Search

Long-term decadal retrospection in spatio-temporal imagery analyses can only be carried out using aerial photographs, which are still the most detailed remotely sensed data available. Visual interpretation of such imagery is most efficient and inexpensive in the light of ecosystem monitoring research in developing countries, which are often unable to cope with the development or the cost of acquisition of commercial space-borne imaging (e.g. IKONOS, Quickbird). In this light, the present paper explicitly analyses the methodological use of image attributes of air-borne imagery from mangrove forests, and investigates the consistency and constraints of mangrove image attributes in visually interpreted air-borne imagery. Six image attributes are analysed, and their application is illustrated using various mangrove sites in Kenya and Sri Lanka. Comparison of identification keys reveals that minor attributes such as 'ecological position' are informative, and that image attributes for a particular species or genus are apparently less plastic and more widely applicable than formerly assumed. Emphasis on compulsory fieldwork is made and constraints related to reflection and interference, amongst others, are discussed.

Recolonisation by crab species and sediment-infauna taxa (at class level) in artificially regenerated mangrove stands of Avicennia marina, Rhizophora mucronata and Sonneratia alba (5 yr old) were studied using respective bare sites (open without mangroves or denuded) and natural sites (relatively undisturbed) as controls. The controls were chosen based on site history, physical proximity and tidal inundation class in reference to the particular reforested mangrove stand and samples randomly taken. A number of environmental variables were measured; interstitial water salinity and temperature (measured at low tide) were lower, whereas sediment organic matter content was higher in the areas with mangrove cover, with the natural sites having the highest content. The bare sites were generally sandier, whereas the areas with mangrove cover had higher proportions of clay and silt. Generally, there was a higher crab density in the reforested sites than in the bare sites, whereas crab species diversity (Shannon diversity index) did not vary from one site to another for any of the mangrove species. In terms of crab species composition, the reforested sites were more similar (Sørensen similarity coefficient) to the natural sites and less to the bare controls. For sediment-infauna, the reforested sites had a significantly higher density than the respective bare controls, while the natural sites had the highest density. The number of sediment-infauna taxa in both the reforested and natural sites of all the mangrove species was similar and higher than in the comparable bare sites. The results suggest that the reforested sites are supporting more faunal recolonisation, and therefore becoming more akin to the natural mangrove sites in terms of the investigated functional indicators. The findings seem to support the use of artificial mangrove regeneration (in areas where natural regeneration has been impeded by physical conditions or otherwise) as an effective management tool in the restoration and conservation of the functional integrity of degraded mangrove habitats.

To date, only two species are known in the laophontid genus Tapholeon Wells, 1967 (Copepoda, Harpacticoida). In the present contribution, a redescription of the type species T. Ornatus Wells, 1967, based on the type material, is provided. Furthermore, two new species are described from the coast of Kenya, T. Inconspicuus sp. nov. and T. Tenuis sp. nov. Two species, formerly attributed to Asellopsis Brady and Robertson, 1873 (namely A. Arenicola Chappuis, 1954 and A. Chappuisius Krishnaswamy, 1957), are allocated to Tapholeon based on the absence of sexual dimorphism in the swimming legs P2-P4. The former of the two species is redescribed based on additional material from the Comoros. An updated generic diagnosis and a key to the six species of Tapholeon are included.

Different deep-sea sites are frequently characterized by a high number of species belonging to the same genus. In addition, some deep-sea genera (e.g. Acantholaimus, Monhystera, Halalaimus) seem to be dominant and present world­wide. The genus Manganonema is present in all oceans in low to medium densities « 2%) and, apparently, restricted to the deep sea (600 m and deeper). The present study deals with a revision of the genus Manganonema based upon known species and nine new species, where only 5 were named due to the lack of males (M. media sp. nov., M. pitilica sp. nov., M. robus­tus sp. nov., M. antarctica sp. nov., M. bussauensis sp. nov.). For the species identification, important characters are sum­marized in a pictorial key. The material studied was collected from six different sites: two in the North Atlantic (Europe), two in the Southern Ocean (Antarctic), one in the South-western Atlantic (Brazil), and one in Western Indian Ocean (Kenya). The species distribution suggests a high turnover of species between sites. Only one Manganonema species is recorded from two different sites in the Atlantic Ocean. These results suggest a high degree of endemism of species within the genus.

Mangroves are in worldwide decline. A valuable tool in the detection of mangrove degradation is satellite imagery. We focus on a tropical bay in Kenya, Gazi Bay, on which very high resolution QuickBird satellite imagery is available. A first objective was to classify the mangroves at species level using unsupervised and supervised (hard and soft) per-pixel classification techniques. Incorporation of texture and normalized difference vegetation index (NDVI) measures in image classification both increased the spectral separability between the image classes, but this was not indicative for the accuracy of the classification. On the contrary, the supervised fuzzy classification of the contrast-stretched multispectral image using a 3x3 pixels convolution window appeared to be the most accurate one (based on visual image interpretation and field knowledge). The accuracy of the supervised classification (using the maximum likelihood decision rule) of the contrast-stretched multispectral image was assessed using the Point-Centred-Quarter-Method (PCQM) transect data. The overall accuracy was found to be 68%. Secondly, automated methods for vegetation assemblage delineation were developed using fuzzy convolution techniques. The automated delineation was compared with the visual delineation done by 3 naïve interpreters. Results showed that there were two possible disagreements between automated assemblages and visual assemblages: more than one automated assemblage could be included in a visual assemblage and vice versa, but overall the boundaries of the automated assemblages corresponded quite well with the visually delineated polygons. The correspondence between these delineations could however not be quantified.We can conclude that it is possible to create a mangrove species map of adequate accuracy through supervised classification of the QuickBird satellite image and to automatically identify assemblages. Therefore QuickBird satellite imagery has proven to be a valuable tool in the early detection of mangrove degradation in which floristic composition is as important as areal extent.

The distribution and abundance of copepods belonging to the genera Candacia and Paracandacia (family Candaciidae) within the inshore, shelf and offshore waters of the Kenya coast are presented. The copepod species are widely distributed, at low abundances (9 to 240 ind.100/m3) within the inshore waters, which increases to a maximum (40 to 360 ind.100/m3) within the shelf waters and decreases again to minimum (10 to 40 ind.100/m3) in the open ocean. They are more abundant during the southeast monsoon period and less so during the northeast monsoon. Abundance decreases with increasing depth, from a maximum of 880 ind.100/m3 at the surface to a minimum of 10 ind. 100/m3 in the deep layers. The Candaciidae are least abundant at the depths ranging of 400 to 800 m, where oxygen concentration is minimum.In this study, Candacia bradyi A. Scott, 1902; C. bipinnata Giesbrecht, 1889; C. curta (Dana, 1849); C. tuberculata Wolfenden, 1905 and C. ethiopica (Dana, 1849) are reported as new records for the Kenyan coast.

In this thesis a description is made of species composition and characteristics of epilithic diatoms in rivers Nyando, Kibos and Kisat draining into Lake Victoria (Kenya part). The water quality of the rivers is evaluated by examining the diatom data alone and in relation to environmental variables. The distributions of diatoms in surface waters of Lake Victoria were also examined in relation to environmental variables. The aim was to assess the potential of diatoms in determining the “ecological” water quality and in supporting management decisions and conservation strategies for these aquatic ecosystems. First, species composition, richness and diversity of the epilithic diatoms in rivers Nyando, Kibos and Kisat were investigated. 224 diatom taxa (218 species) belonging to 32 genera were recorded from the three rivers. Maximum species diversity was observed in less polluted river Kibos followed by Nyando with medium pollution levels and Kisat the most polluted had the lowest values of diversity. Species richness and diversity were significantly correlated with altitude, width of the river channel, depth, current velocity, volume of discharge and dissolved oxygen. Eutrophication, increase in ionic content and organic loading reduced diversity downstream where a few species tolerant to pollution, such as Nitzschia palea dominated the community especially in Kisat. Diatom diversity indices were found to be important in indicating changes in whole diatom assemblages in response to changes in water quality. Secondly, weighted means of known diatom ecological indicator values were used in determining the water quality in rivers Nyando, Kibos and Kisat. The ecological indicator values included Saprobity, Oxygen requirements, Trophic state, Nitrogen uptake metabolism, Moisture, pH and Salinity. Taxa with known ecological indicator values occurred consistently in high abundance in all stations sampled and throughout the sampling period. The ecological indicator values had strong correlations with the measured environmental variables, which they are known to reflect. Saprobity, Oxygen requirements, Trophic state and Nitrogen uptake metabolism tended to increase downstream showing increase in pollution in the same direction. The data from the indicator values was in agreement with the one of measured environmental variables in confirming that Kisat is more polluted than Nyando and Kibos. The diatom ecological indicator values used in this study were found to be suitable for assessing water quality in the three rivers. The diatom “Indice de polluo-sensibilite” (IPS) or pollution sensitivity index was evaluated and was found to give nearly the same information as the known diatom ecological indicator values. The results of the IPS showed that on average, weakly polluted to moderately polluted waters occurred in Kibos and moderate to heavily polluted waters occurred in Nyando. The whole of Kisat was heavily polluted and pollution levels were more acute downstream after the Kisumu industrial area. In the third investigation, the distribution of the epilithic diatoms was assessed in relation to environmental variables in rivers Nyando, Kibos and Kisat. Cluster analysis by Two-Way Indicator Species ANalysis separated the diatom community into two major groups comprising the less polluted waters of Nyando and Kibos together, from assemblages of the more polluted Kisat. The group of kibos and Nyando had Navicula exigua, N. schroeteri and Gyrosigma scalproides as indicator species. Subsequent splitting of the data resulted in assemblages also reflecting different water quality irrespective of the position of the sampling station. Ordination by Canonical Correspondence Analysis revealed that diatom species distributions were significantly influenced by overall effect of the measured environmental variables. Conductivity, alkalinity, turbidity, dissolved oxygen, silicate and altitude were identified as the main factors contributing to variation in diatom assemblages in the three rivers. Species reflecting various environmental gradients were identified. Finally, the distributions of diatoms in the surface waters of Lake Victoria were studied in relation to environmental variables. 101 taxa belonging to 29 genera were identified. Higher species richness and diversity occurred in the Nyanza gulf and bay areas when compared to the open lake. Conductivity and silicate were found to influence species richness, diversity and evenness. The diatom community was separated into two main groups comprising assemblages of the Nyanza Gulf and the ones from the open lake. These assemblages also reflected environmental gradients. The open lake was generally associated with higher abundance of Nitzschia acicularis that was also the indicator species for this group. Aulacoseira agassizii, Cyclotella meneghiniana, Nitzschia fonticola and Cyclostephanos dubius were indicator species for the Nyanza Gulf. Conductivity, alkalinity, dissolved oxygen and lake depth were identified as the main environmental variables that significantly explain variations in the diatom assemblages in Lake Victoria. j The results of this study are a contribution to knowledge on potential diversity and ecology of the present day diatoms in the Lake Victoria basin. Further, they provide evidence that diatoms can be useful indicators of water quality in the basin and that they can be employed in monitoring studies and for management purposes.

A new species, Holothuria (Mertensiothuria) arenacava (Echinodermata, Holothuroidea) from the littoral waters of Kenya is described. This species is characterized by its sand-burrowing behaviour, its small tentacles, the variously developed tables, corpuscules, buttons, plates and rods in the tube feet, and by the smooth, spiny and knobbed rods in the tentacles.

Aspidochirotid sea cucumbers (Echinodermata: Holothuroidea) are heavily fished in the littoral waters of Kenya, and stocks have plummeted. In order to conserve and manage these natural resources, appropriate conservation and management plans must to be developed. This can only occur if high quality research on different levels is done. This paper discusses five layers of understanding that should be achieved before holothurian conservation in East Africa can be effective.

Neosarmatium meinerti is a crab which commonly inhabits the landward Avicennia marina fringe in East African mangroves. Stomach content analysis of individuals collected at Gazi Bay and Mida Creek (Kenya) showed that their diet mainly consisted of mangrove leaves, completed with little animal matter. Experiments designed to offer the crabs a choice of leaves or propagules of the various mangrove species present indicated that N. meinerti has no distinct preference for any of them. Nor is it attracted by spongy material impregnated with the extract of propagules from any particular mangrove species. However, at least for Rhizophora mucronata, this crab species has a slight preference for freshly gathered propagules when presented both matured and freshly gathered ones. There is little evidence that the plant-derived diet of N. meinerti consists of one mangrove species only, though it is probable that this crab will restrict its feeding area within the landward A. marina fringe. Because of the lack of specificity in its feeding behaviour, N. meinerti can also be a threat to the successful regeneration or restoration of mangroves through seedling or propagule planting.

Descriptions and illustrations are provided of one species of Boodleopsis, seven taxa of Bryopsis and one species of Trichosolen, based on specimens collected in Kenya, Tanzania and the Seychelles Archipelago from 1985 to 1996: Boodleopsis pusilla, Bryopsis hypnoides, B. indica, B. pennata var. pennata, B. pennata var. leprieurii, B. pennata var. secunda, B. plumosa, B. sp. and Trichosolen sp.. Bryopsis indica is a new record for Tanzania, Bryopsis hypnoides is new for the Seychelles and Trichosolen sp. is new for Kenya.

Descriptions and illustrations are provided of 14 species. Codium, collected in Kenya, Zanzibar and the Seychelles Archipelago from 1985 to 1994 of C. arabicum, C. cicatrix, C. duthieae, C. dwarkense, C. extricatum, C. geppiorum, C. lucasii, C. ovale, C. pocockiae, C. prostratum, C. repens, C. taylorii, C. vaughanii and C. sp. Codium cicatrix and C. repens are new records for Kenya; C. extricatum, C. lucasii and C. pocockiae are new for Tanzania; C. arabicum, C. cicatrix, C. extricatum, C. vaughanii and probably C. sp. are new for the Seychelles.

In February 1995, eight sites around Lake Victoria and beaches, reefs and creeks along the Kenyan coast from Vanga to Sabaki River mouth (around 220 km of shoreline, split into 15 sites) were surveyed and waterbirds counted. In March 1995, waterbirds were counted on the five large dams along the upper Tana River.These represent the first waterbird surveys for almost all of these sites. Five sites (Vanga Creek, Kilifi-Mida Beach, Malindi Marine Park, Sabaki River Mouth and Masinga Dam) qualify as Globally Important Bird Areas on the basis of their waterbird populations (and hence as potential Ramsar sites).

Cysts produced after inoculation with San Francisco Bay (SFB) strain Artemia were harvested and analysed at Artemia Reference Centre. Results obtained after nutritional analysis indicate a potential source of high quality cysts. Cyst hatching percentage, hatching rate and hatching efficiency was 61%, 24h and 173,400n/g respectively. Hatching percentage (H%) varied slightly with variation in salinity and peroxide treatment. Highly unsaturated fatty acids (HUFA) content was representative of high quality cysts. This was also supported by the good growth performance in test with the marine Mysid, M. bahia M.

The international symposium on The Ecology of Mangrove and Related Ecosystems, Mombasa, Kenya, 24-30 September, 1990, was organized by the Department of Zoology, University of Nairobi, in collaboration with the Kenya Marine and Fisheries Research Institute, and the Regional Dispatch Centre of the Regional Cooperation in Scientific Information Exchange in the West Indian Ocean, Mombasa, Kenya. It was officially opened by Professor F. N. Onyango, Principal, College of Biological and Physical Sciences, University of Nairobi. The closing address was given by Professor M. Hyder, retired Principal and Professor of Zoology, CBPS, University of Nairobi. Scientific investigations of the mangrove and coral reef ecosystems in Kenya have been going on at least since the early 70’s and have been gathering momentum with the involvement of the University of Nairobi, KMFRI, and British, Belgian, Dutch and Italian universities and scientific institutions. So the time was ripe to take stock of the situation and to try to bring together workers in the same field from as many tropical regions as possible. A cursory glance at the list of participants is sufficient proof of the widespread interest in the theme of the symposium. Contributions came from all the main tropical marine areas of the globe, representing twenty-three countries, in West and Eastern Africa, South and Southeast Asia, Central and South America, and Australia. The thirty papers published in this volume were selected from seventy presented at the symposium. It is recognized that the mangroves have intimate and complex linkages with other coastal systems, notably seagrass beds and coral reefs. So, starting from the mangrove forest and its users at the interface between the terrestrial, freshwater and marine environments, the papers presented proceed to the fully submerged seagrasses and further out to the corals. The nature of the coupling between the different systems was touched on at the symposium, but stands out as a serious gap in our knowledge. Next, chemical and physical processes which constitute the mechanisms of linkage received attention. Human uses and abuses of the ecosystems formed the last major topic of the symposium. Workshop discussions were held during the symposium in preparation for the adoption in plenary session of two declarations: A Statement of Priorities for Scientific Research and A Declaration on Management Strategies. The following priorities for basic research were agreed : the interlinkages between the mangrove, coral reef and seagrass ecosystems; the need for more information on nearshore hydrological processes operating at the small and meso-scale and elaboration of predictive models ; more work on nutrient cycling and energy flow including soil processes; biological processes and use of bio-indicators. Priorities were also set for applied research. This, it was agreed, should be directed towards management of the forest or aquatic product on a sustainable basis, taking into account the integrated nature of the ecosystems. Emphasis should be placed on minimizing perturbations to the systems and the maintenance of ecological integrity. Broad areas needing investigation were identified: methods for efficient and ecologically sound land use in the watershed adjacent to the mangal, seagrass beds and coral reefs; effect of management of the mangroves on off-shore fisheries; impact of industralization on the mangal and related ecosystems; effect of domestic and industrial effluents and management of their impact; comparative studies on destructive and non-destructive aquacultural techniques with a view to minimizing negative effects; the effect of human activities on physical, chemical and biological soil processes; research on management practices appropriate to different mangrove forest types and promotion of a biotechnological aproach in mangrove silviculture; socio-economic studies of human coastal settlements; natural products of the mangals; the impact of global climate change; and active rehabilitation of seagrass beds and coral reefs. The Declaration on Management Strategies was positive, concluding that much can be done to stop the degradation of damaged mangals, seagrass beds and coral reefs and to rehabilitate them, but that new techniques must be worked out to allow use on a sustainable basis for long term economic return and for the wellbeing of coastal human settlements and a healthy environment. To achieve the above goals the Symposium recommended the following strategies. The establishment of National Coastal Management Plans including the following components : survey of both natural and human resources and their present uses ; identification of the problems affecting coastal ecosystems; adjustment of legal frameworks with regard to the uses of these ecosystems and enforcement of existing management regulations; provision of technical assistance and training for the introduction of economically and ecologically viable activities in these ecosystems ; rehabilitation of damaged areas ; creation of natural reserves both for tourism and for the recuperation of natural plant and animal populations; education and creation of public awareness on the value and problems of these ecosystems. In formulating and implementing each national Plan all concerned parties should be involved, i.e., the inhabitants and the outside users of these ecosystems, the policy makers, the scientists and technical experts, and also the national and international funding agencies. Use should be made of existing institutions and networks. The scientists gathered in the symposium urged the establishment or strengthening of regional and international associations of scientists to provide the scientific basis to national and regional management plans.

Two new epsilonematid nematode species from Kenyan intertidal areas are describe: Bathyepsilonema anulosum sp. n. -characterized by the large number of body-annules (118-124); small amphid, straight ambulatory setae and the very small copulatory thorns of the males- and Leptepsilonema richardi sp. n., -characterized by the sexual dimorphism in the amphid, the ornamentation of the body cuticle and the umbrella shaped captulum in the males.

In view of preparing a Flora of the Seaweeds from Kenya, material is collected yearly by the authors since 1985. Twelve species of Caulerpa have been collected so far, some including several varieties: C. brachypus, C. cupressoides, C. elongata, C. fastigiata, C. lentillifera, C. mexicana, C. racemosa (with several var.), C. scalpelliformis, C. serrulata, C. sertularioides, C. taxifolia, C. verticillata. An identification key is provided, the different species are described and illustrated (except C. lentillifera and C. racemosa; ecological and biogeographical data are added.

A prostrate Dictyotaceae was collected on the sandy-silty mangrove substratum close to high tide level in Gazi Bay (Kenya). It appears to be the rarely observed Dictyota adnata Zan., characterized by the prostrate growth form, marginal groups of rhizoids, marginal sori of tetraspores, high Cl/Cw and Ml/Mw ratios. According to these observations D. adnata Auct. ("sensu Weber-van Bosse") is another taxon.

This is the first review report on the Kenyan- Belgian Project in Marine Ecology (KBP). It explains our approach and methodology: the linkage between equipment, education and research. Interaction between fundamental and applied research. Real co-operation between Kenyan and Belgian Scientists. We are always accessible to remarks and advices and hope to be able to continue. The aim of the project was to develop a program on Marine Ecology and the Management of the Coastal Zone (living and non-living resources). We started the inventory and descriptions of the different Marine biotopes and their trophic levels. This fundamental research guided us to initiate applied research: we started a small-scale oyster culture to prevent the loss of the high primary production of the mangrove creeks. By doing so we provided work for the local population and used only local materials for the building of the rafts. Both, the fundamental and the applied research must go on with the present project as backbone. Other, subprograms, fitting in the framework of the KBP, will be added. A common project between Kenyan and Belgian Universities will be worked out and submitted to the EEC, on specific mangrove research. The Belgian experts will submit an interuniversity program for fundamental research to the National Science Foundation. And in collaboration with the KMFRI and the Kenyan and Belgian Universities, we will organize a Regional Course on Marine Biology, with the support of UNESCO and UNEP. In this way, we will cover most of the aspects of Marine Ecology, needed for the Management of the Coastal Zone.

Large wild populations of Euchema are absent along the Kenyan Coast (except for the southernmost part, Shimoni, but even here not enough for harvesting). Some Gracilaria species have a large biomass and harvesting of the natural populations might be economically interesting (more detailed studies are necessary). outdoor mariculture in the open sea is in my opinion impossible off Kenya because of the lack of available space (unsuitable coast or other uses of the appropriate habitat). Before starting algal mariculture in outdoor ponds a thorough feasibility and cost/profitability study should be done.

The Caulerpa's with spherical, clavate, turbinate or peltate branchlets collected by the authors along the Kenyan coast from 1985 to 1988 are described and illustrated. They include Caulerpa lentillifera as well as several "varieties" of C. racemosa: var. clavifera, var. laetevirens, var. lamourouxii, var. occidentalis, var. peltata, var. turbinata. Their variability is discussed and an identification key is provided.