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Blooms of red drift macroalgae have emerged along southwest Florida’s coastline, including Sarasota Bay, in recent years.  Most residents are more familiar with toxic algal blooms, or “red tides”, which can cause, among other things, massive fish kills, shellfish contamination, and human respiratory and other health problems. 

Unlike red tides, macroalgal blooms lack direct toxicity but have a broader range of ecological impacts. Macroalgal blooms can result in the displacement of native species, habitat destruction, oxygen depletion, alteration of trophic structure and biogeochemical cycles, and seagrass die-off .  Because the causes and effects of macroalgal blooms are similar in many ways to those associated with toxic phytoplankton species, the scientific community employs the term “harmful algal bloom” (HAB) to describe this diverse array of bloom phenomena.  A study is being undertaken by Dr. Brian Lapointe of Reef Research & Design, to better understand the taxonomic composition and ecology of macroalgal HABs impacting Sarasota Bay.

Red Tides
Red tides, a type of harmful algal bloom (HAB), are a natural phenomenon in coastal
ecosystems, but human activities are thought to contribute to their increased frequency.  Public interest in the social and economic impacts of extended red tide blooms, and questions about the possible role of elevated nutrient supplies from man-made sources, have added a new dimension to the study of Karenia brevis, the organism that causes local red tides, in our area.

The Sarasota Bay Estuary Program is doing its part to contribute to this knowledge by supporting research by Mote Marine Laboratory that addresses the nutrient dynamics during the progress of a bloom of Karenia brevis in the lagoonal environment of Sarasota Bay.
The ability of Karenia brevis to utilize urea as a nitrogen source, and the recent incorporation of this compound in fertilizers, make knowledge of this urea in bay waters of extreme interest.  This study is helping to understand phytoplankton nutrient dynamics by quantifying the entire suite of nitrogen compounds available to K. brevis.  Additional analyses include silica, a necessary nutrient for diatoms, and photosynthetic pigments to follow the progression of phytoplankton communities through time.