Fish kills associated with a bloom of the marine microalgae Pyrodinium bahamense occurred in Old Tampa Bay in late July 2008.
On Sunday, July 27, 2008, the FWC's Fish and Wildlife Research Institute (FWRI) Fish Kill Hotline began receiving reports of a fish kill potentially associated with an ongoing bloom of the marine microalga Pyrodinium bahamense in Old Tampa Bay. FWRI staff began to investigate the fish kill event on Monday, July 28. Researchers observed discolored water and numerous dead fish in upper Tampa Bay, along the south side of the Courtney Campbell Parkway.
Figure 1. Dead marine life observed in Old Tampa Bay
On Wednesday, July 30, FWRI received a report of distressed fish in Allens Creek, East Tampa Bay. FWRI staff investigated two sites at this location and noted a few dead fish. Dissolved oxygen readings were very low (below five milligrams per liter [mg/L]) at both sites. FWRI staff collected moribund (dying) and freshly dead fish from Philippe Park, Safety Harbor on Thursday, July 31. Researchers processed the fish samples by performing necropsy (autopsy on an animal), histopathology (tissue studies), bacteriology, parasitology, and toxinology.
Figure 2. Documented sites of fish kills in Old Tampa Bay in July 2008
According to Fish Kill Hotline reports (either by phone or via the online form), dead fish were first observed on Friday, July 25. Although unconfirmed by FWRI researchers, reports indicated bay anchovies, flounder, mullet, carp, glass minnows, and black drum may also have been affected. On-site investigations confirmed dead fish and invertebrate species including catfish, menhaden, pinfish, triggerfish, puffer fish, spadefish, stingrays, blue crab, brittle stars, and small Florida crown conch.
Figure 3. Skates, rays, and blue crabs affected by the July 2008 bloom in Old Tampa Bay
A particularly intense bloom of the marine microalga P. bahamense had been present in Tampa Bay since the beginning of July 2008, resulting in discolored water throughout Old Tampa Bay. Pyrodinium bahamense is a toxic bioluminescent dinoflagellate (type of microalgae) that blooms annually in upper Tampa Bay but is not usually associated with any impacts on fish and wildlife in this area.
Figure 4. Light micrography picture of Pyrodinium bahamense
On July 30, FWRI staff surveyed western Tampa Bay from the Courtney Campbell Parkway to the Sunshine Skyway Bridge. Researchers found multiple microalgal blooms species including high concentrations of several diatoms (Rhizosolenia and Pseudo-nitzschia spp.) in addition to P. bahamense in Old Tampa Bay.
Concentrations of P. bahamense ranged from negligible to low at sites in the lower bay to moderate concentrations off Philippe Park and high concentrations located 1.5 nautical miles northeast of Snell Isle. Diatom concentrations ranged from low to moderate in the lower bay to high at 1.5 nautical miles northeast of Snell Island. No cells of Karenia brevis, the Florida red tide organism, were observed in any samples. Dissolved oxygen concentrations ranged from zero (anoxic) to low (approximately 5 mg/L). Fish become stressed when dissolved oxygen drops below 5 mg/L and begin dying if levels remain closer to zero.
Based on data and observations, the fish kills were likely the result of poor water quality from a combination of environmental factors that had occurred in upper Tampa Bay. The persistent bloom of P. bahamense and co-occurring diatom blooms depleted dissolved oxygen levels in the upper bay at night and during overcast days. Additional factors (poor flushing in shallow areas, high temperatures, and mixing of bottom sediments by summer storms) further contributed to the low dissolved oxygen levels. Low dissolved oxygen concentrations, possible mechanical damage to fish gills by diatoms, and clogging of the gills by P. bahamense, stressed local fish populations, ultimately resulting in widespread mortalities. Decaying and decomposing fish further degraded the existing poor water quality as well as the depleting dissolved oxygen in poorly flushed areas of the upper bay.
Pyrodinium in Tampa Bay is not currently considered to be a public health risk. However, this species is commonly present from the Indian River Lagoon on Florida's east coast, south to Florida Bay, and since the 1960s has been documented along the west coast of Florida (Steidinger pers. comm.; Steidinger et al. 1980; Phlips et al. 2006). In Florida, P. bahamense was not documented to be a harmful microalgal species until 2002 when saxitoxin puffer fish poisoning incidents became a public health issue in the Indian River Lagoon and resulted in a permanent ban on their harvest in that area (Landsberg et al. 2006). Pyrodinium bahamense produces varying concentrations of saxitoxin, a powerful neurotoxin that is transferred up the food chain and bioaccumulates in puffer fish. Saxitoxin can also accumulate in bivalves (a group of mollusks), posing a public health risk. The Florida Department of Agriculture and Consumer Services (FDACS) may temporarily close shellfish harvesting areas (www.floridaaquaculture.com) based on monitoring and testing results. Blooms of P. bahamense as well as animals that can accumulate saxitoxins are routinely monitored by the FWRI.
FWRI staff continues to sample the waters in Tampa Bay from late spring to early fall every year to document bloom concentrations and locations of P. bahamense. In collaboration with the FDACS, FWRI also continues to monitor shellfish harvesting areas at the mouth of Tampa Bay. The public is asked to report any fish kills observed to the FWRI Fish Kill Hotline by calling 1-800-636-0511 or submitting an online form. Those wishing to harvest shellfish should refer to the FDACS Web site (www.floridaaquaculture.com) for the status of approved shellfish harvesting areas.
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Landsberg, J.H., S. Hall, J.N. Johannessen, K.D. White, S.M. Conrad, J.P. Abbott, L.J. Flewelling, R.W. Richardson, R.W. Dickey, E.L.E. Jester, S.M. Etheridge, J.R. Deeds, F.M. Van Dolah, T.A. Leighfield, Y. Zou, C.G. Beaudry, R.A. Benner, P.L. Rogers, P.S. Scott, K. Kawabata, J.L. Wolny, and K.A. Steidinger. 2006. Saxitoxin puffer fish poisoning in the United States, with the first report of Pyrodinium bahamense as the putative toxin source. Environ. Health Perspect., 114: 1502-1507.
Phlips, E. J., S. Badylak, E. Bledsoe, and M. Cichra, M. 2006 . Factors affecting the distribution of Pyrodinium bahamense var. bahamense in coastal waters of Florida. Mar. Ecol. Prog. Ser. 322: 99-115.
Steidinger, K. A., L. S. Tester, and F. J. R. Taylor. 1980. A redescription of Pyrodinium bahamense var. compressa (Böhm) stat. nov. from Pacific red tides. Phycologia 19: 329-337