Date Awarded

2014

Document Type

Dissertation -- Access Restricted On-Campus Only

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Robert J. Latour

Abstract

The value of habitats in terms of biological production is of interest to ecologists and resource managers. Seagrasses are a commonly occurring habitat type in shallow marine waters and have been shown to support high abundances of fish and invertebrates. In lower Chesapeake Bay, seagrasses grow in a shallow fringe in the subtidal zone. Although, ample evidence exists for the value of these habitats as foraging and rearing areas for a variety of organisms, the connectivity among species and the benefits derived from these habitats in terms of production have not been well described, especially for small, seasonally occurring finfishes. The main objective of this research was to document fish occurrence and abundance, describe trophic interactions within the seagrass community, and quantify export of biomass from the habitat using a model species to demonstrate the value of these habitats in terms of finfish production.;To address the research objective, I employed a variety of models---statistical, ecosystem, and individual-based. In Chapter 1, I conducted as census of finfishes in seagrass habitats and compared contemporary occurrences and abundances to data from the 1970s. This chapter showed that the fish fauna in these habitats is dominated by a small number of abundant and commonly occurring species, including Spot (Leiostomus xanthurus), Silver Perch ( Bairdiella chrysoura), Bay Anchovy (Anchoa mitchilli), Atlantic Silverside (Menidia menidia), Dusky Pipefish ( Syngnathus floridae), and Northern Pipefish (Syngnathus fuscus ). While abundances had changed since the 1970s for some species, most were highly variable with no discernible trend. There was a small decrease in species richness from the historical dataset to the contemporary dataset and multivariate analysis showed a shift in community composition. The data from this chapter formed the basis for the ecosystem model developed in Chapter 2. In this model, biomass, production, and diet data were inputs, and using a mass-balance approach, a food web model was iteratively developed. There were 35 model compartments in the model and scenarios based upon historical data and future projections were developed for comparison. Mesozooplankton were the most highly connected group, while piscivorous birds, several piscivorous fishes, and mesograzers were all considered keystone groups, controlling food web dynamics. In Chapter 3, an individual-based model was developed for Silver Perch, to assess growth and production within a seagrass habitat. Because Silver Perch settle in this habitat, grow during the summer season, and migrate to deeper waters in the fall, they were an appropriate model species for determining the contribution of seagrass habitats to production. With high seasonal abundance and rapid growth (~0.19 g/d), this species contributes a considerable amount of biomass to Chesapeake Bay, biomass that originates in seagrass habitats and moved via trophic transfer.;This study presents a quantitative view of community ecology in lower Chesapeake Bay seagrass habitats. With changing temperatures and habitat loss, these habitats are at risk, and this study demonstrates that their value to the Chesapeake Bay food web extends beyond the small fringe of their occurrence.

DOI

https://dx.doi.org/doi:10.25773/v5-h572-d662

Rights

© The Author

On-Campus Access Only

Share

COinS