Recent Submissions

  • Structure and Biomass Accumulation of Natural Mangrove Forest at Gazi Bay, Kenya.

    Githaiga, Michael Njoroge (Kenyatta University, 2013)
    Mangroves occupy only 0.4% of forested areas globally but are among the most productive ecosystems on earth. They account for about 11% of the total input of terrestrial carbon into the oceans. The above ground carbon stock in mangroves in some parts of the World has been estimated to be as high as 8 kg C m-2; with a similar amount reported for below ground components. Although a lot of research has been done on estimates of mangrove biomass in Kenya, there is no information on biomass accumulation across the zones. The present study aimed at determining the forest structure and estimating above and below ground biomass accumulation in Gazi Bay mangrove forest. Forest structure was determined in the western, middle and eastern forest blocks of the Gazi Bay mangrove forest while biomass accumulation studies were done in the western forest block. In-growth cores of 80 cm long × 20 cm wide and 60 cm-depth were used to estimate below ground biomass accumulation. Data on tree height and stem diameter at breast height (DBH-130) were used to estimate above ground biomass accumulation. Shoots were tagged for monitoring leaf phenology. Periodic measurements of environmental variables across four mangrove species zones were done at the beginning, thereafter every four months for a year. Composition and distribution pattern of natural regeneration was obtained using the method of linear regeneration sampling (LRS). Among the soil environment properties investigated, salinity had a significant negative correlation with above ground biomass accumulation. Comparing the four forest zones, Sonneratia alba had the highest biomass accumulation rate of 10.5 ± 1.9 t ha-1 yr-1. This was followed by Rhizophora mucronata (8.5 ± 0.8 t ha-1 yr-1), Avicennia marina (5.2 ± 1.8 t ha-1 yr-1), and Ceriops tagal (2.6 ± 1.5 t ha-1 yr-1). There were significant differences in above ground and below ground biomass accumulation across zones (F (3, 8) = 5.42, p = 0.025) and (F (3, 8) = 16.03, p = 0 001) respectively. Total biomass accumulation was significantly different across zones (F (3, 8) =15.56, p = 0.001). A root: shoot biomass accumulation ratio of 2:5 was computed for the whole forest. The finding of this study gives better estimates of mangrove carbon capture and storage which can be used in negotiations for carbon credits in the evolving carbon market.
  • Dynamics of carbon and nitrogen in the mangrove forest of Gazi, Kenya: a numerical modelling approach

    Ong'anda, H.O. (Free University of Brussels, 1992)
    The numerical model described in this work has been designed to study the flow of carbon and nitrogen in a mangrove forest at Gazi Bay, Kenya. Several processes and storages of matter considered vital in the functioning of the ecosystem have been reviewed to help in the abstraction of the model and analysis. A numerical model represents the functioning of the ecosystem but is always limited due to the complexity of the system and lack of information on processes. A review of modelling work concerned with coastal ecosystems reveals that modelling is not only a means of summarising data from field studies, but that it can also be an integrated part of research effort useful in formulating research hypotheses and drawing up management options. The objectives of the Gazi model are similar in this respect. The abstraction of the system is presented as a box and arrow diagram showing storages and flows of matter. Changes in each of the state variables are function of some input and output processes and are represented in the model equations as ordinary differential equations. The processes are variously formulated using published ecosystem models, field data and personal effort. For ease of conceptualisation the modelling exercise has been handled in several submodels. The majority of the rate coefficients were estimated from field and literature values whereas a few others were chosen arbitrarily. Computer simulation of the system was done in an IBM compatible PC using a simulation package. A sensitivity analysis was carried out to investigate the sensitivity of the model to changes in input and parameter values. The favourable comparison between model output and information available points to the relative accuracy of the model. The results show that the nutrient contribution of the mangrove ecosystem to the contiguous zones is negative. The system exports carbon largely consisting of detritus poor in nitrogen. The flow of nitrogen through bacteria accounts for 72% of the total system nitrogen through flow (not including the import of nitrogen into the system). The mangrove ecosystem strongly consumes nitrogen and compensates for this by using inorganic nitrogen in the tidal water and possibly from sheetflow and underground seepage. More information is needed on the grazing habits of detritivores.
  • Assessing the Potential of Small-Scale Aquaculture in Embu District, Kenya using GIS and Remote Sensing.

    Mukami, Ngarari M. (Moi University, 2010)
    Site selection for aquaculture development is a complex task involving identification of areas that are economically, socially and environmentally suitable, which can also be available for aquaculture. Geographic information systems and remote sensing technologies, which facilitate the integration and analysis of spatial and attribute data from multiple sources, have been widely used for selecting suitable sites for different land uses. This study used these technologies to identify sites suitable for aquaculture development in Embu District and assessed its potential contribution to food security and economic development in the area. The study developed map-based site selection criteria, using soil quality, water availability and socio-economic factors. These criteria were then implemented, aquaculture potential sites identified, the total area estimated and the economic impact assessed. The study predicted that about 20% (9,563 ha) of the total arable area of 47,800 ha in Embu District is suitable for aquaculture development. The study estimates that if aquaculture is optimally combined with other existing land use activities, it can contribute over Kshs. 9 billion per annum to the district’s revenue. Comparing this with the current 7 ha under aquaculture, Embu District has potential for improving its economic status through aquaculture development. The study recommends that similar studies be carried out throughout the country so as to improve food security and wealth creation.
  • Optimal Management Policy for the Kenyan Marine Artisanal Fishery.

    Warui, Simon Wahome (University of Iceland, 2014)
    A marine artisanal fishery under open access regime was feared to be overexploited and unsustainable to declining catch per unit effort and increased fishing effort. A bioeconomic model on the fishery was developed based on Gompertz-Fox surplus production model (Fox, 1970) to analyse the fishery. The objective was to determine the optimal utilization policy and its benefits and the path and appropriate management system to drive the fishery to the optimality. The analysis indicated the fishery exploitation was lower than maximum sustainable yield (MSY) level and thus sustainable though at sub optimum. The optimum sustainable policy was at maximum economic yield (MEY) level, which was lower than the MSY. The current fishing effort was causing dissipation of the fisheries rent. The fishery can generate over30% more profit than currently is, by reducing the current effort by 36%. An optimum dynamic adjustment path for the fishery to the long run sustainable fishery was developed that was more efficient with high present value of profits. Its implementation was considered drastic to the fishing community and fishery linked industries that are likely notable to adjust quickly to the change. A moderate path considered more acceptable but with 8.6% loss in PV. A property right management system was recommended, with allocation of quota to the fishermen through the existing community based fisheries management system for its administration.
  • Current Status, Utilization, Succession and Zonation of Mangrove Ecosystem along Mida Creek, Coast Province, Kenya

    Warui, Mary Wanjiru (Kenyatta University, 2011)
    Mangrove forests have been destroyed as a result of human activities and this is a threat to the mangrove ecosystem and the living things depending on them. Research on the current status, utilization, succession and zonation of mangrove ecosystem was conducted along Mida Creek, Coast Province, Kenya from September 2009 to February 2010. Objectives were to: assess the changes in the floristic composition of the mangrove forest; identify the most preferred mangrove species; investigate whether accessibility determines utilization of mangrove species; examine whether harvesting of mangroves affect their succession and to explore the current mangrove forest management policies and their effectiveness. Point- Centred Quarter Method (PCQM) was used to collect data that was used to investigate whether accessibility into the mangrove forest determines their utilization and to assess whether succession of the mangroves is affected by their utilization. Questionnaires were distributed and interviews conducted to explore the effectiveness of government policies/ legislation governing utilization of the mangroves and to investigate the most preferred mangrove species by the local community and other users. The total number of respondents interviewed was 136 one from each household out of the 210 households in Mida Creek. Two sets of Aerial photographs (1992 and 2006) were processed and interpreted to assess the temporal changes in the floristic composition of the mangrove forest. Questionnaires were coded and entered into Statistical Package for Social Sciences (SPSS). Analysis of Variance (ANOVA) was performed to investigate whether accessibility of mangroves determine their utilization. Regression analysis was performed to assess whether utilization of the mangroves affect their succession. Importance value was calculated to assess the forest structure. Descriptive statistics were performed to summarize the current mangrove forest management policies and their effectiveness. Results showed that the floristic composition of mangrove forest in Mida Creek has changed between year 1992 and 2006; Area covering mangroves has decreased as follows: Rhizophora mucronata (Rm); 65.09-63.93ha; Avicennia marina (Am); 344.99-310.63ha; Ceriops tagal (Ct); 225.12-223.82ha; Rm and Ct; 52.87-50.22ha; Ct and Am; 143.69- 140.29ha; Rm and Am; 44.36-41.27ha; Rm and Bg; 212.75-199.75ha; Rm and Sonneratia alba (Sa); 47.64-46.32ha; Rm, Ct and Bruguiera gymnorrhiza (Bg); 129.07-128.12ha; Rm, Am, Ct and Bg; 472.44-428.46ha. ANOVA test showed that there was a significant difference (F=3.277; df=2; p=0.040) between the number of cut mangroves in the near settlements, middle and shoreline hence accessibility determines utilization. Results also showed that Rhizophora mucronata is the most preferred mangrove species. Regression analysis showed that there was a relationship between the number of mangrove seedling and the number of cut mangroves (F=8.529, df=1, R=0.198, P=0.004). Utilization of mangroves affects their succession. The policies/legislation governing mangrove utilization have been less effective. Rhizophora mucronata and Ceriops tagal were the key species in Mida Creek. Mangrove forest area in Mida Creek has decreased over a period of time.
  • The Impact of Human Activities on the Ephibenthic Bivalve Community in Protected and Unprotected Marine Areas at the Kenyan Coast

    Boera, Priscillah N. (Moi University, 2001)
    A comparative survey of bivalve fauna found in reef flat, sea grass zones and shallow lagoons «2m) was undertaken in protected and unprotected marine areas to determine the density, diversity and species richness and the possible impacts of human activities on these mollusks. Data was collected by laying 3 transects of 400m2 in each site at the three areas. All bivalves observed were identified, their shell lengths measured and evidence of any kind of human interference recorded. Data was analyzed through use of species richness, diversity and similarity indices, coefficients of dispersion and covariance. These parameters were used to compare and describe species composition at each study site. Human activities were expressed in percentage frequencies of occurrence. The most prevalent human activity was then used to show the impact on the most vulnerable bivalve species A total of 17 bivalve species belonging to 13 families were observed in both the protected and unprotected areas of the Kenya coast from Oct. 1997March 1998. Their distribution showed low densities (2 bivalves/m2), low diversity (1.26 ± 0.005) in species composition and distribution (0.06475 ± 0.03) in the different substrate types. Modiolus auriculatus (0.473 ± 0.02) and Pinna muricata(0.45 ± 0.03) were the most prevalent. There was a significant difference in species diversity between Malindi and Mombasa reef flats at P<0.10. Shallow lagoons had very low relative density (0.49 ± 0.05) and diversity (0.068 ± 0.022) as compared to that of the reef flat which exhibited the highest density of (0.691 ± 0.017). This was attributed to the high deposits of shell, coral, and sand. Species composition classified up to family level showed Mitilidae (54% ad 44%) as the most represented in Kanamai and Malindi areas respectively; and Pinnidae (36%) in Mombasa. Abundance similarities were low (65 %) but for the lagoon (86.9%) and reef flat (90.0%) of Mombasa. Most bivalve species were clumped together (11421) or uniformly distributed (0- 0.395), with a few showing random distribution (1). Swimming, goggling/ SCUBA diving, walking/ trampling and turning of rocks were identified as the main forms of human activities causing disturbance. Frequencies of occurrence of these activities varied in the three areas with Kanamai exhibiting the highest. Results showed that the distribution of bivalve fauna in the protected and unprotected areas is bivalve density independent and not only influenced by human activities and management strategy but by other biological and environmental factors such as substrate type, tide range and wave activity. Human activities however affect those bivalves with fragile shells such as P. . muricata, through trampling resulting in injury and / or death. Therefore decentralisation of human activities within the marine parks is recommended to reduce their impacts. These activities can be carried out in the reserves. Beside marine protected areas are insufficient alone as they are not isolated from other critical environmental impacts and thus should' be complemented with strong conservation efforts outside the parks.
  • Ecology and Restoration of Mangrove Systems in Kenya.

    Kairo, J.G. (Vrije Universiteit Brussel, 2001)
    Chapter 1 presents a global picture of mangroves, what they are, their value, threats and efforts being made to address the problems. Mangroves once occupied 75% of the tropical coasts worldwide (McGill, 1959), but anthropogenic pressures have reduced the global range of the forests to less than 50%. Mangrove forests in Kenya are estimated to occupy about 54,000 ha, 70% of which occurs in Lamu district. There are 9 recorded mangrove species in Kenya. Chapter 2 provides a description of the study area -- the Kenyan coast. The coastline runs for approximately 574 km in a NNE and SSE direction, between latitudes 1~'40'S and 4~'25'S and longitudes 41~'34'E and 39~'17'E, The agro-climatological zones along the Kenyan coast differ markedly from the north to the south. The relative humidity is higher in the south than in the north. These differences in climate and ocean currents cause a strong divide between the vegetation types such that the northern mangroves in Lamu are structurally more complex than the southern mangroves in Mida creek. Chapter 3 details mangroves of Mida creek, defined in this study as young secondary mangrove stand that is vigorously growing, but subjected to periodic harvest. While we may be contented with the good natural regeneration that has taken place in Mida, close analysis reveals that Mida mangroves are in fact degenerating. What was harvested is not what is coming up. Mangrove harvesting in Kenya proceeds in a selective manner. Rhizophora mucronata is the preferred mangrove species because it produces poles that are hard, tall and straight. The most merchantable pole size is the boriti, with butt diameter range of 11.0-13.5 cm. Others are mazio (diameter 7.5-11 cm) and pau (5.0-7.5 cm). Poles greater than 15.0 cm diameter (banaa) are of less economic value and are therefore left standing in the forest. Excessive removal of boriti and mazio sized poles has created complex mangrove silvicultural problems in Kenya. The overgrown banaa canopy shade out juveniles and young trees and cause them to be crooked as they try to grow in an open space inside the closed forest canopy. In open canopy areas, the less preferred Ceriops seedlings are regenerating at the expense of the removed Rhizophora trees. Chapter 4 is about the application of remote sensing and GIS technology in mapping the mangrove forests within and adjacent to the Marine Protected Area (MPA) of Kiunga, Lamu. The stand volume ranged from 6.85 m super(3)/ha to 710.0 m super(3)/ha. The average stand volume was 145.88 m super(3)/ha, which corresponds to a stocking rate of 1736 stems/ha. Given its high potential productivity and regeneration, mangroves within and adjacent to KMNR have excellent prospects for sustainable exploitation. The management of mangroves as renewable resources poses severe problems in that natural regeneration seems to be insufficient where large-scale operations have taken place. To sustain the yield of these forests there is a need to address both artificial and natural regeneration methods. Artificial mangrove planting in Asia has been promising in solving the problems of limited supply of mangrove products as well as maintaining the overall ecological balance of the coastal system. In Chapter 5, assessment is made of the above ground biomass increment of mangrove plantations that were established at Gazi bay in 1991. The above ground biomass of a 5-year old Rhizophora plantation was calculated at 20.25 t dry matter ha super(-1) for trees with stem diameter greater than 5.0 cm. Finally in Chapter 6, a comparative analysis of mangrove forests along the Kenya coast is provided. Emphasis is given to the mangrove areas where this study was done. The variation of mangrove forest structure in Kenya occurs due to differences in environmental settings as well as differences in the levels of human pressure. Mangroves north of Tana river are river and tidal dominated systems, with a lower human pressure than mangroves south of the Tana river.
  • Design of an Efficient Fishing Vessel for the East African Coast.

    Shiundu, Juvenal J.M. (University of Newcastle upon Tyne, 1983)
    This project is divided into two parts, Part A is a feasibility study in which a brief background study of the Kenya Fisheries Department, fishing vessels, efforts and the areas being fished is examined. Fish species, catch and market potential are also examined. From the inference in Part A, a design of a fishing vessel suitable to the local conditions has been developed in Part B. The building cost of the new design was estimated and an economic evaluation studied using the net present value as a measure of merit.
  • The Larval Development and Juvenile Growth of the Silver Mouth Turban, Turbo argyrostomus.

    Kimani, E.N. (University of the Ryukyus, 1996)
    The silver mouth turban, Turbo argyrostomus L. 1758, is an archeogastropod widely distributed throughout the Indo-Pacific region. It is an important marine resource, harvested for food, marine souvenirs and ornamental items. Mass seed production techniques for Turbo marmoratus and T. Argyrostomus, based on the techniques developed for Trochus niloticus in Palau, are currently being developed in the Okinawa prefecture, Japan, to replenish the declining populations of these commercial turbinids. Here, I report on the larval development, metamorphosis and the effect of diet on growth and shell characters of silver mouth turban juveniles, raised in the laboratory. I studied the larval development, metamorphosis and juvenile growth of T. argyrostomus between August 1995 and July 1996. Adults collected from Komesu, southern Okinawa Island, were induced to spawn by packing and UV sterilised seawater treatment on 9 August 1995. The green eggs (180-190 mu m in diameter) hatched within 18 hours, underwent torsion a few hours later and metamorphosis inducing cues. Forty-eight percent of 200 competent veligers spontaneously metamorphosed in the absence of metamorphosis inducing cues between 7 days and 21 days after fertilization without feeding. The protoconch, 170-185 mu m diameter, was colorless and globose in shape with irregular articulations. The juveniles grew to a mean shell length of 3.7mm in 5 months (mean growth rate of 0.7mm per month) feeding on microalgae growing on coral rubble and the sides of the aquaria, and grew to 11.5mm in 9 months (mean growth rate of 2.7mm per month) feeding on macroalgae. Small juveniles of mean shell length 3.9mm, reared on a small fleshy red algae, Gelidiella acerosa, grew approximately 2 times faster than those reared on the green algae, Ulva purtusa, over 18 weeks. The combined diet of these two algae species gave higher growth rates than either algae individually, but did not higher growth significantly in large juveniles with an initial shell length of 5.8mm. Percentage survival after 18 weeks was higher for juveniles reared on red algae (92.2%) compared to green algae (81.1%). The shell color of the snails depended on the algal diet. The shells of juveniles collected from the reef were heavier, for the same size, than those reared in the laboratory. The juveniles reared on mixed algae growing on coral rubble, collected from the reef, and the green algae had higher mean shell weights than snails reared on red algae alone or on a combination of green and red algae.
  • Macrobenthos of Eastern African Mangroves: Life Cycles and Reproductive Biology of Exploited Species (MEAM) - Final Report INCO-DC: contract number IC 18-CT96-0127 (MEAM).

    Institute of Marine Sciences, University of Dar es Salaam, Zanzibar; University Eduardo Mondlane, Mozambique; University Of Transkei (Unitra), Umtata, South Africa; University Of Liverpool; Imar - University Of Lisbon; Museo Zoologico La Specola, University of Florence; Kenya Marine Fisheries and Research Institute (KMFRI) (Museo Zoologica "La Specola", Universita degli Studi di FirenzeFlorence, Italy, 2000)
    The MEAM objectives were: 1) to determine patterns in population structure, along a geographic gradient, of species selected for their commercial and/or ecological importance, by means of a standardised protocol to be developed within the project, 2) to study the growth. population structure and reproductive patterns of the above species, 3) to investigate the temporal pattern of larval release, 4) to analyse the behaviour of the pelagic larvae leading them to settle on the substratum, 5) to study the genetic flow between several coastal populations of a key species, in order to evaluate its interpopulation migratory effect, 6) to identify the relationships between the macrobenthic species and, more generally, the mangrove ecosystem and human activities. At different levels, all the MEAM objectives were fulfilled: 1) a technique of visual census of macrofauna was designed and repeatedly tested, providing comparable results independently of the observer and locality; for the first time, there is a simple method that permits any type of monitoring and ecological survey to be comparable in time and space. Validation coefficients (between 50% and 80%) are also available to correlate the census results with the actual animal density. From stomach content analysis, we could prove that, all along the East African coast, Scylla serrata, one of the most commercially important species, spends most of its time within the mangroves, feeding on macrobenthic species. In contrast, several important prawn species were only found as juveniles; thus for them, mangroves act as a nursery. In both cases, the importance of a healthy mangrove system is the basis for a sustainable management of the stocks of these species. 2) For the first time, we are able to compare the reproductive cycles of different species. Different patterns appear to dominate decapod life: periodic breeding can be found (i.e. Uca vocans), together with both semi-lunar and lunar periodicity; the latter is concentrated in a short period of the year (Neosarmatium meinertl), through most of the year with an interruption for the rainy season (i.e. Sesarma ortmanni) or throughout the year (i.e. U. annulipes). Due to the accurate and synchronous sampling strategy, we can for the first time ensure that the different reproductive patterns actually concern the basic biology of the species and not just latitudinal, geographical, or micro-climatic variations. 3) The results indicate a universal pattern of semi-lunar release centred on post-crepuscular ebbing tides and they allow us to generalise patterns of release for mangroves, namely the cyclic character of the reproductive timing and its relation to the major environmental cycles. 4) Patterns of larval fluxes and settlement in mangrove areas were described and they show a universal character: most species in mangroves will export their newly hatched stages to adjacent neritic water masses where they undergo most of their larval development. Return migration is accomplished by megalopa stages, and our results indicate an interaction between deterministic (cycles of tidal amplitude) and stochastic (wind stress) factors in the recruitment success of the different species. 5) We studied about 530 bp (base pairs) of the mitochondrial DNA cytochrome oxidase subunit I (mtDNA COl). The results indicate that gene flow is unexpectedly low and suggest that a population structuring is currently occurring. In order to prevent inappropriate S. serrata resource exploitation, it is advisable to refer to the local population as the appropriate short-term management unit. 6) The relationship between human activities and the mangrove ecosystem proved to be quite different among the three study sites: mainly timber cutting - mostly illegal - in Kenya; charcoal activity in Zanzibar; artisan fisheries and small-scale gathering in Mozambique. Where mangroves are seriously threatened (Kenya and Zanzibar), our detailed enquiries showed that people are well aware of the ecological and geo-morphological importance of mangroves. Nevertheless, due to the lack of alternative sources of revenue, they will not easily refrain from their destructive activities. Eco-tourism or similar activities are not seen as adequate alternatives, while cattle breeding or increased coconut cultivation could be. Unfortunately, both of these activities are limited by the lack of financial investment (cattle) or available land (coconuts).
  • Suspended sediment transport and exchange in Port Reitz Creek with special focus on the mangrove fringed Mwache wetland, Kenya.

    Kitheka, Johnson U. (Goteborg University, 2000)
    This study deals with dynamics of water exchange and sediment flux in the 17 Km super(2) mangrove-fringed Mwache wetland in Kenya. The study was implemented in the period between March 1998-March 1999. The creek experiences semi-diurnal tides with a spring tidal range of 3m. It receives freshwater only in rainy seasons, mainly from Mwache and Bome rivers whose total catchment area is 1900km super(2) and river discharge is less than 10m super(3)/s in normal rainfall years. There is usually no river discharge in dry seasons. The aim of the study was to determine the influence of tidal circulation on sediment transport in mangrove fringed creek systems. The study involved measurements of suspended sediment concentrations (SSC), salinity, temperature, current velocities and sea levels both in the tidal channels and in the mangrove swamp forest. Long-term SSC, sea level and current velocities were measured with an Orbital Backscatter Sensor, Micro Tide pressure gauges and a SD-6000 current meter respectively. A pressure gauge connected to a Backscatter sensor was also used to measure SSC along the creek. In addition SSC were determined by filtering water samples drawn from different levels of the water column with a Hydrobios water sampler. Water temperatures and salinities were measured in situ using an Aanderaa Salinity-Temperature sensor. The results show that the SSC is higher in the upper mangrove fringed creeks and lower in the frontwater zones bordering the Indian Ocean. The mean near surface SSC in the upper mangrove region is 0.16 g/l. while that in the lower region is 0.03 g/l. Near bottom SSC (in the upper zone) were usually higher and reached 1.40g/l. In the lower frontwater zones, the near bottom SSC was of the order 0.10g/l. At the creek entrance, the mean tidal volume fluxes in spring and neap is 2233 m super(3)/s and 937 m super(3)/s respectively. The (near bottom) mean tidal suspended sediment fluxes in spring and neap are 1220 Kg /s and 400 Kg/s respectively. The tidal sediment flux during flood tide ranged from 460 to 1740 Kg/s as observed at a cross-section near the entrance of the creek. The ebb ones were much lower being in the range 330-690Kg/s. Major resuspension of bottom sediments which raises SSC to values higher than 1.0 g/l, occurs only during flood tide at spring when the current velocities reach 1 m/s or more. The turbidity maximum zone (TMZ) with the highest SSC occurs in the upper middle region of the creek (Stn 3-6) where SSC is in the range 0.07-0.16 g/l. This zone coincides with the salinity maximum zone (SMZ) with salinity in the range 36-38 in the dry season. Calculations using formulas for erosion and deposition within the main tidal channel for the period between 15 and 23 February 1999 showed that erosion reach 6.0 x 10 super(-4) Kg/m super(2)/s while deposition reach 5.0 x 10 super(-5) Kg/m super(2)/s. Erosion dominates during periods of high current velocities and deposition during periods of low current velocities, which occur at low and high waters. A coarse comparison between total sedimentation and river sediment supply indicates that most of the riverborne sediments are trapped within the creek. In dry season with low sediment supply from the rivers, sediments are imported into the creek from Kipevu basin. Sediments re-suspended during spring flood tide enter the mangrove swamp where they are trapped due to the dense mangrove vegetation and sluggish current velocities of the order 0.05 g/l in the mangrove swamp. Sedimentation rate in the mangrove swamp is of the order 250 g/m super(2) per spring tide, corresponding to an accretion rate in the mangroves of the order 30 cm/100 years. This is higher than the estimated local sea-level rise of 22 cm/100 years, implying that Mwache mangrove swamp is keeping up in pace with sea level rise.
  • Are Peri-urban Mangrove Forests Viable? Effects of Sewage Pollution and Wood Exploitation on the Structure and Development of the Mangroves of Mombasa (Kenya)

    Mohamed, M.O.S (Vrije Universiteit Brussel, 2008)
    Acknowledging the increasingly prominent urban character of ecosystems globally, mangroves being no exception, and possible impediments to the viability of these ecosystems (i.e. the inherent capacity or ability to grow, develop or recover after disturbances), we adapt a system‟s approach to establish the viability of the peri-urban mangrove of Tudor creek in Mombasa, Kenya. Three important aspects of the peri-urban mangroves are assessed. These include (i) structural aspects (vegetation structure and regeneration), (ii) functional aspects (productivity) and (iii) human aspects (socioeconomics).
  • The Impact of Indirect Effects of Climate Change on Mangrove Associated Biodiversity.

    Jenoh, E.M. (Vrije Universiteit Brussels, 2009)
    Periodic episodes arising out of global climate changes seem to pose a reasonable threat to the integrity of mangrove ecosystem. Mangrove macrofauna, which are residents of mangrove areas throughout their adult life, stand to be highly affected by the Periodic episodes arising out of global climate changes. During the 1997/8 8 El- Niño event, massive sedimentation due to erosion of terrigenous sediments caused mangrove dieback in many areas along the Kenyan coast. Mwache Creek a peri-urban mangrove forest in Mombasa was the most affected resulting in mangrove death covering about 200ha. Biodiversity in El-Niño impacted sites was compared to reference (natural forests) sites in order to assess the impact of climate change to mangrove associated biodiversity. Transects (sea-landward transect) were laid in both impacted and natural sites where relevant physico-chemical variables were measured and mangrove biodiversity determined as an indicator of ecosystem change. Molluscs densities and diversity were found not to be significantly different between treatments (impacted and reference sites) while crabs diversities was significantly higher in reference sites than impacted sites. Faunal diversity of Molluscs in impacted sites was found to be sustained by invasive shrubs while crab densities and diversity was highly reduced by the mangrove dieback.
  • Community Structure and Spatio-Temporal Variability of Ichthyoplankton in Kenyan Coastal Waters.

    Mwandawiro, James Mwaluma (Moi University, 2010)
    Temporal and spatial variability in abundance and distribution of fish larvae contributes to structuring populations of adults within coral reef habitats and influences connectivity of reef sites. However, few studies have examined this variability at different spatial and temporal scales in the Western Indian Ocean (WIO). In an effort to bridge this gap, this study examined patterns of fish larval supply in Malindi and Watamu Marine National Parks between March 2005 - March 2007. Additionally, the study examined large-scale spatial variations in larval assemblages along lagoonal reef sites at a span > 160 Kms, and the inter-annual variability in alongshore assemblages of fish larvae at this scale. Larvae were sampled using a combination of plankton nets and light-traps. A total of 56 families, 45 genera and 21 species of larvae were identified in Malindi Marine Park, while, 21 families, 14 genera and 6 species were sampled in Watamu Marine Park. The dominant taxa at both sites were; Blenniidae (Parablennius sp. and Omobranchus sp.), Engraulidae (Stolephorus commersonii), Gobiidae n.d, and Pomacentridae (Abudefduf sp.). Seasonality was found to have an effect on the occurrence of larvae over the two parks, with segregation of distinct larval groups within and between the parks on a small spatial scale. Inter-annual variations in distribution of larvae and larval assemblage structure suggested annual differences in spawning patterns. Correspondence Analysis, indicated differences in species-site associations between years. Data suggested overall spawning by fishes on the north Kenyan coast with subsequent likely transport of larvae to the south. Hatch dates derived from otolith analysis of commerson’s anchovy, Stolephorus commersonii, were; January - March 2005, August - September 2005, December - February 2006. Monthly growth rates for S. commersonii larvae and juveniles were highest in the northeast monsoon months of December (0.207 and March 2005 (0.119, and lowest in southeast monsoon months of July (0.056, and April (0.0105 2006, respectively. Finescale temporal variation in larval supply to Malindi Marine Park indicated that larval supply to the park was mostly nocturnal, with a peak during spring tides. Time-series spectral analysis showed that larval supply to Malindi Marine Park occurred after a 30 day cyclical period associated with the new moon lunar phase. This study provides, for the first time, a synoptic account of the taxonomy, distribution and relative abundance of nearshore fish larval assemblages in lagoonal waters of coastal Kenya, and contributes in providing baseline data useful in understanding fish population replenishment in lagoonal reefs.
  • Restoration of Kenyan seagrass beds: a functional study of the associated fauna and flora.

    Mutisia, Lillian Nduku Daudi (Vrije Universiteit Brussel, 2009)
    Seagrass communities are subject to frequent anthropogenic and natural disturbances that can lead to alterations in vegetation complexity and hence may affect associated fauna. Seagrass loss in Kenya has been mainly due to extensive grazing by the sea urchin Tripneustes gratilla which has affected almost the entire coastline. This has led to habitat fragmentation and sometimes vast areas of defoliated beds that were formerly covered with seagrass. The most affected species has been Thalassodendron ciliatum. Diani beach, south of Mombasa, is an area that has been typically affected by seagrass depletion. Natural recovery has been reported in certain areas and transplantation projects were started. The challenge is to see if the system can recover fully and will be able to function as before. To test this, the current study focused on the density, diversity and community structure of meiofauna, and more specifically of harpacticoid copepods as a measure of the ability of the system to recover. Artificial seagrass mimics were planted in natural, replanted and areas of bare sand and harvested in a series of 2, 4, 6, 10, 14 and 21 days in order to collect the associated meiofauna. Related environmental parameters were collected at the same time intervals except for the sediment samples for environmental analysis that were sampled once during the study period at the last day of collection of mimics. Significant differences of meiofauna densities between the sites and the colonization days were found but for harpacticoid copepods there was only a significant effect of the colonisation time. The densities of meiofauna reached those of natural seagrasses by day 4 but most of them were opportunistic species and not true phytal dwelling meiofauna. Both passive migration from neighbouring seagrass patches and active migration from sediments were observed, based on the harpacticoid copepod family composition. In the bare and replanted sites similar community structures of harpacticoid copepods were observed from day 6 onwards while for the healthy site it was from day 10. Colonization by epiphytic biofilm was collected from day 10 in the bare and replanted sites but not the healthy site. In the previous days it was too negligible to be collected. The results thus suggest possible recovery of harpacticoid copepods after disturbance thanks to their mobility and ability to colonize new areas quickly. However, this may depend largely on the time the epiphytic flora are able to recover as well as the recovery time of the seagrass plants which may take approximately 4 years.
  • Wetland Conversion to large-scale agricultural production; implications on the livelihoods of rural communities, Yala Swamp, Lake Victoria basin, Kenya.

    Kinaro, Zachary Omambi (Linköping University, Sweden, 2008)
    Wetlands in most parts of the world are under threat of over-exploitation, loss and/or degradation partly due to agriculture and urban land uses. Yala swamp, the largest fresh water wetland in Kenya measuring about 17,500 ha supports a large biodiversity and is source of livelihoods to communities around it. This study addresses the situation where part of this wetland is converted into large-scale agriculture by a multinational company, Dominion Farms (K) Ltd resulting into a conflict and controversy amongst key stakeholders. The study was undertaken to explore and seek an understanding of the controversy and investigate the livelihood impacts this wetland transformation has for the local community in order to generate relevant data for managing the wetland. This paper gives the status of the wetland using the concepts Stakeholder Analysis (SA) and Sustainable Livelihood Approaches (SLA) to assess the livelihood situation in terms of the socio-economic conditions, rural infrastructure, income diversification, food security and environmental management issues. Data and information have been obtained from primary and secondary sources through field survey in the Yala wetland, in which randomly sampled small-scale farmers, fisher folk, Dominion employees, local leaders and informants, traders and other stakeholders were interviewed using questionnaire and other participatory methods. The main questions were designed to gain information about historical use of the wetland, changes in livelihoods and wetland before and after entry of Dominion Company into the area. From the study, it is evident that assessment of the key stakeholders and their relation to this natural resource is of utmost importance for mapping out an acceptable management strategy for the wetland. Besides being cause to a conflict and controversy over control of and access to the swamp, the conversion of part of this wetland has resulted into both negative and positive short-term and long-term livelihood impacts to the local community. The wetland is a contested resource with multiple users who claim a stake on it requiring a holistic approach to its management that integrates divergent needs and views of key stakeholder groups. Through such a mechanism the planners and policy-makers can identify and fairly address trade-offs therein between large-scale agriculture and sustainable ecosystem utilization, while maintaining the benefit flow to the local community. The study identifies management issues and proposes abroad vision for the future that will help minimize conflicts and food insecurity in the area. General recommendations for planning as well as suggestions for specific research needs that should form the basis of action are given.
  • Environmental Factors and Coral Bleaching in Kenya.

    Mdodo, Rennatus Magina (Moi University, 1999)
    Elevated seawater temperature in March and April 1998 caused by the El Nino Southern Oscillation (ENSO) caused mass coral bleaching along the Kenya coast. The ENSO event had an effect on the climate of the study area and the region in general, with heavy rains starting in October 1997, and continuing to July 1998. Seawater temperature in March and April rose to an average 1.5 °C above values measured in the same period in 1997, with daytime low-tide highs of over 32°C. Coral bleaching is the whitening of corals resulting from the loss of symbiotic zooxanthellae and/or a reduction of the photosynthetic pigment concentrations in zooxanthellae. Bleaching was first observed in October 1997 in Kanamai during and after the El Nino rains, most likely due to sedimentation and seawater dilution in the shallow lagoon. In November 1997 bleaching was recorded in Malindi Marine National Park (MNP) and was mainly caused by sediment discharged from the Sabaki River. Later, extensive temperature induced bleaching and subsequent coral mortality was observed in mid March 1998 covering the entire coast of Kenya. Over 90% bleaching and mortality was recorded in Mombasa MNP, Malindi MNP and Kanamai. Bleaching and mortality was highest in the shallow lagoons such as Kanamai and areas where corals are exposed to sediment influence such as the north reef of Malindi MNP. The coral species most susceptible to bleaching and mortality were Porites nigrescens, Porites lutea, Acropora spp, Pocillopora spp and Stylophora pistillata. There was a distinct relationship between temperature and bleaching. As temperature increased to a maximum 32°C the number of normal coral colonies decreased due to bleaching and mortality. Temperature vs. bleaching relationship indicated a strong positive correlation for normal Porites nigrescens (r2 = 0.779), Porites lutea (r2 = 0.781) and Pocillopora sp (r2 = 0.803). The density of zooxanthellae ranged between 0.7 x 106 and 4.5 x 106 (mean, 2.5 x 106 ± 1.2 x 106, n = 11) per cm 2 for normal corals and 0.02 x 106 and 0.2 x 106 per cm 2 (Mean, 0.2 x 106 ± 0.02 x 106, n = 6) for bleached corals; Total loss of zooxanthellae and pigment was recorded in a few coral fragments. Zooxanthellae densities showed significant differences between species ((P<0.001) and between normal and bleached decussata had the highest zooxanthellae densities while Acropora sp and Stylophora pistillata had the lowest. The concentration of Chlorophyll-a ranged between 0.176 mg/cm2 and 0.795 mg/cm2 (Mean, 0.498 ± 0.287 mg/cm2 , n = 11) for normal corals and 0.002 mg/cm2 and 0.284 mg/cm2 (Mean, 0.0765 ± 0.01 mg/cm2, n = 6) for bleached corals. Chlorophyll-a concentrations differed significantly between bleached and normal colonies (p<0.005) and between species (p<O.OOI). In normal corals Porites nigrescens and Pavona decussata had the highest chlorophyll-a concentrations while Acropora sp and Stylophora pistillata had the lowest. Chlorophyll-a concentration per zooxanthellae was not significantly different between species but was significant between bleached and normal fragments (p<0.05). Bleached corals had higher values of chlorophyll-a per zooxanthellae compared to normal corals as can be observed in Acropora sp, porites nigrescens, porites lutea and Pavona decussata. Only in Slylophora pistillata that bleached fragments had a lower value of chlorophyll-a per zooxanthellae compared to the normal fragments. Overall this study indicates that coral bleaching and consequent mortality was caused by two sets of stressors; sediment/rainfall stress in Kanamai and Malindi in 1997 and elevated sea surface temperatures in all the sites in MarchiApri11998.
  • Land Degradation in the Semi-Arid Catchment of Lake Baringo, Kenya - a minor field study of physical causes with- a socioeconimic aspect.

    Johansson, J.; Svensson, J. (Göteborgs UniversitetGöteborg, Sweden, 2002)
    Growing population in vulnerable semi-arid areas has led to exerted pressure on the land, which often has resulted in severe degraded land, soil erosion and sedimentation of open water bodies. The Lake Baringo region, in mid-west Kenya, exemplifies most of the problems of those marginal areas. The lake is situated in a semi-arid area but its catchment is characterized by large topographic gradients giving rise to considerable climatic and ecological differences. This Minor Field Study (MFS) focus on the environmental degradation in the catchment of Lake Baringo and on the physical causes and consequences of the factors contributing to the constant shrinkage of the lake, as altered hydrological conditions, climatic change, land cover changes and soil erosion. Also social and cultural aspects have been taken into account. Several methods have been used in this study, including field work, remote sensing, data analysis and interviews. During the last decades both the depth and the area of Lake Baringo has decreased dramatically. The study show that the shrinkage of the lake is due to both siltation and inadequate water volumes flowing to the lake resulting in a negative water balance. The increased erosion and sediment transport to the lake and changed hydrologic pattern is primarily caused by altered landcover, as deforestation, in the catchment area, but amplified by changed rainfall conditions. The rainfall data show a slight decreasing trend, but the year-to-year variability of the precipitation is very large so the uncertainty is high. However, our data clearly indicate a significant decrease in the frequency of rainy days. This could mean enlarged rainfall intensity, since the rainfall amount per rainy day is increasing. Even a small increase of intensity could have large effect on the soil erosion since the rains often fall on poorly protected soil with extreme erodibility and very high runoff yield. The soil erosion has a large impact on the arable land, water availability, etc. The bare land is increasing mainly a result of extensive overgrazing, which leads to a constantly decreasing vegetation cover. The changed landcover is in many respects an effect of the increased population combined with the large social importance of livestock. The interviews show that a key factor to solve the overgrazing problems could be to privatise the land.
  • Macroinvertebrate Index of Biotic Integrity for Assessing the Water Quality of Rivers Kipkaren and Sosiani, Nzoia River Basin, Kenya.

    Aura, Christopher Mulanda (Moi University, 2008)
    Globally, IBI is being applied as an integrity tool in monitoring and bioassessment of aquatic ecosystems such as rivers. The study set out to investigate the possibility of establishing an Index of Biotic Integrity (IBI) using macroinvertebrates to asses the water quality with special reference to nutrient levels of Rivers Kipkaren and Sosiani in the upper reaches of River Nzoia Basin, Kenya. Physical water quality parameters like pH, conductivity, temperature, water velocity and discharge were measured while chemical parameters such as DO, TP and TN were determined calorimetrically in the laboratory using standard methods. Habitat and land use characteristics were also recorded. Triplicate macroinvertebrate samples were collected semi-quantitatively on a monthly basis from December 2006 to May 2007 using a 0.5 mm mesh size scoop net in the riffles, pools and runs. Macroinvertebrates were analyzed for abundance and diversity and related to the nutrients (TP and TN) using the Spearman’s correlation analysis. Statistical tests of Mann-Whitney U and Kolmogorov-Smirnov tests were used for pair wise comparison in all the stations and provided 9 macroinvertebrate metrics that contributed significantly (p<0.05) to the final IBI. SPSS for Windows version 10.0 and Microsoft Excel computer packages were used for statistical analyses. A total of 31 macroinvertebrate genera for River Kipkaren dominated by the EPT and 19 macroinvertebrate genera for the lower River Sosiani dominated by dipterans were recorded. Significant differences in the mean abundance (F= 16.371; df = 6; p = 0.000) and diversity (H=7; df=7; p=0.0032) between the stations were found that indicated differences in water quality. A significant positive correlation for TN and TP and macroinvertebrates was obtained (p=0.00; r =0.39). In the final IBI, River Kipkaren stations had better water quality with IBI ranging from 27 to 39 points, while River Sosiani stations fell in classes of fair to poor water quality and IBI ranging from 19 to 22 points out of the total 45 points due to variations in anthropogenic impacts. The study recommends the use of IBI in biomonitoring and bioassessment of rivers to improve the river health and thus biotic integrity because the IBI delineates impacted from less impacted sites along the rivers. An alternative preliminary IBI using fish and algae assemblages should also be explored for comparison in the Nzoia River Basin.
  • Development of a Quality Index Method (QIM) Scheme to Evaluate Freshness of Ice Stored Lake Victoria Nile Perch (Lates niloticus).

    Okeyo, George Otieno (Egerton University, Njoro (Kenya), 2009)
    Despite the Nile perch contributing about 67% of Kenya’s total annual fish export earnings, no specific method exists for evaluating the freshness of the fish when landed and its shelf life when kept in ice. Currently the European Union (EU) sensory scheme is used in sensory evaluation of all commercial fish species available in the Kenyan fishery. This study was conducted to develop a suitable Quality Index Method scheme, that is specific for the Nile perch, using a set of selected sensory parameters to help follow its deterioration profile in order to estimate changes in its freshness in the course of storage in ice. Fish samples for the study were obtained from the beaches. The fish samples from each location were divided into two groups; ungutted and gutted. The selected sensory parameters were correlated with selected biochemical and microbiological parameters. Significant increase (p ≤ 0.05) in the levels of sensory, microbiological and chemical parameters was observed on the 10th and 14th day onwards for the ungutted experimental and control samples, respectively and on the 14th and 18th day for the gutted experimental and control fish samples, respectively. The Quality index scores had a correlation of 0.98 with H 2 S producing bacteria, 0.93 with total viable counts (TVC), 0.97 with total volatile basic nitrogen (TVBN), 0.96 with free fatty acids (FFA) and 0.97 with pH. The ungutted fish from the beaches and fishing ground had a shelf life of 22 and 28 days, respectively. The gutted fish samples from the beaches and fishing grounds had a shelf life of 26 and more than 28 days in ice, respectively. Gutting extended the shelf life of the Nile perch by about 4 days for both the beach - purchased and controls. The microbial, sensory and chemical parameters levels increased with increase in storage days both for ungutted and gutted fish samples from the beaches and fishing ground. The protein content decreased with increasing storage time in the ungutted experimental and control samples than in the gutted fish samples. There was no significant variation (p ≥ 0.05) in the moisture, lipid and ash content for both ungutted and gutted fish samples. The study is useful setting standards and guidelines which will be used by the Fish Inspectors in the enforcement of sensory quality of fish destined for the domestic and export markets. This will prevent occasional interruptions of exports to the European Union markets thereby minimizing the resultant huge financial losses to the industry hence creating steady employment to the locals.

View more