Characterization of the Ashepoo-Combahee-Edisto (ACE) Basin, South Carolina


Common marine phytoplankton image courtesy of the Harmful Algae website

Phytoplankton communities are the base of the aquatic food chain. They are free-floating microscopic plants that are mostly unicellular and produce chemical energy from light, a process called primary production. In general, the primary productivity of these organisms is very high. For example, phytoplankton can be 15 to 175 times more productive than a rice field. The importance of phytoplankton, particularly diatoms and cyanobacteria, to primary production has been observed in southeastern estuaries and freshwater systems (Grant 1974; Molley et al. 1976; Camburn et al. 1978; Davis and Van Dolah 1992; NOAA 1996; Lewitus et al. 1998). Phytoplankton communities in the ACE Basin have not been characterized.

Phytoplankton production is affected by several biological and physical factors. For example, at a grazing rate of 20%, zooplankton can decrease phytoplankton populations by approximately 75% (Dawes 1998). With adequate nutrients, phytoplankton growth and productivity increases with increasing light. Increased sediment loads can result in declines in phytoplankton populations. If these controlling factors are altered, the effects on phytoplankton populations can be detrimental. For example, excess nutrients promote rapid growth of phytoplankton populations and sometimes a shift in the composition of phytoplankton species. Subtle shifts in phytoplankton populations may have significant impacts on organisms that feed on them.