Biological Condition 1999-2000

Phytoplankton:

    Phytoplankton concentrations are measured by SCECAP in the surface waters of South Carolina's estuaries to provide a measure of possible biological response to enriched nutrient concentrations. Because South Carolina does not have any water quality standards that are based on phytoplankton concentrations (measured using chlorophyll-a pigment concentration), SCECAP relies on guidelines that have been published for coastal estuaries by NOAA (Bricker et al., 1999). Using these guidelines, approximately 13% of the state's tidal creek habitat had high phytoplankton concentrations compared to only 3% of the open water habitat (see figure below). The significantly higher chlorophyll concentrations in tidal creeks may be reflective of the higher nutrient concentrations observed in the creeks, or it may also reflect possible re-suspension of benthic algal mats from the creek bottoms and marsh surfaces that would be less likely to be present in the surface waters of deeper, larger water bodies. Analyses conducted to evaluate whether nutrient concentrations are influencing the chlorophyll-a concentrations showed no clear relationships with total nitrogen (TN) or total phosphorus (TP) concentrations. A stronger relationship between nutrient concentrations and measures of phytoplankton concentrations may become more evident with a larger data set that can be partitioned by tidal stage and time of day. Additional chlorophyll-a data collected through this study and through others studies of harmful algal blooms currently being conducted in South Carolina will provide a much better understanding of what chlorophyll-a concentrations represent "eutrophic" conditions in South Carolina.

Comparison of the average chlorophyll-a concentrations observed in tidal creek and open water habitats during 1999-2000, and estimates of the percent of the state's coastal habitat representing concentrations that are indicative of possible eutrophication (dark green).

Benthic Communities:

    Bottom-dwelling (benthic) invertebrate organisms are important because they are the primary consumers for many ecosystems and are common food items for many fish and crustacean species. Benthic organisms are also considered to be excellent indicators of environmental stress because many are sessile or have extremely small home ranges and cannot easily avoid exposure to natural or anthropogenic stresses. Characterizing the benthic community in South Carolina coastal habitats is, therefore, essential to the SCECAP program. Using several measures of benthic community condition, Van Dolah et al., (1999) recently developed a benthic index of biological integrity (B-IBI) for southeastern estuaries to distinguish between degraded and undegraded environments. Using this B-IBI, the majority of South Carolina's coastal habitat sampled in 1999-2000 had undegraded benthic communities, 12% of both creek and open water habitat showed evidence of some possible degradation, and only 4% of tidal creek habitat and 2% of open water habitat had benthic communities that were degraded (see figure below).

Estimates of the percent of the state's coastal habitat having benthic invertebrate communities representing undegraded, marginally degraded, or degraded conditions.

Finfish and Crustacean Communities:

    Estuarine waters support a diverse and transitory fish assemblage, with many species often present only during certain seasons or stages of development (Ogburn et al., 1988). Tidal creeks provide critical habitats for many species because these shallow wetland areas supply food, provide refuge from predators, and are valuable habitats that are utilized by the egg, larval, juvenile, and adult stages of a variety of finfish and crustacean species (Joseph, 1973; Mann, 1982; Nelson et al., 1991). Because these organisms are highly motile, they may or may not be suitable as indicators of biotic condition at a particular site. However, we consider it important to document the relative abundance and diversity of the fish and crustaceans at the various sites, with an ultimate objective to define where these communities are limited and, hopefully, develop a second index of biotic integrity using these species. The data are also useful for defining where recreationally and ecologically valuable species are most abundant and diverse, and what specific habitat characteristics are associated with these conditions. Better knowledge of the most productive habitats is critical for protection against human-induced impacts.

    The biota sampled by trawls at tidal creek and open water stationsdisplayed a similar array of species, including many commercially and recreationally important species such as white shrimp, brown shrimp, blue crabs, and spot. Other important species collected in lower abundances included silver perch, Atlantic croaker, weakfish, Atlantic spadefish, mullet, summer flounder, ladyfish, spotted sea trout, pink shrimp, southern flounder, white catfish, Atlantic sharpnose shark, sea catfish, Spanish mackerel, black sea bass, American shad and southern kingfish (whiting). Some of these species are not commonly harvested recreationally in South Carolina, but they are recreationally important in other areas and many are kept as incidental catch by fishermen in this state.

Comparison of the average abundance, biomass, and number of species collected in trawls at open water versus tidal creek sites during 1999-2000.

    The abundance, biomass and diversity (number of species) of the fish, crustaceans, and other organisms collected in the trawls was significantly higher at tidal creek stations compared to open water stations (see figure above). This indicates that different criteria should be used for each habitat type when defining whether conditions are poor or normal for these measures. SCECAP staff have identified the 25th and 10th percentile values representing each of these measures in both creek and open water habitats based on the sampling conducted to date (Van Dolah et al., 2002). As more sites are sampled, these threshold values will be refined and evaluated for possible incorporation into an index of biotic integrity.

    Contaminant levels in selected fish species were also evaluated beginning in 2000. All of the tissue samples had detectable levels of some contaminants, but only one site (Shipyard Creek, an industrialized drainage basin in Charleston Harbor) had levels that were especially high for fluorene and anthracene, two polycyclic aromatic hydrocarbons. None of the contaminants exceeded Food and Drug Administration (FDA) criteria for safe consumption. In a recent report, the USEPA suggested that southeastern estuaries generally had low tissue contaminant levels compared to the northeast, gulf and west coast regions (USEPA, 2001). The results from the SCECAP data set, although limited to only one year of data, support this evaluation.