Discolored water and odors reported in April and May of 2009 for east Florida coastal waters (Flagler, Volusia and Brevard counties) are due to a large bloom of the non-toxic diatom Thalassiosira spp.
During the last week in April 2009, the Fish and Wildlife Research Institute (FWRI) began receiving reports of discolored water along Volusia County's coastline. Samples collected by FWRI's Fisheries Dependent Monitoring group indicated that a bloom of the diatom, Thalassiosira, was present. Since April 29, FWRI has received numerous reports of discolored, smelly water from Flagler, Volusia, and Brevard counties. Some of these reports indicated that beachgoers have experienced respiratory irritation-type symptoms.
FWRI staff familiar with Karenia brevis red tides observed conditions at Melbourne Beach. They described brown discolored water as "slick" and heavy with organic foam and reported a "throat irritation, not like (Karenia brevis) red tide." Samples collected from these areas (Figure 1) all contained Thalassiosira sp. at high cell concentrations.
The diatom genus Thalassiosira contains several species which form jelly-like colonies. Researchers have shown that natural ocean processes aid in the development of these types of diatom blooms. In addition, these processes also influence the transport of the blooms. (Gould and Wiesenburg 1990 and Hallegraeff and Jeffrey 1993). It is not uncommon for gelatinous colonies of Thalassiosira sp. to get caught up in the Gulf Stream and flow north along the Atlantic coastline (Fryxell et al. 1984). While biotoxins have not been associated with blooms of Thalassiosira, shellfish and finfish mortalities can occur due to gill clogging, starvation due to decreased food quality, and post bloom anoxia (low oxygen) events (Smayda 2006). The last major diatom blooms to impact Florida waters occurred in 2002 off the coast of southwest Florida between Naples and Key West and in 2003 off of Pasco and Hernando counties.
FWRI staff continues to monitor the east coast and are working to identify the particular species of Thalassiosira.
Fryxell, G. et al. 1984. Gelatinous colonies of the diatom Thalassiosira in Gulf Stream Warm Core Rings including T. fragilis, sp. nov. Br. Phycol. J. 19: 141-156.
Gould, R. and D. Wiesenburg. 1990. Single-species dominance in a subsurface phytoplankton concentration at a Mediterranean Sea front. Limnol. Oceanogr. 35: 211-220.
Hallegraeff, G. and S. Jeffrey. 1993. Annually recurrent diatom blooms in spring along the New South Wales Coast of Australia. Aust. J. Mar. Freshwater Res. 44: 325-334.
Smayda, T. 2006. Harmful algal bloom communities in Scottish coastal waters. Scotland Scottish Executive Report #2006/3. 224 pp.