Seasonal Variability of the Texas ‘Brown Tide’ (Aureoumbra lagunensis) in Relation to Environmental Parameters

Abstract

The spatial and temporal variation of salinity, specific conductivity, temprature, turbidity, pH, dissolved oxygen, redox potential, soluble reactive phosphate (SRP), ammonium, nitrate, phytoplankton and mesozooplankton within Baffin Bay, Texas were monitored monthly from April 1995–July 1996 to understand better the seasonal variability of the Texas ‘brown tide’, Aureoumbra lagunensis .High A. lagunensis densities (0·05–5·97×106cells ml−1) were observed in the summer months, whereas low densities (<0·01–3·6×106cells ml−1) occurred during the winter. Statistical analysis of results gave no significant relationship between A. lagunensis densities and any physical parameters during most sampling events. Most sampling events exhibited high salinities (S>40) and A. lagunensis densities were greatest between 25 and 30°C. This suggests that A. lagunensis is well adapted to the warm hypersaline environment. Surface water SRP and ammonium concentrations were inversely related to A. lagunensis densities at all sample stations (P< 0·001 and P< 0·05, respectively). Aureoumbra lagunensis densities showed no relation with other chemical parameters. Acartia tonsa , Oithona brevicornis and Oithona sp. were the predominant mesozooplankton during the study. Although A. tonsa occurred in higher concentrations than other mesozooplankton, A. lagunensis and A. tonsa densities showed no significant relationship. Densities ofOithona sp. were inversely related to A. lagunensis cell densities (P< 0·05) signifying possible grazing pressures. These results suggest that additional parameters other than those investigated are contributing to the seasonal variability and the persistence of Texas ‘brown tide.’