Patterns of juvenile reef-fish recruitment in Kenya’s shallow fringinglagoon reefs

Abstract

Studies to understand local-scale patterns in the recruitment of juvenile coral-reef fishes within the western Indian Ocean (WIO) region are few, yet such knowledge is important in fisheries management. Underwater visual census surveys were conducted at five shallow fringing-lagoon reef sites along the Kenyan coast, between June 2012 and March 2016, to quantify patterns in the abundance of new recruits and juveniles. Recruitment was observed year-round, with a consistent pronounced seasonal peak in recruit densities and species richness during December to April of each year, which was strongly correlated with high sea temperatures. Annual variations in recruitment were also observed, with a higher recruitment peak in 2013 as compared with in other years. A total of 112 species belonging to 19 families were identified, dominated by species belonging to the Pomacentridae, Labridae and Apogonidae, which altogether represented 91% of the total number of recruits recorded. The species with the largest number of recruits (Chromis viridis, Thalassoma hebraicum and Gomphosus caeruleus) showed evidence of year-round recruitment, although the timing of recruitment peaks was not consistent. Multivariate analysis of the species composition separated mainland from offshore fringing-reef sites, and also revealed strong habitat associations, pointing towards increasing recruit abundance with increasing live hard-coral cover and rugosity. Live hard-coral cover, which constituted an average of 21%, was associated with 63% of the total number of recruits recorded. This study contributes new insight into local-scale patterns of juvenile reef-fish recruitment in Kenya and the WIO region, and demonstrates the important nursery function of shallow fringing-lagoon reefs.

Keywords: fish assemblage, habitat associations, nursery habitat, spatio-temporal variability, underwater visual census, western Indian Ocean