A comparison of sampling techniques in the assessment of burrowing crab abundance in saltmarsh and mangrove environments.

Many researchers have recognised the importance of crabs in the mangrove ecosystem. However, very little is known about burrowing crab species living in temperate Australian saltmarsh. In the present study four different survey techniques were employed to investigate the diversity and abundance of crabs in the saltmarsh and mangrove at Towra Point. The four techniques yielded different results for species abundance and diversity. Four different species Heloecius cordiformis, Sesarma erthrodactyla, Helograpsus haswellianus and Paragrapsus laevis were found in saltmarsh. Three of these species H. Cordiformis, S. Erthrodactyla and P. Laevis were also found in the mangrove. A higher diversity of crabs were found in the Sarcocornia and Sporobolus saltmarsh communities than those dominated by Jancus kraussii. Pit traps were an effective means of capturing crabs though under-represented H. Cordiformis, and S. Erthrodactyla but was ineffective at identifying crabs in the more heavily vegetated Sporobolus and Juncus communities. Surveying crabs underneath artificial blocks may have over-represented the density of S. Erythrodactyla. Burrow counting is a quick and effective means of estimating crab density, though gives no information on assemblage diversity. The results of the study recommended a combination of pit-trap and visual census as a means of efficiently sampling crab assemblages.