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 on exposed sandy beaches in Ghana using ghost crabs as ecological indicators. The use of ghost crab burrow density and size ranges of the burrows 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, the mean burrow diameter at the moderately disturbed site was significantly larger than for the disturbed site (t-test; p < 0.01). We conclude that ghost crab burrow sizes is a better estimator of human impacts on exposed sandy beaches and could be employed as a rapid tool for monitoring the quality of beaches.

The ecological effects of beach sand mining in Ghana using ghost crabs ( Ocypode species ) as biological indicators

“…Lower ghost crab abundance have been reported in human impacted areas in several studies that investigated various human impacts such as trampling (Steiner and Leatherman, 1981;Neves and Bemvenuti, 2006), off-road vehicles (Wolcott and Wolcott, 1984;Blankensteyn, 2006;Moss and McPhee, 2006), shore armouring (Barros, 2001;Aheto et al 2011) and beach nourishment and bulldozing (Peterson et al 2000).…”

“…Two species of ghost crabs, Ocypode cursor and Ocypode africana, are found on sandy beaches in Ghana (Aheto et al 2011). Previously, Aheto et al (2011) used these species to assess the ecological impacts of general human activities including shoreline armouring, trampling and presence of inorganic pollutants, on two sandy beaches in the Cape Coast and Elmina area.…”

“…However, the presence, population and distribution of the ghost crabs (Ocypode spp) have been widely regarded as an acceptable biological indicator of beach ecosystem health and has been used by several scientists (Barros, 2001;Moss and McPhee, 2006;Neves and Bemvenuti, 2006;Magalhães et al 2009;Lucrezi et al 2009;Aheto et al 2011;Noriega et al 2012). Ghost crabs are relatively large semiterrestrial invertebrates found on tropical and subtropical shores (Quijon et al 2001) and occupy the apex position of invertebrate predation on sandy beaches (Barrass, 1963;Wolcott, 1978).…”

“…Previously, Aheto et al (2011) used these species to assess the ecological impacts of general human activities including shoreline armouring, trampling and presence of inorganic pollutants, on two sandy beaches in the Cape Coast and Elmina area. According to Jonah (2014) exposed underlying rocks, pronounced erosion scarps and denuded beaches characterize most beach stretches in the Cape Coast and Elmina area.…”

Patterns and intensity of ghost crab predation on the nests of an important endangered loggerhead turtle population

“…Ocypode cursor Linnaeus, 1758 has been found predating turtle nests on the western African coast and the Eastern Mediterranean (Aheto et al, 2011;Smith et al, 1996;Strachan et al, 1999). Former studies on the dispersal, population structure and burrow shape of O. cursor in northern Israel were conducted by Schuchman and Warburg (1978).…”