Current Status and Historical Trends of Brown Tide and Red Tide ...

It is also possible to enumerate the concentration of brown tide cellsmicroscopically. The cells of the brown tide alga are small (4-5 µm in diameter) andvery abundant in areas obviously affected by the brown tide. However, cells of thebrown tide alga are morphologically indistinct, and there are no external characteristicsthat can be used for positive microscopic identification.1. Cell countsIn the spring of 1990 the first "bloom" level abundances of the brown tide algawere observed in Laguna Madre. Prior to this time, the brown tide alga had not beenobserved in this area. Due to its indistinct appearance, this does not mean it was notpresent in low numbers and simply not recognized in phytoplankton samples. As figure17 shows, brown tide levels quickly increased from their initial observed levels of ca.500,000 cells/ml in June 1990 to over 2 x 10 6 cells/ml in July 1990. Populationabundances decreased from this summer high during the winter months but remainedat bloom levels (ca. 1 x10 6 cells/ml). Cell counts once again increased during thesummer months. Unlike A. anophagefferens, the Texas brown tide is able to maintainhigh abundance levels through the winter months. Thus, instead of a bloom which lastsfor several months, Texas has experienced a bloom of brown tide alga which has lastedover 5 years and still has an abundance over 500,000 cells/ml (Figure 18).Brown Tide Counts for Laguna Madre400000035000003000000Cells/ml250000020000001500000STA ASTA BSTA CSTA D10000005000000Oct-89 Jan-90 May-90 Aug-90 Nov-90 Mar-91 Jun-91 Sep-91DateFigure 17. Brown tide cell counts for 4 locations in upper Laguna Madre and Baffin Bayfrom December 1990 through August 1991. Buskey and Stockwell (1993) andunpublished data of Dr. E.J. Buskey, The University of Texas Marine Science Institute.21