Placopecten Magellanicus Research Articles

Isotopic records on the massive death of sea scallops in Vancouver Island of Canada

Carbonate shells can be used in the detection of climate change and ocean acidification in fisheries science and aquaculture. In this study, we reported stable carbon and oxygen isotope ratios (δ13C and δ18O) in sea scallop (Patinopecten caurinus) shells from the Island Scallop Limited (ISL) in Vancouver Island, British Columbia, Canada, where approximately ten million sea scallops died in 2013. The δ13C values of the harvested scallop shells from 1993 ranged from −0.58 to +0.66‰, whereas δ18O values from the same samples ranged from −3.05 to −0.32‰. The harvested scallop shells from 2014 showed similar variation in δ13C but significantly higher δ18O values in the summer of 2013. As compared with the otoliths of Atlantic bluefin tuna and the Zhikong scallop (Chlamys farreri) shells from the northern Yellow Sea of China, our data did not show a steady δ13C decrease in the 2014 samples and thus do not support the hypothesis that ocean acidification led to the massive death of the ISL scallops. Hatchery observations on incoming seawater in 2014 showed normal and stable profiles in temperature, salinity, and pH; thus, the significant increase of δ18O values in the summer of 2013 suggests that an unusually cold-water mass from upwelling might have occurred in the ISL grow-out site.

Modeling larval dispersal and connectivity for Atlantic sea scallop (Placopecten magellanicus) in the Middle Atlantic Bight

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

Methods for Image-based Surveys of Benthic Macroinvertebrates and Their Habitat Exemplified by the Drop Camera Survey for the Atlantic Sea Scallop

Underwater imaging has long been used in the field of marine ecology but decreasing costs of high-resolution cameras and data storage have made the approach more practical than in the past. Image-based surveys allow for initial samples to be revisited and are non-invasive compared to traditional survey methods that typically involve nets or dredges. Protocols for image-based surveys can vary greatly but should be driven by target species behavior and survey objectives. To demonstrate this, we describe our most recent methods for an Atlantic sea scallop (Placopecten magellanicus) drop camera survey to provide a procedural example and representative results. The procedure is divided into three critical steps that include survey design, data collection, and data products. The influence of scallop behavior and the survey goal of providing an independent assessment of the U.S. sea scallop resource on the survey procedure are then discussed in the context of generalizing the method. Overall, the broad applicability and flexibility of the University of Massachusetts Dartmouth School for Marine Science and Technology (SMAST) drop camera survey demonstrates the method could be generalized and applied to a variety of sessile invertebrates or habitat focused research.

Methods for Image-based Surveys of Benthic Macroinvertebrates and Their Habitat Exemplified by the Drop Camera Survey for the Atlantic Sea Scallop.

Underwater imaging has long been used in the field of marine ecology but decreasing costs of high-resolution cameras and data storage have made the approach more practical than in the past. Image-based surveys allow for initial samples to be revisited and are non-invasive compared to traditional survey methods that typically involve nets or dredges. Protocols for image-based surveys can vary greatly but should be driven by target species behavior and survey objectives. To demonstrate this, we describe our most recent methods for an Atlantic sea scallop (Placopecten magellanicus) drop camera survey to provide a procedural example and representative results. The procedure is divided into three critical steps that include survey design, data collection, and data products. The influence of scallop behavior and the survey goal of providing an independent assessment of the U.S. sea scallop resource on the survey procedure are then discussed in the context of generalizing the method. Overall, the broad applicability and flexibility of the University of Massachusetts Dartmouth School for Marine Science and Technology (SMAST) drop camera survey demonstrates the method could be generalized and applied to a variety of sessile invertebrates or habitat focused research.

Do IFQs in the US Atlantic Sea Scallop Fishery Impact Price and Size?

AbstractManagement of the “General Category” component of the US Atlantic sea scallop (Placopecten magellanicus) fishery changed from open access with a soft, or target, catch limit, to limited acc...

Fine-scale temperature-associated genetic structure between inshore and offshore populations of sea scallop (Placopecten magellanicus).

In the northwest Atlantic Ocean, sea scallop (Placopecten magellanicus) has been characterized by a latitudinal genetic cline with a breakpoint between northern and southern genetic clusters occurring at ~45°N along eastern Nova Scotia, Canada. Using 96 diagnostic single-nucleotide polymorphisms (SNPs) capable of discriminating between northern and southern clusters, we examined fine-scale genetic structure of scallops among 27 sample locations, spanning the largest geographic range evaluated in this species to date (~37-51°N). Here, we confirmed previous observations of northern and southern groups, but we show that the boundary between northern and southern clusters is not a discrete latitudinal break. Instead, at latitudes near the previously described boundary, we found unexpected patterns of fine-scale genetic structure occurring between inshore and offshore sites. Scallops from offshore sites, including St. Pierre Bank and the eastern Scotian Shelf, clustered with southern stocks, whereas inshore sites at similar latitudes clustered with northern stocks. Our analyses revealed significant genetic divergence across small spatial scales (i.e., 129-221 km distances), and that spatial structure over large and fine scales was strongly associated with temperature during seasonal periods of thermal minima. Clear temperature differences between inshore and offshore locations may explain the fine-scale structuring observed, such as why southern lineages of scallop occur at higher latitudes in deeper, warmer offshore waters. Our study supports growing evidence that fine-scale population structure in marine species is common, often environmentally associated, and that consideration of environmental and genomic data can significantly enhance the identification of marine diversity and management units.

Estimating similarity in benthic communities over decades and in areas open and closed to fishing in the central Gulf of Maine, USA

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 595:15-26 (2018) - DOI: https://doi.org/10.3354/meps12563 Estimating similarity in benthic communities over decades and in areas open and closed to fishing in the central Gulf of Maine, USA Samuel C. Asci1,3,*, Richard W. Langton2, Kevin D. E. Stokesbury1 1School for Marine Science and Technology, University of Massachusetts Dartmouth, 836 South Rodney French Boulevard, New Bedford, MA 02744, USA 2Northeast Fisheries Science Center, Maine Field Station, 17 Godfrey Drive, Suite 1, Orono, ME 04473, USA 3Present address: New England Fishery Management Council, 50 Water Street, Mill 2, Newburyport, MA 01950, USA *Corresponding author: sasci@nefmc.org ABSTRACT: The ledges and banks of the central Gulf of Maine (i.e. Fippennies Ledge, Jeffreys Ledge, Cashes Ledge, and Platts Bank) have supported groundfish and Atlantic sea scallop fisheries for centuries. The benthic community of Fippennies Ledge was evaluated and compared during 2 time periods separated by more than 2 decades, the first based on a series of photographs collected during manned submersible dives conducted in 1986 and 1987 and the second using photographs collected during drop camera video surveys conducted in 2009 to 2014. Further, Fippennies, Jeffreys, and Cashes ledges were permanently closed to fishing in 2002, while Platts Bank remained open, enabling a spatial comparison of benthic communities in open and closed areas along with the examination of changes in the benthos over the 28 yr period on Fippennies Ledge. In the absence of commercial fishing, the scallop population on Fippennies Ledge appeared to be unchanged between 1986 and 2014, while observed differences in other dominant species were attributed to predator-prey relationships and long-term shifts in benthic conditions. Benthos of scallop habitat in the open and closed areas between 2009 and 2014 were similar in spatially dominant species composition and species richness, likely a result of the study area being a high-energy environment and therefore resilient to both natural and fishing perturbations. Understanding change in benthic communities over decades and between open and closed areas helps better define the dynamic nature of the central Gulf of Maine and may inform fisheries management in this region as the ocean climate changes. KEY WORDS: Benthic imaging · Population dynamics · Placopecten magellanicus Full text in pdf format PreviousNextCite this article as: Asci SC, Langton RW, Stokesbury KDE (2018) Estimating similarity in benthic communities over decades and in areas open and closed to fishing in the central Gulf of Maine, USA. Mar Ecol Prog Ser 595:15-26. https://doi.org/10.3354/meps12563 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 595. Online publication date: May 14, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

A spatiotemporal Evaluation of Atlantic Sea Scallop Placopecten magellanicus Habitat in the Gulf of Maine Using a Bioclimate Envelope Model

AbstractA bioclimate envelope model was developed to evaluate the impacts of climate variability on spatiotemporal availability of suitable habitat for the Atlantic sea scallop Placopecten magellanicus in the Gulf of Maine (GOM). Bioclimate envelopes were established through habitat suitability indices (HSIs) based on bottom temperature, bottom salinity, current velocity, depth, and bottom composition. The relationship between Atlantic sea scallop abundance and each environmental variable was quantified using suitability indices, which were generated based on standardized scallop abundance sampled over 10 years of dredge survey data. Boosted regression tree models were used to determine the relative importance of each environmental variable to scallop abundance, thereby establishing a weighting scheme within the HSI. A regional circulation model was coupled with the weighted HSI to hindcast spatiotemporal dynamics of suitable habitat for Atlantic sea scallop in coastal and offshore waters of the GOM from 1978 to 2013. Higher habitat suitability was found along inshore areas compared with offshore areas. Model predictions indicated an increasing trend in habitat suitability in inshore waters since 1978 and decreasing habitat suitability in offshore waters. This research provides a novel modeling framework with which to enhance research and management of commercially valuable Atlantic sea scallop stocks over broad spatiotemporal scales in the climatically altered GOM.

Sea scallops exhibit strong local spatiotemporal structure associated with seabed stability and high flows

AbstractSea scallops (Placopecten magellanicus) live along the Northwest Atlantic continental shelf and are aggregated over a broad range of spatial scales (m2–105 km2). However, little is known about the spatial distribution of local scallop neighborhoods, the scale at which spawning, intra‐specific competition, and predator–prey interactions occur. We surveyed 30,995 km2 of Georges Bank and the Great South Channel annually from 2003 to 2010 counting the number of scallops in 54,016 locally replicated 3.24‐m2 quadrats with underwater video. There were about 4 billion scallops occupying 11,200 km2 of the study area in concentrations from 1 to 41 scallops per scallop. Scallop spatial distribution switched from dispersed to aggregated at a concentration of 3–4 scallops in every year. High concentrations (>3) occurred in 11% but were only persistent in 4% (449 km2) of scallop habitat. There were 13 persistent high‐concentration aggregations (7–217 km2), and all but two occurred on gravel‐dominated sediments left by prehistoric glacial retreat. Model‐derived benthic boundary shear stresses in the persistent aggregations averaged two times higher than in scallop habitat, but the seabed was about two times more stable because it had significantly less sand and more granule–pebble and cobble sediment. The area occupied by scallops each year varied little (9%) despite a 49% increase in total scallop abundance between 2005 and 2007, suggesting Georges Bank scallops have a proportional density population structure. Most scallops occurred alone or at low concentrations (≤2) where fertilization success is probably poor. The persistent high‐concentration aggregations we identified may be critical for successful reproduction and sustainable harvest. Observing organisms at scales corresponding to their individual interactions reveals important processes shaping their landscape‐scale spatiotemporal distributions. These processes are obscured by the methods typically employed to estimate abundances of commercial fishery species. The spatiotemporal structure of sea scallop distribution has important implications for the design of abundance surveys and the assumptions underlying stock assessment methods. These should be investigated. Finally, this work suggests that natural disturbance (sediment stability) may play a substantial role in shaping spatiotemporal distributions and dynamics of benthic marine populations.

A novel integrated strategy for the detection and quantification of the neurotoxin β-N-methylamino-L-alanine in environmental samples.

We describe a set of new tools for the detection and quantification of β-N-methylamino-L-alanine (BMAA) which includes a novel stable isotope-labeled BMAA standard (13C3,15N2) and a chip-based capillary electrophoresis mass spectrometry platform for separation and detection. Baseline resolution of BMAA from its potentially confounding structural isomers N-2-aminoethylglycine (AEG) and 2,4-diaminobutyric acid (2,4-DAB) is achieved using the chip-based CE-MS system in less than 1min. Detection and linearity of response are demonstrated across > 3.5 orders of dynamic range using parallel reaction monitoring (PRM). The lower limit of detection and quantification were calculated for BMAA detection at 40nM (4.8ng/mL) and 400nM (48ng/mL), respectively. Finally, the strategy was applied to detect BMAA in seafood samples purchased at a local market in Raleigh, NC where their harvest location was known. BMAA was detected in a sea scallop sample. Because the BMAA/stable isotope-labeled 13C3,15N2-BMAA (SIL-BMAA) ratio in the scallop sample was below the limit of quantification, a semiquantitative analysis of BMAA content was carried out, and BMAA content was estimated to be approximately 820ng BMAA/1g of wet scallop tissue. Identification was verified by high mass measurement accuracy of precursor (< 5ppm) and product ions (< 10ppm), comigration with SIL-BMAA spike-in standard, and conservation of ion abundance ratios for product ions between BMAA and SIL-BMAA. Interestingly, BMAA was not identified in the free protein fraction but only detected after protein hydrolysis which suggests that BMAA is tightly bound by and/or incorporated into proteins. Graphical abstract Utilization of novel 13C3,15N2-BMAA and chip-based CE-MS/MS for detection and quantification of BMAA in environmental samples.

Oceanographic variation influences spatial genomic structure in the sea scallop, Placopecten magellanicus.

Environmental factors can influence diversity and population structure in marine species and accurate understanding of this influence can both improve fisheries management and help predict responses to environmental change. We used 7163 SNPs derived from restriction site‐associated DNA sequencing genotyped in 245 individuals of the economically important sea scallop, Placopecten magellanicus, to evaluate the correlations between oceanographic variation and a previously identified latitudinal genomic cline. Sea scallops span a broad latitudinal area (>10 degrees), and we hypothesized that climatic variation significantly drives clinal trends in allele frequency. Using a large environmental dataset, including temperature, salinity, chlorophyll a, and nutrient concentrations, we identified a suite of SNPs (285–621, depending on analysis and environmental dataset) potentially under selection through correlations with environmental variation. Principal components analysis of different outlier SNPs and environmental datasets revealed similar northern and southern clusters, with significant associations between the first axes of each (R 2 adj = .66–.79). Multivariate redundancy analysis of outlier SNPs and the environmental principal components indicated that environmental factors explained more than 32% of the variance. Similarly, multiple linear regressions and random‐forest analysis identified winter average and minimum ocean temperatures as significant parameters in the link between genetic and environmental variation. This work indicates that oceanographic variation is associated with the observed genomic cline in this species and that seasonal periods of extreme cold may restrict gene flow along a latitudinal gradient in this marine benthic bivalve. Incorporating this finding into management may improve accuracy of management strategies and future predictions.

The effect of capture and handling stress in Lophius americanus in the scallop dredge fishery.

Capture and handling stress studies are considered a primary research priority, particularly for species and fisheries where discard rates are high, and/or for overfished stocks and species of concern. Lophius americanus, a commercially valuable finfish in New England, constitutes the second highest bycatch species within the sea scallop dredge fishery. Despite its commercial importance, no data exists on the capture and handling stress of monkfish for any gear type. Given these shortcomings, our goals were to evaluate the stress response of monkfish captured in scallop dredge gear by evaluating physical, behavioural and physiological responses to scallop fishing practices. While 80% of monkfish displayed little to no physical trauma, behavioural and physiological assessment indicated high levels of stress, especially as air exposure and tow duration increased. This finding suggests that the manifestation of stress in monkfish may be a cryptic response necessitating further research in addition to estimates of post-release mortality rates to appropriately advise fisheries management regarding the mortality of monkfish bycatch in the sea scallop fishery.

Growth optimization of marine diatom Amphora sp. by tailoring silica and nitrate concentration

Growth optimization of marine diatom Amphora sp. by tailoring silica and nitrate concentration

Корейский полуостров и Японские острова: сложение особенностей и заимствование культурных традиций в эпоху палеометалла (материалы к учебному курсу «Археология зарубежной Азии»)

Purpose. The period of the most intensive contacts of the ancient population of the Korean peninsula and the Japanese Islands (3rd – 7th centuries AD) is of special interest for study. The period witnessed a wide spread of the tradition of building burial mounds (kurgans). Due to the artifacts found in the kurgans, it becomes possible to study various aspects of the people’s social life, including cultural contacts. We aimed at studying territorial alliances based on the cultural and historical background, such as the spread of agriculture based on wet rice cultivation, bronze and iron production, the emergence of states. Results. The kurgan tradition on the Korean peninsula is associated with the era of the Three Kingdoms (3rd – 7th centuries AD). The tradition of erecting mounds started in Koguryo state in the 1st century BC, then from the 3rd century AD it continued in Baekje, Silla and Kaya, and disappeared in the middle of the 6th century AD because of adopting Buddhism. Common barrows had stone embankments, but they are also found with earthen mounds. Burial chambers were first constructed vertically, then horizontal ones appeared. On the Japanese Islands, kurgans first appeared during the Yayoi period (3rd century BC – 3rd century AD) and were widely constructed during the Kofun period (3rd – 7th centuries AD). The barrows had earthen embankments with burial chambers inside. The barrows differed in the form of their embankment and size. The burials of the Kofun period in Japan continued the Yayoi period traditions to a certain extent. They had earthen embankments and were decorated with bronze mirrors and stone ornaments in the burial chambers. In addition, their feature is clay haniva figurines around the perimeter of the embankment. Starting from approximately the 5th century AD, there began to appear a certain homogeneity in the funerary structures of the Korean peninsula and the Japanese archipelago. Sueci ceramics became a typical element of the funeral rite, as well as bronze and iron objects, gold jewelry and luxury items which appeared in burial chambers. The construction of kurgans acquired some new features, such as stone chambers with side corridors. Both on the Korean Peninsula and the Japanese Islands, we observe similar types of embankments, such as round (embun), square (ho:fun), double round (so:embun), double square (so:ho:fun) and in the form of a “Japanese sea scallop” (hatategaishikikofun). Conclusion. The study of the structural features of the kurgans on the Korean Peninsula and the Japanese Islands allows us to conclude that there are similarities in the forms and materials of embankments and the forms of burial chamber construction. The main difference is the larger size of Japanese kurgans. The similarities we revealed can be explained by the mutual influence of the population of the Korean peninsula and the Japanese islands.

Purely Domestic Giant Scallop Oil as a more Health Beneficial Oil than Fish Oil

Purely Domestic Giant Scallop Oil as a more Health Beneficial Oil than Fish Oil

Estimates of Sea Scallop (Placopecten magellanicus) Incidental Mortality from Photographic Multiple Before—After-Control—Impact Surveys

After several decades of stock decline, the Atlantic sea scallop (Placopecten magellanicus) resource has rebounded to become one of the most valuable fisheries in the United States. The continued sustainability of this fishery is supported by catch limits determined by annual stock projection models. Incidental mortality is an important term in these projection models, but is historically difficult to measure. Current estimates are derived from field experiments that relied heavily on qualitative observations and as a result are based on limited data with low precision. To better quantify incidental mortality, a multiple before—after-control—impact experimental design was used to measure the effect of scallop dredging on the disposition of sea scallops that remain uncaptured on the seafloor following dredging. An autonomous underwater vehicle was used to collect color photographs and side-scan sonar images of the seafloor before and after controlled dredge treatments in the mid-Atlantic and Georges Bank regions. Approximately 170,000 photographs were annotated for instances of mortality. Dredge-induced incidental mortality of 2.5% and 8% was estimated for the mid-Atlantic Bight and Georges Bank sites, respectively, a difference that is likely attributable to the relatively harder substrate of the scallop habitat on Georges Bank that results in greater physical trauma to the uncaptured scallops. This study provides a quantitative estimate of incidental mortality using a noninvasive platform that offers precise mission navigation for repeated surveys. The spatial scale and distribution of the study sites are broad relative to past incidental mortality studies, and the substrate types at each are common in the sea scallop fishery. Estimated mortality rates are lower than the values currently used in fishery stock models and suggest the existing values are conservative, but likely appropriate estimates for management purposes.

Reducing Discards of Flatfish in the Sea Scallop Dredge Fishery by Dredge Pause

Flatfishes are routine bycatch in the Atlantic sea scallop Placopecten magellanicus (Gmelin) dredge fishery but must be discarded at sea. Despite release, a 90% mortality rate is assumed for overfished species such as yellowtail flounder Limanda ferruginae and windowpane Scophthalmus aquosus.When the scallop fishery exceeds the annual catch limit for yellowtail flounder, accountability measures may be triggered and seasonal closures of the scallop fishery can occur in specific areas. Flatfish bycatch is potentially reduced by stopping the scallop dredge in midwater to allow escape. This technique has been voluntarily practiced, but not widely adopted, owing to a lack of knowledge about its efficacy relative to collateral scallop loss. In a test of 122 scallop dredge tows on a commercial vessel using otherwise standard procedures, pausing the dredge during retrieval significantly reduced flatfish bycatch relative to pause length (0, 5, 10, or 15 min) but also allowed some scallop escapement. Flatfish were more likely to escape from paused dredges if there were fewer scallops in the dredge. Video provided evidence that flatfish do escape through the tickler chains and over the lip during pauses, and also showed the benefit of time in allowing them to work free of the suspended scallop load. During rough weather, vessel heave winnowed the dredge contents, increasing scallop loss. Captains can judge the practice as a cost-benefit calculation to avoid loss of revenue from early closure, but it appears to offer only a weak return on the time investment. Escaped fish may still suffer mortality.

Effects of unequal capture probability on stock assessment abundance and mortality estimates: an example using the US Atlantic sea scallop fishery

Most stock assessment models assume that the probability of capture for all individuals of the same size or age in the stock area is equal. However, this assumption is rarely, if ever, satisfied. We used spatially referenced simulations, based on the US Atlantic sea scallop (Placopecten magellanicus) fishery, to generate catch, survey index, fishing effort, and size structure data that we input into a (nonspatial) catch-at-size stock assessment model to estimate abundance and mortality rates. We show that spatial patterns in fishing mortality degrade model performance for sessile stocks. Fishing mortality tended to be overestimated and abundance underestimated because trends in fishing mortality were exaggerated and the model misestimated the numbers of larger individuals due to spatial fishing patterns. These results are particularly relevant to sedentary species such as scallops, but are applicable wherever strong spatial patterns exist in fishing mortality.

Contrasting trends in the Northeast United States groundfish and scallop processing industries

In the northeast United States, groundfish landings have declined almost continually since 1983. Fresh groundfish processors have redeployed their marketing capital by substituting other seafood products in place of regional groundfish and expanding into different markets. Meanwhile, northeast U.S. Atlantic sea scallop landings sharply increased starting in 1998, peaked in 2004, remained relatively constant until declining in 2013 and 2014. In order to leverage their favorable access to increased landings, scallop processors invested in development of new products, such as individually quick frozen (IQF) scallops, and invested in marketing activities to attract new customers, including those located in foreign nations. This behavior is consistent with Montgomery and Wernerfelt's theory of diversification in response to excess capacity of firm-specific resources and investments in product development and marketing in firm specific resources. Price and quantity indicators were used to examine the effects of shifting landings and composition of landings on exvessel values. These indicators show that declines in groundfish exvessel values were driven by declining quantities, which is consistent with processors substituting other products rather than biding up exvessel prices. Increases in scallop exvessel values were driven by both increasing prices for all sizes and by increasing quantities for large scallops, which is consistent with investment in marketing for larger scallops.

Invasive tunicate restructures invertebrate community on fishing grounds and a large protected area on Georges Bank

Marine invasive species can profoundly alter ecosystem processes by displacing native species and changing community structures. The invasive tunicate Didemnum vexillum was first found on the northern edge of Georges Bank in 1998. It can form encrusting colonies on gravel substrates that are also a preferred habitat for a number of other invertebrates. In this study we used data collected via HabCam, a vessel-towed underwater imaging system, to investigate the distribution of D. vexillum and its relationship to other epibenthic macroinvertebrates in a portion of Georges Bank that includes fishing grounds and an area protected from bottom-fishing. This novel technology provides imaging of epibenthic species distributions in areas of the benthic environment that were previously unobservable. We found that D. vexillum density is negatively correlated with the Atlantic sea scallop (Placopecten magellanicus), barnacles (genus Balanus), the tube anemone (genus Cerianthus), the green sea urchin (Strongylocentrotus droebachiensis), the globular sponge of the genus Polymastia, and Bryozoa. However D. vexillum is positively correlated with Cancer spp. Crabs, the tube forming polychaete, Filograna implexa, and Asterias spp. sea stars. The hypothesis that D. vexillum restructures the invertebrate community is supported by principal components analysis, revealing it as a primary driver of variation in the community when present. Additionally, there is an effect of the closed area as compared to fishing grounds on the structure of the invertebrate community and the abundance of certain species as consistent with previous studies, bottom-fishing affects invertebrate community structure. Principal components analysis revealed that bottom-fishing also appears to weaken clustering among species in the invertebrate community as compared to the community structure in the closed area. Biodiversity in high gravel sites of the epibenthic environment, as measured by the Shannon diversity index, also declined with increasing D. vexillum percent cover, while the open and closed areas were not significantly different in their level of biodiversity. D. vexillum appears to be the key driver of biodiversity decline in the epibenthos when present, rather than other processes such as direct disturbance and extraction from dredging. This research evaluates ecological responses to the presence of an invasive tunicate and suggests that this invasive species is a major force in shaping the ecological interactions in invaded areas.