Waterbirds as Bioindicators of Wetland Quality; Case Study of the Muni-Pomadze Ramsar Site Ghana

Abstract

The Muni-Pomadze Ramsar Site is the fifth most important coastal wetland in Ghana. It was designated as a Ramsar Site in 1992, based on its internationally important tem populations and the total population of waterbirds supported by the site. An assessment of the ecological character of the MPRS, habitat use by waterbirds, and the value of waterbirds as indicators of wetland health was carried out from September 2009 to April 2010. This involved the use of satellite imageries in order to assess changes in the habitat, monthly water quality assessment, benthic macroinvertebrates sampling, and waterbird monitoring. The habitat analysis showed that the size of the Muni Lagoon decreased by 50% from 1990 to 2007; the extent of herbaceous shrubs decreased by 99%; and the infrastructural development in the area quadrupled. The water quality analysis showed that Muni remains a shallow, hypersaline lagoon even though the salinity ranges recorded were lower compared to previous years as a result of the opening of the connection between the lagoon and the sea. A total of 1,723 individuals belonging to 10 groups of macrobenthic invertebrates were recorded. Of these, polychaetes- Annelida constituted 90.71%, bivalves- Mollusca 7.84% and the crustaceans-Arthropoda 1.45%. Muni Lagoon is clearly a stressed environment as its benthic population was dominated by a single taxon (Capitellid worms) and influenced by the fluctuating high temperature and salinity. Thirty-three waterbird species belonging to eight families were recorded, with a cumulative total sighting of 14.342 individual birds, of which waders represented 67% terns 28% and herons 5%. The results show decreases in the species as well as populations of waterbirds when compared to the counts recorded in 1986-1998. Changes have occurred also in the waterbird community structure of the MPRS, with the Ringed Plover Charidrius hialicula now being the most abundant wader species instead of the Curlew Sandpiper Calidris ferruginea which was the most abundant in the 1986-1998 counts. The site however still supports nationally important populations of five wader species. Waterbird distribution and activity in the Muni lagoon varied not only according to feeding groups and guilds but also according to time and site. Using the Bray-Curtis similarity index, the Muni Lagoon can be categorised into three sections based on the waterbird distribution. The MPRS remains an important roosting site for the tem, which use mostly Sites C (Mid-Lagoon portion) and E (Seaward section), and foraging ground (mudflat areas A and D) for the non-breeding waders. Waders roosted mostly at Site SP (Salt Ponds). Water depth was the key factor influencing prey accessibility and availability for waterbirds and biomass of polychaetes was the only factor determining the distribution of feeding waders. The highest benthic diversity was recorded at Site E due to recruitment from the sea, while that of waterbird was recorded at Site B due to the heterogeneity of the habitat of that site. Despite the habitat losses and the general deterioration of the health of the MPRS, the site continues to support significant numbers of waterbirds, although the populations have gone down. Thus, based on the finding of this research, it may be concluded that waterbirds are not early indicators of wetland quality. Depending on what has been lost or gained, a change in the environmental health of a wetland may not result in changes in the waterbird community, such that by the time the birds stop using the altered site, the site may be degraded beyond redemption. It is suggested therefore that bird monitoring at the MPRS continues over a longer period to enable the re-assessment of its international importance. The management of the site should be reinforced and accompanied with a habitat restoration program. Changes in the waterbird community structure should also be further investigated.