Occurrence of a dinoflagellate bloom associated with an influx of low salinity water at Galveston, Texas, and coincident mortalities of demersal fish and benthic invertebrates.

Low salinity water and an associated dinoflagellate bloom appeared suddenly off Galveston, Texas, in early June, 1984. An aerial survey showed the bloom extended east at least as far as Cameron, Louisiana. High discharge from the Mississippi-Atchafalaya Rivers between March and late May, and a strong, wind- driven downcoast current preceded the appearance of low salinity water and its associated bloom. Within a week of the first appearance of the bloom, demersal fish, numerically dominated by Atlantic threadfin (Polydactylus octonemus) began dying early in the morning and washing ashore. Calm weather conditions occurred during the latter part of the kill and anaerobic silt accumulated on the bottom offshore from Galveston. We believe the kill was caused by hypoxia and/or hydrogen sulfide production resulting from nocturnal metabolism of the bloom and anaerobic decay of dead dinoflagellate cells. A second kill in mid-July, numerically dominated by Atlantic croaker (Micropogonias undulatus), was probably the bycatch or cull of shrimping vessels working offshore.