INCORPORATION OF BROWN TIDE INTO AN ESTUARINE FOOD-WEB

In Laguna Madre, Texas, USA, a monospecific brown tide bloom began in January 1990 and was still persisting at the time of this writing. Imm ediately following the start of the bloom, abundance, biomass and dive rsity of benthos declined, and have remained low for 6 yr. One explana tion for the decline is that the brown tide organism is a poor food so urce. To determine whether the brown tide was incorporated into the es tuarine food web, benthic invertebrates and fish were studied 14 mo af ter the bloom onset using stable carbon isotope ratios. Fish and benth os were collected from 2 areas, a seagrass habitat in Laguna Madre, an d a muddy bottom habitat in the adjacent Alazan Bay. The muddy bottom fauna had a strong brown tide signature, indicating the incorporation of brown tide or brown tide detritus into the food web. The higher-bio mass seagrass-fauna had heavier isotope values, reflecting incorporati on of seagrass carbon in addition to brown tide. The top predators, Sc iaenops ocellatus and Pogonias cromis, have different niches, but were able to switch food sources and thrive during the brown tide bloom. B rown tide appears to be able to support an estuarine food web, but at the expense of benthic diversity. The loss of benthic diversity could be due to allelopathy or the inability of some species to assimilate b rown tide. Habitats with extensive seagrass beds maintain higher produ ctivity and diversity than muddy habitats. However, seagrass habitats are endangered because brown tide reduces light levels, inhibits seagr ass growth, and is causing seagrass decline.