Ecological and geochemical characteristics of bottom habitats at the northern Jordanian coast of the Gulf of Aqaba

Abstract

Abstract A detailed study to assess the environmental conditions of the benthic habitats at the northern tip of the Gulf of Aqaba has been carried out during the summer of 2003. The texture, geochemical, and biogenic characteristics of bottom sediments as well as a description and distribution of corals, seagrass, fish species, and fish assemblages have been investigated. Results showed that the sea bottom at the study site is mainly a non-coralline sandy bottom covered with seagrass. Well-developed seagrass beds covered about 70–98% of the bottom. No coral cover was recorded. This is to be expected because of the absence of hard substrate and because of high loads of suspended matter. The seagrass habitat in the area serves as important nursery grounds for the fish larvae and hosts sea urchins and sea cucumbers. The bottom sand in the area was undisturbed, animal tracks were rare, but bioturbated holes and mounds were abundant. Bottom surface sediments were fine-grained, black with high quartz, feldspar, and mica, and low in mud content. Chemically, these sediments had low calcium carbonate, organic nitrogen, and high total phosphorus concentrations, suggesting that the sediment mineral composition is derived from existing metamorphic rocks, by weathering and erosion. The biogenous part of the sediments was mainly calcium carbonate, consisting of shells or coverings of some micro- and macro-organisms. The number and diversity of fish species inhabiting the survey site are typical of seagrass-bed sandy-bottom habitats. Some of the fish species observed are characteristic of this site and very rarely found elsewhere on the Jordanian coast. About half the fish population in the area belong to six families: Labridae (12%), Pomacentridae (7%), Mullidae (7.%), Apoginidae (6%), Chaetodontidae (6%), and Gobiidae (6%). Keywords: Seagrass bedsBottom habitatFish assemblagesBottom sedimentsGulf of Aqaba Acknowledgements We thank the technical and administrative staff of the MSS, particularly Mr K. Al-Trabeen, Ms A. Tahan, for their valuable help in the chemical analysis, Mr E. Eid, O. Momany, and Mr Y. Jamal for assistance with fieldwork. This work was supported by the Marine Science Station, Aqaba/Jordan.