Impact of a net cage fish farm on the distribution of benthic foraminiferain the Northern Gulf of Eilat (Aqaba, Red Sea)

Two sediment transects, at 23 m depth, were sampled below a commercial fish farm at the northern end of the Gulf of Eilat in order to describe the ben thic foraminiferal community along an organic enrichment gradient. Sediment organic matter, porewater ammonia and phosphate concentrations reflected t he input from the overlying fish cages and there was generally a decrease i n these variables with distance from the point source. Rose-bengal stained foraminifera were found at all of the stations sampled below the fish farm, i.e. there were no azoic sediments, Fifty-one species of foraminifera (>45 mu m) were found in the sediments around the fish farm but most were rare species. The most abundant (generally > 83% of the foraminifer abundance) s pecies (stained + unstained) found were Amphisorus hemprichii, Amphistegina lessonii, Assilina ammonoides, Borelis schlumbergeri, Challengerella brady i, Hauerina diversa, and Peneroplis planatus. Five of these foraminifera ar e algal symbiont bearing forms. The diatom-bearing species, A. lessonii and A. ammonoides, constituted 40 to 50% of the total number of tests. The mos t abundant stained species were A. ammonoides, B, schlumbergeri, H. diversa and P, planatus. Abundances of foraminifera were highest in the "hypertrop hic" zone, adjacent to the fish cages. The most abundant species showed neg ative correlations between total abundance of tests and organic matter in t he upper centimeter of the sediment. Negative correlations were also found between abundances of both total and stained tests of the most abundant spe cies and integrated ammonia concentrations. No clear indicator species of t he organicaily-enriched benthos were identified. Deformed tests (mainly P. planatus) were observed in the samples and it is not clear whether they for med as a result of adverse conditions related to the fish farm because such variants also occurred at unenriched sites.