The Epibenthos of the Backwaters of a Tropical Mangrove Creek (Tudor Creek, Mombasa, Kenya)

Abstract

The epibenthos of the backwaters of Tudor creek (Mombasa, Kenya), a mangrove-bordered seasonal estuary, was sampled fortnightly with a beam trawl from May 1995 to April 1996. A total of 6396 specimens was collected in 96 tows. Almost 63% of these specimens belonged to 72 species of teleost fish (in 37 families). Penaeid (4 species) and caridean shrimp constituted 27% and 8% of the total catch respectively, while stomatopods and squids were quite rare. At family level, Penaeidae contributed most to the total catch. Gobiidae (15%), Lutjanidae (9%), Plotosidae (9%), Acropomatidae (6%), Gerreidae (5%), and Synodontidae (4%) were the most important fish families. Gobiidae species each, and Peneidae with 4 species. Yongeichthys nebulosus (Gobiidae), Penaeus monodon, P. semisulcatus and Metapenaeus monoceros (Penaeidae), Plotosus lineatus (Plotosidae), Lutjanus fulviflamma (Lutjanidae), Acropoma japonicum (Acropomatidae), Gerres oyena (Gerreidae), and Saurida undosquamis (Synodontidae) were the dominant species (each contributed for more than 4% to the total catch). A TWINSPAN of the catch data identified three monsoon driven communities. Penaeus monodon, Lutjanus fulviflamma and Gerres oyena were the dominant species in the dry period (January to April), while P. semisulcatus and Caridea dominated the community in the long rainy season (May to August), and Acropoma japonicum and Plotosus lineatus were important during the short rains (September to December). Metapenaeus monoceros was abundant in all seasons and Yongeichthys nebulosus reached high densities in both short rainy and dry seasons. The short rains community had the highest numbers of species and densities, while those of the long rainy season were lowest. The three communities had very strong dominance of only a few species, conforming to the general observation that tropical estuarine or coastal ecosystems tend to be very diverse but with very low densities for the majority of species. The restricted size ranges for all individuals caught during this study may be due to two processes: selectivity of the gear and/or dynamic replacement of the populations through seasonal recruitment and fast size progression. All individuals collected during this study were juveniles. The fact and the observed monthly size distributions suggest that most species utilise the urea as a nursery.