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Competing pressures imposed by climate-related warming and offshore development have created a need for quantitative approaches that anticipate fisheries responses to these challenges. This study used a spatially explicit, ecological-economic agent-based model integrating dynamics associated with Atlantic surfclam stock biology, decision-making behavior of fishing vessel captains, and fishing fleet behavior to simulate stock biomass, and fishing vessel catch, effort and landings. Simulations were implemented using contemporary Atlantic surfclam stock distributions and characteristics of the surfclam fishing fleet. Simulated distribution of fishable surfclam biomass was determined by a spatially varying mortality rate, fishing by the fleet was controlled by captain decisions based on previous knowledge, information sharing, and the ability to search and find fishing grounds. Quantitative and qualitative evaluation of simulation results showed that this modeling approach sufficiently represents Atlantic surfclam fishery dynamics. A fishing simulation showed that the captain's decision-making and stock knowledge, and the distribution of fishing grounds relative to home ports controlled the landed catch. The approach used herein serves as the basis for future studies examining response of the Atlantic surfclam fishery to a nexus of simultaneous, complex natural and anthropogenic pressures, and provides a framework for similar models for other resources facing similar pressures.

The Atlantic surfclam (Spisula solidissima) fishery generates approximately USD 30 million in landings revenues annually, distributed across ports throughout the US Mid-Atlantic and Northeast. Overlap between areas of Atlantic surfclam harvests and offshore wind energy leasing make the fishery vulnerable to exclusion and effort displacement as development expands in the region. An existing integrated bioeconomic agent-based model, including spatial dynamics in Atlantic surfclam stock biology, heterogeneous captain behaviour, and federal management processes, was extended to incorporate costs and revenues for fishing vessels and processors and used to evaluate the potential economic effects of offshore wind development on the Atlantic surfclam fishery. Fishing activity and economic outcomes were simulated under different offshore wind energy development scenarios that impose spatial restrictions on Atlantic surfclam vessel fishing and transiting behaviour. Decreases in the number of trips and shifts in the spatial distribution of fishing effort reduced revenues for Atlantic surfclam fishing vessels and processors by ∼3–15% and increased average fishing costs by

We examined evidence for larval spillover (increased recruitment outside the closures) of Atlantic sea scallops (Placopecten magellanicus) due to rotational closures in the Mid-Atlantic Bight using a 40-year fisheries survey time series and a larval transport model. Since the first closure of the Hudson Canyon South (HCS) area in 1998, mean recruitment in the two areas directly down-current from this closure, Elephant Trunk (ET) and Delmarva (DMV), increased significantly by factors of about 7 and 2, respectively. Stock–recruit plots indicate that low biomasses in HCS were associated with reduced mean recruitment in ET and DMV. Simulations indicate that larvae spawned in HCS often settle in the two downstream areas and that model-estimated settlement (based on gonad biomass in HCS and year-specific larval transport between the areas) is correlated with observed recruitment. This study gives strong evidence that the rotational closure of HCS has induced increased recruitment in down-current areas.

Increased bottom water temperatures have caused a relocation and contraction of the range of the Atlantic surfclam, Spisula solidissima, in the Mid-Atlantic Bight (MAB). Consequences include declining stock abundance and landings per unit effort (LPUE) in southern portions of the range. A management strategy evaluation (MSE) assessed the potential of rotational closures to improve surfclam productivity and fishery viability under three levels of abundance. In simulations, fishing vessels harvest the stock under performance and quota constraints and captain behavioral proclivities. Management alternatives examined included the addition of area management to the current management plan using two closure location rules and three closure durations at two levels of incidental mortality. Simulations showed that area management increased stock abundance and fishery LPUE, particularly when surfclam abundance was low. Simulations suggest area management could help insulate the stock and commercial fishery from further shifts in range.

Larval Atlantic sea scallops (Placopecten magellanicus) simulations in the Middle Atlantic Bight (MAB) from 2006 to 2012 were performed to investigate annual and inter-annual dispersal and connectivity patterns among stock regions. These simulations used a circulation model based on the Regional Ocean Modeling System (ROMS) and an individual-based larval model (IBM) that included larval behavior. The circulation model used realistic dynamical forcing (e.g., winds, tides, and open ocean boundary conditions), thermo-dynamical fluxes (e.g., solar radiations, sensible and latent heating), and hydrological forcing; the larval IBM included vertical swimming and sinking behaviour, temperature-dependent growth, and settlement. Simulated larvae that reach settlement size and suitable habitat in 45 days are considered ‘successful’, and two regions are considered ‘connected’ by larval dispersal when larvae successfully disperse from one region to the other. In general, simulated larval dispersal patterns varied seasonally (28% higher in September and October compared to May and June), among years (2007 through 2009 had 5% lower larval success during August and September compared to other years), and spatially, with larvae released from the northern regions like Long Island acting as a substantive larval source with 14% greater dispersal success and 15% greater connectivity with other regions than those released elsewhere. Over the seven years simulated, the MAB scallop stocks showed high rates of connectivity to regions to the south and more limited and variable connectivity to regions to the north. In species like sea scallops with limited adult mobility, larval dispersal supplies recruits, enables range expansion, and connects populations. Thus, appreciation of dispersal patterns are essential for fishery management of this economically valuable stock.

The Atlantic surfclam (Spisula solidissima) is a dominant member of the biological community of the Middle Atlantic Bight continental shelf and a commercially harvested species. Climate warming is affecting the biology and distribution of this species, which provides an opportunity to investigate the processes and conditions that are restructuring this fishery and the implications for ecological and socioeconomic systems. A Management Strategy Evaluation (MSE) developed for the surfclam fishery provides a mechanistic description of the surfclam's response to climate change and understanding of the cascade of effects initiated by changes in oceanographic conditions that ultimately appear as social and economic effects. This understanding in turn informs development of management policies for the resource. This overview considers the components of the surfclam MSE, relevant results, and implications for management and policy. The lessons learned from the surfclam MSE provide a basis for applying si...

Ocean quahogs [ Arctica islandica (Linnaeus, 1769)] are the longest-lived, non-colonial animal known today, with a maximum life span exceeding 500 years. Ocean quahogs are a commercially important bivalve, inhabiting the continental shelf of the North Atlantic basin. We examined growth rates of ocean quahogs that were fully recruited to the commercial fishery (>80-mm shell length) from four sites covering the range of the stock along the east coast of the U.S. through analysis of annual growth lines in the hinge plate. Both geographic and temporal differences (on a scale of decadal or longer) in growth rates exist throughout the range of the stock. The age at which animals reached 60, 80, and 90 mm decreased significantly, and average growth rates to 60, 80, and 90 mm increased significantly with birth year at a New Jersey and a Long Island site, both located in the southwestern portion of the stock, since the late 1700s/early 1800s, likely in response to increasing bottom water temperatures. That is, growth rates vary temporally with birth date at the southwestern sites, with younger animals growing at a much faster rate in recent decades than those born many decades previously, whereas at the northern sites off southern New England and on Georges Bank, changes in growth rates through time are limited to older adult animals or absent altogether. Thus, at the southern portion of the range, variation in growth rate over time exists in all phases of ocean quahog life, whereas on Georges Bank, little evidence exists for any differential in growth rate over the last ~200 years. The fact that ocean quahogs record the rise in ocean temperatures after the Little Ice Age in the Mid-Atlantic Bight southeast of southern New England, yet demonstrate little evidence of such a rise in the southern New England and Georges Bank region, would suggest a differential response of ocean circulation and its control of bottom water temperature between the northern and southern portions of the Mid-Atlantic Bight over the last 200+ years.

Few empirical studies have focused on the effect of sample density on the estimate of abundance of the dominant carbonate-producing fauna of the continental shelf. Here, we present such a study and consider the implications of suboptimal sampling design on estimates of abundance and size-frequency distribution. We focus on a principal carbonate producer of the U.S. Atlantic continental shelf, the Atlantic surfclam, Spisula solidissima. To evaluate the degree to which the results are typical, we analyze a dataset for the principal carbonate producer of Mid-Atlantic estuaries, the Eastern oyster Crassostrea virginica, obtained from Delaware Bay. These two species occupy different habitats and display different lifestyles, yet demonstrate similar challenges to survey design and similar trends with sampling density. The median of a series of simulated survey mean abundances, the central tendency obtained over a large number of surveys of the same area, always underestimated true abundance at low sample densities. More dramatic were the trends in the probability of a biased outcome. As sample density declined, the probability of a survey availability event, defined as a survey yielding indices >125% or

A comprehensive dataset for the Georges Bank region is used to directly compare the distribution of the death assemblage and the living community at large spatial scales and to assess the application of the death assemblage in tracking changes in species’ distributional pattern as a consequence of climate change. Focus is placed on the biomass-dominant clam species of the northwest Atlantic continental shelf: the surfclam Spisula solidissima and the ocean quahog Arctica islandica, for which extensive datasets exist on the distributions of the living population and the death assemblage. For both surfclams and ocean quahogs, the distribution of dead shells, in the main, tracked the distribution of live animals relatively closely. Thus, for both species, the presence of dead shells was a positive indicator of present, recent, or past occupation by live animals. Shell dispersion within habitat was greater for surfclams than for ocean quahogs either due to spatial time averaging, animals not living in all habitable areas all of the time, or parautochthonous redistribution of shell. The regional distribution of dead shell differed from the distribution of live animals, for both species, in a systematic way indicative of range shifts due to climate change. In each case the differential distribution was consistent with warming of the northwest Atlantic. Present-day overlap of live surfclams with live ocean quahogs was consistent with the expectation that the surfclam's range is shifting into deeper water in response to the recent warming trend. The presence of locations devoid of dead shells where live surfclams nevertheless were collected measures the recentness of this event. The presence of dead ocean quahog shells at shallower depths than live ocean quahogs offers good evidence that a range shift has occurred in the past, but prior to the initiation of routine surveys in 1980. Possibly, this range shift tracks initial colonization at the end of the Little Ice Age.

A survey of the adjacent waters east of Nantucket, Massachusetts provided an opportunity to evaluate the epibiota attached to cobbles, rocks, boulders, and Atlantic surfclam shell in a region of high tidal current velocity and sand scour where burial, exhumation, and scour may limit epibiont coverage on exposed, and thus otherwise highly preferred for attachment, substrates. Such conditions may confute the expectation that substrate complexity always adds significantly to ecosystem value by expanding the range of habitat options and consequently increasing species richness and trophic linkages. Sedimentary particles potentially providing good attachment substrate for erect sessile epibiota included surfclam shells, abundant at many locations, cobbles, nearly ubiquitous, rocks, routinely encountered, and occasional boulders. The attached epibiota fell into three categories based on their biases for particle types. Some preferred the largest particles or evidence of their occupation was best preserved on these particles: these included sponges, mussels, and barnacles and their scars. Some preferred intermediate and smaller terrigenous particles; these included tunicates and encrusting bryozoans. Some preferred surfclam shells, namely the slipper shells and erect hydroids. Slow-growing attached epibionts were exceedingly rare and all soft-bodied attached epibionts were rare. Only barnacles and their taphonomic scars and hydroids were common. The frequency of barnacle scars relative to intact barnacles suggests sediment scour under a high-flow regime. Mussels were rarely attached to larger sedimentary particles such as cobbles and rocks, though commonly occurring locally as mussel beds on sand and pebble, further supporting the ephemerality of exposed unscoured attachment sites. The absence of attached epibionts demonstrates that edaphic processes minimize the importance of cobbles, rocks, boulders, and shells in community structure in some subtidal high-energy regimes, defying expectations from their contribution to substrate complexity. Their apparent contribution to habitat complexity belies their resultant much more minor role in determining community composition, thereby limiting their ecosystem value.

Mid-Atlantic Bight (MAB) warming accompanied by a decline in recruitment has slowly reduced surfclam abundance. Simulations examined fishery dynamics during an extended period of low recruitment followed by stock recovery after a high-recruitment event. The model assigned performance characteristics to each vessel and gave captains defined behavioral proclivities including a tendency to search, to communicate with other captains, to use survey data, and to integrate variable lengths of past-history performance in targeting fishing trips. During the simulated excursion in abundance, LPUE (landings per unit effort) declined as lower abundance required an extended time at sea to catch a full load. Captains expanded their geographic range of interest steaming farther from port in an effort to maintain their performance. Net revenue declined. Use of survey data significantly improved performance. About equal in positive effect was moderate searching. Other behaviors incurred penalties. Communication failed to improve performance because both poor and good information was transferred. Reliance on a long period of catch history failed to improve performance because information was out of date during a time of rapidly changing conditions. In these simulations, no captains' behaviors prevented a collapse in vessel economics at low abundance, but certain behaviors limited the degree and duration of economic dislocation.

Larval transport and settlement have been shown in various studies to be essential in determining population abundance and connectivity for benthic invertebrates. This transport is influenced by both the physical environment and biological behavior. The Atlantic surfclam, Spisula solidissima , is a commercially important benthic invertebrate fishery species along the U.S northeastern coast. In this study, a physical circulation model is coupled to a surfclam larval model to investigate the dynamics of larval transport and settlement within the Middle Atlantic Bight (MAB) shelf in 2006. The main physical mechanisms causing variability in larval transport and settlement are also examined. Model results show that surfclam larvae released from July to early October experience relatively larger settlement rates, due to higher average temperatures experienced by larvae. Larval along-shore transport exhibits a mean down-coast pattern following the coastal current from the northeast to the southwest, with most high-frequency (period of 2–10 days) variations caused by fluctuations in the along-shore surface wind stress, and with seasonal variations speculated to be driven mainly by changes in the across-shelf density gradient. Larval across-shelf movement is highly correlated with the along-shore surface wind stress mediated by coastal upwelling and downwelling episodes, but the correlation is further dependent on the vertical distribution of the larvae, particularly their position relative to the thermocline. Most surfclam larvae released from the Middle Atlantic shelf stay below the thermocline and experience a net onshore transport during the summer-stratified season when upwelling-favorable wind forcing dominates. A proposed critical value of water temperature at the thermocline successfully regulates the observed patterns of vertical distribution of surfclam larvae and their across-shelf movement off the New Jersey and South Virginia shelves; that is, when the water temperature at the thermocline is above the critical value (19.0 °C), surfclam larvae tend to escape the warm surface layer to concentrate below the thermocline and follow the across-shelf movement of bottom water, and vice versa . These results provide an important insight into the general mechanism of how physical environmental factors interact with biological behavior of the larvae to influence larval transport, connectivity and population dynamics, and also indicate the potential impact of large-scale climate change on benthic species and coastal ecosystems.

Maximum shell length of Atlantic surfclams (Spisula solidissima) on the Middle Atlantic Bight (MAB) continental shelf, obtained from federal fishery survey data from 1982-present, has decreased by 15–20 mm. Two potential causes of this decreasing trend, fishery removal of large animals and stress due to warming bottom temperatures, were investigated using an individual-based model for post-settlement surfclams and a fifty-year hindcast of bottom water temperatures on the MAB. Simulations showed that fishing and/or warming bottom water temperature can cause decreases in maximum surfclam shell length (body size) equivalent to those observed in the fished stock. Independently, either localized fishing rates of 20% or sustained bottom temperatures that are 2 °C warmer than average conditions generate the observed decrease in maximum shell length. However, these independent conditions represent extremes and are not sustained in the MAB. The combined effects of fishing and warmer temperatures can generate simulated length decreases that are similar to observed decreases. Interannual variability in bottom water temperatures can also generate fluctuations in simulated shell length of up to 20 mm over a period of 10–15 years. If the change in maximum size is not genotypic, simulations also suggest that shell size composition of surfclam populations can recover if conditions change; however, that recovery could take a decade to become evident.

Trematode sporocyst and rickettsia weighted prevalences were found to be extremely high in Gulf of Mexico petroleum seep mussels, Bathymodiolus childressi, in comparison to shallow-water mytilids. Understanding the role that parasites might play in mussel population dynamics and health requires an understanding of the rapidity with which parasite infections and physiological condition respond to changes in host population structure and environment. To evaluate the influence of the seep environment on B. childressi, a transplant experiment was conducted between several donor (population of origin) and receiver (population of transplant) populations from three seep sites on the continental slope of the Gulf of Mexico. Donor and receiver populations varied significantly in prevalence and infection intensity for many parasites and often varied in physiological condition for most physiological indices. Transplanted populations came into equilibrium with the receiver populations relatively fast for single-celled parasites; trematode sporocysts responded less often and more slowly. In a few cases, these transplanted populations retained the donor population condition, most frequently for the trematode sporocysts and rarely for the single-celled parasites. Of the physiological indices, gonadal stage came into equilibrium with all receiver populations in one year. Mussels lost condition rapidly in cases where the receiver population had lower condition but gained condition more slowly in the opposite case. Digestive gland atrophy and gill tissue atrophy responded rapidly in most cases where the transplanted mussels varied initially from the receiver populations. Transmission rates could be approximated from changes in prevalence for gill rickettsia and the trematode sporocysts. For gill rickettsia, transmission rates varied between 0.36 and 0.45 yr−1. Loss rates were much higher, estimated at 1.95 yr−1, suggesting a short life span for any individual rickettsial body and that infection intensity is a balance between rapid rates of proliferation and loss. Transmission rates for the trematodes, likewise approximated, were slower: 0.13 to 0.29 yr−1; nevertheless, infection intensification was rapid, in one case reaching 3 on a 0-to-4-point semiquantitative scale in one year. Apparent loss rates were minimal in one case but reached 1.25 yr−1 in another. Mussels live for a relatively long time and the transmission rates measured for the trematode sporocysts are relatively high, yet population prevalences are often well below 100%. One possibility is that these trematode sporocysts have life spans considerably shorter than their hosts, a fact that is of some consequence because while infected, the mussels lose any capacity to reproduce. The alternative is that infected mussels have a relatively high mortality rate.

A mass mortality event that occurred in the Mississippi Sound in September 2016 provided an opportunity for the first natural field study of the rate of taphonomic loss of oyster shell. At the Pass Christian Reef, limited recruitment in the years following the mortality event resulted in little shell addition over a 2.67-y period, thereby permitting a direct comparison between shell present as living oysters in August 2016 and dead shell collected in April/May 2019. By April 2019, most oyster shell valves were riddled with holes, some of which perforated the valves. Deterioration of the shell surface was ubiquitous, and edge erosion was commonplace. Left valves were preferentially preserved: the left valves comprised 67% of the intact valves and 85% of the minor fragments after 2.67 y. Thus, at the time of collection, minimally 50% of the right valves originally present on the reef had disappeared. The increased differential between left and right valves of the minor fragments suggests a continuing differential in preservation, leading to cultch being overwhelmingly represented by left valves. Based on estimates derived from changes in shell weight at length and estimates of right-valve loss, by April 2019, between 30% and 51% of the carbonate originally added to the reef in 2016 was lost, yielding an estimated oyster shell half-life of between 2.6 and 5.1 y in the Mississippi Sound. The half-lives estimated from this first infield experiment fall precisely within the range of previous less direct estimates from laboratory experiments or survey time series. Oyster shell degrades rapidly: case histories now include a wide latitudinal range and a wide temperature range, which suggests that these rapid shell degradation rates are the norm over most of the range of the eastern oyster. Understanding the impermanence of oyster shell is crucial to the sustainable management of oyster reefs, as the addition of shell to the reef framework must balance rapid shell degradation rates to prevent stock collapse and ultimately the loss of reef structure.

The Atlantic surfclam, Spisula solidissima, is distinguished by a well-documented shift in range that accelerated in the 2000s as the northwest Atlantic warmed. Here the extension of the Atlantic surfclam into heretofore Acadian Province waters off the island of Nantucket is documented and compared to the distribution of surfclam shell as an indicator of recent colonization, to the timing of range expansion, and to the physiological implications of a range extension into deeper water. The primary demographic difference observed is the dichotomous distribution of sizes. Smaller surfclams averaged higher in abundance at the deeper offshore sites, whereat the number of large animals was distinctly fewer; thus, the size-frequency distributions at deeper sites were shifted towards the smaller sizes, a finding consistent with the expectation of recruitment into deeper water during a period of range expansion. In confirmation, deeper-water stations where surfclams were aged yielded surfclams no older than 13 yr, whereas shallow-water stations had a mature age frequency with some surfclams exceeding 20 yr. Further support for the more recent occupation of deeper-water sites comes from the distribution of surfclam shell, that was found in limited quantities at stations where recent colonization is inferred and in greater quantities in shallower water where longer-term occupation is surmised. For the shallower-water sites with a mature demographic, growth rates were comparable or higher than observed elsewhere in the stock and surfclam maximum sizes were larger than elsewhere in the geographic range. In contrast, surfclams colonizing deeper water post-2000 grew at a slower rate likely due to a lower average temperature near the deep-water range boundary. The penalty for colonization pushing the range boundary into deeper, cooler water lasted no more than 4–5 years, however, after which growth rates increased to rates typical of surfclams in shallower water. Thus, surfclams responded quickly to a period of rapid climate change in contrast to expectation from their known longevity.

The degree to which evidence of range shifts in shelf biomass dominants, Atlantic surfclams and ocean quahogs, as a function of climate change is examined by comparing the dissimilarity in distribution of the living community and the record of habitation ensconced in the death assemblage. Comparison of the distribution of live animals and dead shells reveals for both species that live animals are rarely found where dead shells were not collected, but dead shells were collected at a substantively larger number of sites than where live animals were found. The geographic footprint resolved by the dead shells was much broader than that of live animals. Extensive spatially-coherent regions exist inshore and offshore of the present-day habitat of occupation where evidence of previous occupation exists. Sites where ocean quahog shells were found without live ocean quahogs included a portion of the continental shelf inshore of the present-day habitable range, an area only habitable under colder climatic conditions than observed today. Surfclam shells were found offshore of the present-day habitable region, in deeper water: additional warming of bottom waters offshore would be necessary for surfclams to occupy the region now occupied solely by dead shells. The death assemblage shows that these biomass dominants have repositioned themselves across the continental shelf during the past and this repositioning certainly is driven by changes in bottom water temperature. Moreover, the distribution of surfclam shells indicates that the death assemblage may provide a possible window into the future, as movement of the present-day population is towards these deeper-water previously-occupied regions. Overall, the death assemblage may provide an important source of information on range shifts sparing the need to carry out extensive and frequent benthic surveys and may permit reconstruction of ongoing shifts in community composition as a product of climate change when adequate survey data are not available.

We examine the relationship of biomass B and length L in the eastern oyster Crassostrea virginica by focusing on the scaling exponent b in the allometric equation B = aLb using four datasets: Delaware Bay, Chesapeake Bay, Galveston Bay and a regionally extensive compilation from the NOAA Mussel Watch Program. The average value of the scaling exponent in Delaware Bay and Chesapeake Bay is about 2. For Galveston Bay, the value is distinctly higher, near 2.6. Over all Mussel Watch sites, the value is again near 2. Within Delaware Bay, the salinity gradient exerts an important effect. Shells are longer for their meat weight at lower salinities. The range of scaling exponents revealed by Mussel Watch data is exceedingly large (b < 1 to >3). Scaling exponents below 2.5 are unusual in bivalves. Among bivalves, only other oyster taxa have comparably low scaling exponents averaging near 2. We propose that oyster biomass routinely scales nearer the square of the length rather than the cube and that this is a constraint imposed by the exigency of carbonate production for reef maintenance and accretion in the face of high rates of taphonomic degradation. The adaptation as a reef builder requires the formation of carbonate that rapidly breaks down, thus requiring that carbonate produced be maximized. A biomass-to-length scaling exponent of 2 provides a mechanism to maximize shell production relative to biomass, while at the same time providing maximum surface area for the all-important settling of oyster spat to maintain the population.

The response of the surfclam Spisula solidissima to warming of the Mid-Atlantic Bight is manifested by recession of the southern and inshore boundary of the clam's range. This phenomenon has impacted the fishery through the closure of southern ports and the movement of processing capacity north, impacts that may require responsive actions on the part of fishery captains to mitigate a decline in fishery performance otherwise ineluctably accompanying this shift in range. The purpose of this study was to evaluate options in the behavioral repertoire of captains that might provide mitigation. A model capable of simulating a spatially and temporally variable resource harvested by fleets of boats landing in a number of homeports was created. The model includes characterization of each vessel in terms of economics and vessel performance. The model assigns to each vessel a captain with defined behavioral proclivities including the tendency to search, to communicate with other captains, to take advantage of survey data, and to integrate variable lengths of past history performance into the determination of the location of fishing trips. Each captain and vessel operate independently in the simulation providing a spatially and temporally dynamic variability in fishery performance. Simulations showed that a number of behaviors modestly varied performance. Use of survey data and occasional searching tended to increase performance. Reliance on an older catch history tended to reduce performance as did frequent searching. However, in no simulation was this differential large and the differential was little modified by the contraction in the surfclam's range. Simulations showed that the population dynamics of the clam and the low fishing mortality rate imposed by the Fishery Management Plan permit near optimal fishing performance based on a few simple rules: choose locations to fish that minimize time at sea while permitting the landing of a full vessel load; base this choice on the most recent catch history for the vessel. Simulations suggest that the performance of the fishery is primarily determined by surfclam abundance and the location of patches that control LPUE at small geographic scales. Constraints imposed on fishery performance by port location and vessel size far exceed limitations or ameliorations afforded by modifications in the behavior of captains.

To study the primary larval transport pathways and inter-population connectivity patterns of the Atlantic surfclam, Spisula solidissima, a coupled modeling system combining a physical circulation model of the Middle Atlantic Bight (MAB), Georges Bank (GBK) and the Gulf of Maine (GoM), and an individual-based surfclam larval model was implemented, validated and applied. Model validation shows that the model can reproduce the observed physical circulation patterns and surface and bottom water temperature, and recreates the observed distributions of surfclam larvae during upwelling and downwelling events. The model results show a typical along-shore connectivity pattern from the northeast to the southwest among the surfclam populations distributed from Georges Bank west and south along the MAB shelf. Continuous surfclam larval input into regions off Delmarva (DMV) and New Jersey (NJ) suggests that insufficient larval supply is unlikely to be the factor causing the failure of the population to recover after the observed decline of the surfclam populations in DMV and NJ from 1997 to 2005. The GBK surfclam population is relatively more isolated than populations to the west and south in the MAB; model results suggest substantial inter-population connectivity from southern New England to the Delmarva region. Simulated surfclam larvae generally drift for over one hundred kilometers along the shelf, but the distance traveled is highly variable in space and over time. Surfclam larval growth and transport are strongly impacted by the physical environment. This suggests the need to further examine how the interaction between environment, behavior, and physiology affects inter-population connectivity. Larval vertical swimming and sinking behaviors have a significant net effect of increasing larval drifting distances when compared with a purely passive model, confirming the need to include larval behavior.

The potential linkages between warming bottom temperatures and increased mortality and/or reduced growth of the Atlantic surfclam (Spisula solidissima) were investigated using a model that simulates the temperature-dependent growth of the post-settlement population at specific locations on the Middle Atlantic Bight (MAB) continental shelf. External forcing for the individual-based surfclam model is provided by a 50-year simulation (1958–2007) of bottom water temperature obtained from an implementation of the Regional Ocean Modeling System for the northwestern Atlantic. The simulations show that in years with above average bottom water temperature (> 2 °C above average), surfclam assimilation rate is significantly reduced as a result of thermal stress, which leads to starvation mortality and an overall decline in the surfclam population of 2–9%, mainly in the inner shelf regions. Years with warmer bottom water temperatures were preceded by warm winters, which produced an earlier and longer summer season. These results suggest that the long-term observed decline in Atlantic surfclam populations on the MAB is a response to episodic warm years rather than a gradual warming trend in bottom water temperature, as previously suggested. These temperature driven population declines can persist for several years and have the largest effect on older and larger animals, which are the target of the commercial fishery.

One predicted consequence of climate change is increasing variability of local weather extremes such as the frequency and intensity of storms. In August and September of 2011, Hurricane Irene and Tropical Storm Lee generated extreme flooding in the Delaware River watershed that produced prolonged baywide low salinity and consequent historically-high mortalities for the oyster stock in the upper reaches of Delaware Bay. The dynamics, consequences, and projections for recovery from the anomalously high oyster mortality that occurred as a consequence are reported using a combination of physical modeling, field sampling, and metapopulation dynamics modeling. Monthly mortality of 10% and 55% on the upper bay beds (Arnolds and Hope Creek respectively) exceeded the longer-term average at those locations and was associated with a continuous low salinity (

Atlantic surfclams (Spisula solidissima), among the largest extant non-symbiotic clam species in the world, live in dense aggregations along the Middle Atlantic Bight (MAB) continental shelf. The food resources that support these populations are poorly understood. An individual-based model that simulates the growth of post-settlement surfclams was used to investigate the quantity of food needed to maintain existing surfclam populations along the MAB continental shelf. Food inputs to the model were based on measured near-bottom water-column chlorophyll concentrations. Simulations showed that these water-column food sources supported only 65% of the observed body mass of a standard large surfclam (160-mm shell length). Additional simulations using benthic food sources to supplement water-column food sources by 20% generated surfclams that grew to observed size and biomass and exhibited spawn timing consistent with the known surfclam spawning season. The simulation results suggest that measured water-column chlorophyll concentrations may underestimate the food available to the continental shelf benthos. Large continental shelf bivalves are an essential resource for fisheries and higher trophic level consumers. Understanding available and utilized food resources is important for predicting long-term impacts of climate change on benthic secondary production and fishery yield on the continental shelf.

To evaluate oyster food supply, water samples were collected at fifteen sites in Delaware Bay nearmonthly in 2009 and 2010. Food was estimated as the sum of particulate protein, labile carbohydrate, and lipid. Delaware Bay shows a typical spring bloom, centered in March and April, with declining food supply thereafter into early fall, followed sporadically by a minor fall bloom. The geographic and temporal structure of food was more predictable in summer to early fall, and considerably less predictable in spring. Five variables each based on temperature and the spatial and temporal variability of temperature were significant contributors to a multiple regression (R2 = 0.28). Cluster analysis on residuals identified two large groups of sites, one comprising most sites on the eastern side of the bay including all of the sites on the New Jersey oyster beds downestuary of the uppermost beds and one including most of the sites along the central channel and waters west. Food values over the New Jersey oyster beds were often depressed by as much as 50% relative to the bay-wide mean. Food values did not follow an upestuary-downestuary trend anticipated from the salinity gradient. Rather, the differential was cross-bay and was distinctive throughout the estuarine salinity gradient, thus explaining the lack of significance of any salinity-related variable in the multiple regression. The consequence is that food supply cannot be sufficiently predicted or modeled based on observed environmental variables or those predicted from a hydrodynamic model. The cross-bay differential cannot be extracted from such datasets. The oyster reefs of Delaware Bay are dominantly sited on the New Jersey side, where food supply was most depressed and where passive particle residence times were longest. While not conclusive, this dataset suggests that oysters can influence food values on the New Jersey side of the bay at present biomass, and this would explain the cross-bay gradient in food values as an outcome of oyster feeding. 1. Rutgers University, Institute of Marine and Coastal Sciences and The New Jersey Agricultural Experiment Station, Haskin Shellfish Research Laboratory, Port Norris, New Jersey, 08349, U.S.A. 2. Corresponding author. email: eric@hsrl.rutgers.edu 3. Partnership for the Delaware Estuary, Wilmington, Delaware, 19801, U.S.A. 4. Patrick Center for Environmental Science, Academy of Natural Sciences, Philadelphia, Pennsylvania, 19103, U.S.A. 5. Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey, 08901, U.S.A.

The Tikehau atoll (Tuamotu Archipelago, French Polynesia) is located at 14'5 148"W. Phytoplankton and sand microalgae are the most important primary producers of the lagoon. They were studied for 4 years. The relationship between light energy and lagoonal primary production was measured by using the 14C method for phytoplankton and O, method for phytobenthos. Incubations, carried out in situ, were made at different depths and light exposition times. Irradiance was high and 17% of the light energy measured at the surface reached 25 m (lagoon average depth). Maxima of phytoplankton and phytobenthos productions occurred at low depths; there was therefore no photoinhibition of photosynthesis. Correlations between light energy and primary production were strong, especially for phytobenthos. Multiplicative linear regression models (production VS light) associated with an exponential linear regression model (light vs depth), allowed planktonic and benthic primary production to be predicted from the depth and the light energy received at the surface. The benthic primary production exceeded the phytoplanktonic production in the upper 18 m. The total primary production (benthos + plankton) was constant with depth and depended only on light energy at the surface. One Einstein received at the lagoon surface allowed the growth production of 14 mg of carbon (water column + sediments).

The degree of genetic connectivity among populations in a metapopulation has direct consequences for species evolution, development of disease resistance, and capacity of a metapopulation to adapt to climate change. This study used a metapopulation model that integrates population dynamics, dispersal, and genetics within an individual-based model framework to examine the mechanisms and dynamics of genetic connectivity within a metapopulation. The model was parameterized to simulate four populations of oysters (Crassostrea virginica) from Delaware Bay on the mid-Atlantic coast of the United States. Differences among the four populations include a strong spatial gradient in mortality, a spatial gradient in growth rates, and uneven population abundances. Simulations demonstrated a large difference in the magnitude of neutral allele transfer with changes in population abundance and mortality (on average between 14 and 25% depending on source population), whereas changes in larval dispersal were not effective in altering genetic connectivity (on average between 1 and 8%). Simulations also demonstrated large temporal changes in metapopulation genetic connectivity including shifts in genetic sources and sinks occurring between two regimes, the 1970s and 2000s. Although larval dispersal in a sessile marine population is the mechanism for gene transfer among populations, these simulations demonstrate the importance of local dynamics and characteristics of the adult component of the populations in the flow of neutral alleles within a metapopulation. In particular, differential adult mortality rates among populations exert a controlling influence on dispersal of alleles, an outcome of latent consequence for management of marine populations.

In 1993, SSETI (Shelf and Slope Experimental Taphonomy Initiative) deployed shells of a suite of molluscan species in a variety of environments of preservation (EOPs) covering a range of depths and sediment types on the Gulf of Mexico continental shelf and upper slope, with the goal of measuring taphonomic rates over an extended period of time. SSETI retrieved shells from these EOPs after 2, 8, and 13 years. The degree of shell degradation was significantly influenced by species, elapsed time-since-deployment, and EOP. A suite of ‘physical’ taphonomic processes, such as dissolution, abrasion, discoloration, and edge alteration, increased in severity over the 13 years; fragmentation occurred in some species. Dissolution proceeded apace; however the incidence of chalkiness declined from high levels observed after a few years while the more extreme levels of dissolution, such as the development of a soft or deeply-dissolved surface, rose significantly in frequency. The incidence of original color declined, while fading of original color increased. Brown-to-red and green discoloration rose rapidly in the first eight years and then declined, leaving a faded shell surface. Between-habitat differences in degradation rate were significant for most taphonomic attributes. Between-species differences were minor in comparison. Thus, taphofacies, the product of the independent actions of a suite of taphonomic processes, originate from and provide information on environmental conditions. Species composition has a lesser inherent influence on the outcome. Not uncommonly, the rates of change in shell condition differed significantly between EOPs although the direction of change was coincident. This was particularly true of the summary indices such as maximum discoloration or the average degree of dissolution. The taphonomic process is nonlinear in time. Nonlinearity is EOP-dependent, becoming a defining attribute leading to disparate taphofacies types. Some taphonomic processes cannot proceed expeditiously without prior alteration of the shell through other taphonomic means. Some taphonomic conditions such as chalkiness can be intermediate states. The presumption that similar taphonomic characteristics between EOPs indicate similar environmental processes operating at similar rates is falsified by SSETI sites in which similar taphonomic indices at Year 13 accrued from different time-varying degradational rates during the preceding years.

We utilize information from a suite of molluscan species deployed in a variety of Caribbean and Gulf of Mexico environments of preservation (EOP) by SSETI (Shelf and Slope Experimental Taphonomy Initiative) to examine to what degree interpretation of the taphofacies is influenced by the mix of species presented to the observer. The environment of preservation was the overwhelming determinant of taphonomic state at SSETI sites. Species mix played a subsidiary role. A few consistent trends were observed: for example, Arctica islandica, Strombus luhuanus, Mytilus edulis, and Mercenaria mercenaria tended to be more highly dissolved than others. Mytilus edulis consistently was fragmented more than other species. Otherwise, most species behaved uniquely over a range of EOPs: significant species by EOP interactions were the norm. A taphofacies model is developed to examine further the role of species on the degradational state of the assemblage. Two metrics are described: a taphonomic degradation score describes the overall degradational state of the assemblage from pristine to highly degraded; and a taphonomic signature describes the relative importance of a suite of taphonomic processes. Model simulations show that the impact of species on degradational state is low initially because all shells are in relatively pristine condition shortly after death. The impact is high at intermediate degradational states because factors inherent to the species modulate the time course of taphonomic decay. The impact is low again at highly degraded assemblages, as the taphonomic process brings shell condition to a common denominator of relatively intense degradation regardless of species. Fossil assemblages almost certainly express this continuum in some degree. The consequence is that better preserved assemblages are ones in which species can affect taphofacies character and so similar EOPs may be judged distinctive due to differential dominance by one species or another. Teasing out characteristics that might forewarn the observer in this instance is an important goal. Simulations show that low evenness is an important warning sign.

Bivalve shells deployed experimentally in a variety of environments of deposition (EODs) and over a wide range of depths from 15 to 570 m in the Bahamas and Gulf of Mexico were assessed for encrusting and endolithic bionts (sclerobionts sensu Taylor and Wilson, 2002) that accumulated over 1-, 2-, 8- and 12/13-year intervals. Data include percent coverage and, when possible, identification to generic- or species-level taxonomic categories. Data were binned into two further categories based on guilds and whether or not sclerobionts were judged to be preservable. Each study site shows substantial variability in both percent coverage and species richness/composition, which we attribute to partial burial of different individuals or parts of arrays. Average values of taxonomic richness, guild number, and percent coverage, for a given EOD represent a combination of exposed and buried shells as would be typical of a time-averaged fossil assemblage; maximally covered shells give the potential coverage for each site. In both study areas there are characteristic patterns in terms of overall percentage of shells covered by sclerobionts, numbers and extent of coverage by different guilds as well as by different taxa. For most EODs, there is a progressive, though non-linear increase in both species richness and areal coverage through the twelve years; exceptions are in the 30 m site in the Bahamas, and Parker Bank and Flower Garden sites in the Gulf of Mexico, which show a significant decline in areal coverage (though not in richness). This effect may result from differences in sediment cover over time. These sites showed a tendency to have many or all experimental bags completely sediment covered in the later sampling. Cluster analysis and non-metric multidimensional scaling (NMDS) of various shell substrate species at all EODs from the Bahamas and Gulf of Mexico reveal discrete groupings that are related to both depth (light?) gradient and other factors, such as variations in sedimentation and salinity. Similar numbers of guilds are found at various EODs although the specific guild types represented differ. In general, highest average richness values are recorded for carbonate 70–90 m wall and deep reef sites (69 to 70 taxa) and lowest are for the EFG brine pool (no sclerobionts other than bacterial films after 12/13 years) and deeper dysphotic to subphotic sites (max values: 25 taxa); surprisingly, shallow water sites (< 30 m) yield only moderate diversities of 40–50 taxa. This results in part from the fact that certain encrusters, especially the foraminifer Gypsina and coralline algae tend to overgrow others and dominate space, in addition to burial effects. Certain taxa (notably the serpulid Pseudovermilia) are ubiquitous, while other taxa (e.g. larger foraminifera, vermetid gastropods and many bryozoans) are largely restricted to shallower depths. A combination of species richness, average coverage and key taxa permits discrimination of groups of EODs and potentially, in tandem with other evidence, of depth gradients.

The spatial and temporal distribution and diversity of sediment-dwelling foraminifera are reasonably well known, but encrusting (hard-substrate dwelling) foraminifera are little studied. Encrusting foraminifera are common in the world's oceans, attached to floating debris or marine animals in the water column to living on rocks, sand grains and organisms in benthic environments from shallow to deep marine regions. With projected ocean acidification and warming conditions, these important calcifying protists that comprise beaches, buffer sediments, and contribute to complex food webs are potentially in peril. Results indicate that calcifying foraminifera were the first to colonize experimental molluscan substrates within the first year in shallow habitats, with colonization offshore in subsequent years. Agglutinated foraminifera become more common after one year. Species richness (α diversity) remained relatively similar throughout the study, but species turnover (β diversity) was greatest within the first year and between the shelf/slope break and deeper water, following the thermocline and photic zone regions. The equivalent of the Shannon Entropy Index provided important information on β diversity and community structure. Paleobathymetric distributions can be resolved after six years into four distinct foraminiferal distributional zones: shallow shelf (15 m), outer shelf (33 m), shelf/slope break (73–88 m), and slope depths (> 213 m to 267 m). Some encrusting foraminifera are invasive, settling in high numbers within the first year, and increasing their abundance through the duration of the experiment. A foraminiferan, Discorbis bertheloti, was discovered to bioerode carbonate, and is a potentially excellent paleobathymetric indicator for 15–33 m depths. Results differ from previously reported pioneer and climax foraminiferal communities documented for Caribbean coral reefs, because long-term experiments reveal the spatial and temporal development and distribution of carbonate-producing encrusting foraminifera in these climatically-sensitive regions.

The Shelf and Slope Experimental Taphonomy Initiative (SSETI) deployed a suite of molluscan species in environments covering a range of depths and sediment types in the Bahamas and on the Gulf of Mexico continental shelf and upper slope for 8 years. Taphonomic state rarely correlated with the distribution of biont guilds among environments. The preservable and nonpreservable biont guilds were also routinely orthogonal. Several coincidences of taphonomic trait and biont guild occurred, including green discoloration that consistently co-occurred with boring algae and bacterial films associated with the development of chalkiness and a soft shell surface. Environments of preservation (EOPs) of disparate taphonomic signature and biont guild complement occur in similar sediment types and environments with similar rates of burial. A paucity of biont coverage is no more a reliable indicator of rapid burial than is a limited degree of shell degradation. The suggestion that preservable bionts might protect shells from taphonomic processes is not well supported. Certain EOP groups are delineated from others most readily by a combination of biont guild and taphonomic trait. Thus, biont guilds augment taphonomic analysis in differentiating EOPs. Shell preservational state, including taphonomic signature and biont coverage, is influenced in a complex way by environment. The analysis confirms an expectation that the diversity of EOPs should be greater in shallow water. Clustering of EOPs reveals that visually distinctive environments may be taphonomically and biotically similar. Visually similar environments may be quite disparate in taphonomic state and biont complement. EOPs grouped by similarity in taphonomic signature and biont coverage very likely define geographically widespread biological and taphonomic regimes, which, however, are everywhere restricted locally in areal dimension.

The eastern oyster (Crassostrea virginica) is affected by two protozoan parasites, Perkinsus marinus which causes Dermo disease and Haplosporidium nelsoni which causes MSX (Multinucleated Sphere Unknown) disease. Both diseases are largely controlled by water temperature and salinity and thus are potentially sensitive to climate variations resulting from the El Nino-Southern Oscillation (ENSO), which influences climate along the Gulf of Mexico coast, and the North Atlantic Oscillation (NAO), which influences climate along the Atlantic coast of the United States. In this study, a 10-year time series of temperature and salinity and P. marinus infection intensity for a site in Louisiana on the Gulf of Mexico coast and a 52-year time series of air temperature and freshwater inflow and oyster mortality from Delaware Bay on the Atlantic coast of the United States were analyzed to determine patterns in disease and disease-induced mortality in C. virginica populations that resulted from ENSO and NAO climate variations. Wavelet analysis was used to decompose the environmental, disease infection intensity and oyster mortality time series into a time–frequency space to determine the dominant modes of variability and the time variability of the modes. For the Louisiana site, salinity and Dermo disease infection intensity are correlated at a periodicity of 4 years, which corresponds to ENSO. The influence of ENSO on Dermo disease along the Gulf of Mexico is through its effect on salinity, with high salinity, which occurs during the La Nina phase of ENSO at this location, favoring parasite proliferation. For the Delaware Bay site, the primary correlation was between temperature and oyster mortality, with a periodicity of 8 years, which corresponds to the NAO. Warmer temperatures, which occur during the positive phase of the NAO, favor the parasites causing increased oyster mortality. Thus, disease prevalence and intensity in C. virginica populations along the Gulf of Mexico coast is primarily regulated by salinity, whereas temperature regulates the disease process along the United States east coast. These results show that the response of an organism to climate variability in a region is not indicative of the response that will occur over the entire range of a particular species. This has important implications for management of marine resources, especially those that are commercially harvested.

Ocean quahogs (Arctica Islandica) are long-lived bivalves. Distribution patterns and biology of ocean quahogs in the Mid-Atlantic Bight (MAB) off the east coast of North America are directly related to bottom water temperatures. We examined long term recruitment patterns for ocean quahogs across temporal (decadal) and spatial (latitudinal, bathymetric) scales using a spatially defined (Long Island Sound to Chesapeake Bay mouth) population encompassing a broad size (age) range of animals that had not yet recruited to the commercial fishery [

A reduction in population abundance, brought on by an unprecedented 6 years of low recruitment, has reduced shell input through natural mortality on Delaware Bay oyster beds. Quantitative stock surveys provide an estimate of surficial shell over the same time period, permitting the reconstruction of the time history of shell since 1998 and estimation of the rates of shell addition and loss. Shell loss rates were unexpectedly high. In most cases, half of the shell added to an oyster bed in Delaware Bay in a given year is lost over a subsequent period of 2–10 years. Unexpectedly, the shortest half-lives, typically two to three years, are at intermediate salinities. Half-lives increase upbay into lower salinity and downbay into higher salinity to about 10 years. Minimal shell doubling times were calculated under the assumption of no shell loss, a maximum accretion rate. Minimal doubling times vary from somewhat less than a decade to more than a score of years. Doubling times of decadal scale emphasize that shell has the potential to accumulate rapidly on human time scales. The rarity of definitive documentation of shell accumulation, in terms of reef vertical accretion or lateral expansion, can only be explained if most shell produced yearly does not long remain recognizably intact. Doubling times are not rapid on the scale of oyster generation time, however. Management of essential fish habitat in the estuarine realm must include management of the shell budget and management of commercial shell-producing species must include the provision of animals as carbonate producers for habitat maintenance. Shell, at least in estuarine habitats, may have low preservational potential, even in areas that, when preserved, will appear to be shellbeds. The biases in the fossil record may not be minimized in shell-rich environments of preservation because shelliness does not imply good preservability.

The trend towards use of commercial vessels to enhance survey data requires assessment of the advantages and limitations of various options for their use. One application is to augment information on size-frequency distributions obtained in multispecies trawl surveys where stratum boundaries and sampling density are not optimal for all species. Analysis focused on ten recreationally and commercially important species: bluefish, butterfish, Loligo squid, weakfish, summer flounder, winter flounder, silver hake (whiting), black sea bass, striped bass, and scup (porgy). The commercial vessel took 59 tows in the sampled domain south of Long Island, New York and the survey vessel 18. Black sea bass, Loligo squid, and summer flounder demonstrated an onshore-offshore gradient such that smaller fish were caught disproportionately inshore and larger fish offshore. Butterfish, silver hake, and weakfish were characterized by a southwest-northeast gradient such that larger fish were caught disproportionately northeast of the southwestern-most sector. All sizes of scup, striped bass, and bluefish were caught predominately inshore. Winter flounder were caught predominately offshore. The commercial vessel was characterized by an increased frequency of large catches for most species. Consequently, patchiness was assayed to be higher by the commercial vessel in nearly all cases. The size-frequency distribution obtained by the survey vessel for six of the ten species, bluefish, butterfish, Loligo squid, summer flounder, weakfish, and silver hake, could not be obtained by chance from the size-frequency distribution obtained by the commercial vessel. The difference in sample density did not significantly influence the size-frequency distribution. Of the six species characterized by significant differences in size-frequency distribution between boats, all but one was patchy at the population level and all had one or more size classes so characterized. Although the variance-to-mean ratio was typically higher for the commercial vessel, five of the six cases that were otherwise were among the species for which the size-frequency distribution differed between the two vessels. Thus, the origin of the significant differences observed between vessels would appear to lie in the spatial pattern of the species as it interacts with the tendency for one vessel to obtain large catches more frequently for some size classes. One consequence of differential distribution and catchability is that more large fish were present in the commercial vessel catches than in the survey vessel catches in cases where the two vessels obtained different size-frequency distributions. Application of commercial vessels to the evaluation of size frequency hinges on understanding how to interpret differences among boats, gear, and sampling design. Here we show that key ingredients to this understanding are the degree of nonlinearity in catchability across a range of size classes, the interaction of varying spatial arrangements among size classes and the sampling design, and the interaction of varying spatial arrangements with differential catchability. La tendencia hacia la utilización de buques comerciales para incrementar y optimizar los datos de campañas de evaluación requiere la valoración de las ventajas y limitaciones de las distintas opciones para su uso. Una aplicación consiste en aumentar la información referente a distribuciones de frecuencias de tallas obtenidas en campañas de evaluación de pesquerías de arrastre multiespecíficas, en las que los límites de los estratos y la densidad del muestreo no son óptimas para todas las especies. El presente análisis se centró en diez especies importantes, tanto desde el punto de vista recreacional como comercial: Pomatomus saltatrix, Peprilus triacanthus, Loligo pealei, Cynoscion regalis, Paralichthys dentatus, Pleuronectes americanus, Merluccius bilinearis, Centropristis striata, Morone saxatilis y Stenotomus chrysops. El buque comercial realizó 59 lances en la zona muestreada al sur de Long Island, Nueva York, y el buque de investigación, 18. C. striata, L. pealei y P. dentatus presentaron un gradiente desde la costa hacia mar abierto tal que los individuos de menor talla fueron capturados desproporcionadamente en aguas costeras y los ejemplares de mayor talla a mayor distancia de la costa. P. triacanthus, M. bilinearis y C. regalis se caracterizaron por un gradiente sudoeste-nordeste tal que los ejemplares de mayor talla se capturaron desproporcionadamente al nordeste del sector más sudoccidental. Todas las tallas de S. chrysops, M. saxatilis y P. saltatrix fueron capturadas predominantemente en aguas costeras. P. americanus se capturó predominantemente en aguas alejadas de la costa. El buque comercial se caracterizó por una mayor frecuencia de grandes capturas para la mayoría de especies. En consecuencia, la agregación en áreas de alta densidad se mostró superior en el buque comercial en casi todos los casos. La distribución de frecuencias de tallas obtenida por el buque de investigación para seis de las diez especies (P. saltatrix, P. triacanthus, L. pealei, P. dentatus, C. regalis y M. bilinearis no pudo ser obtenida por azar a partir de la distribución de frecuencias de tallas obtenida por el buque comercial. La diferencia en densidad del muestreo no influenció significativamente la distribución de frecuencias de tallas. De las seis especies caracterizadas por diferencias significativas en la distribución de frecuencias de tallas entre buques, todas menos una mostraron agregaciones en áreas de alta densidad a nivel poblacional y todas presentaron una o más clases de talla caracterizadas de esta manera. Aunque la relación varianza-media fue típicamente superior para el buque comercial, cinco de los seis casos en que no fue así se dieron entre las especies en las que la distribución de frecuencias de tallas fue distinta entre los dos buques. Así, el origen de las diferencias significativas observadas entre buques radicaría en la pauta espacial de las especies al interaccionar con la tendencia de un buque a obtener grandes capturas con más frecuencia para algunas tallas. Una consecuencia de la distribución diferencial y capturabilidad es que más individuos de gran tamaño estuvieron presentes en las capturas del buque comercial que en las capturas del buque de investigación en casos en los que los dos buques obtuvieron distintas distribuciones de frecuencias de tallas. La utilización de buques comerciales para la evaluación de frecuencias de tallas depende de la comprensión sobre cómo interpretar las diferencias entre buques, artes de muestreo y diseño de muestreo. Mostramos aquí que ingredientes clave para esta comprensión son el grado de no-linearidad en la capturabilidad a lo largo de un rango de clases de talla, la interacción de distribuciones espaciales distintas entre clases de talla y el diseño de muestreo, así como la interacción de distintas distribuciones espaciales con la capturabilidad diferencial.

Authigenic carbonates are common at deep-sea petroleum seeps as a result of excess bicarbonate production during microbial degradation of hydrocarbons coupled to sulfate reduction. Consequently, these seep environments are supersaturated with respect to carbonates. This finding conflicts with taphonomic data that dissolution is the most pervasive mode of shell alteration at seeps. We provide here the first study linking the preservational process with the chemical characterization of the taphonomically-active zone at petroleum seep sites. This characterization is made possible using fine-scale porewater carbonate chemistry data and skeletal material deployed for 8 years at petroleum seep sites in the northwestern Gulf of Mexico. Microelectrode measurements of pH and pCO2 identify a very restricted zone of CaCO3 undersaturation immediately below the sediment–water interface in otherwise supersaturated environments (i.e., sandwiched between supersaturated bottom seawater and sediment porewater). This zonation characterizes the taphonomically-active zone, and is a result of a highly compressed redox front between acid-generating aerobic oxidation of reduced chemical species including hydrocarbons, H2S, and planktonic-and-terrestrial organic carbon and base-generating sulfate reduction coupled to CH4 oxidation. Porewater geochemistry is spatially variable at seep sites, and produces variable shell-dissolution signatures. Shells deployed at seep sites have moderate to severe dissolution that is consistent with a much higher flux of total dissolved inorganic carbon (DIC) from the porewater to the bottom water. Therefore, a mosaic of preservational conditions is directly related to the spatially and chemically varying taphonomically-active zones found at seep sites. These findings support the variability of carbonate preservation reported for globally-distributed Phanerozoic fossil seeps and the view that data from field taphonomy can significantly upgrade and validate carbonate destruction rates used in geochemical and climatic models. Carbon mass-balance analyses also lead to an important conclusion that carbonate dissolution forms a very important mechanism for benthic carbon recycling, possibly accounting for 50% of the benthic DIC flux to the bottom water in northern Gulf of Mexico petroleum seep sediments.

To evaluate methods for calculating mortality in bivalve molluscs, we analyzed historical data from dredge surveys of both planted and natural oyster (Crassostrea virginica) grounds in Delaware Bay to compare total box-count mortality estimates with those made by accumulating short-term mortality rates obtained from fresh boxes identified by shell condition and degree of fouling. Box-count and cumulative-mortality patterns and values agreed best on grounds with planted oysters, where a cohort with very few dead oysters was broadcast on previously cleaned bottom and was followed over time. This situation is analogous to an artificially created reef with oysters either deployed or naturally set on it. When deaths predominated in late summer and early autumn, the two estimates were similar throughout the following year; when mortality was greatest in spring or early summer, the estimates were similar only through autumn of the same year. Correspondence was much weaker on natural beds, where new individuals constantly recruited to the population and variable numbers of boxes were always present. Nevertheless, total box-count mortality estimates made during autumn stock surveys were significantly correlated with cumulative mortalities calculated for the preceding year. We also estimated disarticulation rates of artificially created boxes by deploying them at three seasons and eight sites in Delaware Bay. Disarticulation time depended on the length of exposure at summer temperatures, with the average time to 50% disarticulation for boxes deployed in spring and in summer being 225 and 345 days, respectively. Disarticulation rates increased with decreasing size, and increasing salinity and temperature. Finally, we compared total box-count and cumulative-mortality estimates with those made using the disarticulation data. Annual averages for the three methods were within 5 percentage points of each other. Our data indicate that total box-count mortality estimates from fall stock surveys can provide a reliable index to total mortality for the previous year, although it cannot describe the seasonal patterns obtainable using the cumulative-mortality method.

The Town of Islip, NY has collected a long-term data set (1977–2004) on northern quahog (hard clam), Mercenaria mercenaria, abundance. The data comprise approximately 350 duplicate 1 m2 samples each year taken with a clam shell bucket. All samples were sieved through a 6.4 mm sieve and the hard clams enumerated by size. In addition, clam landings data for the town waters are available for the same time period. Clam populations have declined from their peaks in the 1970s to very low levels in the 1990s and 00's. These dramatic shifts in population abundance have made the exploration of spawner/recruit relationships possible. A number of alternate models were attempted, but based on knowledge of the biology of the species and other factors, all but two did not appear to be plausible. The two models (2nd order polynomial and Log) yielded high r2 values and intercepted the 0 axis between 0.5 and 0.75 adult clams m−2 indicating a density dependent effect on recruitment. The polynomial model also sugge...

We report results of a survey explicitly focused on ocean quahog recruitment in the Mid-Atlantic Bight. The recruitment survey resampled all NMFS survey sites south of Hudson Canyon and a selection of sites north and east of Hudson Canyon off the Long Island coast over the entire depth range of this species with the exception of the most inshore reaches off Long Island. More ocean quahogs were encountered, on a per tow basis, in the vicinity of and north of Hudson Canyon. The proportion of recruits in the size-frequency distribution was higher in the south and the most recent recruitment events were concentrated there. Analysis of the 104 size-frequency distributions delineated regions of recent recruitment, areas that have not seen significant recruitment for many decades and areas that received heavy recruitment some decades previously but not recently. Overall, the survey suggests that three regionally distinctive processes determine the size-frequency distributions of ocean quahog assemblages...