Seasonal variability of the Texas 'brown tide' (Aureoumbra lagunensis) in relation to environmental parameters

The spatial and temporal variation of salinity, specific conductivity, temp rature, turbidity, pH, dissolved oxygen, redox potential, soluble reactive phosphate (SRP), ammonium, nitrate, phytoplankton and mesozooplankton withi n Baffin Bay, Texas were monitored monthly from April 1995-July 1996 to und erstand better the seasonal variability of the Texas 'brown tide', Aureoumb ra lagunensis. High A. lagunensis densities (0.05-5.97 x 10(6) cells ml(-1)) were observed in the summer months, whereas low densities (<0.01-3.6 x 10(6) cells ml(-1 )) occurred during the winter. Statistical analysis of results gave no sign ificant relationship between A. lagunensis densities and any physical param eters during most sampling events. Most sampling events exhibited high sali nities (S>40) and A. lagunensis densities were greatest between 25 and 30 d egrees C. This suggests that A. lagunensis is well adapted to the warm hype rsaline environment. Surface water SRP and ammonium concentrations were inv ersely related to A. lagunensis densities at: all sample stations (P<0.001 and P<0.05, respectively). Aureoumbra lagunensis densities showed no relati on with other chemical parameters. Acartia tonsa, Oithona brevicornis and O ithona sp. were the predominant mesozooplankton during the study. Although A. tonsa occurred in higher concentrations than other mesozooplankton, A. l agunensis and A, tonsa densities showed no significant relationship. Densit ies of Oithona sp, were inversely related to A. lagunensis cell densities ( P<0.05) signifying possible grazing pressures. These results suggest that a dditional parameters other than those investigated are contributing to the seasonal variability and the persistence of Texas 'brown tide.' (C) 1999 Ac ademic Press.