Sediment turnover by the stalk-eyed mud crab Hemiplax hirtipes (Brachyura: Ocypodoidea) on an intertidal flat in southeastern New Zealand

Abstract

ABSTRACTBioturbation by the stalk-eyed mud crab Hemiplax hirtipes was quantified via simple non-invasive, non-destructive means, to produce a relatively comprehensive estimate of annual sediment turnover. A linear correlation was found between the number of crab burrow holes and crab density, and between sediment excavation mound area and dry weight. Thus, crab density was determined by burrow hole count, and sediment excavation by photography and image analysis. Crab size and sex were ascertained by direct measurement and observation in the field. Burrows and their occupants were sampled once a month for 12 months. Annual sediment turnover (43 kg dry weight m−2 yr−1) was estimated by integrating the relationships established between crab size and the quantity of sediment excavated, plus the influences of temporal change in population density and size structure. Hemiplax hirtipes is likely to be a key bioturbating species influencing ecosystem structure and function where it occurs in relatively high densities on intertidal flats in New Zealand.