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 Florida Fish and Wildlife
Conservation Commission'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
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
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.
View images and learn more about HAB species in our Flickr
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:
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