dinoflagellate blooms

The Red Tide

The appearance of a red is never a good thing. People dread these tides because not only does it look like some horrific biblical omen, it smells terrible and causes schools of fish to choke and die. But what is a red tide and what causes them?

A red tide is an algal bloom. It consists of a type of algae called dinoflagellates.

The bloom occurs when conditions are optimal for the algae. This means the temperatures are perfect, salinity is at good levels, and there is an excess of nutrients. These extra nutrients are usually from agricultural runoff (fertilizers washing into the ocean). The algae is in such excess that it chokes fishes gills causing mass deaths. Shellfish like clams and mussels are filter feeders and will become contaminated by the algae making them toxic to eat. There is no way to control an algal bloom, we just have to wait for the conditions that caused it to return to normal levels (usually this means all of the excess nutrients getting used up)and the algae to die.

Because of the mortality and contamination the bloom causes it has very bad effects on local economies. Some blooms can also give off gases that can cause nausea in the people near it, also making it unsafe to swim in which in turn effects the tourism in these areas. Work is being done to reaserch these blooms to forecast when and where they will occur (like the weather) so that people can prepare for the effects it has.

Now I want to be very clear on one thing: NOT ALL ALGAL BLOOMS ARE HARMFUL. Often they are helpful: they provide extra food for larger organisms that we fish for and eat. The difference between a harmful algal bloom and a non-harmful one is dependent on the type of algae that is blooming.