Surf Clam Spisula Solidissima Research Articles

Structural and dynamic characterization of the hexa-coordinated globin from Spisula solidissima

High energy consumption in the nervous system requires a continuous supply of O2. This role is assisted by proteins from the globin super-family in the nerve cells of invertebrates, where ‘nerve hemoglobins’ (nHbs) are mainly present at mM concentrations and exhibit oxygen affinities comparable to those of vertebrate myoglobins. To gain insight into the structural bases of this function, we report the crystal structure of nHb from the Atlantic surf clam Spisula solidissima (SsHb), previously suggested to display a bis-histidyl hexa-coordinated heme in the deoxy state, high O2 affinity, and ligand binding cooperativity when assayed in situ. The crystallized protein forms a dimer through packing of a 4-helix bundle involving helices E and F of each subunit. The SsHb ‘classic’ globin fold displays bis-histidyl (His71(E7) and His103(F8)) hexa-coordination of the heme-Fe atom, with structural and dynamics variations found in the inter-helix hinge regions. Molecular Dynamics simulations of both monomeric and dimeric species in the bis-histidyl hexa-coordinated, deoxy penta-coordinated, and O2-bound hexa-coordinated states reveal distinct structural rearrangements at the interface between subunits in the dimer; these would affect the magnitude of the conformational fluctuations observed between monomer and dimer, and the topology of cavities within the protein matrix and at the interface. These results point to a distal site opening mechanism allowing access of the exogenous ligand to the heme and cast hypotheses on the dimer interface structural and dynamic properties that may support ligand binding cooperativity in dimeric SsHb.-

Interactive Effects of Climate Change‐Induced Range Shifts and Wind Energy Development on Future Economic Conditions of the Atlantic Surfclam Fishery

AbstractRising water temperatures along the northeastern U.S. continental shelf have resulted in an offshore range shift of the Atlantic surfclam Spisula solidissima to waters still occupied by ocean quahogs Arctica 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.

Potential Repercussions of Offshore Wind Energy Development in the Northeast United States for the Atlantic Surfclam Survey and Population Assessment

AbstractThe Atlantic surfclam Spisula solidissima fishery, 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 simulated F increased by 7% but was still less than the accepted F threshold. 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.

Exploring the Feasibility of Selectively Breeding Farmed Atlantic Surfclams Spisula solidissima for Greater Heat Tolerance

AbstractBivalve aquaculture is an important and rapidly expanding sector in global food production, yet climate change presents numerous challenges to its continued expansion. The Atlantic surfclam Spisula solidissima is emerging as an attractive alternate species for aquaculturists across the northeastern United States since it is native, grows rapidly, and complements the region’s established farming framework. However, the species is vulnerable to prolonged high temperature conditions, an issue that will be exacerbated by rising ocean temperatures and is particularly problematic on shallow coastal farms. In this study, we evaluated the response of adult farmed Atlantic surfclams to heat stress after juvenile exposure and the ability for heat tolerance to be passed to subsequent generations. We found that when juvenile Atlantic surfclams were exposed to prolonged lethal temperatures, the adult survivors withstood subsequent heat stress for significantly longer than individuals not exposed to lethal temperatures as juveniles. We also found that selective breeding enhanced heat tolerance in first‐generation Atlantic surfclam progeny. Moreover, growth of the heat‐selected progeny was not significantly different from that of control Atlantic surfclams. Although more research on this topic is necessary, this work suggests that selective breeding may be a viable strategy for enhancing survival of cultivated bivalves vulnerable to heat stress.

Energetic response of Atlantic surfclam Spisula solidissima to ocean acidification

In this study, we assessed the Atlantic surfclam (Spisula solidissima) energy budget under different ocean acidification conditions (OA). During 12 weeks, 126 individuals were maintained at three different ρCO2 concentrations. Every two weeks, individuals were sampled for physiological measurements and scope for growth (SFG). In the high ρCO2 treatment, clearance rate decreased and excretion rate increased relative to the low ρCO2 treatment, resulting in reduced SFG. Moreover, oxygen:nitrogen (O:N) excretion ratio dropped, suggesting that a switch in metabolic strategy occurred. The medium ρCO2 treatment had no significant effects upon SFG; however, metabolic loss increased, suggesting a rise in energy expenditure. In addition, a significant increase in food selection efficiency was observed in the medium treatment, which could be a compensatory reaction to the metabolic over-costs. Results showed that surfclams are particularly sensitive to OA; however, the different compensatory mechanisms observed indicate that they are capable of some temporary resilience.

Persistence of Hydraulic Dredge Tracks Following Surfclam Harvesting in Shallow Water

Hydraulic dredges used for bivalve harvest are known to create immediate biological and physical changes to the substrate, but the rate of recovery is often site specific and habitat specific. Hydraulic dredging for the Atlantic surfclam Spisula solidissima (Dillwyn, 1817) occurred off Provincetown, MA, from November 2014 through April 2015. Acoustic surveys following the dredge activity were conducted in 2015 (June–August) with a phase-measuring sidescan sonar, yielding colocated sidescan backscatter and swath bathymetry. Dredge tracks were documented in 7.9% (402,309 m2) of the 5.1 km2 surveyed. The survey area was divided into 10 × 10 m grid cells, and track density was calculated within each grid by the aggregated count of dredge tracks within each grid cell. The resulting track densities ranged between 0% and 53%. On October 23, 2017, 875 days after the 2015 hydraulic clamming season, a subset (1.05 km2 ∼20%) of the same area was acoustically surveyed. The 2017 survey (1.05 km2) revealed that dredge tracks covered a total area of 9,784 m2 at a density of 0%–24%. Initial areas (2015) with dredge track density greater than 10% had not fully recovered in 2017, and the rate of dredge tracks remaining was proportional to disturbance (linear regression; r2 = 0.95; F = 110.6; df = 1,7; P < 0.001; SE = 0.206). The adjacent dynamic shoreline and the persistence of dredge tracks reinforce the idea that nearshore energy regimes should not be assumed based solely on more visible shoreline processes.

Changes in the spatial distribution and anatomy of a range shift for the Atlantic surfclam Spisula solidissima in the Mid-Atlantic Bight and on Georges Bank

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 620:77-97 (2019) - DOI: https://doi.org/10.3354/meps12964 Changes in the spatial distribution and anatomy of a range shift for the Atlantic surfclam Spisula solidissima in the Mid-Atlantic Bight and on Georges Bank Jeremy R. Timbs1,*, Eric N. Powell1, Roger Mann2 1Gulf Coast Research Laboratory, The University of Southern Mississippi, Ocean Springs, MS 39564, USA 2Virginia Institute of Marine Sciences, The College of William and Mary, Gloucester Point, VA 23062-1346, USA *Corresponding author: jeremy.timbs@dmr.ms.gov ABSTRACT: The Atlantic surfclam Spisula solidissima supports one of the largest fisheries on the US northeast coast. Using ~30 yr of data from surfclam stock surveys, variance-to-mean ratios (VtMRs) were calculated both temporally and spatially for a range of surfclam size classes to determine the degree of patchiness. The VtMR declined from the 1980s to present in all regions (offshore Delmarva, New Jersey, Long Island, Southern New England, Georges Bank); however, VtMR rose with increasing clam size. Taylor’s power law (TPL) analysis corroborated the VtMR; the surfclam is highly patchy across its range. The surfclam’s proclivity for a patchy distribution varied regionally. Regions supporting the bulk of the stock were characterized by significantly higher degrees of patchiness and exhibited a higher exponent for the TPL. A species distribution function model corroborated findings of declining patchiness over time, supporting the hypothesis that warming of Mid-Atlantic continental shelf bottom waters is both driving the surfclam into new habitat and extirpating it from nearshore and southern areas. Size-dependent and temporal trends in VtMRs and temporal relative stability in TPL suggest that range expansion is conduced by regional settlement of larvae, followed by biased mortality in suboptimal habitats. This biased mortality ultimately re-establishes the increased patchiness characteristic of larger animals but also predisposes the species to a rapid range shift. Declining VtMRs over time may be a symptom of range expansion along the leading range boundary that has increased the proportion of newly occupied habitat without mature patch characteristics while, at the same time, range recession has removed the older mature patches along the range’s trailing edge. KEY WORDS: Patchy distribution · Larval transport · Ocean warming · Larval connectivity · Range shift Full text in pdf format PreviousNextCite this article as: Timbs JR, Powell EN, Mann R (2019) Changes in the spatial distribution and anatomy of a range shift for the Atlantic surfclam Spisula solidissima in the Mid-Atlantic Bight and on Georges Bank. Mar Ecol Prog Ser 620:77-97. https://doi.org/10.3354/meps12964 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 620. Online publication date: June 18, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Assessment of the Relationship of Stock and Recruitment in the Atlantic Surfclam Spisula solidissima in the Northwestern Atlantic Ocean

Atlantic surfclams support a major commercial fishery in the western North Atlantic Ocean with landings consistently between 15,000 and 25,000 metric tons since 1982. The stock is not and historically has not been overfished nor has overfishing occurred; however, in recent years landings per unit effort have declined. Surfclams are a biomass dominant on the continental shelf and a bellwether of climate change in the northwestern Atlantic. This study investigated the relationship of broodstock and recruitment during a period when Mid-Atlantic warming initiated a shelf-wide shift in the surfclams range. A species distribution function model was used to assess the effective area occupied by surfclams for five study regions (Delmarva, New Jersey, Long Island, Southern New England, and Georges Bank). The effective area occupied by small surfclams was consistently much greater than that for large (≥120 mm) surfclams. Three independent statistical analyses of the stock-recruitment relationship found little evidence of a significant association in any of the five regions, suggesting that factors besides spawning stock biomass (SSB) are primary determinants of recruitment success. Interannual variability in recruitment, in part associated with variations in larval transport and in part associated with spatially different rates of mortality post-settlement, is an important source of uncertainty and warming bottom waters driving surfclams into new habitat may decouple any inherent interaction between recruits and SSB. A recruitment index obtained from a fishery-independent survey across the range of the stock, as a consequence, is unlikely to usefully presage changes in abundance of the fishable stock. The wider distribution of settlers relative to the fishable stock, however, positions the species well to respond to changing bottom water temperatures as Mid-Atlantic warming continues.

The death assemblage as a marker for habitat and an indicator of climate change: Georges Bank, surfclams and ocean quahogs

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.

DThe Value of Captains’ Behavioral Choices in the Success of the Surfclam (Spisula solidissima) Fishery on the U.S. Mid-Atlantic Coast: a Model Evaluation.

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.

Character of Shell Beds Flanking Herod Point Shoal, Southeastern Long Island Sound, New York

Abstract High biogenic productivity, strong tidal currents, shoal topography, and short transport distances combine to favor shell-bed formation along the lower flanks of a cape-associated shoal off Herod Point on Long Island, New York. This shell bed has a densely packed, clast-supported fabric composed largely of undegraded surf clam (Spisula solidissima) valves. It is widest along the central part of the western flank of the shoal where topographic gradients are steep and a stronger flood tide results in residual flow. The bed is narrower and thinner toward the landward margins where currents are too weak to transport larger valves and topographic gradients are gentle, limiting bed-load transport mechanisms by which the shells are concentrated. Reconnaissance mapping off Roanoke Point suggests that shell beds are also present at the other cape-associated shoals off northeastern Long Island, where relatively similar geomorphic and oceanographic conditions exist. These shell beds are important to the Lon...

Characterization of a novel octopamine receptor expressed in the surf clam Spisula solidissima

We have cloned and sequenced a cDNA from the surf clam ( Spisula solidissima, a pelecypod mollusc) that encodes an octopamine receptor which we have named Spi-OAR. The sequence of Spi-OAR shares many similarities with two Aplysia and three Drosophila octopamine receptors belonging to a sub-group of β-adrenergic-like octopamine receptors. Using an expression vector and transient transfections of Spi-OAR into HEK 293 cells, we observed an increase of cAMP upon addition of octopamine and, to a lesser extent, of tyramine, but not after addition of dopamine, serotonin, or histamine. Using a battery of known agonists and antagonists for octopamine receptors, we observed a rather unique pharmacological profile for Spi-OAR through measurements of cAMP. Spi-OAR exhibited some constitutive activity in HEK 293 cells and no Ca 2+ responses could be detected following addition of octopamine to Spi-OAR-transfected cells. RT-PCR analysis revealed ubiquitous expression of Spi-OAR mRNA in all adult tissues, oocytes and early embryos examined. While addition of serotonin to isolated clam oocytes resulted in meiotic activation, similar additions of octopamine had no effect, suggesting that its potential role in clam reproductive physiology differs significantly from that of serotonin. This work identifies Spi-OAR as a novel mollusc octopamine receptor closely related to other invertebrate β-adrenergic-like octopamine receptors, with possible reproductive and other physiological functions. This initial characterization of Spi-OAR makes possible further investigations and comparisons with more studied and familiar insect or gastropod mollusc octopamine receptors.

Small-scale, patchy distributions of infauna in hydrodynamically mobile continental shelf sands: Do ripple crests and troughs support different communities?

Spatial variability of infauna with respect to distribution of topographic habitat features was examined in hydrodynamically mobile sandy sediments on the inner continental shelf off New Jersey, USA (39° 27.69′ N, 74° 15.81′W). Sediment cores for infauna were taken by SCUBA divers at multiple spatial scales over time at 12-m depth in the LEO-15 research area on Beach Haven Ridge. Crests, troughs and less consistently flanks of sand ripples 5–15-cm in height, were characterized by different infaunal community patterns at spatial scales of centimeters to kilometers on several sampling dates. Overall, infaunal community differences among ripple crests, troughs, and/or flanks within areas <1-m 2 were greater than those found for each of these habitats (i.e., either crests, troughs, or flanks) that were separated by distances of 2 m–4 km. Infaunal density and species richness were consistently higher in troughs compared to crests. Indirect measures of food resources such as particulate organic carbon, chl a, and pheophytin were associated with ripple crests and troughs. Troughs contained significantly higher levels of particulate organic carbon (~1.2 times higher) associated with finer sediments, compared with crests and flanks. Various combinations of taxa had higher densities in either crests or troughs of sand ripples depending on date, and the relative abundances of three taxa, the deposit-feeding polychaete Polygordius jouinae, the suspension-feeding surfclam Spisula solidissima, and predatory nemerteans were important in distinguishing between crests and troughs on most dates. Thus, a priori knowledge of whether a benthic sample comes from a crest or trough helped to explain small-scale infaunal patchiness in relatively homogeneous, subtidal sandy sediments. Consideration of such topographic features in sampling designs can help in explaining variation in species’ distributions at several spatial and temporal scales.

William D. Cohen: Biologist, Educator, Editor (1938–2008)

William D. Cohen: Biologist, Educator, Editor (1938–2008)

INITIAL RECRUITMENT AND GROWTH OF SURFCLAMS (SPISULA SOLIDISSIMA DILLWYN) ON THE INNER CONTINENTAL SHELF OF NEW JERSEY

Abstract Surfclam (Spisula solidissima Dillwyn) larval settlement and the initial growth of recruits were studied on the inner shelf of New Jersey. Initial recruitment was measured by taking weekly benthic core samples during the summer settling season, and larval supply was characterized using meroplankton samples taken every four hours in July. The temporal variation in recruitment at two inshore stations (12-m depth) was linked to larval supply from the water column, and spatial differences (inshore vs. offshore) in recruitment also appeared to be related to larval supply. Spatial and temporal variation in larval concentrations was associated with wind-driven cross-shelf circulation. Contrasting recruitment patterns between the two inshore stations could not be explained by larval supply alone and were likely affected by near-bottom flows. Growth rates of initial surfclam recruits (with initial shell lengths 360 μm shell l...

Tools for Estimating Surplus Production andFMSYin Any Stock Assessment Model

Abstract Surplus-production calculations can be made in any stock assessment model that includes catch data and that estimates biomass. Maximum sustainable yield (MSY) reference points can also be estimated if there are sufficient data. The “external” method estimates production model parameters after the assessment model is fitted. External calculations are simple and useful; we recommend that they be done routinely. The “internal” method fits a more complicated assessment model and a surplus-production model simultaneously. It includes the external and “all-measurement-error” modeling methods (e.g., ASPIC) as special cases. External MSY estimates for Atlantic surfclam Spisula solidissima off northern New Jersey, cowcod Sebastes levis in the Southern California bight, and yellowtail flounder Pleuronectes ferrugineus on Georges Bank and internal MSY estimates for northern Atlantic surfclam were similar to conventional estimates. Surplus-production calculations and both internal and external modeling appro...

Cysteine‐containing histone H1‐like (PL‐I) proteins of sperm

We have determined the presence of cysteine in the protein PL-I from the sperm of the surf clam Spisula solidissima. The existence of cysteine in this histone H1-related protein is responsible for its previously described aggregation behavior. The location of this residue, within the trypsin-resistant domain of the protein, has been established. We have also shown that cysteine is ubiquitously present in the PL-I proteins from the sperm of other bivalve mollusks but is absent from other PL of smaller molecular mass (PL-II, PL-III, PL-IV). We have also found cysteine to be present in the PL-I from a tunicate (Chelysoma productum) but absent in a PL-I from a fish (Mullus barbatus). The possible significance of the unusual occurrence of cysteine in these histone-H1-related proteins is discussed. Mol. Reprod. Dev. 54:402–409, 1999. © 1999 Wiley-Liss, Inc.

Cysteine-containing histone H1-like (PL-I) proteins of sperm.

We have determined the presence of cysteine in the protein PL-I from the sperm of the surf clam Spisula solidissima. The existence of cysteine in this histone H1-related protein is responsible for its previously described aggregation behavior. The location of this residue, within the trypsin-resistant domain of the protein, has been established. We have also shown that cysteine is ubiquitously present in the PL-I proteins from the sperm of other bivalve mollusks but is absent from other PL of smaller molecular mass (PL-II, PL-III, PL-IV). We have also found cysteine to be present in the PL-I from a tunicate (Chelysoma productum) but absent in a PL-I from a fish (Mullus barbatus). The possible significance of the unusual occurrence of cysteine in these histone-H1-related proteins is discussed.

Additive interactions between the moon snail Euspira heros and the sea star Asterias forbesi, two predators of the surfclam Spisula solidissima.

A laboratory experiment was conducted to determine whether the sea star Asterias forbesi and the naticid gastropod Euspira heros feed on surfclams, Spisula solidissima, in an additive or non-additive manner. Predators were allowed to feed on clams with conspecifics and in the presence of the other predator species. Clam mortality (measured as the rate of decline of clam number) and predator feeding rates were noted. To determine the effects of temperature on interactions among the predators, the experiment was conducted at three different temperatures. At all temperatures, feeding rate of each predator was not affected by the presence of the other species, and clam mortality in the presence of both predators was predictable from mortality in the presence of a single predator species. These additive interactions are most likely a result of habitat partitioning between the predators, with naticid snails being infaunal and sea stars being epifaunal. Previous studies in a variety of systems show no clear pattern of occurrence of non-additive interactions. Relatively small differences in predator or prey behavior may be responsible for the presence or absence of non-additive interactions.

Effect of the T/B North Cape Oil Spill on the Surf Clam (Spisula Solidissima) in the Coastal Waters of Southern Rhode Island1

ABSTRACT On 19 January 1996, the T/B North Cape grounded on the south shore of Rhode Island and spilled approximately 828,000 gallons of home heating oil. Storm waves mixed the oil into the water column, and currents transported the plume of contaminated water over an area of about 400 km2. Immediate post-spill observation of animals stranded on the beach within the impact area estimated 330,000 surf clams (Spisula solidissima), along with hundreds of thousands of crustaceans including lobsters and crabs. Field studies of the impact of the oil spill on the surf clam resource within the impact area and an adjacent control, unimpacted area were conducted over a 2-year period. Mortality of surf clams within the impact area was high. Using the density estimates of the adjacent control area, it is believed that most of the surf clams killed in the impact area were stranded ashore. More interesting, however, has been the recovery of the surf clam resource in the impact area, as compared to the control area. Densities of young of the year surf clams in the impact area, as observed in the winter/spring of 1997, about 1 year after the spill were very high, greater than 400/km2 at one station. Control area mean densities of the same year class were less than 2/m2 at all stations. A second field sampling conducted about 2 years after the spill indicated surf clam densities were reduced to maximum of 100/m2 within the impact area, and between 0–1/m2 in the control area. It is believed that the success of the post-spill set of surf clams in the impact area, as compared to the control area, is due to the loss of predators associated with the spill. Thus, with respect to the surf clams, this fishery resource has not only recovered, but has been enhanced by the spill.