Non-native marine and estuarine fouling bryozoans detected along North American Coasts: a twenty-year synthesis

Bryozoans are one of the most diverse and abundant marine invertebrates in coastal ecosystems and provide a valuable model for evaluating patterns of invasion. We present a synthesis of non-native bryozoans detected from standardized surveys across 35 coastal bays and estuaries, spanning coasts of the continental United States and Canada (26°N to 61°N), including additional records of non-native bryozoans reported in bioblitzes and literature for the same region. We document 48 non-native bryozoan species, considered to have established populations, with 42 species from our settlement plate surveys and 6 from the literature). Nine of these species were new records for the continental United States, and 20 species had new records for one or more localities. Combining our data from 20 years of settlement plate surveys with an extensive literature review, we show that more bryozoan introductions are known from the Pacific than Atlantic and Gulf coasts of North America. Our data show declining non-native species richness of bryozoans with latitude on both the Atlantic and Pacific coasts, with several hot spots with elevated numbers of non-native species on the Pacific coast, similar to previously reported patterns for non-native tunicates. Finally, native source regions for these bryozoan introductions to the Atlantic and Gulf coasts are primarily from the Pacific and Indo-Pacific (respectively), whereas those introduced to the Pacific are primarily by Atlantic coast species. The dominance of Atlantic-sourced invasions to the Pacific coast in bryozoans contrasts with tunicate and sessile polychaete invasions, which are predominately from Pacific source regions.