PHYTOPLANKTON ECOLOGY OF NORTH-CAROLINA ESTUARIES

Numerous phytoplankton-oriented ecological studies have been conducted since 1965 in the extensive North Carolina estuarine system. Througho ut a range of geomorphological estuarine types, a basic underlying pat tern of phytoplankton productivity and abundance following water tempe rature seasonal fluctuations was observed. Overlying this solar-driven pattern was a secondary forcing mechanism consisting of a complex int eraction between meteorology and hydrology, resulting in periodic wint er or early spring algal blooms and productivity pulses in the lower r iverine estuaries. We winters caused abundant nitrate to reach the low er estuaries and stimulate the blooms, whereas dry winters resulted in low winter phytoplankton abundance and primary production. Dinoflagel lates (Heterocapsa triquetra, Prorocentrum minimum, Gymnodinium spp.) and various cryptomonads dominated these cool-weather estuarine blooms . Sounds were less productive than the riverine estuaries, and were do minated by diatoms such as Skeletonema costatum, Thalassiosira spp., M elosira spp., and Nitzschia spp., as were the most saline portions of riverine estuaries. Nutrient-limitation studies found that nitrogen wa s the principal limiting nutrient in these estuarine systems over a ra nge of trophic states, with phosphorus occasionally co-limiting. Fresh water and oligohaline portions of large coastal plain rivers were ofte n subject to summer blue-green algal blooms. Formation of these blooms on a year-to-year basis was also determined by meteorology and hydrol ogy: wet winters or springs and consequent nutrient loading, coupled w ith low summer flow conditions and regeneration of nutrients from the sediments. Dry winters or springs resulted in less available nutrients for subsequent summer regeneration, and high flow conditions in summe r flushed out the blooms. In recent years, there has been a dramatic i ncrease in reported fish kills attributed to toxic dinoflagellate bloo ms, particularly in nutrient-enriched estuarine areas. This issue has become a major coastal ecological and economic concern.