Patterns of juvenile reef fish assemblages across a mangrove-seagrass-coral continuum in Shimoni, Kenya

Abstract

Understanding juvenile fish distribution across habitat mosaics is essential for interpreting ecosystem connectivity and function. This study assessed seasonal variations in juvenile reef fish assemblages across a mangrove-seagrass-coral reef continuum in Shimoni, southern Kenya. Using a beach seine net, sampling during the Northeast Monsoon (NEM) and Southeast Monsoon (SEM) seasons, a total of 8,575 individuals representing 228 species and 52 families were recorded. Species richness and diversity (H') were highest in the coral associated site (n = 168; H' = 3.77), followed by the seagrass associated site (n = 132; H' = 3.69) and the mangrove associated site (n = 119; H' = 3.64). Two-way ANOVA and Kruskal-Wallis tests revealed significant differences in diversity and mean species richness, respectively across habitats, with post-hoc pairwise tests identifying the most pronounced differences between coral and mangrove sites. While 69 species were common to all three habitats, multivariate analysis demonstrated distinct species-habitat associations, particularly in the mangrove associated habitat, influenced by salinity and temperature. The Kolmogorov-Smirnoff test further confirmed differences in the trophic signatures of the assemblages between mangrove-coral and seagrass-coral interfaces. These findings underscore the importance of the coastal habitat mosaic in sustaining fish recruitment and population dynamics, highlighting the need for integrated seascape management in the Western Indian Ocean.

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