Use of replanted mangroves as nursery grounds by shrimp communities in Gazi Bay, Kenya

This study quantitatively assessed the distribution of postlarval and juvenile shrimps in natural, degraded and replanted stands of Sonneratia alba mangroves in Gazi Bay, Kenya in 2002-2003. Two plantations (matrix and integrated) differing in historical status and planting strategy were studied. Sampling was conducted using stake nets (2 mm mesh), each net enclosing 9 m2 of intertidal microhabitat. A total of 615 shrimps from 19 species/taxa were caught, including several penaeid species of major commercial importance. Penaeids dominated the catch (66%) followed by Macrobrachium spp. (16%) and Acetes sp. (6%). Shrimp abundance ranged from 0.42 to 10.0 ind. per net (9 m2) for individual sites across spring tides and significant differences were detected between sites and over time (p<0.001). Results showed no significant difference in diversity of species/taxa between sites. However, multivariate analysis revealed significant differences in community assemblages between sites, except for the natural stand and integrated plantation. These two sites harbored higher abundances of the majority of all taxa caught. The observed distribution patterns are discussed with regard to measured environmental parameters such as elevation, structural complexity and sediment characteristics.