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Coastal areas are especially vulnerable to habitat loss, sea-level rise, and other climate change effects. Oyster-dominated eco-engineered reefs have been promoted as integral components of engineered habitats enhancing coastal resilience through provision of numerous ecological, morphological, and socio-economic services. However, the assessed ‘success’ of these eco-engineered oyster reefs remains variable across projects and locations, with their general efficacy in promoting coastal resilience, along with related services, often mixed at best. Understanding factors influencing the success of these eco-engineered habitats as valuable coastal management tools could greatly inform related future efforts. Here, we review past studies incorporating reef-building oysters for coastal resilience and enhanced ecosystem services. Our aims are to better understand their utility and limitations, along with critical knowledge gaps to better advance future applicability. Success depends largely on site selection, informed by physical, chemical and biological factors, and adjacent habitats and bottom types. Better understanding of oyster metapopulation dynamics, tolerance and adaptation to changing conditions, and interactions with adjacent habitats will help to better identify suitable locations, and design more effective eco-engineered reefs. These eco-engineered reefs provide a useful tool to assist in developing coastal resilience in the face of climate change and sea level rise.

A total of 3612 ha of seagrass habitat was restored to the Virginia coast along with services like blue carbon and fisheries., There have been increasing attempts to reverse habitat degradation through active restoration, but few large-scale successes are reported to guide these efforts. Here, we report outcomes from a unique and very successful seagrass restoration project: Since 1999, over 70 million seeds of a marine angiosperm, eelgrass (Zostera marina), have been broadcast into mid-western Atlantic coastal lagoons, leading to recovery of 3612 ha of seagrass. Well-developed meadows now foster productive and diverse animal communities, sequester substantial stocks of carbon and nitrogen, and have prompted a parallel restoration for bay scallops (Argopecten irradians). Restored ecosystem services are approaching historic levels, but we also note that managers value services differently today than they did nine decades ago, emphasizing regulating in addition to provisioning services. Thus, this study serves as a blueprint for restoring and maintaining healthy ecosystems to safeguard multiple benefits, including co-benefits that may emerge as management priorities over time.

Virginia supported the most productive bay scallop ( Argopecten irradians ) fishery in the United States in 1930, but the fishery disappeared three years later and never recovered. This collapse highlights a tipping point, but managers of extant bay scallop fisheries have not looked to this case for guidance, because the collapse has long been attributed to an exogenous eelgrass ( Zostera marina ) ‘wasting disease’ pandemic. Consequently, it remains little understood. However, efforts to restore the fishery, following successful eelgrass restoration, now warrant a thorough examination of its economic significance and disappearance. This study comprehensively surveyed information on the original fishery and reconstructed the pre-collapse population to evaluate restoration prospects and management strategies that reduce the risk of future scallop-seagrass system collapses. Harvest records suggest that overharvesting possibly contributed to the Virginia fishery disappearance—a factor that influenced other bay scallop fisheries but did not alarm contemporary managers in Virginia. The harvest peaked before managers observed eelgrass disappearing and exceeded most pre-collapse population estimates. Intensive dredging possibly precipitated a feedback that reduced scallop recruitment by lowering seagrass shoot densities. Managers should, therefore, consider a potential tradeoff between future scallop harvest and eelgrass restoration goals. The restored wild scallop population in Virginia cannot yet support a commercial fishery at historic levels, which removed between 270 and 380x as many individuals. However, the economic risks associated with reestablishing this fishery are low. The collapse did not cause a significant loss in total economic value, because harvesters rapidly shifted focus to clams, supplanting lost scallop revenue.

Aquaculture of the northern quahog (=hard clam) Mercenaria mercenaria (Linnaeus, 1758) is widespread in shallow waters of the United States from Cape Cod to the eastern Gulf of Mexico. Grow-out practices generally involve bottom planting and the use of predator exclusion mesh. Both the extent and scale of clam farms have increased in recent decades resulting in concerns regarding the impacts of these practices on estuarine fauna. Seasonal distribution, abundance, biomass, species richness, and community composition of nektonic, demersal, epibenthic, and infaunal organisms were examined in cultivated and uncultivated shallow-water habitats in Virginia and New Jersey. The results reveal that clam aquaculture, as practiced in both Virginia and New Jersey, has remarkably few quantifiable impacts on estuarine fauna. Seasonal variations were observed in the biota, but of the 39 population and community metrics tested, mean values associated with 26 did not differ between cultivated and uncultivated are...

As bivalve aquaculture expands worldwide, an understanding of its role in nutrient cycling is necessary to ensure ecological sustainability and determine the potential of using bivalves for nutrient mitigation. Whereas several studies, primarily of epifaunal bivalves, have assessed denitrification, few have considered nutrient regeneration processes such as dissimilatory nitrate reduction to ammonium (DNRA), which competes with denitrification for nitrate and results in nitrogen retention rather than loss. This study compares sediment nitrogen cycling including mineralization, DNRA, and denitrification within U.S. clam aquaculture sediments to nearby uncultivated sediments, seasonally. Clam aquaculture significantly increased sediment ammonium and phosphate effluxes relative to uncultivated sediments. Both DNRA and denitrification were significantly enhanced at clam beds compared to uncultivated sediments in July and November, while in May only DNRA was increased. The ratio of DNRA to denitrification was significantly higher at clam beds compared to uncultivated sediments, demonstrating that DNRA may be favored due to a ready supply of labile organic carbon relative to nitrate and perhaps sulfidic conditions. Functional gene abundances, nrfA (DNRA) and nirS (denitrification) followed similar patterns to nitrate respiration rates with highest nrfA abundances in the clam sediments and similar nirS abundances across seasons and sediment type. Ultimately clam sediments were found to be a significant source of nutrients to the water column whereas uncultivated sediments retained ammonium produced by microbial mineralization. Thus, clam cultivation may promote local eutrophication (i.e., increased primary production) by facilitating nutrient regeneration and retention of ammonium in the sediments.

Predation is a key determinant of community structure and function, and thus should play a central role in successful ecological restoration strategies. The bay scallop, Argopecten irradians, was once abundant in the coastal bays of Virginia, U.S.A., until the complete loss of their eelgrass habitat, Zostera marina, in the 1930s. With the successful restoration of Z. marina in these coastal bays, attention has turned to reintroducing A. irradians with the intent of producing a self-sustaining population. The success of this effort requires an understanding of the sources and degree of natural mortality that A. irradians experiences throughout their ontogeny. The objectives of this study were to: (1) quantify predatory mortality during two successive life history stages of A. irradians, in both spring and fall spawns and (2) identify possible predators of A. irradians in the Virginia coastal bays. We conducted tethering experiments to quantify the proportional losses due to predation, and used otter trawls and suction samples to characterize the predator community over two consecutive years. Losses due to predation ranged from 4 to 80% per day, with smaller juveniles ( 20 mm shell height) in 2014, which we infer is driven by the absence and presence of adult blue crabs in 2013 and 2014, respectively. We propose that managers should look toward relatively inexpensive predator surveys to best judge both when and at what size restored species should be introduced into the wild.

Shellfish aquaculture is a widely practiced way of producing food for human consumption in coastal areas. When farming intertidal clams, farmers commonly protect young seedling clams from predatory losses by covering farmed plots with netting or screening. Recent discussion of the effectiveness of protective nets or screens and their environmental effects has raised questions concerning the utility of the practice. We provide data based on a review of more than 35 peer-reviewed articles, as well as our own research that demonstrates the efficacy of predator protection for clam farms in various habitats around the world. In addition, we evaluate the effects of screening on temperature, and comment on ancient practices of clam gardening as conducted in the Pacific Northwest.

Restoration of degraded ecosystems is an important societal goal, yet inadequate monitoring and the absence of clear performance metrics are common criticisms of many habitat restoration projects. Funding limitations can prevent adequate monitoring, but we suggest that the lack of accepted metrics to address the diversity of restoration objectives also presents a serious challenge to the monitoring of restoration projects. A working group with experience in designing and monitoring oyster reef projects was used to develop standardized monitoring metrics, units, and performance criteria that would allow for comparison among restoration sites and projects of various construction types. A set of four universal metrics (reef areal dimensions, reef height, oyster density, and oyster size–frequency distribution) and a set of three universal environmental variables (water temperature, salinity, and dissolved oxygen) are recommended to be monitored for all oyster habitat restoration projects regardless of their goal(s). In addition, restoration goal-based metrics specific to four commonly cited ecosystem service-based restoration goals are recommended, along with an optional set of seven supplemental ancillary metrics that could provide information useful to the interpretation of prerestoration and postrestoration monitoring data. Widespread adoption of a common set of metrics with standardized techniques and units to assess well-defined goals not only allows practitioners to gauge the performance of their own projects but also allows for comparison among projects, which is both essential to the advancement of the field of oyster restoration and can provide new knowledge about the structure and ecological function of oyster reef ecosystems.

Enhancingpopulations ofsuspension feedingbivalves,particularlythe easternoyster,Crassostreavirginica, has been proposed as a means of mitigating eutrophication in coastal waters. Review of studies evaluating the effects of C. virginica on nitrogen (N) cycling found that oysters can have effects on water quality that vary by orders of magnitude among sites, seasons, and growing condition (e.g., oyster reefs, aquaculture). Nitrogen contained in phytoplankton consumed by oysters may be returned to the water column, assimilatedintooystertissue and shell,buriedin the sediments,orreturnedtothe atmosphereas dinitrogen gas, primarily via denitrification. Accurately quantifying oyster-related N removal requires detailed knowledge oftheseprimaryfatesofNincoastalwaters.Areviewofexistingdatademonstratedthatthecurrentstateof knowledgeisincompleteinmanyrespects.Nitrogenassimilatedintooystertissueandshellpergramofdry weight was generallysimilaracrosssitesand in oysters growingon reefscomparedto aquaculture.Data on long-term burial of N associated with oyster reefs or aquaculture are lacking. When compared to suitable reference sites, denitrification rates were not consistently enhanced. Depending on environmental and oyster growing conditions, changes in denitrification rates varied by orders of magnitude among studies and did not always occur. Oyster aquaculture rarely enhanced denitrification. Unharvested oyster reefs frequently enhanced denitrification rates. Incorporating oysters into nutrient reduction strategies will require filling gaps in existing data to determine the extent to which relationships between N removal and environmental and/or growing conditions can be generalized.

article i nfo Epifauna Mesograzers Predation Seagrass Predation strongly influences populations of numerous benthic invertebrates, although many predation studies to date have focused on macroscopic individuals, ignoring critical early life stages. Juveniles of the bay scallop, Argopecten irradians, settle and grow on the blades of eelgrass, Zostera marina, then migrate to the sediment sur- face when their mobility and size provide a refuge from benthic predators. During their time in the eelgrass can- opy, scallops co-occur with a diverse array of small invertebrates, including peracarid and small decapod crustaceans, whose role as predators is largely unexplored. We measured consumption by amphipods, isopods, and a shrimp on recently settled bay scallops ranging in size from 0.5 to N1.5 mm in a series of 24-hour experi- mental laboratoryassays.These invertebrate predators,which were common concurrent epifaunal surveys of re- stored eelgrass beds in the mid-Atlantic, consumed up to 63% day �1 of juvenile scallops when the scallops were b1 mm, but predation impacts decreased as scallops exceeded this size. Our data have implications for current restoration of both bay scallops and their eelgrass habitat, suggesting that previously unrecognized consumers may significantly affect scallop population dynamics at early life stages.

Small (∼15 mm) and large (∼30 mm) calcein-marked bay scallops, Argopecten irradians, held for 2, 4, and 6 wk in the laboratory under natural illumination and conditions of high and low flow rates deposited significantly more striae on the surface of the left (dark) shell valve compared with the right (light) shell valve. Small scallops deposited an average of 0.55 stria per day, 0.42 stria per day, and 0.34 stria per day, respectively, during the 2-, 4-, and 6-wk experiments, whereas large scallops had a lower frequency of stria formation (0.20 stria per day, 0.18 stria per day, and 0.17 stria per day, respectively). Striae deposition and interstria distance were highly variable among small A. irradians. No relationship in interstria distance was obvious in A. irradians that deposited the same number of striae during 6 wk (0.45 striae per day) and held under conditions of high flow rate, indicating that stria formation is not synchronous with changes in the environment. Our results demonstrate unequivocally that in, A. irradians, stria formation is nondaily and is related to shell growth rate. The largest and oldest scallops (∼30 mm and 1.4 y old) formed striae at a rate of 0.17–0.2 stria per day whereas smaller and younger fast-growing A. irradians formed between 0.34 striae per day and 0.55 stria per day—clear evidence of nondaily and nonrhythmic deposition of striae in this pectinid species. Thus, striae cannot be used as a chronological marker with which environmental conditions can be compared.

It was with great excitement that we planned the combined meetings of Northeast Aquaculture Conference and Exposition (NACE) and the International Conference on Shellfish Restoration (ICSR) with the 33rd Milford Aquaculture Seminar (MAS). Bringing these different but complementary audiences together resulted in a meeting that combined many different aspects of fisheries restoration and aquaculture under one umbrella.Four hundred attendees including government representatives, research scientists, industry, and academia at both the university and vocational high school levels attended this event. The meeting commenced on Wednesday December 12th 2012, with over eighty people attending seven field trips to area aquaculture farms and research facilities. The formal program began on Thursday, December 13th with a plenary session including invited speakers Eric Schwabb, Acting Assistant Secretary for Conservation and Management at NOAA; Sebastian Belle, Executive Director of the Maine Aquaculture Association and Boze Hancock from the Nature Conservancy, who discussed the role of aquaculture in fisheries restoration. John Bullard, the Northeast Regional Administrator of NOAA Fisheries Service, addressed the group during the luncheon the following day. The technical papers and workshops presented were divided into 35 sessions over three days of the meeting and included topics such as the history of aquaculture, aquaculture hatchery innovations, siting and planning issues, risk management, aquaculture business management, ocean acidification, climate change, as well as aquaculture disease issues and potential remedies. Having persons present who have experienced problems and successes, along with those in manufacturing and government responsible for addressing concerns and sharing best practices, was invaluable. Discussions among this cross-section of persons who represent different aspects of aquaculture were as important as the well-presented and interesting formal papers and poster sessions. These discussions were facilitated by the many opportunities presented during the large trade show, reception, breaks, lunches, banquet and lobster bake held throughout the meeting.The importance of and need for aquaculture were made evident by all who were in attendance. We are grateful to the twenty four meeting sponsors and to all those who participated and made this such an important and memorable meeting.While oyster restoration efforts have been under way in the Chesapeake Bay for more than two decades, until recently, varying reporting methods and success criteria made it difficult to determine how much progress had been made. A goal to “Restore native oyster habitat and populations in 20 out of 35 to 40 candidate tributaries by 2025” was set in the 2010 strategy to implement the Chesapeake Bay Protection and Restoration Executive Order (signed by President Obama in 2009). This goal made it a priority for state and federal fishery managers, academics, and scientists working on oyster restoration to collaboratively define a “restored tributary” and a “restored reef” to enable them to track progress. A team of these people, led by NOAA staff, agreed on “oyster metrics” in 2011 (http//preview.tinyurl.com/8kmbdpm) that specify key metrics and target ranges for them, including tributary size, how to determine how much restorable bottom a tributary contains, how much of that restorable bottom needs to be restored, and the minimum oyster density and biomass in that restored bottom to count a tributary as restored. These new metrics enable experts to clearly see how oyster restoration efforts are working and use adaptive management to improve these efforts. These metrics serve as a tool to plan and evaluate oyster restoration consistently across the Chesapeake Bay, and the consensus-based framework used to develop them may have broader application to other restoration activities.In the past, oyster restoration in Maryland was performed primarily

Oysters, like the vast majority of sessile marine invertebrates, shed sperm and eggs into the water column where fertilization subsequently occurs. The fate of the gametes depends on their passive movements at various scales in a high-viscosity environment, the longevity of the sperm's ability to affect oriented movement, the rate of sperm movement toward the egg target, and the ability of sperm to effect fertilization. Oyster sperm swim in a helical pattern with a mean forward progression velocity of 0.057 ± 0.010 mm/sec (SE; n = 25) with the 95 percentile range extending from 0.036–0.078 mm/sec, a value comparable with that reported for echinoderm sperm.

Estuaries around the world are in a state of decline following decades or more of overfishing, pollution, and climate change. Oysters (Ostreidae), ecosystem engineers in many estuaries, influence water quality, construct habitat, and provide food for humans and wildlife. In North America's Chesapeake Bay, once-thriving eastern oyster (Crassostrea virginica) populations have declined dramatically, making their restoration and conservation extremely challenging. Here we present data on oyster size and human harvest from Chesapeake Bay archaeological sites spanning ∼3,500 y of Native American, colonial, and historical occupation. We compare oysters from archaeological sites with Pleistocene oyster reefs that existed before human harvest, modern oyster reefs, and other records of human oyster harvest from around the world. Native American fisheries were focused on nearshore oysters and were likely harvested at a rate that was sustainable over centuries to millennia, despite changing Holocene climatic conditions and sea-level rise. These data document resilience in oyster populations under long-term Native American harvest, sea-level rise, and climate change; provide context for managing modern oyster fisheries in the Chesapeake Bay and elsewhere around the world; and demonstrate an interdisciplinary approach that can be applied broadly to other fisheries.

A century-long decline of the fishery for the Eastern oyster Crassostrea virginica (Gmelin, 1791) in Maryland and Virginia stimulated numerous efforts by federal, state, and nongovernmental agencies to restore oyster populations, with limited success. To learn from recent efforts, we analyzed records of restoration and monitoring activities undertaken between 1990 and 2007 by 12 such agencies. Of the 1,037 oyster bars (reefs, beds, or grounds) for which we obtained data, 43% experienced both restoration and monitoring, with the remaining experiencing either restoration or monitoring only. Restoration activities involved adding substrate (shell), transplanting hatchery or wild seed (juvenile oysters), bar cleaning, and bagless dredging. Of these, substrate addition and transplanting seed were common actions, with bar cleaning and bagless dredging relatively uncommon. Limited monitoring efforts, a lack of replicated postrestoration sampling, and the effects of harvest on some restored bars hinders evaluations of the effectiveness of restoration activities. Future restoration activities should have clearly articulated objectives and be coordinated among agencies and across bars, which should also be off limits to fishing. To evaluate restoration efforts, experimental designs should include replication, quantitative sampling, and robust sample sizes, supplemented by pre- and postrestoration monitoring.

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and eco regions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the world's remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs. in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services.

The costs and benefits of non-native introductions as a restoration tool should be estimated prior to any action to prevent both undesirable consequences and waste of restoration resources. The suggested introduction of non-native oyster species, Crassostrea ariakensis, into Chesapeake Bay, USA, provides a good example in which the survival of non-native oysters may differ from that of native oysters, Crassostrea virginica, during the larval stage. Experiments were conducted to compare the predation vulnerability of native and non-native oyster larvae to different predator types (visual vs. non-visual, benthic vs. pelagic). The results suggest that the non-native larvae are more vulnerable to visual and non-visual pelagic predators. Although vulnerability was similar for larvae exposed to benthic non-visual predators, the consumption of one non-native strain was higher than the consumption of native C. virginica larvae. When vulnerability data are combined with predator feeding rates, the predation mortality for non-native larvae in the wild can be much higher than for native larvae. Small changes in larval mortality rates can yield large changes in total larval delivery to the reef for settlement, so these differences among species may contribute to differences in settlement success. These results provide an example of how a comprehensive examination of the perceived benefits of non-native introductions into complex ecosystems can provide important information to inform management decisions.

During their transition from the pelagic larval form to the benthic adult form, larvae are likely to encounter a diverse assemblage of resident invertebrates on oyster reefs. Fouling epifauna are generally believed to reduce the settlement of interspecific larvae through competitive exclusion and predation. Studies of these interactions, however, often utilize artificial settlement panels, which can exhibit different recruitment patterns to those observed on natural substrates. Native (Crassostrea virginica) and non-native (Crassostrea ariakensis) oyster larvae were exposed to reef-collected shells, each supporting a single species of reef-associated fauna, over a series of laboratory microcosm studies. The presence of adult bryozoans (Membranipora tenuis) had little effect on rates of larval settlement or mortality. The boring sponge (Cliona sp.) significantly decreased oyster larval settlement, and generally increased oyster mortality. Barnacles (Balanus improvisus) typically facilitated settlement. Barnacle molds and empty barnacle tests, intended to mimic the surface area and rugosity of live barnacles, did not significantly affect settlement. In some trials, adult barnacle bathwater enhanced settlement of oyster larvae, highlighting the importance of waterborne cues. Barnacle bathwaters, adult clam worm (Neanthes succinea) bathwaters and bathwaters created using adult oysters were all found to cause oyster larval mortality. Predation by clam worms, which were observed at very high densities on field-collected oyster shells, caused significant oyster larval mortality in these experiments. The combined effects of positive and negative interactions between oyster larvae and resident invertebrate reef fauna require enumeration under field conditions. The results from this study highlight the need for a more thorough understanding of settlement behavior and mortality sources of recruiting oyster larvae.

We examined the possibility that a nonnative oyster species would provide an ecologically functional equivalent of the native oyster species if introduced into the Chesapeake Bay. Habitat complexity and associated benthic communities of experimental triploid Crassostrea virginica and Crassostrea ariakensis reefs were investigated at 4 sites of varying salinity, tidal regime, water depth, predation intensity, and disease pressure in the Chesapeake Bay region (Maryland and Virginia). Four experimental treatments were established at each site: C. virginica, C. ariakensis, 50:50 of C. virginica and C. ariakensis, and shell only. Abundance, biomass, species richness, evenness, dominance, and diversity of reef-associated fauna were evaluated in relation to habitat location and oyster species. Although habitat complexity varied with location, no differences among complexity were associated with oyster species. Similarly, differences in faunal assemblages were more pronounced between sites than within sites. Our results show functional equivalency between oyster species with respect to habitat at the intertidal site and the low-salinity subtidal location. At subtidal sites of higher salinity, however, the numbers of organisms associated with C. virginica reefs per unit of oyster biomass were significantly greater than the numbers of organisms associated with C. ariakensis reefs. Multivariate analyses of data from subtidal high-salinity sites revealed unique communities associated with C. virginica treatments, whereas mixed-oyster species assemblages were functionally equivalent to monospecific C. ariakensis experimental treatments. Our study represents the first effort to quantify the potential habitat function of C. ariakensis, which has been proposed for an intentional introduction into Chesapeake Bay, and provides evidence of species-specific similarities and differences in reef-associated communities.

Many of the world's coastal ecosystems are impacted by multiple stressors each of which may be subject to different management strategies that may have overlapping or even conflicting objectives. Consequently, management results may be indirect and difficult to predict or observe. We developed a network simulation model intended specifically to examine ecosystem-level responses to management and applied this model to a comparison of nutrient load reduction and restoration of highly reduced stocks of bivalve suspension feeders (eastern oyster, Crassostrea virginica) in an estuarine ecosystem (Chesapeake Bay, USA). Model results suggest that a 50% reduction in nutrient inputs from the watershed will result in lower phytoplankton production in the spring and reduced delivery of organic material to the benthos that will limit spring and summer pelagic secondary production. The model predicts that low levels of oyster restoration will have no effect in the spring but does result in a reduction in phytoplankton standing stocks in the summer. Both actions have a negative effect on pelagic secondary production, but the predicted effect of oyster restoration is larger. The lower effect of oysters on phytoplankton is due to size-based differences in filtration efficiency and seasonality that result in maximum top-down grazer control of oysters at a time when the phytoplankton is already subject to heavy grazing. These results suggest that oyster restoration must be achieved at levels as much as 25-fold present biomass to have a meaningful effect on phytoplankton biomass and as much as 50-fold to achieve effects similar to a 50% nutrient load reduction. The unintended effect of oyster restoration at these levels on other consumers represents a trade-off to the desired effect of reversing eutrophication.

The Suminoe oyster (Crassostrea ariakensis) is being considered for introduction into the Chesapeake Bay. However, our current understanding of the biology and ecology of C. ariakensis is insufficient to predict whether an introduction will be successful, provide desired benefits, or have adverse impacts. Behavior of native Eastern oyster (C. virginica) pediveligers has been studied for many years and it is well established that they use a variety of habitat characteristics when selecting a site for colonization. Perhaps the most important of these are chemical cues emitted by adult conspecifics, which can lead to gregarious larval settlement and dense, persistent reef communities. Conversely, almost nothing is known about the mechanisms that regulate larval settlement and metamorphosis for C. ariakensis or how pediveligers might respond to conditions found in Chesapeake Bay. In a comparative study with C. virginica, we examined how environmental factors such as substrate type, natural biofilms, sediment and waterborne chemical cues influence larval settlement for two C. ariakensis strains (''south China'' and ''west coast''). Our results demonstrate many similarities but also potentially important differences. Both species and strains of larvae greatly prefer natural substrates (e.g., shell) covered with biofilms for colonization but the west coast strain of C. ariakensis exhibited greater attachment onto manmade substrates (e.g., fiberglass) than C. virginica. Waterborne chemical cues emitted by adult oysters were also found to enhance substrate attachment for all larval forms but cues do not appear to be species specific. These results provide critical insight to the ability of C. ariakensis larvae to identify and colonize suitable substrates in the Chesapeake Bay, which will have a large impact on recruitment success and their ability to establish self-sustaining populations.

In high salinity habitats along the Middle and South Atlantic coasts of the United States the Eastern oyster, Crassostrea virginica occupies an intertidal refuge from predation, facilitated by its tolerance of aerial exposure and associated desiccation and temperature stress. Observations of the Suminoe oyster, C. ariakensis in its native environments in Asia reveal that this species is most commonly found subtidally or in the very low intertidal zone, suggesting that it may be less tolerant of aerial exposure. With serious consideration being given to introducing C. ariakensis to the mid-Atlantic region, it is important to understand the ability of this non-native species to invade and become established in the intertidal zone. We conducted experiments in an outdoor quarantined facility to compare the tolerances of C. virginica and C. ariakensis to varying levels of aerial exposure. Diploid C. virginica and C. ariakensis were set on 10 cm × 10 cm PVC tiles, held in a flow-though quarantine syste...

Efforts to restore the Eastern oyster (Crassostrea virginica) reef habitats in Chesapeake Bay typically begin with the placement of hard substrata to form three-dimensional mounds on the seabed to serve as a base for oyster recruitment and growth. A shortage of oyster shell for creating large-scale reefs has led to widespread use of other materials such as Surf clamshell (Spisula solidissima), as a substitute for oyster shell. Oyster recruitment, survival, and growth were monitored on intertidal reefs constructed from oyster and Surf clamshell near Fisherman’s Island, Virginia, U.S.A. and on a subtidal Surf clamshell reef in York River, Virginia, U.S.A. At the intertidal reefs, oyster larvae settlement occurred at similar levels on both substrate types throughout the monitoring period but higher levels of post-settlement mortality occurred on clamshell reefs. The oyster shell reef supported greater oyster growth and survival and offered the highest degree of structural complexity. On the subtidal clamshell reef, the quality of the substrate varied with reef elevation. Large shell fragments and intact valves were scattered around the reef base, whereas small, tightly packed shell fragments paved the crest and flank of the reef mound. Oysters were more abundant and larger at the base of this reef and less abundant and smaller on the reef crest. The availability of interstitial space and appropriate settlement surfaces is hypothesized to account for the observed differences in oyster abundance across the reef systems. Patterns observed emphasize the importance of appropriate substrate selection for restoration activities to enhance natural recovery where an underlying habitat structure is destroyed.

Cultural eutrophication in estuaries and other coastal systems has increased over the last 50 yr. Some recently proposed strategies to reverse this trend have included the restoration of bivalve suspension feeders as an ecological tool for reducing phytoplankton biomass. The ecolog- ical benefits accruing from such bivalve restoration will be dependent on the characteristics of the estuary, as well as how restoration is implemented. We developed a filtration model to estimate the effect of bivalve restoration on the rate of phytoplankton removal over a range of spatial and tempo- ral scales and used it to compare alternate restoration strategies for the eastern oyster Crassostrea virginica in Chesapeake Bay, USA. Model results suggested that currently accepted restoration goals for oysters in the bay are unlikely to result in significant bay-wide reductions in phytoplankton bio- mass. This is partially due to low current biomass targets for oyster restoration, but also important are several spatial and temporal mismatches between oyster and phytoplankton biomass that may limit the ecological benefit of oyster restoration. Our model did predict important increases in phytoplank- ton removal by oysters at the tributary scale, and this effect was dependent on where oyster restora- tion was achieved and whether restoration and management plans affected the size distribution of oysters. Our findings suggest that the ecological benefit of restoring bivalve populations are variable, and a comparative model analysis of restoration plans in particular systems can be highly beneficial to maximizing the benefit-to-cost ratio of restoration efforts intended to reduce the negative effects of cultural eutrophication.

The importance of restoring filter-feeders, such as the Eastern oyster Crassostrea virginica, to mitigate the effects of eutrophication (e.g. in Chesapeake Bay) is currently under debate. The argument that bivalve molluscs alone cannot control phytoplankton blooms and reduce hypoxia oversimplifies a more complex issue, namely that ecosystem engineering species make manifold contributions to ecosystem services. Although further discussion and research leading to a more complete understanding is required, oysters and other molluscs (e.g. mussels) in estuarine eco- systems provide services far beyond the mere top-down control of phytoplankton blooms, such as (1) seston filtration, (2) benthic-pelagic coupling, (3) creation of refugia from predation, (4) creation of feeding habitat for juveniles and adults of mobile species, and for sessile stages of species that attach to molluscan shells, and (5) provision of nesting habitat.

The most commonly used methods for measuring the amount of seston removed from the water column (uptake) by populations of suspension-feeding bivalve molluscs involve taking discrete water samples followed by laboratory analyses. Here we describe a new method based on in situ fluorometry that provides rapid measurement of seston removal rates. The new system is comprised of two identical units, each consisting of an in situ fluorometer, data logger and peristaltic pump with plastic tube attached to a deployment device. The deployment device allows precise placement of the fluorometer probe and intake end of the plastic tube so that in situ fluorescence (chlorophyll a) can be measured and water can be sampled for seston analyses in the laboratory from the same height. The typical setup involves placing one unit upstream and the other downstream of the study area and sampling the water at periodic intervals. Changes in seston concentration are revealed in the field by the fluorometers, and the sampled water can be analyzed in the laboratory for various seston parameters. Comparisons of the in situ data with data from laboratory analyses of pumped water samples were made for three species at four study sites: the eastern oyster (Crassostrea virginica), hard clam (Mercenaria mercenaria), and blue mussel (Mytilus edulis). Comparisons of measured upstream versus downstream seston concentrations indicated significant (t-tests, P < 0.05) differences (uptake) for six of eight trials based on in situ fluorometry, but only marginally significant (P < 0.10) differences at two of the four trials using laboratory chlorophyll a measurements. These data demonstrate that compared with sampling methods requiring laboratory analyses, the new in situ method provides much more rapid quantitative assessments and may provide more accurate estimates.

Many of the methods currently employed to restore Chesapeake Bay populations of the eastern oyster, Crassostrea virginica, assume closed recruitment in certain sub-estuaries despite planktonic larval durations of 2–3 weeks. In addition, to combat parasitic disease, artificially selected disease tolerant oyster strains are being used for population supplementation. It has been impossible to fully evaluate these unconventional tactics because offspring from wild and selected broodstock are phenotypically indistinguishable. This study provides the first direct measurement of oyster recruitment enhancement by using genetic assignment tests to discriminate locally produced progeny of a selected oyster strain from progeny of wild parents. Artificially selected oysters (DEBY strain) were planted on a single reef in each of two Chesapeake Bay tributaries in 2002, but only in the Great Wicomico River (GWR) were they large enough to potentially reproduce the same year. Assignment tests based on eight microsatellite loci and mitochondrial DNA markers were applied to 1579 juvenile oysters collected throughout the GWR during the summer of 2002. Only one juvenile oyster was positively identified as an offspring of the 0.75 million DEBY oysters that were planted in the GWR, but 153 individuals (9.7%) had DEBY ×wild F1 multilocus genotypes. Because oyster recruitment was high across the region in 2002, the proportionately low enhancement measured in the GWR would not otherwise have been recognized. Possible causes for low enhancement success are discussed, each bearing on untested assumptions underlying the restoration methods, and all arguing for more intensive evaluation of each component of the restoration strategy.

The dinoflagellate Prorocentrum minimum ( P. minimum ) can be found in all seasons and over a broad range of habitat conditions in the Chesapeake Bay and its tributaries. Blooms (>3000 cells ml −1 ), locally referred to as ‘mahagony tides’, were restricted to salinities of 4.5–12.8 psu, water temperatures of 12–28 °C, and occurred most frequently in April and May. P. minimum blooms have been detected at routine water quality monitoring stations located in the main channel of the Bay and tidal tributaries. Nearshore investigations of bloom events, however, have accounted for the majority of events recorded in excess of 10 5 cells ml −1 . Mahogany tides were associated with widespread harmful impacts including anoxic/hypoxic events, finfish kills, aquaculture shellfish kills and submerged aquatic vegetation losses. We summarize the state of knowledge regarding physical and chemical factors related to P. minimum blooms, their abundance, distribution and frequency, and ecological effects in Chesapeake Bay.

The use of plastic row covers (plastic mulch) on vegetable farms increases runoff of pesticides after rainfall events and has been linked to toxic events in adjacent tidal waters. In coastal Virginia, USA, runoff from tomato fields with plastic mulch was suspected of causing mortality of commercial hard clam larvae at a hatchery located downstream of farming operations. Concern about the putative impacts of this practice on local waters resulted in a collection of studies to: (1) determine the sensitivity of early life stages of bivalves to copper, a commonly used fungicide; (2) examine acute and chronic biological effects of runoff on tidal creeks; and (3) examine the efficacy of management practices designed to reduce the delivery of pesticides to adjacent creeks. Laboratory bioassays revealed that 48-h LC50 values for embryonic clams Mulinia lateralis and Mercenaria mercenaria were 38 and 20 μg/l, respectively. In situ bioassays with Palaemonetes pugio showed that pulsed toxic conditions sometimes occur downstream of some tomato farms in plastic mulch following rainfall events. Growth, mortality rates and bioaccumulation of copper and organic pesticides in oysters were not correlated with the use of plastic mulch in watersheds. Sediment bioassays indicated potential toxicity in sediment collected downstream of some tomato fields in plastic mulch, but the effects were not consistent between years. Closer examination of management practices on the farms suggests that controlling runoff can prevent toxic impacts. Elevated levels of crop protectants measured at the outflow of farm ponds suggested that they may do little to reduce loadings of some pesticides. However, forested buffer zones and ephemeral sedimentation basins appeared to be effective in reducing pesticide concentrations in runoff and pulsed toxicity in tidal creeks.

Habitat restoration encompasses a broad range of activities, emphasizing very different issues, goals, and approaches depending on the operational definition of ‘restoration’. This is particularly true for many shellfish (molluscan) dominated systems (e.g. oyster reefs, mussel beds, vermetid gastropod reefs). In contrast to other well-studied biogenic habitats, such as seagrasses, mangroves, or salt marshes, bivalves are directly consumed as a resource. Hence resource extraction has direct consequences for habitat health. Restoration objectives have typically included reduction of public health risks through improved water quality to increase harvest. Restoration or enhancement of populations of commercially exploited shellfish depressed by overharvesting and/or reduced environmental quality remains the principal motivation behind most shellfish ‘restoration’ efforts. Direct and indirect ecosystem services (e.g. filtering capacity, benthic–pelagic coupling, nutrient dynamics, sediment stabilization, provision of habitat, etc.) derived from oyster habitat have been largely ignored or underestimated. Only recently, the restoration of lost ecological function associated with shellfish communities has been included in our discussions and related research examining habitat development and function through a scientific approach. The former area has been reviewed extensively and will not be our focus here. In this review, we examine some of the restoration efforts made in the name of fisheries enhancement, address their effectiveness, and discuss some of the issues associated with realizing the broader goal of ecological restoration. We note the importance of linking success criteria to specific goals and make the case for a greater need in clarifying the ecological functions of shellfish and shellfish habitats. We recognize the limitations of existing datasets and summarize ongoing attempts to address oyster habitat restoration throughout the broad geographic distribution of the American oyster, Crassostrea virginica (Gmelin). In many ways this topic parallels the ongoing debate over ‘attraction versus production’ associated with artificial reef management. We consider how local conditions (e.g. tidal range, bottom topography, turbidity, salinity) and resulting habitat traits affect restoration strategies. We also discuss the underappreciated value of shellfish populations from those areas designated as closed to harvesting due to their intrinsic worth as habitat/larval reserves. The necessity of ecosystem (adaptive) management strategies emerges from this discussion. Finally, this overview supports our contention that shellfish habitat should be included in discussions of ‘essential fish habitats’ (or EFH).

Intertidal oyster reefs, 3-dimensional structures created by years of successive settlement of larval oysters on adult oyster shells, provide levels of surface and interstitial heterogeneity that are rare in marine ecosystems. Surprisingly, little is known about the ecological benefits for oysters (Crassostrea virginica) in these aerially exposed, structurally complex systems. In this study a 210 m×30 m intertidal reef was constructed. During three, 28-day sampling periods in the summer and early fall, growth and mortality of two size classes of oysters placed in cages at three tidal heights (25 cm above mean low water (MLW), MLW, and 90 cm below MLW) and at two substrate levels (reef surface and 10 cm below the reef surface) within the reef setting were examined. Mid-intertidal oysters residing within the reef interstices grew faster and enjoyed greater survival than mid-intertidal oysters at the reef surface during certain times of the year. Conversely, subtidal oysters inhabiting subsurface environments did not grow faster than surface dwelling subtidal oysters, but some oysters within the reef fabric (larger size class) experienced significantly higher survival. Along a tidal continuum, oysters at the reef surface grew best in subtidal locations, yet experienced the lowest mortalities in the low intertidal zone (MLW). Reef heterogeneity, which allows for residence along both interstitial and tidal gradients, may provide physical and biological refugia for oysters and furnish ideal spatial platforms for growth. Therefore, location within the reef habitat has a significant impact on the biology and ecology of C. virginica.

Eelgrass, Zostera marina, relies upon seed dispersal for colonization of new habitats. The seeds are not readily transported in suspension; however, they have low erosion thresholds and are subject to horizontal transport as bedload at relatively low bottom shear stress. Field germination patterns suggest that seeds rarely travel far from the point of release and quickly become buried in the sediment, even in habitats where boundary-layer flows exceed those necessary to erode seeds. In many sedimentary habitats it is likely that the activities of benthic and demersal organisms will affect the horizontal movement and burial of seeds, thus providing an explanation for the patterns of seedling establishment in previously reported experiments. We investigated the effects of a common animal in estuarine sediments on the entrapment of Z. marina seeds. In a series of flume experiments we manipulated the densities of the subsurface deposit-feeding polychaete Clymenella torquata (Low: 96 worms m−2; Medium: 192 worms m−2; High: 288 worms m −2) and related trapping of seeds to worm density and bioturbation rates. The results suggest that modifications to the sediment surface (i.e. topographic relief) resulting from feeding and defecation activities of subsurface deposit feeders can act to trap seeds. Seeds were trapped in the medium and high density worm treatments in greater numbers than in the low density and no worm treatments. Our findings indicate that benthic invertebrates, through their modification of sediments may affect the horizontal (bedload) and, hence, vertical (burial) transport of Z. marina seeds.

Historic baselines are important in developing our understanding of ecosystems in the face of rapid global change. While a number of studies have sought to determine changes in extent of exploited habitats over historic timescales, few have quantified such changes prior to late twentieth century baselines. Here, we present, to our knowledge, the first ever large-scale quantitative assessment of the extent and biomass of marine habitat-forming species over a 100-year time frame. We examined records of wild native oyster abundance in the United States from a historic, yet already exploited, baseline between 1878 and 1935 (predominantly 1885–1915), and a current baseline between 1968 and 2010 (predominantly 2000–2010). We quantified the extent of oyster grounds in 39 estuaries historically and 51 estuaries from recent times. Data from 24 estuaries allowed comparison of historic to present extent and biomass. We found evidence for a 64 per cent decline in the spatial extent of oyster habitat and an 88 per cent decline in oyster biomass over time. The difference between these two numbers illustrates that current areal extent measures may be masking significant loss of habitat through degradation.

Although previous evidence indicates that larvae of benthic marine invertebrates can respond to waterborne cues in still water, the importance of waterborne cues in mediating natural settlement out of flowing water has been questioned. Here, we summarize the results of flume experiments demonstrating enhanced settlement of oyster larvae in small target wells (circles of 7-cm diam) with the release of a waterborne settlement cue compared to identical substrates without the cue. In concurrent still-water experiments, more oyster larvae settled in solutions of waterborne cue than in seawater controls. Velocity and electrochemical measurements of a conservative tracer verified that at low flow velocities (2 and 6 cm s-l) with U, values ~0.25 cm s-l, the waterborne cue was present above the targeted substrate to a height of 14 mm. Rapid vertical swimming or sinking in response to the waterborne cue can concentrate larvae in near-bottom waters and enhance larval settlement. Our investigation provides the first experiimental evidence to demonstrate that dissolved chemical cues can mediate settlement by larvae under hydrodynamic conditions approaching those of natural benthic habitats.

Seagrasses rely on both vegetative (rhizome elongation) and sexual (seeds) propagation for maintenance of existing beds and colonization of new areas. Yet mecha- nisms of seed dispersal and survival of seeds in new areas remain poorly described. We conducted seed dispersal experiments in the field and laboratory to better describe seed dispersal characteristics in one species, Zostera marina L. (eelgrass), the dominant seagrass species in the temperate zone of the United States, Japan, and Europe. Seeds were broadcast by hand into unvegetated 5 m diameter plots at three locations over 3 yr (1989-1991) in the York River, Virginia (Chesapeake Bay). These sites had been previously vegetated but were devoid of any vegetation prior to (since 1972) and during the course of the experiments. Resultant seedling distributions closely matched broadcast patterns, with 80% of all seedlings found within the 5 m diameter plots, despite the fact that geophysical processes would appear sufficient to transport seeds greater distances. Wind records for the 2-mo period between seed broadcasting and germination revealed time-averaged wind speeds in excess of 40 km/h on 12 d in each of the 3 yr and gale- force winds (72 km/h) in 2 of 3 yr. A three-dimensional hydrographic computer simulation model of the York River provided instantaneous current velocity estimates from which maximum bottom shear velocities (u.) in the study area were approximated (flood tide: 1.26 cm/s, ebb tide: 1.20 cm/s). These estimates exceeded the critical erosion threshold (ucrit = 0.7 cm/s) for Z. marina seeds determined from laboratory flume experiments. We postulate that small-scale topographic features on the bottom (burrows, pits, mounds, ripples) shield the seeds from the flow. Our results suggest that seeds settle rapidly, dispersing only up to a few metres under the influence of currents and become rapidly incorporated into the sediment. The limited dispersal capabilities of seeds underscore the need to address restoration goals and questions of seagrass ecology in the context of landscape-scale distributional patterns and metapopula- tion analyses.

The ABC method for evaluating pollution-induced stress was tested using data from the Chesapeake Bay, Virginia, collected between 1985 and 1989. Three predictions were tested: (1) benthic communities from estuarine transitional regions with salinities near the range of 5 to 8 parts per thousand (horohalinicium) should be classified highly stressed due to major shifts in ionic composition producing physiological stress; (2) benthic communities from regions subjected to summer low dissolved oxygen conditions (anoxia or hypoxia) should be classified as highly stressed after such events; and (3) benthic communities from sediments contaminated with heavy metals and polynuclear aromatic hydrocarbons should be classified as highly stressed. Only partial support for each of these predictions was found and several problems with the ABC method were obvious. A small number of large-sized species, particularly in mesohaline and polyhaline regions of the estuary, greatly affected the analysis. Similar designations of stress could be produced by simply sampling only for these rare, large species. Regions of the estuary considered a priori as highly stressed were sometimes designated as unstressed due to (1) minor shifts in dominance patterns in benthic communities with low absolute numbers of individuals and biomass, e.g. in regions affected by anoxia/hypoxia, and (2) collection of rare, but large species, such as the tubiculous polychaete, Diopatra cuprea, in contaminated sediments. Regions of the estuary considered a priori as unstressed were sometimes designated as highly stressed due to dense recruitment events. Contrary to assumptions of the ABC method, increased sample size (replication) may result in the collection of rare, large-sized individuals in highly stressed communities. Partial dominance curves were applied to the data and (1) removed the effect of biomass dominants in contaminated sediments changing the classification of communities from unstressed to stressed, (2) did not change the stressed classification due to dense recruitment events, and (3) changed the classification of mesohaline and polyhaline communities from unstressed to stressed, even in the absence of low dissolved oxygen events or contaminated sediments. No single method or analysis is likely to produce stress classifications without unacceptable misclassifications. We propose that ecological stress, from any source, is best measured using multiple methods or analyses with different assumptions. The consistency of classification between different approaches would provide the robustness necessary to judge the reliability of a stress classification.

The free-living fourth crab stage of the inquiline pea crab Pinnotheres ostreum (Say) lacks typical antipredator defenses frequently found in planktonic and pelagic crustaceans, such as spines, cryptic coloration and/or diel vertical migration. However, in laboratory feeding trials, four species of estuarine fishes consumed many more first stage juvenile blue crabs Callinectes sapidus Rathbun than P. ostreum even though the prey were similar in size. Observations of predator-prey interactions in the laboratory revealed that, once captured, pea crabs were frequently rejected by mummichogs Fundulus heteroditus (L.). Experiments in which mummichogs were offered six prey items (live, heat-killed and cold-killed crabs of each species above) revealed that live pea crabs were rejected >90% of the time, killed crabs were rejected approximately one-third of the time, and blue crabs, live or dead, were always consumed. These data indicate that the unpalatability of pea crabs is not a consequence of akenisis and suggest an active component to the defense. We argue, on the basis of morphological and behavioral evidence, that mechanical irritation is not the source of pea crab unpalatability. The accumulated evidence strongly suggests that this stage of P. ostreum employs a noxious antipredator substance. The origin and composition of this substance and the prevalence of this defensive system (in other stages and species) remain to be investigated.

Straight-hinge, umbo and pediveliger larvae of the mactrid bivalves Spisula solidissima, Mulinia lateralis and Rangia cuneata were exposed to intense salinity discontinuities of 0, 5, 10 and 15 O/w in vertically oriented swimming chambers. Larvae concentrated in the region of highest gradient, i. e. at the salinity discontinuity, regardless of species, stage of development or larval brood. S. solidisima larvae, initially swimming at 30 O/w salinity, crossed discontinuities of both 5 and 10 %O but not of 15 %o. M. lateralis larvae, initially swimming at 25 %O salinity, also crossed a discontinuity of 5 %O but not of 10 or 15 %o. R. cuneata larvae, initially swimming at 10 %O salinity, generally preferred to remain at that salinity. Swimming and passive sinking velocities, defined as vertical distance traversed per unit time, were measured in different salinities under constant temperature and light. For all species, swimming rate changed with larval stage, highest velocity occurring at the umbo stage. Upward swimming rate of S. solidissima larvae ranged from 0.18 to 0.49 mm S-' and increased with increasing salinity. Upward swimming rate of M. lateralislarvae ranged from 0.25 to 0.50 mm S' , but was not consistently related to salinity. Upward swimming rate of R. cuneata larvae ranged from 0.18 to 0.53 mm S-'; swimming rate of pediveliger larvae increased consistently as salinity decreased. Downward swimming rates were similar to upward rates. No significant differences in downward swimming rate were detected in relation to salinity. Passive sinking was more frequent than active downward swimming in umbo and pediveliger larvae. Sinking rate increased with larval size of S. solidissima and M. lateralis larvae; however, R. cuneata straight-hinge larvae sank faster than umbo and pediveliger larvae. Species-specific differences in larval sinking and swimming are related to the different habitats occupied by adults. Larvae of S. solidissima, a marine stenohaline species, remained in high salinity water. Larvae of M. lateralis, a euryhaline species, use their preference for discontinuities or higher salinity water to assist retention in partially mixed estuaries. High sinking rate and short larval period of R, cuneata may offset the behavioural characteristic and aid in the retention of R. cuneata larvae in the low salinity zone of most partially mixed estuaries.

Potential effects of impounding tidal creeks include alterations in the resource value of downstream wetland habitats. Benthic invertebrates serve as food for higher trophic levels (e.g. crabs and fishes) and, because of their sedentary life style, are constrained to cope with local environmental conditions. Comparisons of macrobenthic invertebrate biomass available to higher levels were made between two impounded and non-impounded creek pairs in coastal Virginia. The results indicate that neither the total amount nor the distribution of this resource varied between impounded and non-impounded creeks. The implication is that impounding the headwater regions of a tidal creek does not severely reduce the resource value of downstream habitats to higher trophic levels.

Habitat selection capabilities of the recruiting larval stages of marine invertebrates are limited, in part, by their ability to maneuver in flowing water. Distributional and experimental evidence suggest that blue crab (Callinectes sapidus) megalopae may preferentially settle into vegetated habitats. However, the behavior and swimming capabilities of megalopae in flowing water have not previously been investigated. Laboratory experiments were conducted in a small, recirculating seawater flume to determine the swimming response of megalopae to varying flow velocities. Nighttime trials were conducted at six flow velocities: 0, 1.9, 3.6, 4.8, 6.3, and 9.3 cm s−1. Behavior and swimming velocities of field-collected C. sapidus megalopae were video recorded. Megalopae exhibited negative phototaxis and were found in the water column at all flows in the dark. The maximum sustained swimming speed observed was 12.6 cm s−1 and the mean swimming speed in still water was 5.0 cm s−1, with short bursts in excess of 20 cm s−1. Megalopae frequently oriented into the current and were capable of swimming upstream against the current at flow speeds

Observations were made of the location and duration of foraging by five species of shorebirds in relation to the tubes of Diopatra cuprea (Polychaeta). Infaunal abundances in sites with D. cuprea tubes exceeded those in surrounding tubefree areas (120 individuals vs 29 individuals per 0·01 m 2 , respectively). Of 112 shorebird foraging episodes observed only 4 were in the vicinity of D. cuprea tubes. Despite a greater abundance of prey items around worm tubes, shorebirds avoided feeding in such areas. D. cuprea tubes appear to provide an effective refuge for macrofauna from shorebird predation.

Feeding rates, and hence growth, of suspension-feeding organisms are determined by many interacting factors including efficiency of particle capture, food-particle concentration, and ambient flow regimes. Studies in a recirculating seawater flume were conducted to examine the growth rates of juvenile bay scallops Argopecten irradians irradians (L.) (3–10 mm in shell height) in four flow velocities (0, 1, 6, and 15 cm · s−1) over a range of food concentrations (0–75 000 cells · ml−1) in a four-by-four factorial design. Particle flux (algal cells · cm−2· s−1) encountered by the scallops is the product of food concentration (cells · ml−1) and flow velocity (cm · s−1). The experimental levels of food concentration and flow velocity were chosen to produce a wide range of fluxes. Several treatments with equal flux derived from different flows and food concentrations were used to decouple the effects of each factor. Within a given flux of particles, growth rates were not significantly different between flows or particle concentrations. Growth was only weakly correlated to flux of particles over the range of fluxes tested. The effects of algal concentration were more pronounced than the effects of flow velocity suggesting that differences in growth were a result of differences in algal concentrations. Additional experiments were run to determine the clearance rates of scallops at different food concentrations. These experiments support the findings of the flume experiments; clearance rates were seen to decrease with increasing food concentrations. Flux of food particles is not a predictor of growth, rather it is the combination of the effects due to food concentration and flow velocity which determine the response of the individual juvenile bay scallop.

Etude menee sur des M. l. vivant au sein d'une biocenose de substrat meuble intertidal heterogene de la Debidue Creek, Caroline du Sud

Abundances of many macrofaunal species are enhanced around biogenic structures, yet some species show a reduced survival around such structures. High densities of macrofauna occur around the tubes of Diopatra cuprea (Bosc), but successful recruitment of the bivalve Mulinia lateralis (Say) is inhibited by high post-settlement mortality. Laboratory experiments were conducted to test the effects of two polychaetes, Nereis succinea (Frey and Leuckart) and Streblospio benedicti (Webster), on the survival of newly-recruited Mulinia lateralis. In the field these polychaetes are abundant around Diopatra cuprea tubes and rare in the same habitat when tubes are absent. Recently metamorphosed Mulinia lateralis were added to azoic sediment cores in the laboratory which contained 0, 1×, 2× or 4× field densities of either Nereissuccinea or Streblospio benedicti. Survival of Mulinia lateralis in treatment cores ranged from 29 to 70% in control cores and both Nereis succinea and Streblospio benedicti were found to reduce survival of the bivalve. These results suggest that, in the field, Diopatra cuprea indirectly modify the environment by altering local fauna which then inhibit the recruitment of some taxa.