Trophic ecology of dominant zooplankton and macrofauna in a temperate, oligotrophic South African estuary: a fatty acid approach

Fatty acid profiles of food sources, dominant zooplankton, macrofauna and a few small ichthyofauna in a temperate estuary on the southeastern coast of South Africa were used to trace the original carbon sources and the degree of feeding plasticity of consumers within an oligotrophic environment. Fatty acid analysis is seldom used to examine food web ecology in estuaries, as these systems are typically highly complex owing to the variety of potential food sources and the variable nature of detritus. We hypothesized that generalist consumers would exhibit similar and overlapping fatty acid compositions, whereas any specialist consumers would 'stand out' as they may contain high proportions of fatty acids specific to their preferred food sources. Within-species variation was very small in the food sources, and Principal Component Analysis (PCA) allowed resolution of most species and sample types into distinct clusters. Variation of fatty acid composition was greater within the consumers, with PCA resolving several clusters by collection location within the site and feeding mode of the animals (suspension feeders, grazers and omnivores). We considered the fatty acid profiles (with particular reference to polyunsaturated fatty acids and essential fatty acids) of the consumers in relation to the food sources to determine which organisms played significant roles in the sequestration and cycling of high quality organic material within the estuary.