A study of food chains in seagrass communities. III. Stable carbon isotope ratios

Abstract

Stable carbon isotope determinations have been used to obtain a general background to food chains being studied by a range of chemical and biological techniques. δ¹³C values indicate that animals (δ¹³CC - 11.4‰ to - 14.9‰), including two locally important commercial fish, Platycephalus laevigatus (rock flathead) and Hyporhamphus melanochir (southern sea garfish), from the Corner Inlet seagrass and non-seagrass communities are dependent to varying degrees upon seagrass (δ¹³C - 7.0‰ to - 9.3‰) and benthic algae for their carbon source. The largest changes in δ¹³C values in the food chains is at the point involving seagrasses and their direct herbivores. The latter have more negative δ¹³C values (H. melanochir - 12.1%o, isopods - 11.4%o). Little or no change in δ¹³C values is apparent at the higher trophic levels (carnivores - 13 .0‰ to - 14.9‰). Epiphytic material on the fresh leaves of the two seagrass species in the Inlet is depleted in ¹³C when compared with the seagrass leaves. An opposite effect is observed for epiphytic material on Posidonia australis detritus.