Temporal and spatial dynamics of the non-indigenous bryozoan, Amathia verticillata, and its associated invertebrate community

The widespread non-indigenous bryozoan, Amathia verticillata primarily colonizes in coastal bays and harbors on anthropogenic structures. Although this habitat-forming bryozoan is widely recognized to house a variety of marine invertebrates within its structure, little is known about their spatiotemporal dynamics and their associated invertebrate community in Southern California, USA. Thus, we undertook a comprehensive yearlong study (July 2021–2022) in an urbanized estuary (Mission Bay, San Diego) to quantify A. verticillata percent cover and abiotic conditions at 6 stations with varying environmental conditions. The seasonal and spatial gradients in temperature and salinity within Mission Bay were as expected with seasonal hypersalinity typical of Mediterranean climate regions. The percent cover of A. verticillata was positively correlated with temperature with the highest percent cover found during the warmest periods, and higher average percent cover found in the warmer, eastern parts of Mission Bay. We also collected three replicate A. verticillata colonies to characterize the marine invertebrate community associated with this non-indigenous bryozoan. We identified 25 families, 24 genera, and 19 organisms to species belonging to the taxonomic groups: amphipods, isopods, tanaids, and polychaetes. Furthermore, we identified juvenile stages and ovigerous females living within A. verticillata. None of the identified invertebrate families contributed more than 21 % to the community. The seasonal growth and annual temporal patterns of A. verticillata may prevent competitively dominant species from becoming established within the invertebrate community and allow A. verticillata to harbor a diverse invertebrate community. Sphaeromatidae isopods were the most common family found in the bryozoan colonies, likely reflecting their broad environmental tolerances. Additionally, while some of the invertebrates found within A. verticillata were also non-indigenous species, more work needs to be done to determine if A. verticillata disproportionately supports these species over native species. Collectively, our results imply that A. verticillata functions as a nursery habitat on anthropogenic structures for peracarid crustaceans and polychaetes. Furthermore, A. verticillata assemble analogous communities across their distribution, which may indicate that invasions are homogenizing biota globally.