Epizoic Bryozoans, Horseshoe Crabs, and other Mobile Benthic Substrates

Two species of horseshoe crabs, Carcinoscorpius rotundicauda (Latreille) and Tachypleus gigas (Müller), were collected from the seas adjacent to Singapore to study the fouling rates of epizoic bryozoans. None of the 19 C. rotundicauda specimens were encrusted by bryozoans. Of the 56 individuals of T. gigas collected, 77% were infested by the bryozoans Electra angulata (Levinsen) and Membranipora savartii (Audouin). This difference in fouling rate between the two host species was attributed to several factors including size and age differences of the hosts, morphological differences of the hosts' carapaces, and habitat differences between the hosts. Most importantly, C. rotundicauda tends to occupy shallower, more estuarine, brackish water where bryozoans are less abundant. The costs and benefits of epibiosis on mobile benthic substrates such as crustacean carapaces are discussed.