The effect of disturbance by soldier crabs Mictyris platycheles H. Milne Edwards on meiobenthic community structure

Abstract

On a sheltered intertidal sandflat at Eaglehawk Neck, Tasman Peninsula, south-eastern Tasmania, the burrowing and feeding activities of the soldier crab Mictyris platycheles H. Milne Edwards are evidenced as intensely disturbed areas of sediment which form discrete patches interdispersed with smooth undisturbed areas. This situation was used as a “natural experiment” on the effects of disturbance on meiobenthic community structure. Meiofauna samples were collected in a spatially blocked design such that each block comprised two disturbed and two undisturbed samples. For the nematodes, species richness, species diversity and evenness were significantly reduced in disturbed as opposed to undisturbed areas although total abundance was unaffected. For the copepods, however, there were no significant differences in any of these univariate measures, k dominance curves also revealed significant differences in the relative species abundance distributions for nematodes but not for copepods. Multivariate ordinations (multidimensional scaling), however, revealed significant differences in species composition for both nematodes and copepods: the effects of crab disturbance were similar within each block and similar for nematodes and copepods. These differences resulted from an overall change in the balance of relative abundances of many species, rather than from changes in a few dominants. Mechanistic explanations for the effects of disturbance on meiobenthic community structure are at present hampered by a lack of knowledge of the natural history of the species involved.