Phytoplankton Distribution Off the North Carolina Coast

Abstract

The spatial distribution of phytoplankton was studied along transects directed south and east of the North Carolina coastline. Water samples were taken over the continental shelf, in the Gulf Stream, and the Sargasso Sea, to 300 m. A distinct and predominantly diatomaceous flora existed at the coastal stations and in waters over the shelf. The phytoplankton composition changed seaward in the Gulf Stream and the Sargasso Sea to predominantly flagellate forms composed of dinophyceans and coccolithophores. The concentration and distribution of individual phytoplankters are further discussed along each transect. INTRODUCTION Hulburt (1967) has described the surface phytoplankton between Jacksonville, Florida, and Cape Hatteras, North Carolina. He sampled three different water types extending from the coast seaward: the shallow water over the continental shelf, the Gulf Stream, and waters from the western limit of the Sargasso Sea. His results indicated that the major change in phytoplankton composition off Jacksonville occurred between the shallow water and the Gulf Stream. There were lesser, but definite, differences between the Gulf Stream and the Sargasso Sea flora. This paper discusses the phytoplankton composition and vertical distribution in waters over and beyond the continental shelf. Stations were established along two transects, one directed southward and one eastward, from the North Carolina coastline. Samples were taken from coastal waters over the shelf, in the Gulf Stream, and from the northwest Sargasso Sea. The spatial distribution of the phytoplankton was 'studied to 300 m. METHODS Phytoplankton and hydrography data were obtained during cruises on 16-18 August 1965 and 8-9 May 1967 (Fig. 1). The station locations are given in Table 1. Nansen bottles were used to obtain water samples at the surface, 10, 30, 75, 100, 150, 200 and 300 m. A 500-ml water sample was preserved immediately with neutralized formalin for phytoplankton analysis. After a settling period of six weeks, a 10-40 ml concentrate was obtained by a siphoning procedure. Two different examination procedures were used for the samples. Five 0.1-ml portions of the concentrate from each sample of the E-42-65 cruise were placed in a Palmer-Maloney counting cell and examined 1 This work was supported in part by National Science Foundation Grant GB-3406. The writer thanks Duke University Marine Laboratory for the use of the facilities of the R/V EASTWARD on cruises E-42-65 and E-21-67 in the Cooperative Oceanographic Program supported through National Science Foundation Grant G17669.