Red Tide is caused by a large growth of algae. During the growth period of algae, each cell can reproduce around one million times in just two or three weeks. Algae are a microscopic plant, and like all plants, need sunlight to grow. Therefore, the algae cells can be seen in shallow sea water moving to the surface in order to get as much sunlight as possible. This happens during the reproduction time, or “bloom” time, and often turns the sea water red or brown. Obviously this is where the name “Red Tide” originated.
This is a large concern for pearl farmers, as red tide is potentially harmful to their oysters/mollusks. The main food source for oysters is algae. This excess algae is potentially poisoness for oysters to eat during red tide. Therefore, red tide is always on the mind of a pearl farmer, as this phenomenon has been known to wipe out entire crops of oysters.
There are a few ways that a red tide can end up killing marine animals, such as oysters/mollusks. One of the ways is that the algae take most of the oxygen out of the water, leaving the sea animals oxygen depleted. At times during a red tide, the algae may begin to die because of a lack of nutrients. These dying and dead cells attract a lot of bacteria, which in turn is hazardous to the sea life in the area. The result is the bacteria using up all the oxygen in the waters. One such occurrence happened in Hong Kong in 1988, where a red tide bloom collapsed, resulting in the death of 35 tones of fish.
Toxins are also sometimes produced by the red tide algae, which is also hazardous to the oysters. Different algae produces different toxins, and when there are millions and millions of algae cells in one spot, such as in the case of a red tide, these toxins can become overwhelming for the oysters.
As you can see, there are countless ways for oysters/mollusks to die when there is a red tide present. Red Tides have been responsible for more than one harvest being destroyed. Therefore, the Pearl Farmers are now always watching for the dreaded red tide, as such a thing can make for a very bad year in pearl farming, this in turn affects the pearl jewelry industry.