Daphne M. Munroe

The Role of Larval Dispersal in Metapopulation Gene Flow: Local Population Dynamics Matter

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

Clam predator protection is effective and necessary for food production

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.

The Exposed Surface Area to Volume Ratio: Is Shell More Efficient than Limestone in Promoting Oyster Recruitment?

ABSTRACT Planting oyster cultch is a common management approach used to enhance recruitment. The two most popular cultch materials are shell and limestone. Both are sold by volume or weight; however, once deposited on oyster grounds, only a small portion of the total surface area of each particle is available for recruitment. Shell and limestone have different surface area to volume properties, and thus provide differential settlement opportunities. Exposed surface area to volume (expSA/V) ratios of oyster shell and limestone fragments were compared, as an indicator of their recruitment potential and cost-effectiveness for cultch planting. Samples were collected from the Primary Public Oyster Seed Grounds in Louisiana by vibracore, and from the Pass Christian TongingGrounds in Mississippi by dredge. Shell (including whole shell and fragments) and limestone particles greater than or equal to 8 mm by geometric shape were classified and their expSA/V was calculated. Mean expSA/V ratios of shell were approximately three to nine times higher than limestone. For limestone of similar particle size to provide an equivalent recruitment benefit for the same cost would require that the cost of purchase, transport, and planting be three to nine times lower than shell. Thus, shell is likely to be a more efficient material than limestone for recruitment enhancement. Nevertheless, the higher variability in expSA/V of shell and other factors such as the expected lifetime and the relative performance of small and large particles of materials should also be considered. Analysis of a Louisiana limestone plant and associated oyster cultch showed that the proportion of small and large limestone particles and the relative proportion of whole shells and fragments can greatly alter expSA/V. In this case, the a priori expectation that oyster shell would outperform limestone did not materialize because of the quantity of small limestone particles of favorable shapes in the deployed material. Even so, as yet unknown is the possible reduction in performance in situ of smaller particles that might occur if they increase the one-dimensionality of the plant.

Morphological Variability Among Broods of First-Stage Blue Crab (Callinectes sapidus) Zoeae

External morphology has been shown to influence predation and locomotion of decapod larvae and is, therefore, directly related to their ability to survive and disperse. The first goal of this study was to characterize first-stage blue crab zoeal morphology and its variability across larval broods to test whether inter-brood differences in morphology exist. The second was to identify possible correlations between maternal characteristics and zoeal morphology. The offspring of 21 individuals were hatched in the laboratory, photographed, and measured. Zoeae exhibited substantial variability, with all metrics showing significant inter-brood differences. The greatest variability was seen in the zoeal abdomen, rostrum, and dorsal spine length. A principal component analysis showed no distinct clustering of broods, with variation generally driven by larger zoeae. Using observed morphology, models of drag induced by swimming and sinking also showed significant inter-brood differences, with a maximum twofold difference across broods. In contrast to trends in other decapod taxa, maternal characteristics (female carapace width and mass and egg sponge volume and mass) are not significant predictors of zoeal morphology. These results suggest that brood effects are present across a wide range of morphological characteristics and that future experiments involving Callinectes sapidus morphology or its functionality should explicitly account for inter-brood variation. Additionally, inter-brood morphological differences may result in differential predation mortality and locomotory abilities among broods.

An Overview of Factors Affecting Distribution of the Atlantic Surfclam (Spisula solidissima), a Continental Shelf Biomass Dominant, During a Period of Climate Change

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

Evaluating the Potential for a Sex-Balanced Harvest Approach in the Recreational Summer Flounder Fishery

AbstractSummer Flounder Paralichthys dentatus support important recreational and commercial fisheries along the northeast and mid-Atlantic coasts of the USA. In the recreational sector, management efforts to constrain harvest below the maximum allowable catch have typically involved increasing the minimum landing size; however, females grow faster than males. Thus, reliance on increased minimum size limits as a management strategy has resulted in approximately 90% of the recent recreational landings being large, female fish. We evaluated the potential for slot limits to produce a sex-balanced harvest in the recreational Summer Flounder fishery. To estimate the size- and sex-specific vulnerability, we sampled the landed and discarded fish (n = 3,290) caught by recreational anglers on select party boats from New Jersey to Rhode Island during the 2016 recreational fishing season. We then examined the performance of a wide array of slot limits to estimate which would have promoted a more sex-balanced harvest ...

Bivalve Molluscs: Barometers of Climate Change in Arctic Marine Systems

Bivalve molluscs store a complete history of their life in the growth lines in their valves. Through sclerochronology, in combination with isotope signatures, it is possible to reconstruct both post-recruitment growth history at the individual level and commensurate environmental records of temperature and salinity. Growth patterns are integrators of local primary productivity; spatial and temporal changes in growth illustrate commensurate patterns of food availability. Mactrid clams are long-lived, benthic dominant species found on inner continental shelves throughout the Northern Hemisphere where they variously support major fisheries (Spisula solidissima in the Mid-Atlantic Bight, Mactromeris polynyma in eastern Canada, Spisula sachalinensis in Japan) and recreational fisheries (Mactromeris polynyma in Alaska), and serve as dietary items for charismatic species such as bearded 062 Mann et al.—Bivalve Mollusks, Barometers of Climate Change seals (Erignathus barbatus) and walrus (Odobenus rosmarus divergens). Ongoing studies, employing sophisticated adult growth and larval dispersal models of the response of Spisula solidissima to climate change in the Mid-Atlantic Bight, suggest the general use of mactrids as barometers of climate change over broader geographic footprints. Mactromeris polynyma is a candidate species for shallow arctic marine systems, having a pan-arctic distribution from the Gulf of Maine in the Atlantic to the Bering Sea and Gulf of Alaska in the northern Pacific. The longevity of extant individuals (≤25 years) provides opportunity for detailed reconstruction of the benthic environment and food regimes at the decadal level.

Predicting the Influence of Seed and Commercial Oyster Fisheries on Metapopulation Genetic Connectivity Using Model Simulations

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How Do Marine Protected Area Strategies Influence Metapopulation Genetic Connectivity? A Modeling Study with Oysters

S OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATIONS OF TECHNICAL PAPERS Presented at the 104 Annual Meeting NATIONAL SHELLFISHERIES ASSOCIATION