Effects of Co-Varying Diel-Cycling Hypoxia and pH on Growth in the Juvenile Eastern Oyster, Crassostrea virginica.

Shallow water provides important habitat for many species, but also exposes these organisms to daily fluctuations in dissolved oxygen (DO) and pH caused by cycles in the balance between photosynthesis and respiration that can contribute to repeated, brief periods of hypoxia and low pH (caused by elevated pCO2). The amplitude of these cycles, and the severity and duration of hypoxia and hypercapnia that result, can be increased by eutrophication, and are predicted to worsen with climate change. We conducted laboratory experiments to test the effects of both diel-cycling and constant low DO and pH (elevated pCO2) on growth of the juvenile eastern oyster (Crassostrea virginica), an economically and ecologically important estuarine species.

Effects of air-exposure gradients on spatial infection patterns of Perkinsus marinus in the eastern oyster Crassostrea virginica.

Spatial distributions of species can be shaped by factors such as parasites, mortality, and reproduction, all of which may be influenced by differences in physical factors along environmental gradients. In nearshore tidal waters, an elevational gradient in aerial exposure during low tide can shape the spatial distributions of benthic marine organisms. The eastern oyster Crassostrea virginica is an ecologically and economically important species that can dominate both subtidal and intertidal habitats along the east coast of the USA.

Landscape-level variation in disease susceptibility related to shallow-water hypoxia.

Diel-cycling hypoxia is widespread in shallow portions of estuaries and lagoons, especially in systems with high nutrient loads resulting from human activities. Far less is known about the effects of this form of hypoxia than deeper-water seasonal or persistent low dissolved oxygen. We examined field patterns of diel-cycling hypoxia and used field and laboratory experiments to test its effects on acquisition and progression of Perkinsus marinus infections in the eastern oyster, Crassostrea virginica, as well as on oyster growth and filtration.

Ecosystem engineers in the pelagic realm: alteration of habitat by species ranging from microbes to jellyfish.

Ecosystem engineers are species that alter the physical environment in ways that create new habitat or change the suitability of existing habitats for themselves or other organisms. In marine systems, much of the focus has been on species such as corals, oysters, and macrophytes that add physical structure to the environment, but organisms ranging from microbes to jellyfish and finfish that reside in the water column of oceans, estuaries, and coastal seas alter the chemical and physical environment both within the water column and on the benthos. By causing hypoxia, changing light regimes, and influencing physical mixing, these organisms may have as strong an effect as species that fall more clearly within the classical category of ecosystem engineer.

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

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).

Hypoxia, nitrogen, and fisheries: integrating effects across local and global landscapes.

Anthropogenic nutrient enrichment and physical characteristics result in low dissolved oxygen concentrations (hypoxia) in estuaries and semienclosed seas throughout the world. Published research indicates that within and near oxygen-depleted waters, finfish and mobile macroinvertebrates experience negative effects that range from mortality to altered trophic interactions. Chronic exposure to hypoxia and fluctuating oxygen concentrations impair reproduction, immune responses, and growth.

Interspecific Competition and the Abundance of Nest Sites: Factors Affecting Sexual Selection.

The abundance of suitable nest sites and competition with other species for such sites appears to affect the intensity of intersexual selection in Coryphopterus nicholsi, a temperate goby that is a protogynous hermaphrodite. Field manipulations demonstrated that, within a population, the proportion of males that breed, and therefore the intensity of sexual selection, depends on the number of suitable nest rocks. The abundance of nest sites may also affect the timing of sex change in this species.

Development of a subtidal epibenthic community: factors affecting species composition and the mechanisms of succession.

Macroinvertebrate grazers and temporal variability were found to strongly influence species composition of communities that developed subtidally on plexiglas panels. On panels exposed to the naturally high densities of sea urchins and sea stars, only grazer-resistant algal crusts, a diatom/blue-green algal film and short-lived filamentous algae became abundant. On those panels protected from grazers, however, other algae and sessile invertebrates were also common.