally negative, indicating stably coexisting fish communities. However, the negative relationships weakened over time, implying that the coexisting fish communities gradually became unstable. Our findings provide an assessment of changes in spatially geographical aspects of multiple species, for decades and at mid- to high latitudes, to allow the detection of global ecological changes in marine systems by alternative estimation of geographic overlaps of species interaction networks. Such species co-occurrence estimation can help stay vigilant of strategies for accelerating climate change mitigation particularly at coarser spatial scales.

Jointly modeling marine species to inform the effects of environmental change on an ecological community in the Northwest Atlantic

Single species distribution models (SSDMs) are typically used to understand and predict the distribution and abundance of marine fish by fitting distribution models for each species independently to a combination of abiotic environmental variables. However, species abundances and distributions are influenced by abiotic environmental preferences as well as biotic dependencies such as interspecific competition and predation. When species interact, a joint species distribution model (JSDM) will allow for valid inference of environmental effects. We built a joint species distribution model of marine fish and invertebrates of the Northeast US Continental Shelf, providing evidence on species relationships with the environment as well as the likelihood of species to covary. Predictive performance is similar to SSDMs but the Bayesian joint modeling approach provides two main advantages over single species modeling: (1) the JSDM directly estimates the significance of environmental effects; and (2) predicted species richness accounts for species dependencies. An additional value of JSDMs is that the conditional prediction of species distributions can use not only the environmental associations of species, but also the presence and abundance of other species when forecasting future climatic associations.

Estimating North Atlantic right whale prey based on Calanus finmarchicus thresholds

The planktonic copepod Calanus finmarchicus is a fundamental prey resource for the critically endangered North Atlantic right whale Eubalaena glacialis. Incorporation of prey information into E. glacialis decision support tools could improve management. Zooplankton time series are usually analyzed with respect to abundance, but predators such as E. glacialis forage based on whether prey aggregations exceed energetic thresholds. In order to better understand the distribution and dynamics of the high-abundance end of C. finmarchicus on the northeastern US continental shelf, where E. glacialis feed, we modeled the environmental conditions associated with C. finmarchicus densities that exceed nominal feeding thresholds. Threshold values were chosen based on a review of E. glacialis feeding behavior throughout the domain. Following model selection procedures, we used a random forest model with bathymetry, bottom temperature, bottom salinity, day of year, sea surface temperature, sea surface temperature gradient, bathymetric slope, time-integrated chlorophyll, current velocity gradient, and wind covariates. Model performance was highest with thresholds that matched reported E. glacialis feeding thresholds equivalent to 10000 copepods m-2. The high-density aggregations of C. finmarchicus had some different covariate responses compared to previous statistical abundance models, such as a warmer temperature range at both the surface and at depth, as well as a much higher degree of spatial variability. The output data layers of the model are designed to link with E. glacialis models used in US governmental decision support tools. Including this type of foraging information in decision support tools is a step forward in managing this critically endangered species.

Resource Occurrence and Productivity in Existing and Proposed Wind Energy Lease Areas on the Northeast US Shelf

States in the Northeast United States have the ambitious goal of producing more than 22 GW of offshore wind energy in the coming decades. The infrastructure associated with offshore wind energy development is expected to modify marine habitats and potentially alter the ecosystem services. Species distribution models were constructed for a group of fish and macroinvertebrate taxa resident in the Northeast US Continental Shelf marine ecosystem. These models were analyzed to provide baseline context for impact assessment of lease areas in the Middle Atlantic Bight designated for renewable wind energy installations. Using random forest machine learning, models based on occurrence and biomass were constructed for 93 species providing seasonal depictions of their habitat distributions. We developed a scoring index to characterize lease area habitat use for each species. Subsequently, groups of species were identified that reflect varying levels of lease area habitat use ranging across high, moderate, low, and no reliance on the lease area habitats. Among the species with high to moderate reliance were black sea bass (Centropristis striata), summer flounder (Paralichthys dentatus), and Atlantic menhaden (Brevoortia tyrannus), which are important fisheries species in the region. Potential for impact was characterized by the number of species with habitat dependencies associated with lease areas and these varied with a number of continuous gradients. Habitats that support high biomass were distributed more to the northeast, while high occupancy habitats appeared to be further from the coast. There was no obvious effect of the size of the lease area on the importance of associated habitats. Model results indicated that physical drivers and lower trophic level indicators might strongly control the habitat distribution of ecologically and commercially important species in the wind lease areas. Therefore, physical and biological oceanography on the continental shelf proximate to wind energy infrastructure development should be monitored for changes in water column structure and the productivity of phytoplankton and zooplankton and the effects of these changes on the trophic system.

Multi-decadal trends in contingent mixing of Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic from otolith stable isotopes

The Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic is comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in US fished regions. Thus, assessment and management of this population can be sensitive to levels of mixing between contingents, which remain unknown. Multi-decadal trends in contingent mixing levels within the US fisheries region were assessed, and the contingent composition across seasons, locations, ages, and size classes were characterized using archived otoliths and developing a classification baseline based on juvenile otolith carbon and oxygen stable isotopes (δ13C/δ18O values). Classification of age ≥ 2 adults demonstrated that northern contingent mixing was prevalent within the US continental shelf waters during the past 2 decades (2000–2019), providing an important seasonal subsidy to the US winter fishery despite substantial depletion in spawning stock biomass of the dominant northern contingent. While the majority of older fish were of the northern contingent during the early 2000s, the southern contingent contribution increased with age/size class during the recent period (2013–2019). Spatial mixing was most prevalent during February and March when the northern contingent occurred as far south as the Delmarva Peninsula, but were mostly absent from US waters in May. A positive relationship (albeit not significant; r = 0.60, p = 0.07) occurred between northern contingent mixing and US fisheries landings, which could imply that higher contingent mixing levels might be associated with greater landings for the US winter mackerel fishery. The yield of the Northwest Atlantic mackerel depends upon the status of the northern contingent, with the southern contingent possibly more prone to depletion. Spatially explicit stock assessment models are recommended to conserve both productivity and stability in this two-component population.

Offshore Oil and Gas Safety: Protection against Explosions

Offshore oil and gas operations carry a high risk of explosions, which can be efficiently prevented in many cases. The two most used approaches for prevention are: (1) the “International Electrotechnical Commission System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres” (IECEx) and (2) European “Atmosphere Explosible” (ATEX) schemes. The main shortcoming for the IECEx scheme is in the fact that it does not cover nonelectrical equipment, while for the ATEX scheme, it is due to the allowed self-certification for a certain category of equipment in areas with a low probability of explosions, as well as the fact that it explicitly excludes mobile offshore drilling units from its scope. An advantage of the IECEx scheme is that it is prescribed by the US Coast Guard for protection against explosions on foreign mobile offshore drilling units, which intend to work on the US continental shelf but have never operated there before, with an additional requirement that the certificates should be obtained through a US-based Certified Body (ExCB). Therefore, to avoid bureaucratic obstacles and to be allowed to operate with minimized additional costs both in the US and the EU/EEA’s offshore jurisdictions (and very possibly worldwide), all mobile offshore drilling units should be certified preferably as required by the US Coast Guard.

Northern Shortfin Squid (Illex illecebrosus) Fishery Footprint on the Northeast US Continental Shelf

Northern shortfin squid (Illex illecebrosus) have presented a challenge for US fishery management because of their life history traits and broad population distribution. They are characterized by a short semelparous lifespan and high interannual variability in recruitment. Much of the stock resides outside of the boundaries of existing US fisheries surveys and US fishing effort. Based on the annual migration pattern and broad geographic distribution of shortfin squid, it is believed that the US squid fishery in the Mid-Atlantic has not had a substantial impact on the stock; however, recent catches are viewed as tightly constrained by quotas. To better estimate the potential impact of fishing on the resource, we worked with industry representatives, scientists, and managers to estimate the availability of the northern shortfin squid stock on the US continental shelf to the US fishery. Taking a novel analytical approach, we combine a model-based estimate of the area occupied by northern shortfin squid with the empirical US commercial shortfin squid fishery footprint to produce estimates of the area of overlap. Because our method overestimates the fishery footprint and underestimates the full distribution of the stock, we suggest that our estimates of the overlap between the area occupied by the squid and the fishery footprint is a way to develop a conservative estimate of the potential fishery impact on the stock. Our findings suggest a limited degree of overlap between the US fishery and the modeled area occupied by the squid on the US continental shelf, with a range of 1.4–36.3%. The work demonstrates the value of using high-resolution, spatially explicit catch and effort data in a species distribution model to inform management of short-lived and broadly distributed species, such as the northern shortfin squid.

Modeling the impacts of climate change on thorny skate (Amblyraja radiata) on the Northeast US shelf using trawl and longline surveys

AbstractClimate change has been shown to impact marine fish populations and communities. With small population sizes, long reproduction times, and a rapidly warming habitat, thorny skate (Amblyraja radiata) could be particularly vulnerable. To examine this possibility, we used a two‐stage generalized additive model to project future thorny skate abundances under two different climate scenarios. This is the first study in the northeastern United States to compare projections based on different survey methods (bottom trawl and longline), and results were heavily impacted by survey methodology. Models trained with the NOAA Bottom Trawl Survey projected a decrease in abundance of ~60%–80% in the Gulf of Maine and Georges Bank under the RCP 8.5 climate scenario. With aggressive mitigation (RCP 4.5), these decreases could be reduced to ~35%–45%. Models trained with a recent NOAA longline survey indicated that thorny skate abundance would be reduced 22% and 37% under business as usual and mitigation, respectively. There are substantial methodological differences between the two data sets, including capture technique and efficiency, total habitat coverage, and spatio‐temporal coverage. This underscores the importance of continued, methodologically diverse surveys on the Northeast US continental shelf. Our results indicate that climate change will continue to negatively impact thorny skate populations by reducing the amount of thermally suitable habitat in the southern extent of their range. This information should be considered in future management decisions.

Multispecies functional responses reveal reduced predation at high prey densities and varied responses among and within trophic groups

AbstractUnderstanding predator–prey interactions is critical for marine fisheries and ecosystem management as they shape community structure, regulate prey populations and present energy demands critical for community sustainability. We examined multispecies functional responses of 17 fishes (48 predator‐size combinations) spanning piscivores, planktivores and benthivores for the northeast US continental shelf. Similar to previous work, linear relationships between predation and prey density (Holling type I response) were not supported, since model estimates of handling time were greater than zero for the prey considered. Instead, a clear majority of the predators sampled were Holling type III feeders (sigmoidal; prey switching or learning). For piscivores, nearly all responses were Holling type III with the exception of one being Holling type II (hyperbolic; satiation). Planktivores and benthivores exhibited a combination of type IV (feeding confusion at high prey density) and Holling type III responses. The relationships were predator‐ and prey‐dependent, which is counter to assumptions that are often made of trophic groups. Decreased predation at high prey densities (type IV response) present among planktivores and benthivores suggests an overestimation of predation can occur if ignored. This contrasts with fish and squid prey which primarily invoked a Holling type III response. Functional responses are key to modelling trophic interactions for multispecies and ecosystem models. By refining these inputs in a multispecies context with empirical data, we can advance our understanding of whole‐shelf ecology and improve decision‐making tools for resource management.

An ensemble high‐resolution projection of changes in the future habitat of American lobster and sea scallop in the Northeast US continental shelf

AbstractAimTo address the uncertainty associated with climate‐driven biogeographical changes in commercial fisheries species through an ensemble species distribution modelling (SDM) approach.LocationNortheast US Continental Shelf Large Marine Ecosystem (NEUS‐LME).MethodsWe combined an ensemble SDM platform (BIOMOD 2) and a high‐resolution global climate model (NOAA GFDL CM2.6) to quantify spatiotemporal changes in habitat of two commercially important species in the Northeast US Continental Shelf Large Marine Ecosystem (NEUS‐LME); American lobster (Homarus americanus); and sea scallop (Placopecten magellanicus). An ensemble SDM was calibrated using multi‐decadal fisheries‐independent surveys (1984–2016). Statistically weighted species‐specific ensemble SDM outputs were combined with 80 years of projected bottom temperature and salinity changes in response to a high greenhouse gas emissions scenario (an annual 1% increase in atmospheric CO2).ResultsStatistically significant changes (p < .05) in habitat suitability for both species were found over a large portion of the study area. Sea scallop undergoes a northward shift over the study period, while American lobster moves further offshore. The ensemble projections showed that several management zones were identified with increases and decreases in species‐specific habitat. Uncertainty due to variations in ensemble member models was also found in the direction of change within each management zone.Main conclusionsThis study provides ensemble estimates of climate‐driven changes and associated uncertainties in the biogeography of two economically important species in the United States. Projected climate change in the NEUS‐LME will pose management challenges, and our ensemble projections provide useful information for climate‐ready management of commercial fisheries.

Patterns in fish biodiversity associated with temperate reefs on the southeastern US continental shelf

Temperate reef fishes provide many benefits to humans including food, sport, and ecotourism, yet remain severely understudied compared to coral reef fishes in tropical environments. We used 3 years of underwater video data (n = 4130 samples) from hardbottom reefs along the continental shelf of the southeastern US Atlantic coast (i.e., North Carolina to Florida; ~ 100,000 km2) to quantify the spatial and temporal patterns of temperate reef fish biodiversity in the region. Overall, 210 taxa were identified on video from 53 families, 138 of which could be identified to the species level. Species with the highest percent occurrence were gray triggerfish (Balistes capriscus; observed on 45.6% of all videos), tomtate (Haemulon aurolineatum; 42.7%), and red porgy (Pagrus pagrus; 39.4%), and 23 species were observed on more than 10% of videos. Latitudinal variability swamped temporal changes (2015–2017) for most taxa. After accounting for the influence of water clarity and current direction on video detectability, generalized additive models suggested that species and family richness were highest at sites characterized by moderate depths, a high proportion of hardbottom, high substrate relief, and warm water. Our results can be used to predict areas of highest reef fish biodiversity at large (regional) and small (microhabitat) scales to improve marine protected area design, delineate essential fish habitats, and parameterize ecosystem models.

Elemental composition of suspended particles across the southeastern continental shelf off the coast of North Florida and South Georgia: Provenance, transport, fate and implications to mid-outer shelf water column processes.

This paper reports on the chemistry of suspended particulates collected in waters of the southeastern US continental shelf off the coasts of North Florida and South Georgia. Approximately 350 suspended sediment samples were analyzed for particulate organic carbon and nitrogen (POC and PON), particulate aluminum and calcium and a suite of trace metals which included particulate alkaline earths (magnesium, strontium, barium), particulate rare earth metals (lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium and dysprosium), particulate transition metals (cobalt, copper, iron, manganese, nickel. scandium, titanium and vanadium) and others: particulate cadmium, zinc, thorium and uranium. The samples were collected in the fall of 1987 during a multidiscipline expedition (FLEX) focused on cross shelf exchange of water and materials during northward wind stress and fall Gulf Stream intrusions. Although samples were analyzed shortly after collection, archived data have not been previously presented. Results are interpreted with regard to how they relate to particle provenance, transport and fate.Results indicate that significant influence of terrestrial sources of suspended particles is limited to the inner shelf, however the concentrations of some metals, such as rare earths, appear to reflect this provenance across the entire shelf. Mid-outer shelf particles are dominated by re-suspended biogenic carbonates and biogenic organic carbon rich particles formed in response to Gulf Stream up welled nutrients. Particulate trace element concentrations and primary production in mid-outer shelf waters are interpreted as a response to not only nutrient, but also trace metal enrichment of up welled Gulf Stream water intruded onto the shelf. Based on particle chemistry, micro nutrients such as Fe in upwelled waters may be limiting in sustaining mid-outer shelf production. Other trace metals such as Sc appear to be enriched due to adsorption on organic rich particles. And the formation SrSO4 particles, originating from Acantharian spicules, appear to create an environment for the precipitation of barite in outer shelf surface waters.

Complex patterns of temperature sensitivity, not ecological traits, dictate diverse species responses to climate change

Despite widespread interest in describing and forecasting the impacts of climate change on species distributions, poor understanding of the climate variables that shape distributions and conflicting perspectives on the role that species traits play in mediating shifts have limited our ability to interpret and project changes in species distributions. Using standardized survey data along the northeast US continental shelf, we assessed the historical exposure and sensitivity of 81 species of marine chordates, arthropods, and molluscs to 24 sea surface temperature (SST) variables in two seasons. By comparing temperature trends in geographies available to species against temperature trends in geographies used by them we were able to identify which variables species track consistently through space and time. Logistic regression analyses were then used to assess whether species traits affected the likelihood of niche tracking while accounting for the season and temporal window in which temperatures were summarized and methodological constraints that might have limited our ability to detect tracking responses. A slight majority of species (52%) clearly shifted their distributions to track at least one temperature variable through space and time. Tracking rates were much lower on a per variable basis (5.1% of 3432 variables), despite widespread exposure to changing temperatures (89.2% of 3432 variables). None of the twelve ecological traits we investigated – including traits related to dispersal ability, ecological specialization, reproductive capacity, and commercial harvest – accounted for differences in tracking responses across species even after accounting for differences in climate exposure. Our results suggest widespread behavioral or physiological flexibility among our study species, or ongoing genetic adaptation to changing temperatures. They also suggest that divergent selection on climate sensitivities of close relatives may limit the utility of ecological traits for predicting distributional responses to future climate change.