Richard S. Fulford

Oyster-sea nettle interdependence and altered control within the Chesapeake Bay ecosystem

Research on the effects of declining abundances of the Eastern oyster (Crassostrea virginica) in Chesapeake Bay and other estuaries has primarily focused on the role of oysters in filtration and nutrient dynamics, and as habitat for fish or fish prey. Oysters also play a key role in providing substrate for the overwintering polyp stage of the scyphomedusa sea nettle,Chrysaora quinquecirrha, which is an important consumer of zooplankton, ctenophores, and icthyoplankton. Temporal trends in sea nettle abundances in visual counts from the dock at Chesapeake Biological Laboratory, trawls conducted in the mesohaline portion of the Patuxent River, and published data from the mainstem Chesapeake Bay indicate that sea nettles declined in the mid 1980s when overfishing and increased disease mortality led to sharp decreases in oyster landings and abundance. Climate trends, previously associated with interannual variation in sea nettle abundances, do not explain the sharp decline. A potentially important consequence of declining sea nettle abundances may be an increase in their ctenophore prey (Mnemiopsis leidyi), and a resultant increase in predation on icthyoplankton and oyster larvae. Increased predation on oyster larvae by ctenophores may inhibit recovery of oyster populations and reinforce the current low abundance of oysters in Chesapeake Bay.

Evaluating ecosystem response to oyster restoration and nutrient load reduction with a multispecies bioenergetics model

Many of the worlds 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.

Fecundity and Egg Diameter of Primiparous and Multiparous Blue Crab Callinectes Sapidus (Brachyura: Portunidae) in Mississippi Waters

ABSTRACT Blue crabs Callinectes sapidus Rathbun, 1896 support large commercial and recreational fisheries along the Atlantic coast and in the Gulf of Mexico (GOM). Female blue crabs are traditionally believed to produce one to six broods in their lifetime. However, recent evidence has shown that females have the ability to spawn up to eight broods in a single spawning season, with as many as 18 broods over their lifespan. In this study, fecundity and egg diameter were examined by brood class (primiparous, multiparous) in the spring and summer/fall. Mean carapace width of females was significantly different between brood class and season, with the largest females in the spring. There was a positive relationship between fecundity and carapace width. Although primiparous spring females were the most fecund (3.2 ± 1.5 million eggs), no statistically significant differences in fecundity by brood class and season were found. Loss of eggs occurred during embryonic development; primiparous females lost ∼0.9 million eggs whereas multiparous females lost ∼0.1 million. Egg diameter and carapace width of the female were positively correlated. There was no difference in egg diameter between brood classes, but eggs were 9.9% larger in diameter during the spring than summer/fall. There was an inverse relationship between fecundity and egg diameter. Seasonality appeared to play an important role in the reproductive life history of blue crabs in the northern GOM. Larger crabs and larger eggs in the spring may be related to quality and quantity of available food and temperature conditions for optimal growth.

Habitat Suitability Modeling to Evaluate Conservation and Enhancement Efforts for Gulf-Strain Striped Bass in Mississippi Coastal Rivers

Abstract Conservation of native populations such as Gulf-strain striped bass Morone saxatilis is a priority for preserving historic fisheries and maintaining biodiversity. Habitat alteration is thought to be the primary driver of native striped bass decline in Mississippi coastal rivers, so it is a priority to understand current habitat suitability as part of a comprehensive restoration plan. A bioenergetics model is a useful tool to examine habitat suitability by using growth rate potential as an indicator of habitat quality. The purpose of this study was to develop a habitat suitability model for Gulf-strain striped bass that incorporates seasonal and spatial variability in temperature, salinity, and dissolved oxygen in an index river system along the Gulf of Mexico coast, Mississippi. Environmental data collected with a stratified-random survey during fall, winter, spring, and summer of 2008–2009 were incorporated into a spatially explicit bioenergetics model. Model-predicted growth rates were analyzed...