Epizoic bryozoans on predatory pycnogonids from the south Orkney Islands, antarctica: “if you can’t beat them, Join them”: Fouled pycnogonids from Antarctica

Abstract

Antarctic bryozoans are poor spatial competitors compared to many sessile invertebrates. Antarctic bryozoans are frequently destroyed by ice scouring of the substratum during open water periods, and Antarctic bryozoans are specifically preyed upon by pycnogonids. Based on this, it was hypothesized that Antarctic bryozoans should foul pycnogonids more than other motile hosts and other sessile biotic and abiotic substrata. To test these hypotheses, 115 live pycnogonids were collected in the South Orkney Islands, Antarctica. Their carapaces were examined for epizoic bryozoans, and each colony’s size was measured and its location mapped. Nine species of pycnogonids were identified containing 156 bryozoan colonies belonging to seven cheilostome species. Of the 115 pycnogonids, 26% were fouled by bryozoans. The bryozoan species richness on pycnogonids is similar to that on the adjacent boulders. Compared to other motile host animals, the number of bryozoan species per unit host surface area is an order of magnitude higher on pycnogonids. This may be attributed to carapaces of pycnogonids acting as refugia for the bryozoans from competition for space on hard substrata, ice scour, and predation by their host.