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No description available.

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Macrofauna-based biocriteria to assess impairment in aquatic communities are well-developed and have been widely accepted as useful for coastal monitoring programs worldwide. Meiofauna-based methods are not as well developed, but meiofauna are intimately associated with sediments through their life cycles and are functionally important. Thus, an understanding of meiofauna relationships with environmental quality is also important. Relationships between the abundance and composition of major meiofauna taxa for two shallow water habitat types (protected, with muddy sediment; exposed, with sandy sediment) were investigated along gradients associated with changing land use, sediment contamination and environmental stressors in Chesapeake Bay. Principal component analysis shows that urbanization, eutrophication and sediment contamination affect shallow water sites in the lower Chesapeake Bay, Virginia ecosystem. Multidimensional scaling ordination of meiofauna community data reveals gradients associated with human activities and major habitat types. Both sediment enrichment (high percent organic carbon and percent nitrogen) and sediment toxicity were associated with shifts in meiofauna community composition in muddy sediment. Benthic Foraminifera, known to be pollution sensitive, were rare or absent in collections from sites with sediment enrichment or toxicity. Nematodes were abundant at a site with enrichment, but not at a site with significant sediment toxicity. Major meiofauna taxa also differed clearly between protected and exposed sites, with greater abundances in collections from mud versus sand sediment. Results of analyses matching biotic to environmental patterns point to the importance of regional historic salinity and chlorophyll-a levels in addition to other habitat properties, including sediment organic carbon, total nitrogen and sediment toxicity as predictors of meiofauna community structure. The Benthic Index of Biotic Integrity (B-IBI) developed for Chesapeake Bay based on macrofauna was negatively correlated with nematode abundance at muddy sites when a site with significant sediment toxicity was excluded. There were no other significant relationships between meiofauna metrics and the B-IBI. The ratio of nematodes to copepods was not effective for discriminating relationships among sites relative to anthropogenic effects.

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No description available.

The maintenance of a population within the geographic range is influenced by the physical and environmental conditions under which breeding occurs. It is hypothesized that environmental conditions under which egg capsules are successfully hatched will influence the range of potential habitat of the invasive veined rapa whelk, Rapana venosa, and the native Atlantic oyster drill, Urosalpinx cinerea, in the Chesapeake Bay. This study examines the environmental conditions of temperature, salinity, and the time of deposition of egg capsules within the reproductive period (here quantified as cumulative number of day degrees at egg capsule deposition). The range of R. venosa and U. cinerea habitat in the Chesapeake Bay, in relation to environmental conditions, is important given the potential impact of both species on native shellfish stocks. Egg capsule hatching success and egg capsule incubation time for R. venosa and U. cinerea were examined at temperatures (18oC, 22oC, 26oC, 30oC, and ambient York River water temperature) and salinities (7 ppt, 14 ppt, 21 ppt, 28 ppt, and ambient York River salinity) reflective of the Chesapeake Bay during egg capsule deposition. Salinity is the greatest factor influencing R. venosa and U. cinerea egg capsule hatching success. Increasing salinities increase the percentage of R. venosa and U. cinerea egg capsules to hatch as well as the percentage of U. cinerea embryos alive at hatch. For R. venosa, the percentage of egg capsules to hatch is greatest at 21 ppt. For U. cinerea the percentage of egg capsules to hatch and the percentage of embryos alive at hatch are greatest at salinities of 21 ppt or 28 ppt. R. venosa and U. cinerea egg capsules do not hatch at 7 ppt in the temperature range examined. Temperature within the range examined was not found to be an important factor influencing egg capsule hatching success for either species. However, temperature was an important factor influencing the rate at which the egg capsule hatching process occurs. The percentage of R. venosa egg capsules to hatch increases and the percentage of U. cinerea alive at hatch decreases along the egg capsule deposition time series. For R. venosa, an increase in the percentage of egg capsules to hatch occurs if egg capsules are deposited later in the time series. For U. cinerea the percentage of egg capsules to hatch is not affected by position in the egg capsule deposition time series, but the percentage of embryos alive at hatch decreases along the time series examined. The temperatures and salinities for optimal R. venosa egg capsule hatching range from 18oC to 30oC and from 11 ppt to 28 ppt and vary based on the timing of egg capsule deposition. The temperatures and salinities for optimal U. cinerea egg capsule hatching range from 18oC to 30oC and from 20 ppt to 28 ppt and do not vary based on the timing of egg capsule deposition. Optimal egg capsule hatching for R. venosa and U. cinerea occur at different temperature-salinity combinations throughout the majority of the egg capsule deposition time series.

With the recent growth of the hard clam aquaculture industry, sites of intensive aquaculture have emerged as large-scale agro-ecosystems where the success of aquaculture production is dynamically linked to ecosystem function. Large scale clam aquaculture operations are associated with a range of potential positive and negative feedbacks related to nutrient dynamics, water and sediment quality, proliferation of macroalgae, and carrying capacity. Quantitative modeling tools are needed to support system-level planning related to site selection, scale of operations, production capacity and ecosystem function. The purpose of this study was to develop a model for Cherrystone Inlet, VA, where one-third (1.9 km2) of the sub-tidal bottom area is held as 37 separate, private shellfish leases with an estimated 100-150 million cultured clams. A reduced complexity estuarine ecosystem model was coupled with a hard clam energetics and growth model and a watershed loading model. The linked models facilitate ecosystem-based management and enable regional spatial planning in a full ecosystem context, through coupled simulations of aquaculture activities, land use changes, nutrient loading, climate change, and estuarine response. Modeled output for hard clam growth and water column chlorophyll-o, dissolved oxygen, and dissolved inorganic nitrogen and phosphorous reproduced in situ data. Simulations with increasing clam numbers up to 500 million resulted in diminishing returns in terms of reduced growth rates, increased time to harvestable size, and reduced harvestable biomass, confirming observations by Cherrystone farmers of reduced clam growth rates above 200 million cultured clams. Modeled hard clam production capacity decreased in the absence of benthic microalgal resuspension (6%) and without the input of external production from the Chesapeake Bay (41%), and increased in simulations with increased water column chlorophyll-o (11%) and the removal of predator exclusion nets (13%). Simulations to optimize siting indicated that the highest hard clam growth rates occurred up-estuary. Model simulations with changes in land use and climate indicated that clam growth is most sensitive to increasing temperature, with rates decreasing by 37% when temperatures were increased by 5°C, while changes in land use, sea level rise and salinity did not result in large changes in hard clam production. At the system scale hard clam aquaculture was predicted to account for 14% of total nitrogen inputs to the water column between sediment recycling of clam feces (13%) and direct clam excretion (1%). The Cherrystone ecosystem model fills a critical gap on the Eastern Shore of Virginia and in similar coastal systems, providing resource managers with the most current available science in a decision-support framework to promote effective regional spatial planning and sustainability of hard clam operations and the surrounding coastal ecosystems.

Several studies have documented the occurrence of substantial numbers of zooplankton carcasses in marine field samples. However, the potential effect of carcasses on conclusions resting on zooplankton abundance estimates, and the reasons for carcass occurrence have been largely disregarded. Many field studies do not account for the presence of carcasses in their sampling methodology. Zooplankton carcasses in situ are significant for several reasons. as concentrated particles of organic matter in the water column, zooplankton carcasses can be important vehicles for organic matter transport and hotspots of microbial abundance and activity. If dead animals are treated alive, carcasses could bias the ecological conclusions of field studies. Finally, naturally occurring carcasses lacking injuries likely represent instances of non-predatory mortality, a poorly studied phenomenon in marine zooplankton ecology. The goal of my research was to resolve the importance of naturally occurring zooplankton carcasses with regard to the roles described above. A detailed evaluation was made of the neutral red vital staining method, to resolve method limitations for quantifying zooplankton carcasses in situ. The method gave reliable results for common copepods in the lower Chesapeake Bay, and artifact collection mortality was negligible. Thus, neutral red is a valuable method for quantifying naturally occurring copepod carcasses in the lower Chesapeake Bay. A two year study was then done to quantify carcasses in the lower Chesapeake Bay. Carcasses were a persistent feature in the water column throughout the study, with a repeating pattern of higher carcass abundance during the summer and fall in each year. The fate of carcass organic matter was then determined using a combined laboratory, field, and mathematical modeling approach to quantify removal by sinking, necrophagy (consumption of carcasses), and microbial decomposition. Carcass removal due to sinking was impeded by turbulent mixing in the estuary, and the rate of removal depended on the magnitude of ingestion by necrophages and the effects of water temperature on microbial decomposition. The resulting carcass abundances and removal rates were then used to determine errors resulting from counting carcasses as alive in ecological field studies, and also to determine the contribution of non-predatory factors to zooplankton mortality in the lower Chesapeake Bay. When carcasses were treated as alive, there were substantial errors in mortality rates derived from field abundances. This demonstrated the importance of identifying carcasses in zooplankton field samples. Non- predatory mortality accounted for 8% to 42% of total zooplankton mortality. The importance of non-predatory factors (e.g. disease, starvation, environmental stress) deserves more attention in ecological studies of marine zooplankton mortality and population dynamics.

Eelgrass (Zostera marina L.) is the northern hemisphere's dominant marine angiosperm, a species with both ecological and economic importance. Initial allozyme surveys of eelgrass populations in Chesapeake Bay (Virginia, USA) revealed substantial amounts of geographically-partitioned genetic variation, which could be the result of nonselective demographic processes, including founder events and drift. However, strong spatial variation in the environment and in eelgrass morphology suggests that differential adaptation of isolated beds to local environmental conditions could also produce these patterns. This dissertation used three sets of studies to investigate microevolutionary processes might produce the observed variation among Chesapeake eelgrass beds: (1) an allozyme survey of genetic diversity within and among twelve beds of different ages and sizes, (2) controlled breeding experiments to characterize the mating system of Z. marina and determine its susceptibility to inbreeding or outbreeding depression, and (3) reciprocal transplants to test for local adaptation within Zostera marina demes. Results showed considerable genetic diversity within beds and strong differentiation among beds but no relationship between genetic diversity and bed age or size, suggesting that founder events or clonal competition do not strongly depress genetic variation in this system. Artificial matings revealed no evidence of inbreeding depression in the 3 beds tested; seed production was significantly higher in selfed crosses than in either outbred or within-bed (inbred) crosses. Finally, reciprocal transplants showed some evidence of local adaptation in shoot density and seed production, but this was inconsistent in space and time. Phenotypic plasticity, perhaps bounded by genetic constraints, appeared to be the primary means by which Chesapeake eelgrass responded to local environmental variation. These studies support the emerging idea that eelgrass is not a panmictic obligate outbreeder, and they support important influences of non-selective processes (restricted gene flow and phenotypic plasticity) on the population structure of Chesapeake Bay eelgrass.