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Abstract
Despite the critical roles played by arthropods in ecosystem functioning and nutrient cycling, a general lack of information about the ecology of many arthropods in West African coastal wetlands persists. An investigation into the abundance, distribution and forage potential of ground arthropods to waterbirds inaWest African Coastal Ramsar site, indicated that the distribution and abundance of the arthropods were similar along both the latitudinal and longitudinal axes of the lagoon's flood plain. Agelenidae (house spiders), Formicidae (ants) and Gryllidae (True crickets) respectively constituting 52.68%, 36.58% and 5.85% of the total arthropod abundance, dominated the 23 families of arthropods. On the basis of percentage biomass and per capita biomass compositions, Gryllidae and Agelenidaewere of the most important to waterbird foraging. Although Formicidae occurred in large numbers, the small-size nature of the individuals indicated that they wereof little importance to waterbird foraging. Ocypodidae (Ghost and Fiddler crabs) (0.3%) and Acrididae (short-horned grasshoppers) (0.3%) constituted a negligible fraction of the arthropod abundance buthad the highest per capita biomass and would be the most profitable forage.The low abundance of Ocypodidae and Acrididae were attributed to marginalisation of the sampling method employed in the study.
Sakumo II is an urban wetland and a receptacle for domestic and industrial waste from two cities in Ghana. It however supports viable populations of fish and crabs, is cultivated for food crops and grazed by farm animals. Components of the wetland can therefore accumulate pollutants but the public health and phytoremediation implications of this are yet to be evaluated. We analysed Cd, As, Hg, Cu and Pb in the lagoon water, sediment, green algae, eight species of aquatic macrophytes, seven species of arthropods and one species of fish. The concentrations of Pb were generally below detection limit whilst Cu was detected only in the lagoon water and Pheropsophus vertialis. Cadmium ranged from 21 ± 4 ppb in algae to 69 ± 12 ppb in Typha domingensis and was generally higher than As and Hg. The highest concentration of As was 11.7 ± 2.1 ppb in Pistia stratiotes whilst Hg was highest in lagoon water (4 ± 2 ppb). The Cd concentrations generally, and Hg concentrations in macrophytes, were higher than US EPA guidelines indicating the wetland’s resources were unsafe for regular consumption. Among the emergent aquatic macrophytes, Typha domingensis, Ludwigia sp. and Paspalum vaginatum respectively had the highest accumulation capacity for Cd, As and Hg but the floating aquatic plant Pistia stratiotes appeared to be a better accumulator of Cd and As.
We applied a rapid assessment methodology to estimate the degree of human impact of exposed sandy beaches in Ghana using ghost crabs as ecological indicators. The use of size
ranges of ghost crab burrows and their population density as ecological indicators to assess extent of anthropogenic impacts on beaches was explored in this study. For each site, three
transects were laid perpendicular to the shoreline over a 100 meter distance at 50 m intervals, i.e., at reference points 0, 50 and 100 meter points. Sampling locations were randomly
selected along the three transects using a 1 m x 1 m quadrat. Measurements were done twice weekly for a period of four weeks. The results showed that even though the moderately
disturbed beach had higher burrow density than the disturbed beach on the average, the difference is not statistically significant (T-test; p > 0.01). However, mean burrow diameter at the moderately disturbed site was statistically found to be significantly larger than for the disturbed site (T-test; p < 0.01). We conclude that burrow sizes is a good estimator for
verification of human impacts of exposed sandy beaches. It confirms that burrow density even though an important factor, may not necessarily be a significant estimator of the impacts
of human activity on beaches. On this basis, it appears that the estimations of the diameter of burrows of crabs of the Ocypode genera provides a rapid tool for impact verification of sandy
beaches and for use in environmental quality monitoring of beach programs in coastal areas.
The study presents results of a floristic and mammal survey undertaken in the Sefwi-Wiawso District within moist semi-deciduous vegetation zone of the Western Region of Ghana. The floral survey involved estimating the floral distribution, abundance and diversity using the standard indices, Shannon-Wiener, Simpson's, evenness, species richness, similarity, and β-diversity, while the mammal survey was conducted using direct opportunistic observation, live-trapping (small mammals), animal spoors/trophies, and interviews. There were 271 plant species recorded, out of which 174 species comprising 172 species and 67 families of angiosperms (Angiospermae) and two species of ferns (Pterydophyta) were scientifically-named. Forty species of mammals representing eight orders were recorded, with the dominant orders being Rodentia and Artiodactyla. The greatest faunal diversity occurred in the forest reserves, where suitable habitat niches still occur. There were 48 individuals of seven species of rodents and one individual of one insectivore species captured during live-trapping, with the commonest species being common mice (Mus spp.) and brush-furred mice (Lophuromys flavopunctatus). The greatest threat to the survival of the fauna is habitat destruction. Generally, the Sefwi-Wiawso District is very rich in forest tree species, the commonest being the Celtis-Triplochiton Associations, but bad agricultural practices, bush burning, intense logging, fuelwood harvesting and pollution have resulted in poor soil quality and land degradation in certain areas. Hunting of animals for meat, and destruction of habitats were the greatest threats to faunal diversity and abundance in the Sefwi-Wiawso District. Introduction It is generally acknowledged that the forests of Africa are gravely threatened largely through anthropogenic influences like unsustainable farming practices, fuelwood over-exploitation, unauthorised logging, bushfire setting and pollution (Holbech, 1996). The forests of the Western Region of Ghana have, to a large extent, been subjected to increasing degradation over the years due to such unfavourable anthropogenic influences (Martin, 1991; Hawthorne & Abu-Juam, 1993). This situation poses serious threats to the biodiversity of the region, and its socio-economic and ecotourism potential. Located in the Western Region of Ghana, the Sefwi-Wiawso District faces increasing deforestation due to its high population growth rate and the attendant negative anthropogenic impacts outlined above. The forests of the District are being encroached upon at alarming rates, resulting in the degradation of large sections of hitherto pristine forests. This situation requires detailed and comprehensive biodiversity inventories to ascertain the current ecological status of the District's forests, to assess the extent of the negative anthropogenic impacts, and to provide the requisite data to enable the monitoring of anthropogenic disturbances over time (Bridgewater, 1996). The specific objectives of this study were to (i) identify and define the biodiversity features of sample areas of contrasting habitats in the District, particularly the floral and faunal (mammal) characteristics, (ii) assess the impact of human activities on the forest ecosystem, and (iii) recommend appropriate guidelines for conservation and sustainable use of the natural resources of the area.
Seasonal patterns in human fisheries resource utilisation and the capture characteristics of fish, swimming crabs and land crabs harvested from four coastal lagoons in Ghana between September 2005 and August 2007 are described. These are discussed in relation to sustainable management of the lagoons' fisheries for both human and waterbird use. With the exception of small pelagic foraging fish-eating birds, human fishing practices in the lagoons were in direct competition with crab- and fish-eating birds, because of the overlap of same-sized fish and crabs, and also in indirect competition because many of the exploited fish and crabs were immature. Fishing practices were also in direct competition with food foraging by invertebrate-eating birds. Intense exploitation of swimming crabs was linked to the use of drag nets, in comparison to the exclusive use of cast nets in some lagoons. In order to reduce the incidence of waterbird-human interactions and conflict during the energy-demanding phase of the birds' non-breeding season, it is recommended that the practice of closed seasons be extended to include crab fisheries and be strictly enforced at all Ramsar sites on the Ghanaian coast.
Reported in this paper are waterbird census data collected from four coastal
wetlands in Ghana over a period of 16 mo, with extrapolations made to indicate
possible changes in population trends and bird distribution in the study area. Results
indicated that Ramsar sites continue to play invaluable roles in the support of
waterbirds on the coast of Ghana despite the presence of waterbird species on a large
number of smaller, unmanaged wetlands. On the other hand, results also indicate that
waterbird populations and distributions in Ghana, as reported previously, have
changed. The need for conservation action for the waterbird species in Ghana
increased with respective dependency on unmanaged wetlands, with 56% of species
possibly affected.
A small coastal lagoon near Tema, Ghana, has been studied from August to December 1971. Data on temperature, salinity and exchange of water with the sea are given for January to December 1971. The extreme hydrographic conditions in the lagoon cause a reduction of the fauna, as compared with a typical "open" lagoon or with the marine shore. The structure of the food web in the lagoon is given. The main part of the animal biomass consists of the gastropod Tympanotonus fuscatus var. radula and the cichlid fish Tilapia melanotheron which feed on bottom deposit and associated microorganisms and are well adapted to the rapid changes of salinity that characterize the lagoon. After the rain period (MaY-July) there is a steady increase of marine species, represented mostly by juvenile stages.
Ghana's 550 km coastline has about 100 wetlands out of which five large ones are managed as Ramsar sites, the rest being unmanaged. Recent pollution and misuse of unmanaged wetlands have necessitated a study into their roles in the support of waterbirds. Waterbird survey on four wetlands between September 2005 and April 2006 revealed that 51 waterbird species make use of the managed compared to 44 in the unmanaged wetlands. Average numbers of waterbirds were higher on the managed wetlands (10,510 ± 4862) than on the unmanaged wetlands (1348 ± 602) (P < 0.05) but mean population density of waterbirds (n/ha) was the same for both the managed (1860 ± 310) and unmanaged (1400 ± 220) (P > 0.05) wetlands. The population densities of waterbirds belonging to guilds 1, 5 and 7 were significantly higher on the managed wetlands (P < 0.05). In contrast, guilds 2 and 4 have significantly higher population densities on the unmanaged wetlands while the population density of guild 3 was the same (P > 0.05). There was an indication that during mid and late periods of the nonbreeding season, the unmanaged wetlands altogether may support a larger number of waterbirds belonging to guilds 2, 3 and 4 than the five managed wetlands.
A survey on the aquatic ecology of Muni Lagoon was carried out during the period December 1993 to July 1994. Samples of zooplankton, aufwuchs and benthos were taken from a number of stations, representative of the different habitat types that occurred in the lagoon. The aquatic invertebrate fauna of the lagoon is listed and the temporal and spatial distribution of the fauna is described. The fauna is depauperate and biodiversity was related closely to the hydrology and salinity of the lagoon waters. During the early part of the study period, with dry weather conditions, there was very little macro-invertebrate life within the waters of the lagoon. The invertebrate fauna was confined to crabs, which occupied the fringing vegetation in the southernmost portions of the lagoon. With the onset of rains and the flooding of the lagoon, the sand bar separating the lagoon from the sea was opened turning the lagoon into a tidal system. This event brought a radical change to the fauna of the lagoon with very diverse marine zooplankton in some stations. Within weeks, worms and juvenile crabs were found several kilometres inland from the sea opening, an indication of the rapid re-colonisation of a previously hypersaline environment. The anthropogenic threats to the aquatic portion of this Ramsar site have been assessed and prioritised.
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