Land crabs show habitat health
18 August 2009
Assessing the degree of ecological damage can be an expensive and lengthy ordeal for conservation projects. But scientists have found that land crabs respond readily to change and can be used as a quick and cheap habitat assessment tool.
'Land crabs could be very good indicators of habitat quality on tropical oceanic islands, allowing rapid evaluation with potential use in monitoring and restoration programmes,' says Sarah Brook, who led the research while completing a Masters in the University of East Anglia.
Having a quick and cheap tool to assess habitat and environmental health would be very useful for conservation programmes, as field costs are often the most expensive element of projects.
Brook was interested in land crabs because they are relatively little studied but are key components of tropical island ecosystems - land crabs consume forest detritus, recycle nutrients, oxygenate the soil with their burrows and, by feeding on seeds and seedlings, manage forest growth, often preventing the spread of invasive plants.
With such close ties to their environment, Brook and colleagues suspected that land crabs could become indicator species in conservation and restoration programmes.
The scientists set up a project on five small islands of the Seychelles archipelago in the Indian Ocean. They focused on Seychelles because 'they are a diverse group of islands, with a long history of habitat alteration but also more recently of conservation success through restoration of degraded ecosystems,' says Brook.
Brook surveyed the five islands with different levels of habitat degradation. She was looking for the biodiversity and overall number of land crabs in three different island environments: the tidal zone, the area just above high tide and inland habitat.
The survey shows that the smooth-handed ghost crab (Ocypode cordimana) is more abundant in areas with native vegetation than in areas dominated by imported coconut palm-trees. The relationship between the species' abundance and vegetation type makes this crab a good indicator of habitat quality, suggests the report published last week in the journal Acta Oecologica.
Brook also found that the hermit crab Coenobita rugosus is highly dependant on intact native vegetation. This means that the presence of the species can be used to detect an undamaged habitat.
'Further research still needs to be done on the seasonal variation of land crab populations and on other islands,' says Brook. 'But this study highlights the potential of survey and monitoring land crabs as a useful tool.'
Taking seasonal and local variations into account, land crabs can be very useful. 'If you are undertaking a restoration programme on Island A, monitoring the population of the land crab over the programme's duration should provide a good indicator of the programme's success.'
Forrás: http://planetearth.nerc.ac.uk/news/story.aspx?id=508