Rapid Assessment of Anthropogenic Impacts of Exposed Sandy Beaches in Ghana using Ghost Crabs (<i>Ocypode</i> Spp.) as Ecological Indicators

Abstract

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.