Burrowing abilities and swash behavior of three crabs, Emerita analoga Stimpson, Blepharipoda occidentalis Randall, and Lepidopa californica Efford (Anomura, Hippoidea), of exposed sandy beaches

To investigate factors related to the distribution of intertidal species, a nd specific predictions of the swash exclusion hypothesis for exposed sandy beaches, we compared the burrowing abilities and swash behavior of three s pecies of anomuran crabs in the superfamily Hippoidea (Emerita analoga, Ble pharipoda occidentalis and Lepidopa californica) which commonly inhabit the intertidal and shallow subtidal zones of beaches along the California coas t. Burrowing times in the laboratory increased significantly with crab size for all species in five sediment grain sizes ranging from fine sand to gra vel (0.15 to 3.24 mm). For each species, burrowing times differed significa ntly among sand grain sizes, ranging from 0.3 to 21.5 s. Burrowing times fo r the hippid crab, E. analoga, were relatively constant across sediment typ es, while those of the albuneid crabs, B. occidentalis and L. californica, were rapid in fine to medium sands, and much slower in coarser sediments. O ur results indicate that E. analoga is a substrate generalist while L. cali fornica and B. occidentalis are substrate sensitive. Pre-burrowing times an d behavior, distance moved, and burrowing times differed among the species in the swash zone. Combined times of preburrowing and burrowing were shorte r than the swash period (6 s) for most E. analoga individuals. Fifty percen t of the individuals of L. californica, reached the substrate and burrowed in the swash period, while no individuals of B. occidentalis burrowed in th at time. Pre-burrowing behavior and time may be valuable in explaining spat ial and temporal patterns in the distribution of hippoid crabs on Californi a beaches. Our results support predictions of the swash exclusion hypothesi s concerning the burrowing and locomotory abilities of sandy beach macrofau na. The substrate generalist characteristics, and unique orientation and sw imming abilities of the hippid crab, E. analoga, in intertidal swash may he lp explain the success of this species and its congeners, and have importan t implications for understanding patterns of macrofauna community structure on exposed sandy beaches in California and other regions. (C) 2000 Elsevie r Science B.V. All rights reserved.