Dinoflagellates and Red Tides

Compiled by
Bernadette Pate Holt

WSFC 611
Fall 1997

Red Tide:

The very mention of red tides brings to mind the fear of dead fish and toxic seafood. But just what is red tide? Red tide is a naturally-occurring, higher than normal concentration of the microscopic algae Gymnodinium breve. The massive multiplication (or 'bloom') of this tiny, single-celled algae is usually found in warm saltwater. When red tide algae reproduce in dense concentrations they are visible at discolored patches of ocean water, often red in color.

Red tides are normally isolated patches. They are often concentrated around wind or tide protected areas like man-made jetties. In Texas the red tides have occurred from August to February. They typically begin in the Gulf of Mexico where currents and winds then transport the blooms toward shore.

While the cause of red tide has not been established, scientist believe that it is a natural phenomena that is not caused by mankind. When temperature, salinity, and nutrients reach certain levels, a massive increase in Gymnodinium breve algae occurs. Some experts believe high temperatures combined with a lack of wind and rainfall are usually at the root of red tide blooms.

Dinoflagellates:

The microscopic organisms that are the culprit of red tide are called dinoflagellates. They are usually unicellular, flagellated, and often photosynthetic. They have a characteristic transverse flagellum that encircles the body in a groove referred to as the cingulum. They also possess a longitudinal flagellum perpendicular to the transverse flagellum. This gives them a distinctive spiral to their swimming motion. The cell wall of many dinoflagellates is divided into plates of cellulose. These plates form a distinctive geometry known as tabulation, which is the main means for classification.

Dinoflagellates form a major part of primary planktonic production in oceans. Most dinoflagellates have a somewhat complex life cycle involving several steps, both sexual and asexual, motile and non-motile. Some of the species for cysts comprised of sporopollenin (an organic polymer), and can be found as fossils.

Even though they are important producers and a key component to the food chain, dinoflagellates are also known for producing deadly toxins, especially when they are present in large numbers. They can not only kill a large range of marine species, but can also impart fatal toxins into several species, especially shellfish. Filter-feeding shellfish such as oysters, clams and mussels consume gynnodinium breve and concentrate the toxins in various organs. Usually deadly to finfish, shellfish are relatively unaffected. These shellfish may then be eaten by humans, who are then affected by the stored toxins. These toxins, may not prove fatal, yet can produce several neurological difficulties.

Effects on us:

Humans can also be affected by these toxins when they are incorporated in to the marine aerosol. Irritation of the eyes, nose, throat, tingling lips and tongue are commonly symptoms that occur in humans during red tide. Waves and boat propellers in high concentrations of red tides disperse the toxin particles into the air. The particles are then carried to shoreline by coastal winds. Symptoms usually disappear within 24 hours once the exposure is halted

.Severe economic and public health effects of red tides prompt consideration of an attempt to controlling the blooms. Such control is only feasible within confined areas, such as fish hatcheries and aquaculture ponds, and research is underway to assess various control methods. Until we learn how to control these blooms, it is advisable that individuals with respiratory difficulties avoid areas where red tide is present. As to those of us who crave our seafood - caution is advised.

 

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