Spatial heterogeneity in subtidal gravel generated by the pit-digging activities of Cancer pagurus

Abstract

In a coarse gravelly substratum exposed to high current velocities the crab Cancer pagurus was observed to dig pits, approximately 30 cm in diameter and 10 cm deep. Experiments were conducted to identify macrobenthic recolonization processes and differences in abundance between pits and unmanipulated areas. Surveys of the abundance of recently dug pits indicate a frequency of approximately 9 pits 100 mA2. Analysis of species abundances in artificial pits at various times after construction revealed colonizing species to be highly variable. In a second experiment statistically significant differences in the abundances of various species were found between artificial pits and adjacent unmanipulated sediment, but trends in the data were not consistent between experiments. Generally, macrofaunal recolonization processes were haphazard. These results are contrasted with initial recolonization processes in soft sediments. The mobllity and large particle size of the sediment are considered to be important in precluding predictable recoloruzation patterns.