The Decline and Recovery of a Persistent Texas Brown Tide Algal Bloom in the Laguna Madre (Texas, USA)

Abstract

The Laguna Madre has experienced a persistent bloom ofAureoumbra lagunensis 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 the growth ofA. lagunensis. Above-normal rainfall in the fall of 1997 reduced the salinities in Baffin Bay from >40 to 106 cells ml−1 in July 1997 to c. 200 cells ml−1 in January 1998. During this time of low brown tide density, phytoplankton biomass generally remained high and the Laguna Madre experienced successive blooms of diatoms (Rhizosolenia spp.) and cyanobacteria. Hypersaline conditions returned in 1998 and brown tide densities increased to>0.5 × 106 cells ml−1 by summer. The extraordinary persistence of the brown tide and the unusual sequence of intense blooms may be related in part to the reduction of zooplankton populations. Microzooplankton populations declined following the above-normal rain in the fall of 1997; populations did not recover until fall 1998. Copepod populations also declined sharply and remained low in Laguna Madre, but recovered by summer 1998 in Baffin Bay. Dilution experiments indicated that microzooplankton grazing and phytoplankton growth were usually balanced when measured during our cruises. The rapid recovery of theA. lagunensis bloom suggests that this alga may be a more resilient component of the Laguna Madre flora than previously suspected.