Surface water samples were collected in early August 2007 from five selected stations in the near-shore waters of Al-Hodeidah (between 14^º 50.193^'-14^º 46.218^' N and 42^° 54.058^'-42° 56.928^' E). Generally, diatoms are found to be the dominant planktonic algae, representing about 89% of the total number of species. The dinoflagellates, the blue-green algae and the prymnesiophyceans contribute about 11% to the total number of species. The overall average count of all stations was 7.722 × 10⁴/L. Skeletonema costatum was the dominant species, occurring in large numbers at all stations, representing, on an average, about 51% of the total number of planktonic algae. A positive correlation was found between inorganic phosphate concentration and the standing crop (total count) of planktonic algae in the near-shore waters of Al-Hodeidah.

In the marine ecosystems planktonic algae are the most important primary producers to which considerable attention is being given on account of their supreme status in the marine food chain. Growth of planktonic algae depends on the hydrographic parameters of the particular environment and since the hydrographic parameters such as light intensity, temperature, salinity and nutrients vary from place to place and from time to time, species composition and abundance of planktonic algae varies latitudinally and seasonally.

In tropical inshore waters, over the Gulf of Panama the micro algae were remarkably constant in composition and were dominated by diatoms (Smayda, 1963). In the Laccadive Sea (south-west coast of India), the composition of phytoplankton changed considerably with time and depth, the total count being between 1.2 × 10³ and 2.9 × 10⁵ cells/L (Shah, 1973). Phytoplankton geographical regions of the Indian Ocean, show that the rich regions (Antarctic, Sub-Antarctic, west wind drift and major upwelling areas) are dominated by diatoms and may have concentrations of 10⁴ -10⁵ cells/L (Krey, 1973). In the Indian Ocean, off south-east Arabia, rich phytoplankton was observed in the coastal area, during the upwelling season. The cell concentrations inshore were about 10⁵ cells/L (Currie et al., 1973). Maps of nutrient distribution confirm the richness of phosphate off Somalia and Southern Arabia and in other upwelling areas (Krey, 1976). There was a positive correlation between phosphate concentration and primary productivity in the south-west coast of India (Jacob and Vasantha Kumar, 1987). A close relationship was reported between the phosphate and chlorophyll-a values in the Gulf of Aden (El-Sayed and Korthara, 1991).

The highest values of 1.65 µg/L and 2.4 mg/m³ for phosphate and chlorophyll-a, respectively, were recorded during August from the north-eastern part. In open surface water of the Red Sea, phosphate concentration is about 0.3 µg/L (Rushdi et al., 1994), however, in near-shore and coastal waters the concentration of inorganic phosphate is expected to be higher. Phytoplankton studies in the Red Sea are very scarce, and only few observations have been done during coastal surveys. No detailed account of phytoplankton distribution or productivity is available for Yemen Red Sea region. The only available data were those reported by IUCN (1987) and Rushdi et al. (1994). The aim of this research work is to study the relationship between the species composition and species abundance of planktonic algae and the concentration of inorganic phosphate in the near-shore waters of Al-Hodeidah during summer season.

Environmental Sciences Journal, Summer Planktonic Algae, Marine Ecosystems, Hydrographic Parameters, Phytoplankton Studies, Phytoplankton Distribution, Marine Resources, Marine Environment, Anthropogenic Wastes, Agricultural Wastes, Phytoplankton Biomass.