Periodic testing of water samples and clams provides an early warning of bloom occurrences and shellfish toxicity and minimizes the risk of human exposure to saxitoxins.
From January 2002 to May 2004, 28 cases of human illness from saxitoxin puffer fish poisoning (SPFP) in Florida, New Jersey, Virginia, and New York were linked to the consumption of puffer fish caught from Florida's Indian River Lagoon. Tests found the toxin in three species of puffer fish--southern (Sphoeroides nephelus), checkered (S. testudineus), and bandtail (S. spengleri)--and researchers for the FWC identified the dinoflagellate alga Pyrodinium bahamense (Figure 1) as the source of saxitoxin for the first time in the United States.
Figure 1. Pyrodinium bahamense (light microscope image)
Globally, similar food poisoning incidents, known as paralytic shellfish poisoning (PSP), have resulted from consumption of marine shellfish that have fed on saxitoxin-producing microalgae. Both PSP and SPFP can be fatal.
The FWC and its state and federal agency partners assessed the significant risk of SPFP from saxitoxins in the Indian River Lagoon and implemented management plans accordingly. In 2004, the FWC imposed a permanent ban on the harvest of puffer fish from the area. The extreme toxicity of the puffer fish fillets from the 2002-04 SPFP events and continued high concentrations in later samples demonstrate the danger that puffer fish pose to the public and support the FWC's action.
Also in 2002, saxitoxins were confirmed in shellfish from the Indian River Lagoon. As a result, the Florida Department of Agriculture and Consumer Services (FDACS), in collaboration with the FWC, established the Biotoxin Contingency Program to monitor shellfish for saxitoxin. Since April 2003, Agriculture Department staff have collected samples each month from east coast shellfish harvesting areas in Brevard and Indian River counties (see Figure 2 for collection sites, indicated by red dots). The FWC's Fish and Wildlife Research Institute (FWRI) analyzes the water and clam meat for P. bahamense cell counts and saxitoxin, respectively. If saxitoxin levels in shellfish increase (usually during the warmer months), sample collection is increased to weekly and the geographic collection sites are expanded to the north and south.
These programs provide an early warning of bloom occurrences and shellfish toxicity and minimize the risk of human exposure to saxitoxins. Since 2003, the Agriculture Department has ordered 30 shellfish harvesting area closures when saxitoxin levels equaled or exceeded the international standard tolerance limit, 80 micrograms per 100 grams. As of mid-2011, there had been no reports of PSP illnesses in Florida.
Additional Studies of Algal Blooms
Beginning in 2005, the Indian River Lagoon National Estuary Program funded the FWRI, together with its project partners--the University of Florida, Innovative Health Applications, and Ocean Research & Conservation Association--and a collaborator, the St. Johns River Water Management District, to monitor harmful algal blooms in the Indian River Lagoon. The goal of this study was to monitor the variable distribution, frequency of occurrence, and composition of algal blooms, especially P. bahamense.
The Indian River Lagoon spans more than 220 km (137 miles) of the east coast of Florida and is the site of numerous commercial and recreational clam and oyster beds. While harmful algal blooms have been observed throughout the lagoon, the northern portion appears to be particularly prone to significant blooms of P. bahamense. Project partners actively monitored six stations biweekly in the northern lagoon (see Figure 2 for collections, indicated by green dots) and sent water samples to FWRI and the University of Florida to analyze for algal species. Agency partners received data for use in management decisions pertaining to the puffer fish and shellfish industries.
Work from 2006 to 2009 indicated that the frequency of harmful algal blooms, including blooms of P. bahamense, in the Indian River Lagoon related in part to nutrient inputs from rainfall and to water residence time, or the amount of time that water remains in the lagoon. Pyrodinium bahamense has a resting stage, called a cyst, that resides in the sediments. Beginning in 2009, FWRI researchers began monitoring the sediments for the geographic expansion of P. bahamense within the Indian River Lagoon, recording the number and distribution of cysts. FWC and its partners continued to collect samples biweekly and analyze data to determine the role that environmental factors play in P. bahamense blooms until September 2011 when funding for the project ended.
FDACS continues to send water and shellfish samples to FWRI for analysis as part of the biotixin contingency plan to monitor shellfish for saxitoxin. FWRI continues to cooperate with other agencies to assist with response in the event of an algal bloom in the Indian River Lagoon.
Figure 2. Map of collection sites for Pyrodinium bahamense and saxitoxin monitoring
Pufferfish Consumption Confirmed as Cause of Saxitoxin Poisoning Cases
Saxitoxin Puffer Fish Poisoning in the United States
Concentrations of Saxitoxin and Tetrodotoxin in Three Species of Puffers
Puffer Fish Prohibition
Saxitoxin Monitoring in Three Species of Florida Puffer Fish
Harmful Algae Species in the Indian River Lagoon