The distribution of algae epiphytic on pneumatophores of the mangrove, Avicennia marina, at different salinities in the Kosi System

Abstract

Samples of algae epiphytic on the pneumatophores of Avicennia marina (Forssk.) Vierh. were collected at different seasons of the year. The distribution of this mangrove, which extends from the mouth of the estuary to Wankute island, approximately 6.5km upstream, covers a salinity range from 35‰ to 7‰ at its upper limits, and includes the Ukhalwe inlet in which the surface water of the upper reaches is 0‰. Thirty-six species of epiphytic algae were collected across this distribution range, of which there were 11 rhodophycean, 17 cyanophycean (cyanobacteria), 7 chlorophycean and 1 phaeophycean. Most of the red algae were restricted to the high (> 25‰) salinity areas, while the blue-green algae generally appeared to have a wider salinity and exposure tolerance. Six algal species were found to have a distribution covering the entire salinity range, 10 species were recorded in waters ranging from 35‰ to 7‰, 16 and 2 species were limited to high (> 25‰) and lower (5-18‰) salinity areas, respectively, while one species occurred only in freshwater. The ecological implications of these results are discussed. The need for additional collections from localities to the north is stressed to establish the affinities of this community with those in more tropical areas.