Identifying sources of organic matter in sediments from a detritivorous coral reef fish territory

Sediment and filamentous algae were collected from territories of the detritivorous blenny, Salarias patzneri, to identify sources of dietary detritus. Samples were collected during summer and winter and analysed for fatty acid, hydrocarbon and sterol biomarkers. Sediments predominantly contained: even carbon number fatty acids, a high percentage of polyunsaturated fatty acids and a prevalence of n-heptadecane and n-pentadecane. This composition of lipids is typical of organic matter derived from recently deposited algae, or living microalgae. Similarities between sediment and filamentous algal lipids imply filamentous algae may be a major source of detritus in the sediments. Sediments did however have a higher percentage of 16:1ω7 than filamentous algae samples and this is most likely due to inputs to the sediments from diatoms and bacteria. Based on 20:5ω3 concentrations, it was estimated that diatoms accounted for 18% of the organic matter in sediments during summer and 4% in the winter, whilst 18:1ω7 concentrations suggest bacteria accounted for 10% of organic matter in both seasons. In addition, lipid biomarkers indicated that dinoflagellates, corals, cyanobacteria and zooplankton also contribute to sediments, providing a diverse range of dietary nutrients. It is this combination of inputs to sedimentary detritus that provides S. patzneri with essential dietary nutrients.