Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Robert J Latour
Mark J Brush
Marjorie A M Friedrichs
Jeffrey A Buckel
Geneviève M Nesslage
Taking an ecosystem approach to fisheries requires the consideration of relevant ecological processes within research and assessment frameworks. Processes affecting ecosystem productivity can be categorized as biophysical (climate variability, primary production), exploitative (fishing), or trophodynamic (food web interactions). This dissertation incorporates these three governing processes to characterize spatiotemporal diversity and population abundance trends for multiple demersal fish and invertebrate species that inhabit the nearshore zone (15-30 ft. depth) along portions of the U.S. Atlantic east coast.
Two large marine ecosystems (LMEs) encompass the U.S. East coast – the Southeast and Northeast U.S. Continental Shelf LMEs. The level of connectivity within and between these two ecosystems is well understood for some individual species, but not generally for the nearshore assemblage. The first research chapter of this dissertation is a spatial diversity analysis of 141 fish and invertebrate species that inhabit nearshore waters from Florida to New York. Latitudinal diversity patterns revealed multiple biotic ecotones, or areas of high species turnover. An ecotone was evident in northern spring near the Cape Hatteras border of the two LMEs, but this barrier dissipated as water temperatures homogenized and assemblage connectivity between ecosystems increased throughout the year. Multiple other biotic ecotones were evident within the Southeast U.S. LME and were explained by seasonality and the proximity and area of adjacent estuarine habitat.
The second and third research chapters of this dissertation focus on explaining temporal abundance trends for multiple nearshore fish and invertebrate species within the Southeast U.S. LME. For the second research chapter, abundance trends for 71 species were analyzed during 1990-2013 within a univariate time series modeling framework with the goal of determining the relative importance of climate variability and fishing pressure as governing influences on abundance. A decrease in bycatch mortality explained changes for multiple species, while climate variability governed the dynamics for others. Multivariate ordination revealed similar trends for groups of taxonomically related species, indicating governing processes act on species with similar life histories. An extension of results from the second research chapter, research chapter three explores trophic interactions between the bonnethead shark (Sphyrna tiburo) and five of its prey species within Southeast U.S. LME nearshore waters. Multivariate time series modeling supports a negative effect of bycatch on bonnetheads, and population-level predation effects of larger sharks on multiple prey species. Abundance trends for most prey species were also explained by environmental variability associated with the Pacific Decadal Oscillation, although trophic effects were stronger.
This body of work incorporates relevant ecological factors in characterizing diversity and abundance trends for fish and invertebrate species comprising the nearshore demersal assemblage within Southeast and Northeast U.S. LMEs. Results indicate seasonal connectivity between LMEs that require further exploration at multiple spatial scales. Abundance time series modeling for multiple species in the Southeast U.S. LME reveals that fishing and trophodynamics may be relatively more influential drivers than climate variability in this sub-tropical system.
© The Author
Stratton, Mark A., "Spatiotemporal Abundance Patterns and Ecological Drivers of A Nearshore U.S. Atlantic Fish and Invertebrate Assemblage" (2017). Dissertations, Theses, and Masters Projects. Paper 1499450080.