Gazing over the waters of Monterey Bay this week, you would be forgiven if you thought you were in the tropics. A bloom of tiny phytoplankton called coccolithophores has recently appeared in Monterey Bay. These organisms can only be seen under a specialized microscope and are unique in that they have plates made of calcite (a stable form of calcium carbonate) called coccoliths. It’s the calcite coccoliths that reflect sunlight and cause the brilliant turquoise color.
Red Tide, Blue Tide
Algal blooms occur when environmental conditions allow for explosive growth of phytoplankton. Very dense blooms can change the color of ocean water and typically lead to red, brown, or orange blooms. In California, strong winds and an influx of cold, nutrient-dense waters along the coast often lead to spring phytoplankton blooms of species that are colorless. In fall, the warmer, stratified conditions of the water tends to favor phytoptoplankton that cause the red tides.
Phytoplankton blooms can produce toxins, which may be harmful to humans, fish, marine mammals and seabirds—these blooms are called Harmful Algal Blooms, or HABs. The words Red Tide and Harmful Algal Bloom mean different things—a red tide refers just to an algal bloom that discolors the water. Many red tides are harmless, while others may contain toxins or be detrimental in other ways. Discoloration of the water alone is not an accurate way to determine whether harmful conditions are present. HABs can occur during red tides, or they can be colorless and difficult to detect.
This week’s blue tide of coccolithophores is harmless and not a HAB (phew!). The bloom is definitely unusual and may be due to the unseasonably warm water since coccolithophores are most commonly found in the subtropics.
Chalk it up to the Coccolithophores
Coccoliths deposited in the ocean between 65 to 144 million years ago created a large chalk deposit forming the main component of the White Cliffs of Dover in southern England. Coccoliths are also a major component of the calcareous oozes that cover about 35% of today’s ocean bottom.
Many thanks to Anna McGaraghan, Scientist and Education Coordinator at the Raphael Kudela Lab, University of California Santa Cruz, for much of the information in this post and for hooking us up with the photo by Laura Beach. Thank you Laura!