Abstract Biological and abiotic processes influence ecosystem structure and species distribution. For bryozoan assemblages, depth, substratum and habitat structure are among the main factors influencing their distribution. Ecological studies on bryozoan fauna from Brazil are scarce and factors affecting the distribution and/or diversity of this common group are obscure. Here we attempted to verify the influence of bathymetry on bryozoan richness on the north shore of Bahia State, north-eastern Brazil. We identified 57 bryozoan taxa, comprising 35 families and 50 genera, all belonging to the Cheilostomata. Retevirgula multipunctata Winston, Vieira & Woollacott, 2014 and Tetraplaria dichotoma (Osburn, 1914) and the genus Aimulosia Jullien, 1888 were recorded for the first time from Bahia State. Species growing as encrusting sheets were dominant at all depths. There was a significant difference in richness among samples at different depths, with highest values of richness at 40 meters (Kruskal-Wallis Test). Analysis of similarities revealed a significant difference among the bryozoan assemblages, mainly when comparing assemblages from 10 and 20 meters with deeper ones. Also, shallower assemblages composition varied much than assemblages from 30 and 40 meters. Since depth is a proxy for several environmental parameters, further studies are needed to identify other factors influencing bryozoan distribution.

ABSTRACT Bryozoans constitute an important component of marine-fouling communities of anthropogenic substrata. Many species have been reported as exotic or widespread around the world, typically in ports and harbors of non-polar regions. Here we present the first record of a species of the bryozoan Triphyllozoon in the Atlantic Ocean. Triphyllozoon arcuatum (MacGillivray, 1889), described originally from Australia, is reported herein from natural substrata in Singapore and natural and artificial substrata in Brazil. Although easily recognizable, the species has not been previously reported from anywhere else in the Atlantic. In the latter instance, the species was collected during monitoring of the invasive scleractinian corals Tubastraea spp. on an oil platform originally from Singapore and now located at Todos os Santos Bay, northeastern Brazil. Colonies of T. arcuatum were also found associated with three species of sponges, giving evidence that it is also growing in the natural environment. Todos os Santos Bay is characterized by intense commercial shipping traffic and oil exploration and the finding of T. arcuatum on an oil platform provides strong evidence that it represents a non-indigenous species in the Atlantic. Owing to the possible impact of T. arcuatum in Brazil, further studies and monitoring of its bioinvasion are recommended.