Watersipora subtorquata and the Possible Role of Its Associated Microbes: An Attempt to Explain the Extraordinary Invasion Success of This Marine Bryozoan Species

Abstract

The Watersipora species complex comprises several sessile marine bryozoan clades which have successfully invaded human-influenced coastal areas worldwide over the last decades. These encrusting fouling bryozoa do not have physical means of defense against predation and overgrowth and are thriving in human-influenced and polluted environments in contrast to many native bryozoan species. A thin biofilm, which mainly consists of bacterial species and pennate diatoms of the genus Cocconeis, is generally associated with the frontal membranes and opercula of the Watersipora zooids. Ongoing research has indicated that epibiotic bacterial species of W. subtorquata sampled from locations in Japan and California predominantly belonged to different alpha-proteobacterial species within the family Rhodobacteraceae, but also Cyanobacteria and members of the Sphingobacteria have been identified. Some of these bacteria produce strong antifungal metabolites, or have genes involved in copper tolerance, which might increase their host's ability to be more competitive in eutrophic and polluted environments. An endosymbiotic bacterial species associated with W. subtorquata larvae has been identified in the past as well, but specific function of this Endowatersipora sp. remained unknown.