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Salinity is a major environmental factor that influences the population dynamics of fish and shellfish along coasts and estuaries, yet empirical methods for hindcasting salinity at specific sampling stations are not widely available. The specific aim of this research was to predict the salinity experienced by juvenile and adult oysters (Crassostrea virginica) collected at sampling stations in Delaware Bay. To do so, empirical relationships were created to predict salinity at five oyster bed stations using observing systems data. These relationships were then applied to construct indices of salinity exposure over an oyster’s lifetime. Three independent salinity data sources were used in conjunction with observing systems data to construct and validate the predictive relationships. The root mean square error (RMSE) of the models ranged from 0.5 to 1.6 psu when model predictions were compared with the three independent data sets. Results demonstrated that data from an observing system near the head of Delaware Bay could be used to predict salinity within ± 2 psu at oyster bed stations as far down-estuary as 39 km. When these models were applied to estimate low salinity exposure of 2-year-old oysters via the metric of consecutive days below 5 psu, the indices suggested that there could be as much as a 42-day difference in low salinity exposure for oysters at stations just 31 km apart. The approach of using observing systems data to hindcast salinity could be applied to advance understanding of salt distribution and the effect of low salinity exposure on organisms in other estuaries, especially bottom-associated species.

 

This study examines the physiological response of the Atlantic surfclam (Spisula solidissima) to ocean acidification in warm summer temperatures. Working with ambient seawater, this experiment manipulated pH conditions while maintaining natural diel fluctuations and seasonal shifts in temperature. One-year-old surfclams were exposed to one of three pH conditions (ambient (control): 7.8 ± 0.07, medium: 7.51 ± 0.10, or low: 7.20 ± 0.10) in flow-through conditions for six weeks, and feeding and digestive physiology was measured after one day, two weeks, and six weeks. After six weeks of exposure to medium and low pH treatments, growth was not clearly affected, and, contrastingly, feeding and digestive physiology displayed variable responses to pH over time. Seemingly, low pH reduced feeding and absorption rates compared to both the medium treatment and ambient (control) condition; however, this response was clearer after two weeks compared to one day. At six weeks, suppressed physiological rates across both pH treatments and the ambient condition suggest thermal stress from high ambient water temperatures experienced the week prior (24–26 °C) dominated over any changes from low pH. Results from this study provide important information about reduced energy acquisition in surfclams in acidified environments and highlight the need for conducting multistressor experiments that consider the combined effects of temperature and pH stress.

 

The Atlantic surfclam (Spisula solidissima solidissima) is an economically valuable clam species that supports a major US fishery. Until recently, fishery efforts along the southern edge of the surfclam range were low due to clam mortalities there in the 1990s. Recent surfclam fishing efforts off Virginia raised questions of whether the surfclam population has returned in the southern region or if a single cohort is supporting the fishery there. Questions have also arisen about whetherS. s. similisis among the population fished off the coast of VA.Spisula solidissima similisis a warm-water cryptic subspecies of the Atlantic surfclam. Although morphologically indistinguishable,S. s. similisgrows to a smaller size and is genetically distinct. Atlantic surfclams (n = 103) were collected from the fishing grounds off the coast of VA. Each surfclam was aged, and shell length and tissue weight recorded for comparison to surfclams of the same age from the center of the population. Analyses of mitochondrial (mtCOI) sequences suggests that the two groups sampled off VA are genetically homogeneous, both groups contain two divergent mitochondrial lineages, and one surfclam sampled shares theS. s. similismtCOI sequence. There are multiple cohorts of surfclams, suggesting that environmental conditions may have improved for surfclams in the south, or that this population has acclimated to altered conditions. Further research should investigate the potential for subspecies hybridization.

 

The Mid-Atlantic Cold Pool is a seasonal mass of cold bottom water that extends throughout the Mid-Atlantic Bight (MAB). Formed from rapid vernal surface warming, the Cold Pool dissipates in the fall due to mixing events such as storms. The Cold Pool supports a myriad of MAB coastal ecosystems and economically valuable commercial and recreational fisheries. Offshore wind energy has been rapidly developing within the MAB in recent years. Studies in Europe demonstrate that offshore wind farms can impact ocean mixing and hence seasonal stratification; there is, however, limited information on how MAB wind development will affect the Cold Pool. Seasonal overlap between the Cold Pool and pre-construction wind lease areas at varying distances from shore in the MAB was evaluated using output from a data-assimilative ocean model. Results highlight overlap periods as well as a thermal gradient that persists after bottom temperatures warm above the threshold typically used to identify the Cold Pool. These results also demonstrate cross-shelf variability in Cold Pool evolution. This work highlights the need for more focused ocean modeling studies and observations of wind farm effects on the MAB coastal environment.

 

The Eastern Oyster (Crassostrea virginica) is a commercially important aquaculture species and food resource along the Atlantic and Gulf coasts of the USA. In addition to its economic value, oyster aquaculture provides ecological value such as water quality improvement. Oyster filtration is highly variable as filtration behavior is influenced by environmental conditions, oyster size, and oyster energetic demands. However, average rates generated in laboratory experiments are often used to estimate the ecological impact of oyster filtration, and there is a need for field-based, farm-specific estimates of filtration that account for this variation. In this study, field experiments were conducted between September 2020 and September 2021 to estimate seasonal oyster filtration physiology at oyster farms in three different bays in the Mid-Atlantic (Barnegat Bay and Delaware Bay in New Jersey and Rehoboth Bay in Delaware). The physiological activity of oysters at each farm varied such that oysters at Barnegat Bay were the most active and oysters at Rehoboth Bay were the least active. Seasonal physiological trends were observed such that filtration behavior generally increased in warmer months. An increase in physiological activity across all farms was associated with an increase in salinity and temperature, but physiological activity at each farm was associated with a different suite of environmental variables including total particulate matter and the organic content of seston. This study provides a robust dataset which can be incorporated into models estimating ecological filtration rates in the Mid-Atlantic and adds to the growing body of evidence supporting bivalve aquaculture as a nutrient reduction strategy.

 

Eastern oysters (Crassostrea virginica) are sessile, relying on a larval phase to disperse in estuaries. Oyster larval swimming behavior can alter dispersal trajectories and patterns of population connectivity. Experiments were conducted to test how both (1) acclimation time to new environmental conditions and (2) larval swimming behavior change with salinity and larval age. Acclimation time to changes in salinity was longest in lower salinity (6 ppt) and decreased with age. To test changes in behavior with salinity, larvae were placed into four salinities (6, 10, 16, and 22 ppt) where swimming was recorded. To test changes in behavior with age, larvae aged 6, 12, and 15 days were recorded. In both experiments, swimming paths were mapped in two dimensions, behavior of each path was categorized, and speed, direction, and acceleration were calculated. The frequency of upward, neutral, and downward swimming behaviors did not differ across salinity treatments but did vary with age, whereas the frequency of behavior types varied with both salinity and ontogeny. As an example, diving was observed more frequently in low salinity, and more downward helices were observed in moderate salinity, while younger larvae swam upward with more frequency than older larvae. Surprisingly, diving was observed in 10%–15% of all larvae across all ages. Given the consequence of larval behavior to marine invertebrate dispersal, changes in swimming over larval age and in response to environmental changes have important implications to marine population stability and structure. 

Estuaries provide valuable habitat for the eastern oyster (Crassostrea virginica). Although salinity at a given location fluctuates regularly with tides, upbay and downbay salinity differences span a broad estuarine salinity gradient. Higher salinity habitats downbay support faster oyster growth, whereas lower salinities upbay act as a refuge from predation and disease but slows growth. Two experiments were performed to investigate the effect of salinity, postsettlement salinity changes, and shell morphology on juvenile oyster growth. One experiment used wild oyster spat collected from three distinct Delaware Bay salinity zones that were then transplanted into various salinity conditions in the laboratory, where growth was monitored. Transplanting into low salinity led to decreased growth compared with transplanting to higher salinity, and growth of oyster spat was overall highest for spat from the lowest salinity source. Growth did not differ among shell morphologies. A second experiment used hatchery reared larvae set in one of four different salinity conditions. Those spat were maintained in settlement salinities 22, 16, 10, and 6 for 2–3 wk postsettlement, then measured before fully factorial transfer into new salinity conditions with measurement 3 wk later. Lower final salinity treatments were associated with lower growth, lower initial salinity treatments were associated with faster final treatment growth, and final growth depended on the interaction between initial and final salinity. Therefore, in addition to the effects of acute salinity changes on growth, early postsettlement hyposalinity stress can generate compensatory juvenile oyster growth. As increased freshwater events due to climate change are expected in the Delaware Bay and regionally in the Northeast, these results indicate that nonlinear early life stress responses are important to quantify to better understand oyster stock resilience and plan management. 

Rising water temperatures along the northeastern U.S. continental shelf have resulted in an offshore range shift of the Atlantic surfclamSpisula solidissimato waters still occupied by ocean quahogsArctica islandica. Fishers presently are prohibited from landing both Atlantic surfclams and ocean quahogs in the same catch, thus limiting fishing to locations where the target species can be sorted on deck. Wind energy development on and around the fishing grounds will further restrict the fishery. A spatially explicit model of the Atlantic surfclam fishery (Spatially Explicit Fishery Economics Simulator) has the ability to simulate the consequences of fishery displacement due to wind energy development in combination with fishery and stock dynamics related to the species' overlap with ocean quahogs. Five sets of simulations were run to determine the effect of varying degrees of species overlap due to Atlantic surfclam range shifts in conjunction with fishing constraints due to wind farm development. Simulations tracked changes in relative stock status, fishery performance, and the economic consequences for the fishery. Compared to a business‐as‐usual scenario, all scenarios with less‐restrictive fishing penalties due to species overlap exhibited higher raw catch numbers but also greater reductions in revenue and increases in cost after the implementation of wind farms. This analysis serves to demonstrate the response of the Atlantic surfclam fishery to combined pressures from competing ocean uses and climate change and emphasizes the potential for economic disruption of fisheries as climate change interacts with the evolution of ocean management on the continental shelf.

 

The Atlantic surfclamSpisula solidissimafishery, which spans the U.S. Northeast continental shelf, is among the most exposed to offshore wind energy development impacts because of the overlap of fishing grounds with wind energy lease areas, the hydraulic dredges used by the fishing vessels, and the location of vessel home ports relative to the fishing grounds. The Atlantic surfclam federal assessment survey is conducted using a commercial fishing vessel in locations that overlap with the offshore wind energy development. Once wind energy turbines, cables, and scour protection are installed, survey operations within wind energy lease areas may be curtailed or eliminated due to limits on vessel access, safety requirements, and assessment survey protocols. The impact of excluding the federal assessment survey from wind energy lease areas was investigated using a spatially explicit, agent‐based modeling framework that integrates Atlantic surfclam stock biology, fishery captain and fleet behavior, and federal assessment survey and management decisions. Simulations were designed to compare assessment estimates of spawning stock biomass (SSB) and fishing mortality (F) for scenarios that excluded the survey from (1) wind energy lease areas or (2) wind energy lease areas and potential wind energy lease areas (“call areas”). For the most restricted scenario, the simulated stock assessment estimated 17% lower SSB relative to an unrestricted survey, placing it below the SSB target. The simulatedFincreased by 7% but was still less than the acceptedFthreshold. Changes in biological reference points were driven by the inability to access the Atlantic surfclam biomass within the wind energy lease areas. Deviations in reference points reflected the proportion of the population excluded from the survey. Excluding the Atlantic surfclam assessment surveys from the regions designated for offshore wind development can alter long‐term stock assessments by increasing uncertainty in metrics that are used to set fishing quotas.