Primary production in a desert-enclosed sea- the Gulf of Elat (Aqaba), Red Sea

Chlorophyll a, primary production, nutrient levels, and microphytoplankton abundances were determined during 1976 and 1977 in the northern basin of the Gulf of Elat (Aqaba). During most of the year (April-November) the photic zone extends to great depth (170 m) and is oligotrophic (chl. a 16 to 54 mg m^-2, primary production 200 to 900 mg C m^-2 day^-1). During winter (mainly December to March) the upper waters are much more productive (chl. a 33 to 70 mg m^-2, primary production 690 to 1,120 mg C m^-2 day ^-1). The seasonal pattern is also expressed in the depth-distribution of these parameters. Overall the gulf is moderately productive, averaging 160 g C m^-2 year^-1. The biological characteristics are closely related to nutrient distribution in the water column. Nutrient distribution is determined by the circulation regime in the gulf, which is stratified in summer and mixed in winter. Phytoplankton blooms following peaks of the NO₂ + NO₃ - N and of N/P ratios suggest that nitrogen is the major limiting factor. There is also an increase in productivity from the open waters towards the coral reef, as well as from the northern to the southern basin at the approaches to the more productive Red Sea proper.