Recent Submissions

  • Impact of Human Physical Disturbance on Mangrove Forest Structure at the Gazi Bay, Kenya

    Kihia, C.M. (2014)
    Human physical disturbance is prevalent in mangrove forests of the Western Indian Ocean. This study investigated the impact of human physical disturbance on the structure of mangrove forests by comparing forest attributes such as density, taxon richness, stem diameter and tree height between disturbed and relatively undisturbed sites. Physical disturbance was evaluated through tree harvesting intensity, roads and footpaths and other human activities, such as digging for fish bait at the sites. Disturbed sites recorded significantly (ANOVA, P<0.001) higher tree cutting intensity than comparable undisturbed sites, corresponding to lower forest complexity and changes in dominant tree species. Disturbance increased prevalence of Avicennia marina and Ceriops tagal species at the landward margin of disturbed sites. Disturbed sites also recorded significantly lower abundance of harvestable trees and stand volume (223 stem.ha-1, 14.56 m3 .ha-1, respectively) than undisturbed sites (288 stem.ha-1, 19.69 m3 .ha-1, respectively). In addition, accessible sites recorded lower marketable trees, heights, pole size classes (mazio 4-6cm, boriti >10cm) and species (Rhizophora and Bruguiera), being dominated by juvenile and stunted Ceriops and Avicennia. These results indicate that overexploitation of mangrove forests affects the species composition and structural complexity of the forest and hence may impair forest functioning and regeneration and subsequently, sustainable exploitation. Thus, human physical disturbance leads to exponential decline in forest complexity and requires management intervention.
  • Fisheries in the Southwest Indian Ocean: Trends and Governance Challenges

    Kimani, E.N.; Okemwa, G.M.; Kazungu, J.M.; Laipson, E.; Pandya, A. (The Henry L. Stimson CenterWashington DC, 2009)
    This assessment presents an overview of the current and prospective fisheries in the context of other transnational issues that affect the Southwest Indian Ocean (SWIO) region. It also examines key governance challenges, as well as trade-offs that can be made in the short and long term to meet the needs and interests of local fisher communities, national governments, and the international trade mechanisms that shape the region’s maritime policies. Finally, it reviews the work of regional and global fishery organizations in managing the IO fisheries.
  • Scleractinian Coral Fauna of the Western Indian Ocean.

    Obura, D.; Obura, D.O.; Tamelander, J.; Linden, O. (Sida-SARECMombasa, Kenya, 2008)
    Scleractinian coral species surveys were conducted at 10 sites in the western Indian Ocean, between 2002 and 2006. Each site varied from approximately 50-200 km in extent and was sampled with from 7 to 27 dives. Accumulation curves based on successive samples at each site were used to construct logarithmic regression curves, which provide estimated species numbers at each site at an arbitrary value of 30 samples per site, assumed to reflect the total number of species. The highest diversity of corals was found in southern Tanzania to northern Mozambique (from Mafia Island to Pemba town), with 280-320 species estimated per site. Species diversity was lower in the central Indian Ocean islands (140-240 species) and declined steadily to a minimum in northern Kenya (150 species). These patterns are consistent with the central coast (around 10oS in Tanzania/Mozambique) accumulating and retaining species due to the South Equatorial Current (SEC) and mixing/reversing currents locally, respectively. The islands may have restricted diversity due to low area but nevertheless be stepping stones to the East African mainland coast. Lower diversity northwards into Kenya may reflect distance and low dispersal from the center of diversity at 10oS, and poorer conditions due to the Somali Current influence in the north. Observer effects and unclear taxonomy of scleractinian corals may significantly affect the dataset, as may faunal changes due to bleaching or other impacts at individual sites during the course of the study. Finally, it is likely that the diversity gradient northwards into Kenya is replicated southwards into southern Mozambique and South Africa, providing a means to test latitudinal changes in diversity and species distributions.
  • Mangrove conservation and management: a structural regime for the Kenyan coastline.

    Ouko, E.M.; Manohar, S.; Hoorweg, J. (Acts PressNairobi , Kenya, 1998)
    Structural attributes of mangrove forests; were studied at Shimoni, Gazi, Mida Creek and Ngomeni swamps along the Kenyan coast. The study was conducted using the transect method and the diameters, densities, forking, tree height, crown diameters and regeneration of mangals were recorded. The mangrove stand at Shimoni had the highest complexity index of 20.17 while Ngomeni, Mida Creek and Gazi stands had complexity indices of 14.49, 12.29 and 5.97 respectively. Shimoni had the highest M.S.D. at 17.7cm. Both Mida Creek and Gazi with M.S.D. ofS.9cm and 7.7cm respectively were ranked higher d1an Ngomeni which stood at 7.Ocm and indicated that Ngomeni harboured a young population. R. mucronata, A. marina and C. tagal had the highest Importance Value Index (l.V.!.) within the four stands except at Shimoni where B. gymnorrhiza was ranked second to R. mucronata. The lowest ranked species were S. alba, X. granatum and L. racemosa with an exception only at Shimoni where S.alba was ranked third. L racemosa was absent in Shimoni, Gazi and Ngomeni swamps. The results of this study indicate that there is an urgent need for a multi-disciplinary approach for the conservation and management of this complex mangrove ecosystem.
  • The challenge of value addition in the seafood value chain along the Kenyan north coast

    Mwirigi, F.M.; Theuri, F.S. (2012)
    The general objective of this study was to identify the challenges faced in the process of adding value in the sea food supply chain along the Kenyan coast, with particular interest on fish, and propose sustainable solutions to these challenges. This study looks closely at the key value chain activities that characterize the sea food industry along the Kenyan coastline with the view of establishing their completeness and efficiency. It further identifies the gaps that exist in the chain and recommends measures that can be implemented to improve the chains. To achieve this objective the researchers identified the value chain activities that characterize the seafood industry in Kenya with specific reference to the Kenyan coastline and analyzed the gaps and challenges that exist in the value chain. The study has gone further to develop recommendations on policy and non-policy mitigation options to the value chain gaps and challenges that have been identified. Information gathered and the recommendations thereof will help to create a more complete and efficient chain and, therefore, optimize the economic as well as social benefits of the seafood industry to the country.
  • Comparison of Species Diversity and Ecology of Reef-Living Invertebrates on Aldabra Atoll and at Watamu, Kenya

    Brander, K.M.; Mcleod, A.A.Q.R.; Humphreys, W.F.; Stoddart, D.R.; Yonge, Maurice (Academic PressLondon, UK, 1971)
    Extensive quantitative samples of components of the invertebrate fauna (Errant Polychaeta, Decapod and Stomatopod Crustacea, and Echinodermata) associated with intertidal and subtidal reef areas on Aldabra and at Watamu, Kenya are analysed statistically to give estimates of population sizes, species diversity, dominance and distribution. A brief description of the topography and general ecology of the reefs studied is given and the two areas are compared. Techniques for sampling reef fauna are discussed and a method of obtaining quantitative samples of the infauna of hard substrates is described. Results are given for several "habitats" (e.g. channel, subtidal coral platform, intertidal cobble ridge) and for different substrates within the same "habitat" e.g. live coral, dead coral) in order to test the validity of existing "habitat" classifications and to determine which factors may account for species diversity. In a section on the breakdown and colonization of dead coral, the action of boring organisms is considered and also their interaction with subsequent colonizers. It is concluded that, in general, hard substrates support a larger and more varied infauna than soft substrates; that biotic interactions play a very important part in determining species diversity (a measure of the importance is given in the section on colonization of coral) and that reef areas at Watamu support a greater diversity of species than similar "habitats" and substrates on Aldabra.
  • Composition, structure and distribution of coastal dune vegetation between Malindi and Mambrui

    Musila, W.M.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    The coastal sand dunes are one of the coastal ecosystems in Malindi District, which borders the Indian Ocean. The dunes between Malindi and Mambrui town extend to over about 10 km and cover an area of about 700 ha. This study describes the composition, structure and distribution of the dune vegetation. Possible edaphic factors which may affect the distribution of the vegetation were also investigated. The area was studied by air-photo interpretation, field sampling and laboratory analysis. Six transects were demarcated perpendicular to the sea. With the help of these techniques geomorphology units were distinguished, namely; the beach berm, unridged dune platform, transgressive, dunes 1, 2 and 3, incipient foredune ridges, primary and secondary slacks, drowned valley and fossil foredune ridges. A total of 156 plants species were identified representing sixty families with Gramineae (17 species) and Papilionaceae (16 species) being the most represented. Fifteen plant communities were described in the different geomorphological units. A distinct zonal distribution of the plant communities was found. A TWINSPAN analysis grouped geomorphological units of similar localities, mainly on the basis of their species composition. The Halopyrum mucronatum and Ipomoea pes caprae communities were common in the more unstable beach berm, unridged dune platform, transgressive dune 1 and 2. While the Cordia somalensis community was found in the more stable geomorphological units including transgressive dune 3, incipient foredune ridges and fossil foredune ridges. Significant variations in the soil parameters in different geomorphological units were detected (p=.001). Sand dynamics and mean particle size of the sand were the most important factors influencing the vegetation composition, structure and distribution. Other important research studies are proposed to help in the proper management of these dunes. It is recommended that the dunes should be preserved for nature conservation and prosperity of the area.
  • Environment effects of coastal sedimentation: A case study of Shirazi-Funzi Lagoon

    Munyao, T.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    The aims of the study were to determine factors that affect sedimentology of the Shirazi-Funzi lagoon in Kenya; sediment mineralogy and source environments; economic importance of the lagoon; environmental problems within it; possible management policies for Kenya's coastal lagoons. Sediment grains distribution, composition and dynamics were studied; suspended sediment discharge by Ramisi River was determined, and POC was studied to investigate possible contribution of the river to nutrient replenishment in the lagoon. Geomorphology, hydrodynamics and socio-economic activities were also studied. The lagoon is dominated by terrigenous sediments, comprising mostly of fine quartz sand. Grain size diminishes gradually from mainland shoreline towards the tidal inlet. Carbonate mineral content ranges from 0.01 to 5.0% by weight in most parts of the lagoon, but adjacent to the coral reef, it increases to over 80% by weight. Total organic matter ranges between 0.01 to 2.0% by weight in the channels, but increases to over 50% by weight at channel banks, and decreases to minimum levels towards the centre of the mangrove islands. Cliffs, beaches, channels, sandbars and mangrove islands are the physiographic features of the lagoon. Off the lagoon, sea-wards is a trough, due to Pemba channel, with a maximum depth of 207 m. Wave energy is dissipated exponentially from the tidal inlet toward mainland shoreline. Annually, Ramisi River discharges about 1.534 x 10 super(3) tons of suspended matter. POC of surface water at Mamuja channel ranged from 645 mg/CI to 1940mgC/I in 24 hours, the highest values occurring during tidal ebbs. The main socio-economic activities in the lagoon are fisheries and mangrove exploitation. The rate of harvesting of fisheries resources is negatively correlated with that of mangrove resources. The main environmental problem in the lagoon are shoreline erosion, lagoonal sedimentation, mangrove felling and vulnerability of the lagoon to global-induced sea-level rise. Policies are suggested, which require research-based data, on management of Kenya's lagoons, in light of the observed environmental problems.
  • Geology, geomorphology, oceanography and meteorology of Malindi Bay

    Abuodha, J.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    Malindi Bay covers a shoreline of about 45 km between Ras Ngomeni Peninsula in the north and Leopard point in the south, encompassing townships of Malindi and Mambrui and the Sabaki river estuary. In the 1980's a number of geological investigations were carried in the Kenya south coast area, which has similar rock outcrops as in Malindi area. However, a few geological studies have been conducted in Malindi area mainly involving geological mapping. Data on the Sabaki river flow discharge rates has been collected by Ministry of Water Development from the 1960's. In addition, other pertinent information on the historical changes of the coastline over the past 40 years are obtainable from a series of Arial photographs during 1954 and 1994. The coastal belt of Kenya experiences an equatorial Monsoon climate with Southeast Trades prevailing from April to October and Northeast Monsoon from November to March. Wind speeds seldom exceed 14 ms super(-1) during both monsoon seasons. The coastal area has a humid climate with average rainfall of 1058 mm year super(-1) with two rainy seasons respectively referred to as the long and short rains. Monthly variations in air temperature from normal are slight, and closely related to the sea water temperature. The continental slope is generally characterised by gentle gradients of about 1:20 to the shelf edge and shows dissected appearance due to sub-aerial fluvial action. Sediment distribution off the Kenya coast in general shows that sand appears to be the principal constituent of the shelf floor, with mud dominant in the deeper water.
  • Groundwater resources and sea water intrusion in Kwale District

    Anyango, S.O.; Tole, M.P.; Ucakuwun, E.K.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    This work describes the results of water quality analysis carried out along the coastal plains of Kwale District, Kenya, to determine the influence of sea water intrusion, the relationship between tidal changes and water quality in boreholes close to the sea shore, and the effectiveness of the pumps in the provision of potable water in the study area. Four types of water were found in the study area; calcium bicarborbonates, sodium bicarbonate, sodium chloride and calcium chloride water. Total dissolved solids (TDS) in sodium-rich waters varied from 800 ppm to 10,000ppm with most of the TDS concentrations being below 1000 ppm (recommended concentration limits for drinking water). The salinity hazards for the water are greater than 750 mu s/cm at 25 degree C. Consequently this water has limited practical use. A salt tongue (sea water intrusion) was detected covering a distance ranging from 1.5 to 6.5 km from the shoreline in Mwabungo-Waa area. But in the Msambweni area, sea water intrusion is still limited and waters are safe for drinking up to the shoreline except adjacent to Msambweni hospital and South Kigwede in the Shirazi area. During periods of high tide some wells exhibit higher levels of water and higher salinity than during the time of low tides. This effect decreases with distance away from the seashore.
  • The impact of geology and pit latrines on groundwater quality in Kwale District

    Mzuga, J.M.; Tole, M.P.; Ucakuwun, E.K.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    Dissolution of rocks and infiltration from pit-latrines can cause pollution of groundwater. In this study, TDS, TSS, conductivity, COD, BOD, dissolved oxygen, calcium, Magnesium, sulphates, chlorides, fluorides, coliform counts and Escherichia coli as well as pH and temperature, were determined from selected borehole, springs and wells in Kwale District, Kenya, underlain by either sandstones or coral limestone. Water samples were taken from each of the water sources between September and November 1993 which represented the wet season (short rains) and between January and February 1994 which represented the dry season. Data for most parameters i.e. conductivity, TDS, CL super(-), F super(-) Ca2 super(+), sulphates with means 706.7, 487, 175, 0.3, 74, and 10.4 respectively. The pH showed no change, with a mean of 6.63, while dissolved oxygen, COD, BOD, and coliform counts showed a decrease with means 0.64, 151, 1.61 and 160.5 respectively. Analysis using trilinear plots showed the major anions as chlorides and bicarbonates while the major cations are calcium and sodium. The safe distance to locate a pit latrine from a water source in sandstone regions is recommended to be approximately 120m, while in limestone regions it should be at least 150m.
  • East coast Akalat: Habitat selection and distribution in Arabuko-Sokoke forest

    Matiku, P.M.; Bennun, L.A.; Odanga, J.F.E.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    This study carried out on a nearly threatened East Coast Akalat (Sheppardia gunningi sokokensis Van Someren 1921) in two forest types (Cynometra woodland and mixed forest) in Arabuko-Sokoke Forest to determine the proximate factors that influenced its spatial distribution. Playback was used to stimulate the bird to reveal its presence. Fifteen habitat factors predicted to be important as cues for habitat selection were recorded from territory and non-territory sites and compared. Normal and logistic regression models were used to select the best habit predictors of Akalat distribution and density. The best habitat predictors for the occurrence of Akalat (in both habits combined) were mossy logs and vegetation cover at 2m; sites without Akalat had higher numbers of cut stems. The greatest amount of food was associated with the presence of Akalat; large territories were located in the mixed forest compared to the Cynometra woodland; the bird was more evenly distributed in the Cynometra than in the mixed forest; higher population density was recorded in the Cynometra than in the mixed forest. Results suggest that; East Coast has the ability to select micro habitats suitable for its survival; human activities affect the population density and distribution of Akalat by affecting vegetation structure suitable for the Akalat; mossy logs and vegetation cover at 2m high can be used as quick rapid indices in predicting habitat quality for the Akalat.
  • Mangrove forests along the tidal flats and lagoons of Ngomeni, Ungwana Bay

    Kamau, F.K.; Hoorweg, J. (Acts PressNairobi, Kenya, 1998)
    The study was carried out from November 1995 to March 1996 during the dry season period, and concentrated on mangrove forest under different anthropogenic pressures. A total of six stations with 13 sub-stations were demarcated representing five biotopes; mangrove forest, degraded mangrove areas, saltwork ponds, sandflat, and aquaculture ponds. Macroflora and macrofauna composition, soil characteristics, extent and status of mangrove forests at Ngomeni, Kenya are presented and discussed. There are no statistically significant differences between the various biotopes for epifauna; differences in fauna densities and species diversity in different biotopes were statistically significant. Mangrove forest biotope had the highest infaunal densities, while no infauna were recorded for sandflat and the saltworks ponds. Species diversity (no. of species or taxa/station) was highest in the mangrove forest and lowest in the saltworks ponds. Sediment texture was mainly sand (>50% sand) in all the biotopes, temperature and salinity were moderate in mangrove forest biotope (28.1 degree C and 41.1 ppt, respectively) and extreme in the sandflat (30.8 degree C and 6.1 ppt respectively) the pH was highest in saltworks and aquaculture ponds (9.5 and 7.9 respectively) and lowest in the mangrove forest (6.4). Percentage organic and water content were highest in mangrove forests (13.45% and 43.7%) and saltwork ponds (12.12% and 40.6% respectively) and lowest in sandflats (5.14% and 21.1% respectively). There are statistically significant differences in the nutrient status between the biotopes: Ammonium-nitrogen 0.066 mu g/g of wet sediment in the sandflat to 0.783 in saltworks ponds; nitrate-nitrogen ranged between 0.022 in saltworks to 0.047 in degraded areas; phosphates ranged between 0.007 in aquaculture ponds to 0.021 in saltworks ponds; and sulphate areas; phosphates ranged between 1.022 in aquaculture ponds to 3.174 in saltworks ponds. Biotopes with moderate temperature and salinity levels, and high levels of organic matter and water content had greater species diversity. Simple correlation analysis was performed. A great deal of mangrove forest cover has been lost to aquaculture and saltworks developments, on comparison between earlier (1960s) and recent (1992) aerial photographs. Destruction of mangroves has led to decline in both forestry output and macroinvertebrate diversity, and changes in soil physical and chemical parameters. Rehabilitation conservation, and sustainable of the mangrove forest resources is highly recommended.
  • Observations on Salvinia and its Environment at Lake Naivasha (Kenya).

    Tarras-Wahlberg, Nils (1986)
    Lake Naivasha is a freshwater lake in the Rift Valley of Kenya. It was infested in the 1960s by the floating fern Salvinia molesta Mitchell. This fern is indigenous to Brazil where it is apparently harmless. At lake Naivasha, as in several other inland waters of the tropical Old World, it is capable of an explosive population increase, and it can occupy the surface of calm nutrient-rich waters very quickly. By forming a surface-mat, it stops sunlight from reaching submerged plants and so it kills the submerged vegetation. This has resulted in serious setbacks to the local fishing industry. It is shown that in nutrient-rich waters young Salvinia has a doubling time of 4.5 days. Optimal growing conditions exist near Papyrus stands. Old mats of Salvinia may be invaded by vascular plants, and so a formation of sudd may start.
  • The Distribution of Skates and Rays along the Kenyan Coast.

    Ochumba, P.B.O. (1988)
    The distribution, abundance, reproductive biology and the economic importance of skates and rays along the Kenyan Coast was studied between January 1980 and December 1981. The common species described in this paper are Raja miraletus, Taeniura lymna. Myliobatis aquila, Dasyatis thetidis. D. uarnak and D. sephen. These fish were present throughout the year with increased catches being realised in August, December and March. The size distribution of each fish is described. Linear regression analysis of the length/weight relationship for all the species indicate allometric growth. Raja miraletus. D. thetidis and D. uarnak exhibit sexual dimorphism. All fish, except Manta birostris, are carnivorous, feeding on crustaceans, molluscs and fishes. The distribution of skates and rays is discussed with reference to depth, temperature, salinity and the monsoonal phenomena. Temperature changes and low salinity water during the rainy season may act as a trigger mechanism for spawning.
  • Shell collecting and coral reefs.

    McClanahan, Tim (1990)
    Conservationists have long held that excessive shell collecting will damage the health of coral reefs and result in the extinction of some mollusc species. But does the evidence support this belief?
  • The distribution and economic importance of the mangrove forests of Kenya

    Kokwaro, J.O. (1985)
    The mangroves form a group of higher plants which form a unique ecosystem, in that they grow in that part of land which is neither in demand for human settlement nor for agricultural use. They are also unique in their adaptation to both soil and water conditions. They are useful as a source of timber, for building poles, fuel, dyes, tannins, and are also known to provide both shelter and food for part of the marine fauna. Their value to the country, therefore, calls for proper utilization and conservation of all the available mangrove forests along the coast. The demand for forest products, including those from the mangroves in Kenya, is greater than the available resources from the forests, and unless proper and prompt planning for their protection is implemented our mangroves will soon be among the endangered ecosystems in the country.
  • Kenya's coastal fisheries

    McClanahan, Tim; Muthiga, Nyawira (1988)
    Opinions differ as to whether the sea of the Kenyan coast is being under or over-fished, and as to what effect this is having on the abundance and diversity of marine life.
  • Chemical Factors Limiting Growth of Phytoplankton in Lake Victoria.

    Fish, G.R. (1956)
    Investigations on the problem of phytoplankton productivity in the waters of Lake Victoria have been pursued since 1949. Observations from the shallow bays and inlets showed that no annual cycle of phytoplankton occurred. In view of the favourable climatic conditions found in this area, factors limiting growth of phytoplankton were sought in the form of deficiencies in chemical nutrients dissolved in the water.
  • Status of Coral Reefs in the Western Indian Ocean and Evolving Coral Reef Programmes.

    Salm, Rod; Muthiga, Nyawira; Muhando, Chris; Wilkinson, Clive (Australian Institute of Marine Science for the Global Coral Reef Monitoring NetworkTownsville, Australia, 1998)
    The region has all reef types from atolls to fringing reefs with many endemic species shared within the Western Indian Ocean (WIO), which suggests that the reefs are linked by currents to make this a discrete biogeographic region. This also means there is a need for regional collaboration among the ten WIO states to manage these reefs. Reef management is not well developed in the WIO, and is focused at the site rather than at national or regional levels. Poorly regulated fisheries and coastal development, together with increasing populations and tourism are major contributors to reef destruction. This is ironic, as both fisheries and coastal tourism are heavily dependent on healthy coral reefs, and make major contributions to the economies of most countries. Many of the reefs in the region are showing distinct signs of damage from human activities, and bleaching in 1998 has been particularly severe in the Seychelles and Kenya. The principal reef management activity is the establishment of marine protected areas (MPAs) mainly for tourism, and little is being done to safeguard reefs for biodiversity or fisheries conservation. Although progress is being made in collaborative reef management at the community-government level, there is the need for collaboration among the WIO states to conserve reefs. This will enable sharing of successful approaches for management problems that are common to the region, use of a standard methodology and database for reef assessments to facilitate data sharing and analysis, understanding of processes sustaining the regional linkages, and will facilitate regional collaboration.

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