Differential use of seagrass assemblages by a suite of odacid species

Members of the teleost family Odacidae were sampled over five seasons from three seagrass assemblages, comprising predominantly either Amphibolis grif fithii, Posidonia sinuosa or Posidonia coriacea, in marine waters at depths of 4-9 m in south-western Australia. These three assemblages were characte rized by different seagrass or meadow structure, thereby creating three dis tinct seagrass habitats. Four odacid species were relatively abundant in th e seagrass meadows, although each species displayed a 'preference' for one habitat. Odax acroptilus, which had the largest body size, was restricted a lmost entirely to meadows of A. griffithii, the most structurally complex h abitat with open spaces below a dense canopy. In contrast, smaller species, such as Neoodax balteatus and Siphonognathus radiatus, were either restric ted to or found in higher densities in P. sinuosa meadows, which form dense foliage near the substrata. Haletta semifasciata was also restricted to P. sinuosa meadows, albeit in low densities. The patchy landscape produced by P, coriacea housed far fewer fish of all species, except Siphonognathus at tenuatus, which was found almost entirely, but in low numbers, in this habi tat. Additional sampling of P. sinuosa meadows in nearshore waters revealed that, compared to the more offshore meadows, fewer species occurred in the se seagrass meadows. Even the most abundant species, S. radiatus, was prese nt in far lower densities in nearshore waters. The presence of fish ranging from small juveniles to large adults with mature and running-ripe gonads i n offshore meadows throughout the year indicates that odacids are capable o f completing their life-cycle within offshore seagrass meadows. (C) 2001 Ac ademic Press.