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Common Occurrence of Harmful Algal Blooms in South Carolina Brackish Lagoonal Ponds

Alan J. Lewitus
Baruch Institute, University of South Carolina
Marine Resources Research Institute, South Carolina Department of Natural Resources
lewitusa@mrd.dnr.state.sc.us

When Rick DeVoe (South Carolina Sea Grant Consortium) organized the first meeting of the South Carolina Task Group on Harmful Algae in fall 1997, the focus was on developing research plans to determine whether Pfiesteria was a potential problem in South Carolina (SC) estuaries, and implementing response strategies to possible Pfiesteria outbreaks. The establishment of the Task Group was truly proactive, as Pfiesteria was not known to occur in SC waters at that time.

The multi-institutional Task Group (SC Sea Grant, SCDHEC, SCDNR, USC, NOAA-NOS, Hollings Research Institute, MUSC, Charleston VA Medical Center, Clemson U.) has remained cohesive since its beginning, but its focus has expanded to include investigations into all harmful algal blooms (HABs) in SC.

With funding from CDC, ECO-HAB, EPA, SC Sea Grant, Kiawah Lake Management Office, and
NOAA (establishing the South Carolina Harmful Algal Bloom Program in October 2000), our understanding of the distribution, ecology, and adverse impacts of harmful algal blooms (HABs) in SC estuarine systems has greatly advanced.

One of the issues that has come to light with this increased surveillance effort is the near-ubiquity of HABs in
brackish (lagoonal) retention ponds associated with housing developments or golf courses. These retention
(detention) ponds are widely used as deposition buffers to prevent (or at least restrict) transport of pollutants into tidal creeks and open estuaries, and/or for their aesthetic value. They characteristically receive high levels of nonpoint source pollutants from lawn care practices such as fertilization and irrigation, the latter often through the use of biologically treated sewage effluent. However, in their function as pollutant traps, ponds may contribute to the creation of another potential environmental problem. That is, ponds may become natural "incubators" for estuarine microorganisms such as certain HABs that thrive under low flow, high pollutant (e.g., nutrient) levels.

Of the 1456 ponds documented along the SC coast (from 1994 aerial images, using a lower size limit of 1 acre), 45 brackish ponds have been sampled at varying frequencies since spring 2001. Potentially harmful algal species were observed in 37 of the ponds, and, in 21 of these, HAB species were found in "bloom" proportions (i.e., were dominant or co-dominant members of the phytoplankton community, and exceeded 1000 cell ml-1 or in the case of Pfiesteria-like organisms, 100 cell ml-1). In those 21 ponds, HABs were documented a combined total of 65 times.

All of the observed HABs have precedence for toxicity and causing fish kills (Table 1). Among the 22 fish kills documented in SC brackish-to-marine waters in 2001-2002 and sampled for HABs, an association with high HAB species abundances and dissolved oxygen concentrations was found in ponds on six occasions. However, the association of HABs with fish kills does not necessarily reflect cause-and-effect.

Evidence for toxicity towards fish was obtained in two of these six fish kills (i.e., one associated with Pfiesteria and another with Karlodinium micrum), but toxicity assays were not conducted during the four other HAB-associated fish kills, and therefore their role in fish death could not be determined. On another occasion, a dense algal bloom (Chattonella spp.) was observed one day prior to a fish kill that was associated with low levels of dissolved oxygen, suggesting a role of the bloom in oxygen depletion.

Table 1. Data on 7 of the harmful algal species observed in 45 SouthCarolina brackish ponds sampled from 2001 to 2002. Listed are the number of sampling times (out of 285 total) the species was present or
in bloom proportions, and the maximum abundance observed. “Bloom” is defined as cases where the species was dominant or co-dominant, and abundance exceeded 1000 cell ml-1(or 100 cell ml
-1 for Pfiesteria-like organisms).

These lagoonal ponds are marked by close human interaction – fishing, crabbing, swimming, jet skiing, boating, golfing. In addition to their potential environmental or human effects within or near pond boundaries, tidal transport of harmful algal cells, cysts, or toxins may adversely affect fish or shellfish in adjacent tidal creeks or open estuaries.

The SC coastal zone is among the fastest growing areas in the U.S., and population epicenters such as Myrtle Beach, Charleston, Kiawah Island, and Hilton Head Island are marked by dense pond coverage closely associated with housing complexes and golf courses.

The recent discovery of widespread, frequent, and often dense HABs in SC residential and golf course ponds introduces the need to consider mitigation measures to existing ponds and HAB preventive strategies for future pond construction associated with coastal zone development.