Based on results of analyses conducted since mid-January 2006,
FWC/FWRI researchers have attributed the aquatic animal mortalities
in Choctawhatchee Bay to post-bloom brevetoxin exposure.
Since mid-January 2006, the FWC's Fish and Wildlife Research
Institute (FWC/FWRI) has been investigating an aquatic animal
mortality event in Choctawhatchee Bay. The event has been primarily
affecting fish in the Garnier Bayou area (NW Choctawhatchee Bay).
Dead and dying species reported to the FWRI Fish Kill Hotline
(1-800-636-0511) included Gulf sturgeon (Acipenser oxyrinchus
desotoi), bay anchovies (Anchoa
mitchilli), skipjack shad (Alosa chrysochloris),
and juvenile spot (Leiostomus xanthurus). Reports of dead
invertebrates included lion's mane jellyfish (Cyanea
capillata)and blue crabs (Callinectes sapidus).
FWRI/FWC staff and volunteers collected samples of the reported
species as well as live bivalves for health evaluation. In March
2006, FWC/FWRI staff sampled four dead and one live longnose gar
(Lepisosteus osseus), one live mullet (Mugil
sp.), and numerous dying juvenile spot fish from further east in
Choctaw Beach and Basin Bayou (northern shore of the central Bay).
Samples collected on the southern shore of the Bay included
bivalves and water from Sandestin and Alligator Point. Incidental
bird mortalities were reported and tissue samples were collected
and archived for future analysis. Concurrently, water and
sediments were sampled throughout the Bay to analyze water quality,
potential presence of harmful algal bloom species and potential
presence of toxins. Since the fall of 2005, the National
Oceanic and Atmospheric Administration (NOAA) with assistance from
FWC/FWRI has been investigating a bottlenose dolphin (Tursiops
truncatus) mortality event in the Florida Panhandle.
During the fall of 2005, a red tide bloom was present in the
Florida Panhandle following an extensive red tide event in west
central Florida, which persisted throughout 2005. In late August
2005, transport of the west central Florida bloom initiated the
Florida Panhandle bloom. High red tide (Karenia
brevis) cell concentrations were detected just north of
Cedar Key in late August and in the Apalachicola Bay area one week
later. The bloom spread rapidly west. By September 12, red tide
cell populations were detected in Panama City. By October 3, the
bloom spread to waters off Escambia County on the Florida-Alabama
border. Bloom concentrations remained elevated in the Panama City
region until December 10. Significant red tide cell concentrations
were detected in mid-December in the Cedar Key region. Weekly
monitoring has not detected any red tide in the northwest Florida
region since the end of December 2005.
Through mid-April, no red tide was observed and only background
levels of brevetoxin (toxin produced by K. brevis) were
present in water samples from the area. Dying fish from the
affected areas behaved as if they had been exposed to neurotoxic
brevetoxins. High concentrations of brevetoxins found in the
internal organs of fish (sturgeon, gar, and multiple samples of
juvenile fish) indicate toxin exposure was post-bloom. Most
significantly, brevetoxin was detected in several food web
components. Toxin levels were higher than would be expected since
the last red tide in the area was in December 2005. Based on the
results, brevetoxin is considered the primary cause of the fish
kills. These findings also indicate that a reservoir of brevetoxin
is present in Choctawhatchee Bay.
It has been well documented that brevetoxin has caused extensive
aquatic animal mortalities in the Gulf of Mexico. While mortality
events usually occur at the same time as red tide blooms, FWC/FWRI
researchers have documented that effects can continue after the
bloom has ended. Animals can be exposed to lethal doses of
brevetoxins weeks to months after a bloom has dissipated. Toxins
released from red tides often persist in the environment and
circulate through the food web.
No other HAB species or toxins have been identified in connection
with the Choctawhatchee Bay aquatic animal mortalities. Although
background levels of a potentially toxic diatom
(Pseudo-nitzschia sp.) were detected in some samples, no
domoic acid (toxin produced by the diatom) was present in any
biological or water samples tested. As part of the Choctawhatchee
Bay mortality investigation, the Florida Department of
Environmental Protection provided data on contaminant sampling from
Garnier Bayou. This data did not provide any evidence to suspect
any contaminant involvement in the ongoing fish kill.
Reports of "pink water" in the vicinity of Garnier Bayou were not
related to red tide. The "pink water" was likely caused by a high
amount of purple bacteria in the water column. These bacteria can
be attributed to local environmental conditions and are not
considered responsible for the Choctawhatchee Bay mortalities.
FWC/FWRI acknowledges the Association for Bayou Conservation, the
Choctawhatchee Basin Alliance, and the Healthy Gulf Coalition for
their collaboration and assistance in collection of samples and
provision of data.