Kenya Diani Marine Reserve Expedition 1993: Report on the Distribution of Habitats and Species of the Diani Coast - Part 1. Item Type Report Publisher Universities of York & Hull Download date 27/09/2021 21:10:40 Link to Item http://hdl.handle.net/1834/7240 KENYA DIANI MARINE RESERVE EXPEDITION. 1993 REPORT ON THE DISTRIBUTION OF HABITATS AND SPECIES OF THE DIANI COAST. PAR T 1. MAY, 1994 UNIVERSITIES OF YORK & HULL, UK. 2 PAR T 1 EXECUTIVE SUMMARY CON TEN T S PAGE PART 1 EXECUTIVE SUMMARY. 2 l. INTRODUCTION 8 2. THE SURVEY AREA: GENERAL CHARACTER AND TOPOGRAPHY 19 3. HABITAT DISTRIBUTION SURVEY 22 4. IMPACT STUDY 28 5. CORALS AND REEFS 47 6. FISHES 57 7 . INVERTEBRATES- 92 8. CONCLUDING REMARKS 105 3 REPORT ON THE DISTRIBUTION OF COASTAL AND MARINE HABITATS AND SPECIES OF THE DIANI COAST. EXECUTIVE SUMMARY 1. INTRODUCTION This report arises from field work carried out between November 1993 and December 1993 in response to recommendations made by Schoorl and Visser (1991) in their discussion paper 'Towards sustainable coastal tourism' environmental impacts of tourism on the Kenya Coast \ commissioned by the Netherlands Minister of Agriculture, j Nature Management and Fisheries. Funding and support for J • this project was provided by the Royal Geographical Society UK, the Kenya Wildlife Service and various companies and trusts. 2. OBJECTIVES Specific targets for the project were as follows:­ 1) To determine the occurrence and distribution of species which may be of conservational concern and/or which serve to indicate the general pattern of distribution of species within the study area. 2) To identify and map the occurrence and distribution of various coastal zone natural habitats including coral reefs and other sub littoral zones, Inter tidal, Mangrove, Estuarine and off-shore islands. 3) To prepare a coastal zone management plan which will suggest various methods of regulating use and other activities affecting the marine resources of the area. 4) To identify sites appropriate for the establishment of protected areas located so as to protect the best examples of habitats representative of Kenyan reefs and to make recommendations for the establishment, management and operation of these areas. 5) Working directly with Kenya Wild Life Service Staff a number of permanent environmental monitoring sites to be established. KWS staff to be trained in continuous monitoring techniques enabling these sites to act as stati:t)ns for biological monitoring, in particular for marine pollution of the whole Diani coastline. The work presented in this report has been carried out under the direction of Dr. Rupert Ormond, Director of the Tropical Marine Research Unit at the University of York, York, UK, on behalf of Kenya Wildlife Service. Much of the field work was assisted by the involvement of specialist consultants. 4 During the course of the 6 weeks field work, 16 sites were surveyed on the reefs between Chale island in the south and the Mwechema river in the north. 3. METHODOLOGY AND OBSERVATIONS Survey work was carried out at three different levels of detail or intensity, with the more superficial forms of study applied over very large areas, or at a large number of sites and detailed observation restricted to a small number of selected sites. The three levels of study and their extent of observation were as follows:­ Type of Study Extent of Application 1. Above water observations Applied over the whole study of critical habitats. area. (supplemented by exploratory snorkelling and diving) 2. Qualitative underwater 'Reefwatch' observations observations using the were made at 16 stations. 'Reefwatch' format. 3. Detailed Study Sites 6 Detailed Study Sites were detailed quantitative Sites were established observations taking 3 days at each site This work has resulted in the production of a set of maps at a scale of 1:50000 showing the occurrence and extent of different off shore coral reef habitats and associated critical marine habitats. Particular attention has been paid to the distribution .. ; and status of critical habitats. Critical habitats are those which either are highly productive and hence support dense populations of animals, fish, etc., either within \ them or in surrounding areas or are habitats that are the i breeding or nursery areas of species of commercial importance , , or scientific significance. The principal critical habitats within the study area are the coral reefs, mangrove stands, sea grass beds and inter tidal areas. 1 The coral reefs in the survey area were found to be highly productive providing food and shelter for many species of commercial fish and scenically of a quality that would compare favourably with sites in other parts of the Indo Pacific set aside for diving tourism. Coral communities are mainly distributed as an off-shore fringing reef which runs parallel and almost unbroken along the entire Diani Coastline. Sedimentation can inhibit coral growth and reef formation and this appears to be occurring on the reefs over the whole study area as a result of natural depositing of fine sediments from rivers and mangrove areas. The coral assemblages throughout the study areas appear to be very similar and naturally arranged in zones of similar 5 groups of species by depth and degree of exposure to wave acti9n. Small patch reefs and inner reef formations occur' within the lagoon formed by the fringing reef most prominently close to high energy areas at breaks in the 'reef crest. The coral cover of the seaward facing reef slope is often dominated by soft corals representing up to 70% of total cover.· Sarchophyton species being the most evident and much smaller proportions of hard corals represented mainly by Porites and Acropora species. Extensive sea grass beds occur throughout the study area on suitable soft substrate in shallow water especially within the Lagoon and in the lee of the Chale island. Thalassodendron ciliatum and Thalassia. Halodule and Halophila species are widely distributed. Small stands of mangrove occur within the inter tidal zone all along the estuary of the Mwechema river and on Chale island. Four species are common. Avicennia maria-OJ, and Rhizophora Mucronata being the most dominant. These sea grass areas and mangrove stonos are a major contributor to the nutrition of the coral reefs of the ares and provide nursery grounds for a large number of commercially valuable fish and shellfish. It is essential that a rational plan be developed to prevent pollution and damage to these areas not only to safeguard these processes but also to assure t: hatfhe--8t-a billslng-eTfecttheseplant-s·provldetot-h-e . environmentally extremely fragile estuarine systems will help to prevent estuarine erosion and the resulting sedimentation of the reefs. Apart from studies of these critical habitats and of the plants and animals already referred to. observations have been made of marine fish, echinoderms. molluscs. crustaceans and 'other invertebrates. The observations on fish have principally been of interest in providing a detailed quantitative account of the main components of the fish assemblage present on the reefs of the study area. The choice of species studied are based upon a list of key fish species that are included by the Tropical Marine Research Unit in their Reefwatch programme and used in studies undertaken in all parts of the Indo Pacific area. The occurrence and numbers observed of these key species is regarded as a good indicator of the quality of the reef in a given area. An additional advantage of adhering to a standard approach is that studies in one part of the Indo Pacific can be readily compared with other Indo Pacific locations and zoogeographic trends established. Further studies were conducted to compare the populations of commercial fish species of the Kisite Marine National Park with those of the detailed study sites at Diani by adding calculations of, biomass to data provided by Reefwatch underwater site inspections. As the sites at Diani are similar to Kisite both topographically and in terms of the 6 form of coral reef habitat provided such 8 comparative study is an admirable basis to assess the status of the Diani sites. The results of the study appear to give clear evidence of a serious deficiency in the survey area in that species diversity and abundance were much lower in the unprotected Diani sites by comparison with the Park. The calculated biomass of commercially important species was also far' smaller in the unprotected Diani sites and indicated a strong possibility of non sustainable impacts to the fishery. Observations of echinoderms indicate that, as was found in earlier studies at Shimoni, populations of most species are very variable according to location and this includes the needle spine urchins (Diadema spp). There is some evidence to support earlier observations by other workers (Muthiga and McClanahan 1987) that exploited reefs are dominated by urchin populations due to lack of predators and are poor in fin fish populations and corals whilst protected coral reefs are typified by an abundance of both. The long spine (Diadema spp) and rock boring (Echinometra mathaei) urchins are present in large numbers within the lagoon and on the outer reef slopes. These urchins can cause extensive damage to corals and when found in excessive numbersis~~oftenan ind ic.ationof. a ser:i_QJ.I~_i_mJ~Q:l.a~c;.e :lJ:'l the natural condition of the reef. Similar intensive surveys were conducted to assess the numbers and distribution of the Crown of Thorns Starfish (Acanthaster planci) a further species of echinoderm that in large numbers can cause extensive damage to live hard corals. Numbers throughout the survey area were very low and are considered to be at a level within natural mass and distribution patterns taking account of the low level of hard coral cover at the sites observed.