Community metrics and trophic dynamics in tidal creeks in an anthropogenically fragmented, coastal landscape

Michael Robert Lowe, University of Southern Mississippi

Abstract

Salt marsh landscapes are among the most anthropogenically altered ecosystems in the world. Urbanization (i.e., accumulation of impervious cover and man made structrues) of the coastal landscape can disrupt the delivery of numerous ecosystem services. Among the many services provided by salt marsh habitats, they serves as the primary habitats for distinct macroinfauna (i.e., benthic and epibenthic macrofauna) and nekton (i.e., fish and decapod crustaceans) assemblages. In this dissertation, I used a number of metrics to test the overarching hypothesis that coastal urbanization has negative consequences for salt marsh faunal assemblages. Chapter I uses a landscape ecology approach to show that intact natural salt marsh landscapes, coastal landscapes with very little urbanization, host a greater abundance of individual species and nekton assemblages that are different from those in urbanized coastal landscapes (partially fragmented and completely fragmented salt marsh landscapes). The amount of developed shoreline and various metrics related to salt marsh fragmentation were important drivers of observed patterns in both macroinfauna and nekton assemblages. Chapter II examines the growth response of blue crab ( Callinectes sapidus ), brown shrimp ( Farfantepenaeus aztecus ), spot ( Leiostomus xanthurus ), and Gulf killifish ( Fundulus grandis ) to increasing levels of urbanization in salt marsh habitats. Further, the diets of spot and Gulf killifish were also examined. While blue crab and brown shrimp growth did not differ among the landscapes, spot and Gulf killifish growth dynamics were markedly reduced in the completely fragmented landscapes. Reduced growth, or poor body condition, for both species was related to differences in landscape-specific foraging patterns. Chapter III uses δ 13 C, δ 15 N, and δ 34 S stable isotope ratios and a suite of quantitative stable isotope metrics to relate the composition and configuration of coastal landscapes to the structure of salt marsh food webs. Overall, nekton assemblages in completely fragmented landscapes incorporated a narrower range of autotrophs, had a greater estimated trophic position, and an overall isotopic niche that was markedly reduced compared to both intact natural and partially fragmented salt marsh landscapes. Overall, these results suggest that urban growth that progresses in a manner that both consumes and isolates critical habitats within a human-dominated landscape is unsustainable.