The decline and recovery of a persistent Texas brown tide algal bloom in the Laguna Madre (Texas, USA)

The Laguna Madre has experienced a persistent bloom of Aureoumbra lagunensi s for over eight years. The persistence of this bloom may be due in part to the often hypersaline conditions in Laguna Madre (40-60 psu) that favor th e growth of A. lagunensis. Above-normal rainfall in the fall of 1997 reduce d the salinities in Baffin Bay from > 40 to < 20 psu. A. lagunensis cell de nsities dropped from > 10(6) cells ml(-1) in July 1997 to c. 200 cells ml(- 1) in January 1998. During this time of low brown tide density, phytoplankt on biomass generally remained high and the Laguna Madre experienced success ive blooms of diatoms (Rhizosolenia spp.) and cyanobacteria. Hypersaline co nditions returned in 1998 and brown tide densities increased to > 0.5 x 10( 6) cells ml-1 by summer. The extraordinary persistence of the brown tide an d the unusual sequence of intense blooms may be related in part to the redu ction of zooplankton populations. Microzooplankton populations declined fol lowing the above-normal rain in the fail of 1997; populations did not recov er until fall 1998. Copepod populations also declined sharply and remained low in Laguna Madre, but recovered by summer 1998 in Baffin Bay. Dilution e xperiments indicated that microzooplankton grazing and phytoplankton growth were usually balanced when measured during our cruises. The rapid recovery of the A. lagunensis bloom suggests that this alga may be a more resilient component of the Laguna Madre flora than previously suspected.