Biochemical Markers of the Effects of Canal-Induced Nutrient Gradients on Food-Webs in a Taylor Slough Freshwater Marsh

The Florida Everglades ecosystem is controlled to a large extent by the interactions between hydrological and biological processes. Climatic factors and Everglades restoration plans will have strong impacts on water flow, nutrient levels, and, consequently, ecosystem productivity. A critical question that remains is how these hydrological changes will affect trophic interactions and community structure. Here, we are applying a lipid biomarker approach to address this question, focusing on the role of nutrient gradients on the quality and quantity of detritus and algae available for primary and intermediate trophic levels. Lipid biomarker analysis relies on specific lipid patterns in basal resources that become transferred to higher trophic levels upon ingestion, thereby providing important insights into food sources and consumer dynamics.

Periphyton, flocculent material (floc), chironomids, amphipods ( Hyalella azteca ), snails ( Haitia spp. ), grass shrimp ( Palaemonetes paludosus ), eastern mosquitofish ( Gambusia holbrooki ), flagfish ( Jordanella foridae ), and dollar sunfish ( Lepomis marginatus ) were collected from a freshwater marsh in Taylor Slough at sites adjacent to and removed from the C-111 canal in January 2010. Although periphyton and floc contained a similar suite of fatty acids, floc was characterized by larger proportions of bacterial (15:0i, 15:0a, 17:0i, 17:0a) and terrestrial (C ₂₄ - C ₃₀ saturated) fatty acids, highlighting the heterogeneity of organic matter sources to flocculent material. Floc also contained lower proportions of fresh algal markers (C ₁₆ , C ₁₈ , and C ₂₀ polyunsaturated fatty acids) than periphyton, especially at sites far from the canal, suggesting decreasing quality of organic matter in floc with distance from the canal. In addition, a monounsaturated C ₁₉ fatty acid was present in floc, but absent from periphtyon, suggesting a potential marker to differentiate contributions of these basal resources to higher trophic levels. Preliminary analysis of amphipods and snails revealed the presence of this marker, implying floc as a food resource for both species. Feeding experiments are presently underway to test basal resource lipid assimilation and metabolism in these primary consumers. Carbon and nitrogen stable isotopic composition of basal resources and consumers will be coupled to fatty acid compositional analysis to further resolve the linkages between hydrology, community assembly, carbon quality and quantity for consumers, and trophic position.