DISTRIBUTION AND COMMUNITY STRUCTURE OF ICHTHYOPLANKTON IN LAGUNA MADRE SEAGRASS MEADOWS - POTENTIAL IMPACT OF SEAGRASS SPECIES CHANGE

Seasonal ichthyoplankton surveys were made in the lower Laguna Madre, Texas, to compare the relative utilization of various nursery habitats (shoal grass, Halodule wrightii; manatee grass, Syringodium filiforme ; and unvegetated sand bottom) for both estuarine and offshore-spawned larvae. The species composition and abundance of fish larvae were det ermined for each habitat type at six locations in the bay. Pushnet ich thyoplankton sampling resulted in 296 total collections, yielding 107, 463 fishes representing 55 species in 24 families. A broad spectrum of both the biotic and physical habitat parameters were examined to link the dispersion and distribution of both pre-settlement and post-settl ement larvae to the utilization of shallow seagrass habitats. Sample s ites were grouped by cluster analysis (Ward's minimum variance method) according to the similarity of their fish assemblages and subsequentl y examined with a multiple discriminant function analysis to identify important environmental variables. Abiotic environmental factors were most influential in defining groups for samples dominated by early lar vae, whereas measures of seagrass complexity defined groups dominated by older larvae and juveniles. Juvenile-stage individuals showed clear habitat preference, with the more shallow Halodule wrightii being the habitat of choice, whereas early larvae of most species were widely d istributed over all habitats. As a result of the recent shift of domin ance from Halodule wrightii to Syringodium filiforme, overall reductio ns in the quality of nursery habitat for fishes in the lower Laguna Ma dre are projected.