Diversity and Zonation of Intertidal Macroalgae in Relation to Water Quality at Kanamai and Vasco Da Gama Point of the Kenyan North Coast.

Abstract

Spatial and temporal changes in a-diversity and zonation of macroalgae in the intertidal zones at Kanamai and Vasco da Gama Point along the Kenyan north coast were studied from March 1999 to August 2000 in order to investigate their relationship with water quality and season. Sampling was done monthly during spring low tide for 18 months. Quadrats of 0.5 m by 0.5 m were studied at specified habitats along established permanent belt transects from the sandy beach to the edge of the deep sea. In each quadrat, surface and sub-surface water was mixed and the pH, temperature and salinity measured. Macroalgae were collected from various substrata, identified and their percentage cover estimated. The water was ana lysed for total suspended coliforms, N- and P-based nutrients. Chlorophyll-a, of the macroalgae species solids, oil\grease, protein and carbohydrate faecal content Ulva retic ulata, U jasciata, Cystoseira myrica, Padina boergesenii, Gracilaria salicomia and Amphiroa fragilissima were determined. epiphytic load on the large macroalgal trinoides, Turbinaria The species (Sargassum, Cystoseira myrica, C. conoides) and the seagrass Thalassadendron ciliatum was determined. Species richness, Shannon's index, Simpson's Dominance Modified Hill's Ratio were used as indicators of macroalgal index and the species diversity. Zones were characterised by one dominant species or by two or three co-dominant species or by mixed species in relation to percentage cover. Data analysis was done using Kruskal- Wallis test Pearsons correlation and F-Test.30 species of Chlorophyta, 36 of Rhodophyta and 21 of Phaeophyta were collected. The highest species richness was recorded for the reef platforms but there was no significant difference in the species richness at this habitat between Kanamaivi and Vasco da Gama Point (Excel F-Test Probability, p at the two sites were similar Probability, p = 0.9804). The deep-sea edge in relation to dominance of species (Excel F-Test = 0.6952). There were significant differences in the species richness, abundance and evenness in distribution of the macroalgae at the near shore and seagrass bed habitats of Kanamai and Vasco da Gama Point. Macroalgal was positively correlated with nutrients and faecal coliforms abundance (r = 0.850 and 0.76 respectively) while high levels of total suspended solids and oil in water resulted in low macroalgal diversity. Distinct bands of particular species running parallel to the seashore were recorded between the mean high water spring and mean low water spring. Moving seawards five zones of macroalgae identified at Kanamai were 1. Cladophora sp./Chaetomorpha crassa; 2. Halimeda opuntia/Turbinaria sp.!Gracilaria corticata; 3. Halimeda opuntia/Amphiroa fragilissima; 4. Cystoseira myrica/Padina sp., 5. Mixed macroalgal type. Three zones identified Graci/aria salicornia/Ulvasp'/Boergesenia at Vasco da Gama Point were l. forbesiilSarconema jiliforme; 2. Graci/ariacorticata, 3. Mixed macroalgal type. Within-zone variation in species composition and abundance occurred with change in season as well as with total suspended solids, nutrient and faecal coliform count of water. Habitat-season-water zonation, a-diversity quality interactions influenced variations in, and composition of macroalgae. Evidence of sewage pollution and eutrophication is also a need to monitor constantly needs further research. There the water quality and chemical macroalgae to explain further the higher diversity at Kanamai. content of the Attention should not only be on effect of pollution on beaches, coral reefs and seagrass beds but also on macroalgae.