A Molecular and Stable Isotopic Approach to Investigate Algal and Detrital Energy Pathways in a Freshwater Marsh
The relative importance of algal and detrital energy pathways remains a central question in wetlands ecology. We used bulk stable isotope analysis and fatty acid composition to investigate the relative contributions of periphyton (algae) and floc (detritus) in a freshwater wetland with the goal of determining the inputs of these resource pools to lower trophic-level consumers. All animal samples revealed fatty acid markers indicative of both microbial (detrital) and algal origins, though the relative contributions varied among species. Vascular plant markers were in low abundance in most consumers. Detritivory is important for chironomids and amphipods, as demonstrated by the enhanced bacterial fatty acids present in both consumers, while algal resources, in the form of periphyton, likely support ephemeropteran larvae. Invertebrates such as amphipods and grass shrimp appear to be important resources for small omnivorous fish, while Poecilia latipinna appear to strongly use periphyton and Ephemeroptera larvae as food sources. Both P. latipinna and Lepomis spp. assimilated small amounts of vascular plant debris, possibly due to unintentional ingestion of floc while foraging for invertebrates and insect larvae. Physid snails, Haitia spp., were characterized by considerably different fatty acid compositions than other taxa examined, and likely play a unique role in Everglades’ food webs.
KeywordsFatty acids Stable isotopes Food webs Detritus Algae Everglades
This work was supported by the U. S. National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Grant No. DBI-0620409 and by funds from Cooperative Agreement H5000060104, Task No. J5284060023, between FIU and Everglades National Park. Analytical support through the SERC Stable Isotope Facility is kindly acknowledged. This is SERC contribution #543.
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