Diversity and distribution of seagrasses around Inhaca Island, southern Mozambique

Nine seagrass species were identified around Inhaca as well as a more narrow form of Thalassodendron ciliatum (Forsk.) den Hartog occurring in rocky pools at the north east coast. Seagrasses were mapped and grouped in seven distinct community types (in order of areas covered): Thalassia hemprichii/Halodule wrightii, Zostera capensis, Thalassodendron ciliatum/Cymodocea serrulata, Thalassodendron ciliatum/seaweeds, Cymodocea rotundata/Halodule wrightii, Cymodocea serrulata and Halophila ovalis /Halodule wrightii; with the ninth species Syringodium isoetifolium occurring in three of these communities. A dichotomous identification key is presented. Seagrasses covered half of the whole intertidal area around Inhaca Island and diversity was also high at community level. Transects at macro and micro scales showed zonation of species which may be due to tidal gradients or topographic variation. Cluster analysis indicated ecological dissimilarities between co-dominant species. A decline of Zostera capensis has recently been seen outside the local village. Baseline studies like this are important for coastal zone management in developing countries, where large future changes in seagrass cover can be expected.