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Types of Plankton in the Florida Keys

The Florida Keys archipelago contains North America's largest and only living coral barrier reef. This complex ecosystem supports diverse plants and animals, including drifting microorganisms called plankton, which sit at the base of the coral reef food web. The term "phytoplankton" refers to unicellular algae and other photosynthesizing organisms, while "zooplankton" indicates tiny animals that feed on phytoplankton.

Marine Sanctuary
- Adjacent to the 126-mile chain of islands forming the Florida Keys, the barrier reef ranks as the third-largest in the world, bested only by Australia's Great Barrier Reef and the barrier reef of Belize. Threats to the ecological health of this nationally significant biological resource prompted the U.S. Congress in 1990 to designate 2,800 miles of coastal and oceanic waters as the Florida Keys National Marine Sanctuary. One of only 13 underwater parks with the National Marine Sanctuary designation, it's managed by the National Oceanic &Atmospheric Administration's Ocean Service.
Zooplankton
- Ichythyoplankton are the eggs or larvae of fish.
  
  Researchers often categorize zooplankton as either holoplankton, animals that spend their entire lives as plankton, or meroplankton, which spend just a portion of their life cycle as plankton. In a 2009 study published in the "Journal of Plankton Research," Karla Heidelberg and her team found that copeopods, a holoplanktonic crustacean, dominate the zooplankton communities at the Keys' Conch Reef. Larvaceans and chaetognaths also appear in abundance.
  
  Zooplankton that vertically migrate in the water column during a single day -- known as demersal plankton -- include species of isopods, ostracods, polychaetes and decapods. Eggs and larvae of fish, known as ichythyoplankton, also are widespread in surface waters.
Phytoplankton
- Seasonal fluctuations in sunlight and nutrients influence phytoplankton abundance. In the Florida Keys, species of dinoflagellates, diatoms and blue-green algae dominate the phytoplankton community. Dinoflagellates are small, unicellular organisms living mostly in surface waters, with a potentially toxic species -- Pyrodinium bahamense -- found in the Keys. This bioluminescent species, capable of producing its own light, also causes the shellfish poisoning known as red tide.
  
  One type of unicellular algae, diatoms, exhibit a thin, glass-like shell composed of silica. Mostly unicellular blue-green algae, or cyanobacteria, can achieve photosynthesis. Cyanobacteria also rank as the oldest known fossil, at more than 3.5 million years old. Species of cryptophytes, green algae and Euglenoids, also appear in the Keys, but in fewer numbers.
Harmful Algal Blooms
- Dinoflagellates cause red tide -- a harmful algal bloom.
  
  Harmful algal blooms -- sudden explosions in the populations of specific types of phytoplankton -- have been associated with poisoning shellfish, smothering corals and discoloring water and beaches. In the Florida Keys, a large die-off of sea grass in the 1990s led to an increase in nutrients associated with decomposition, which caused a surge in a cyanobacteria species called S. elongatus. In the Keys' Western Bay, diatoms bloomed throughout the 1990s in response to freshwater discharge.

Nature