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A close look at dinoflagellates around the islands

By SANIBEL-CAPTIVA CONSERVATION FOUNDATION - | Sep 16, 2020

Ceratium. SCCF

There is an amazing variety of life within a single droplet of seawater from the Gulf of Mexico. Phytoplankton is a word with Greek roots phyto (plant) and plankton (wandering, drifting). There are about 5,000 known phytoplankton species described from microscopic examination of water in the world’s oceans.

The most common types of phytoplankton include diatoms, cyanobacteria and dinoflagellates. The word dinoflagellate has roots in both Greek dino (whirling) and Latin flagellum (whip). Dinoflagellates are mostly in marine environments and are uncommon in freshwater. Many dinoflagellates are known to be photosynthetic like plants, but can also be mixotrophic, which means they can supplement photosynthesis by ingesting prey, such as small flagellates and bacteria.

Many Florida residents have heard about dinoflagellates because of the toxic species that form red tide, Karenia brevis. Karenia brevis blooms typically form in the Gulf in offshore areas when a moderate amount of upwelling of nutrient-rich, deep ocean water is transported to the photic zone. This combined with warm Gulf temperatures in September can cause red tide blooms.

The blooms are then pushed to the coast by ocean currents and the blooms tend to concentrate on beaches when the prevailing winds push onshore. Karenia brevis blooms in Southwest Florida have occurred 57 of the last 66 years, according to the FWC Fish and Wildlife Research Institute’s microscopic cell count database. While it occurs nearly every year, there are many years when people do not experience the coughing and irritation typical of a strong red tide near the beach. It is because the blooms sometimes are localized to one barrier island, or they can be relatively mild.

The Sanibel-Captiva Conservation Foundation’s Marine Laboratory has been monitoring red tide blooms and other dinoflagellates since 2002. There are other dinoflagellate species that we’ve identified under the microscope and recently have begun to catalog them using a imaging flow cytometer.

Some, but not all, dinoflagellates are toxic. Given the upcoming fall red tide season, we thought we would share a few images to show some local dinoflagellates.