Benthic Standing Stock and Metabolic Activity in the Bathyal Red Sea from 17°N to 27°N

Abstract

Abstract. To study the impact of the gradient of primary production between the southern, central, and northern Red Sea, benthic metabolism and standing stocks were investigated in the axial trough between 17°N and 27°N. Data on sediment chloroplastic pigments, macrofauna and meiofauna abundance, particulate adenylate, protein and carbohydrate biomass, as well as electron transport activity of the sediment community give evidence for an enhanced benthic standing stock and activity in the southern Red Sea south of 18°N; this is related to the increased primary productivity in the area south 16°N. Despite a large primary production only small benthic standing stocks were found in all areas investigated; they are much smaller than in other parts of the world's deep oceans with comparable primary production. The low benthic biomass is caused by two factors: a large proportion of particulate organic carbon is remineralized in the water column, while only a relatively small amount sediments to the sea floor; nearly all sedimented particulate organic matter is respired by the benthic community of the deep Red Sea and only a minute proportion is used for the production of benthic biomass.SummaryEuphotic zone primary production in the Red Sea decreases in a strong gradient from south to north. Highest primary production occurs south of 16°N. Benthic stocks of the Red Sea axial trough from 17°N to 27°N (water depth ≤ 1000 m), depending on the sedimentation rate of particulate organic matter from the euphotic zone, exhibited a corresponding south to north decrease in macro‐ and meiofauna abundance, biomass (particulate total adenylates, proteins, carbohydrates) and activity (ETS‐activity). All data give evidence for an enhanced benthic standing stock and metabolic activity south of 18°N. In contrast to other subtropical regions with comparable surface primary production, the biomass of the Red Sea benthos appears extremely low. This is caused by two factors: a large proportion of the sedimenting particulate organic matter is already remineralized in the water column, while only a small part reaches the sea floor; nearly all sedimented material is respired by the benthic community and only a minute proportion is channelled into biomass production.