A comparison between fish assemblages in mangrove forests and on intertidal flats at Ungwana Bay, Kenya

Abstract

Fish assemblages of mangrove forest patches and adjacent intertidal flats in Ungwana Bay were compared using stake-net sampling in the mangrove forest and intertidal flat habitats between December 2002 and November 2003. Four forest sites were compared with paired intertidal flat sites with either sand or mud substrata. Distinct ichthyofaunal differences were found between the habitats. Pooled data indicated a significantly higher fish density and biomass in the forests compared to the intertidal flats. Mean fish densities were 0.2–2.7 fish m−2 in the forest and 0.1–2.1 fish m−2 on the flats. Thirty-five species were sampled, eight of which occurred exclusively in the forest and six were limited to the intertidal flats. However, species exclusive to either the forest or intertidal flats contributed <1% towards the total number of fish sampled. Anchoviella commersonii dominated the forest habitat and Pellona ditchela the open intertidal flats. Cluster analysis grouped fish assemblages into two groups, based primarily on whether the substratum was sand or mud, rather than on mangrove forest or open flat habitats. This study represents a component of a larger project on artisanal mangrove fisheries within the area.