Nutritional value of detritus and algae in blenny territories on the Great Barrier Reef

Abstract

The salariin blenny, Salarias patzneri, primarily ingests detrital aggregates and inorganic sediment, with small quantities of filamentous algae. Samples of particulate matter <125 μm and filamentous algae were collected from the territories of S. patzneri and the nutritional value of these resources assessed using organic content and protein/energy ratios calculated from protein, carbohydrate and lipid content. Samples were collected throughout the day, during both summer and winter, to enable temporal comparisons of nutritional value. The particulates <125 μm, which were predominantly amorphic detritus, accounted for 41±2% and 44±3% of the organic matter in the epilithic algal matrix (EAM) during the summer and winter, respectively, whilst filamentous algae accounted for 37±3% and 41±3% of the organic matter in the summer and winter, respectively. Carbohydrate and lipid concentration in the algal samples was significantly greater than in particulate matter <125 μm, although no significant difference was detected in protein levels of algal samples and particulates <125 μm. Consequently, the protein/energy ratio of particulates <125 μm in the summer (11±1 mg kJ −1) and winter (10±1 mg kJ −1) was similar to that of filamentous algae in the summer (9±1 mg kJ −1) and winter (8±1 mg kJ −1). These results suggest detrital aggregates are at least comparable to filamentous algae as a nutritional resource. The large contribution of high quality detritus to organic matter in the epilithic algal matrix collected from S. patzneri territories throughout the day and between seasons provides strong evidence that detritus is a valuable component of small territorial fish diets and is an integral part of coral reef food webs.