Seafood Poisoning Syndromes Caused by Toxic Algae in Florida

A synopsis of human seafood poisoning syndromes associated with toxic algae in Florida's coastal waters.

Most marine phytoplankton are beneficial – they make up the base of the marine food web and produce half of the world’s oxygen. However, some harmful algal bloom (HAB) species produce toxins, which can cause human illnesses and, in extreme cases, fatalities. Fish and shellfish that feed on toxic phytoplankton can become contaminated with toxins, either directly by filter-feeding toxic phytoplankton, or indirectly by eating filter-feeding prey. In turn, humans can be exposed to marine algal toxins by eating contaminated seafood. 

The table below lists the major toxin producing phytoplankton found in estuarine and marine waters of Florida and the poisoning syndromes associated with these species.  Neurotoxic Shellfish Poisoning (NSP) and Diarrheic Shellfish Poisoning (DSP) are not known to be lethal to humans; however, Paralytic Shellfish Poisoning (PSP), Ciguatera Fish Poisoning (CFP), and Amnesic Shellfish Poisoning (ASP) can be deadly. No cases of ASP or DSP have been documented in Florida.

In partnership with the Florida Department of Agriculture and Consumer Services (FDACS), the Florida Fish and Wildlife Conservation Commission (FWC) monitors shellfish harvesting areas to detect toxic phytoplankton and prevent the occurrence of poisoning syndromes. Since this partnership between FWC and FDACS was initiated during the 1970s, state officials have prevented occurrences of poisoning due to K. brevis, P. bahamense, and Pseudo-nitzschia spp. from lawfully harvested shellfish. Before harvesting shellfish in Florida waters, check the status of shellfish harvesting areas by visiting the department’s Division of AquacultureExternal Website website. For more information or to report health issues related to exposure to marine algal toxins, please call the Florida Poison Information Center at (800) 222-1222. Additional information on shellfish poisoningsExternal Website and ciguateraExternal Website can be found on the Florida Department of HealthExternal Website website.

Download these factsheets to learn more about different algae species.
Karenia brevis factsheet (Adobe PDF 490 KB)
Pseudo-nitzschia factsheet (Adobe PDF 563 KB)
Pyrodinium bahamense factsheet (Adobe PDF 496 KB)


Algae Species (and Associated Toxins) Associated Seafood  Syndrome Symptoms (not comprehensive) Syndrome Documented in FL?
 Karenia brevis
Karenia brevis, (brevetoxins)
Clams, oysters, mussels, whelk Neurotoxic
Shellfish Poisoning
  • numbness/tingling
    of mouth and extremities
  • vertigo
  • slurred speech
  • muscle weakness
    nausea, vomiting, diarrhea
  • reversal of hot/cold sensations
  • pupil dilation
Yes. Officials have documented fewer than 100 non-fatal cases of NSP in the southeastern U.S. These cases were the result of recreationally harvested shellfish from unapproved waters.
 Pyordinium bahamense

Pyrodinium bahamense,
Alexandrium species,
Gymnodinium catenatum

bivalve shellfish and puffer fish

Shellfish Poisoning (PSP) and Saxitoxin Pufferfish Poisoning (SPFP)

  • numbness/tingling of the mouth and/or lips
  • nausea, vomiting
  • respiratory distress
  • drowsiness
  • muscle weakness
  • incoherent speech
Yes. Seven documented cases of SPFP between 1974 and 2004 originating from the Indian River Lagoon have been documented. There have been no cases of PSP from contaminated shellfish
 Gambierdiscus species
Gambierdiscus species (ciguatoxins1)
large reef fish species such as barracuda, grouper, snapper, jack, mackerel, and triggerfish Ciguatera
  • nausea, vomiting, diarrhea
  • numbness/tingling
    of the mouth and other extremities
  • reversal of hot/cold sensations
  • chills, headache
  • abdominal pain
  • tearing
  • giddiness
Yes. CFP has been documented from fish originating from the Florida Keys, the Dry Tortugas, and SE Florida. 
 Pseudo-nitzschia species

Pseudo-nitzschia species (domoic acid)

clams, scallops, oysters, mussels Amnesic
Shellfish Poisoning
  • short-term memory loss
  • dizziness, disorientation
  • respiratory distress
 Dinophysis species
Dinophysis species, Prorocentrum2 species (okadaic acid)
clams, oysters, mussels, whelk Diarrhetic
Shellfish Poisoning (DSP)
  • diarrhea, nausea, vomiting
  • abdominal cramps
  • chills

1Gambierdiscus spp. produce ciguatoxin precursors, which are transformed to ciguatoxins in fish.

2Some Prorocentrum species produce okadaic acid, but only Dinophysis spp. have been associated with DSP.


FWC Facts:
Otoliths, commonly known as "ear stones," are hard, bone-like structures located directly behind the brain of bony fishes. These structures aid fish in balance and hearing.

Learn More at AskFWC