The occurrence of hypoxic bottom water off the upper Texas coast and its effects on the benthic biota.

Hypoxic bottom water occurred off the upper Texas coast in May-July 1979 after heavy spring runoff and a diatom bloom. Benthic assemblages at two study sites off Freeport, Texas decreased from spring densities of 3000-4000 individuals/m super (2) to 300-600 individuals/m super (2) by late July. Species diversity also decreased and perturbations occurred in the Shannon-Weiner diversity indices. Of the dominant taxa, polychaetes were least affected by hypoxia and amphipods and echinoderms the most affected. Storm-caused waves in late July initiated the breakup of hypoxic conditions these conditons had completely abated by late September. A short-lived irrupton occurred immediately afterward as depopulated bottoms were reinvaded. Diversity and abundances appeared to be returning to more normal conditions by early 1980.