Trophic Position of Two Mysid Species (Crustacea: Mysidacea) in an Estuarine Ecosystem in Auckland, New Zealand, Using Stable Isotopic Analysis

Abstract

The trophic position of an organism can be determined by the stable isotope studies of nitrogen and carbon. The main objective of this study was to determine the trophic position of two mysid species, Tenagomysis chiltoni and T. novaezealandiae in the Kakamatua stream ecosystem in using 13C and 15N isotopes. Samples were collected during two weeks period in late December 2008 and early January 2009 including primary producers, leaf litter, aquatic invertebrates, fish species and sediment samples. Aquatic invertebrates and fish were collected from the stream using a hand net. Litter samples were collected randomly from the stream floor. Samples were sealed in plastic bags, and stored in a freezer until processing. All the samples were oven-dried, then ground to obtain a homogeneous powder. Three replicates of each sample were prepared. Samples were processed by the Waikato Stable Isotope Unit, of , . A trophic-level effect of 13C and 15N enrichment was clearly observed. Stable isotopic data indicated that T. chiltoni and T. novaezealandiae exhibited variety of feeding habits (feeding on the first and the second trophic levels) and can be considered as omnivores. Among the other invertebrates analysed, mysids seem to be an important invertebrate fauna which are capable of energy transferring towards the higher trophic level both from primary food sources and the secondary consumers as well. Differences in the isotopic composition were observed among same species depending upon the ontogenetic development.