The colonial marine bryozoan, Bugula neritina, harbors an uncultured endosymbiont, “Candidatus Endobugula sertula” throughout its life stages. The bacterial symbiont has been proposed to be a source of complex polyketide metabolites, the bryostatins, that chemically defend B. neritina larvae from predation. Within a bryozoan colony, significantly higher amounts of bryostatins are found in ovicell-bearing zooids where the developing larvae are brooded, as compared to ovicell-free zooids. It is hypothesized that signaling between B. neritina and “Ca. Endobugula sertula” may be involved in the regulation of bryostatin production in different zooids, as well as in maintenance of the symbiosis. In this study, suppression subtractive hybridization (SSH) was used to identify differentially expressed host genes during this association. The identified genes suggest that the host plays a role in the distribution and localization of bacterial symbionts in different host zooids, possibly to regulate levels of bryostatin production in the zooids.

Bugula neritina is a sessile marine bryozoan with a pelagic larval stage. Larvae frequently settle on boat hulls, facilitating the introduction of B. neritina to bays and estuaries worldwide. Adrenergic agonists, such as the vertebrate hormone noradrenaline, inhibit larval settlement in a variety of marine invertebrate species, including B. neritina. Light also inhibits B. neritina larval settlement, yet the underlying mechanisms by which light and adrenergic compounds exert their effects on larvae are not well understood. Octopamine is considered the invertebrate analog of noradrenaline, and may be an endogenous hormone involved in larval settlement pathways. I observed the effects of the adrenergic agonist noradrenaline and the adrenergic antagonist phentolamine on larval settlement, and found that high concentrations of noradrenaline increased larval mortality, inhibited larval attachment, and increased larval swimming behavior. High concentrations of phentolamine also increased larval mortality, but increased larval attachment and decreased larval swimming behavior. I used fluorescent labeling and microscopy to localize sensory system components, and found that larvae possess adrenergic-like receptors, as well as tyrosine hydroxylase-like and octopamine-like immunoreactivity. I also exposed larvae to phentolamine in both dark and light conditions, and found that light significantly inhibited larval attachment, but phentolamine blocked those inhibitory effects. These results suggest that B. neritina larvae possess adrenergic-like receptors, which serve as the binding sites for noradrenaline and phentolamine. These are likely octopamine receptors, and octopamine may be one endogenous compound involved in controlling larval phototaxis and settlement behavior. Light may increase octopamine production, thereby stimulating cilial activity, extending swimming behavior, and preventing larvae from attaching to a substrate. This research sheds light on previously unknown sensory mechanisms in B. neritina larvae, and may aid in the development of new biofouling control strategies.

The spread of exotic species is considered to be one of the most significant threats to ecosystems and emphasises the need for appropriate management interventions. The majority of marine non-indigenous species (NIS) are believed to have been introduced via ship biofouling and their domestic spread continues to take place via this mechanism. In some countries, biosecurity systems have been developed to prevent the introduction of NIS through biofouling. However, implementing biosecurity strategies is difficult due to the challenges around identifying high-risk vectors. Reliable predictors of risk have remained elusive, in part due to a lack of scientific knowledge. Nonetheless, invasion ecology is an active scientific field that aims to build this knowledge. Propagule pressure is of particular interest in invasion ecology as it describes the quantity and quality of the propagules introduced into a recipient region and is considered to be an important determinant in the successful establishment of NIS. Environmental history affects health and reproductive output of an organism and, therefore, it is beneficial to examine this experimentally in the context of biofouling and propagule pressure. The aim of this thesis was to examine how voyage characteristics influence biofouling recruitment, survivorship, growth, reproduction and offspring performance through the ship invasion pathway. This was to provide fundamental knowledge to assist managers with identifying high-risk vessels that are likely to facilitate the introduction or domestic spread of NIS, and to understand the processes affecting biofouling organisms during long-distance dispersal events. Chapter One provides an introduction to the issues addressed in this thesis. Each data chapter (Chapters Two – Five) then focused on a stage of the invasion process and included field experiments using a model organism, Bugula neritina. Finally, Chapter Six provides a summary of key findings, discussion and the implications to biosecurity management. Throughout this thesis, the effect of donor port residency period on the success of recruits was highlighted. Chapter Two focused on recruitment in the donor region. As expected, recruitment increased with residency period. Importantly, recruitment occurred every day on vulnerable surfaces, therefore, periods as short as only a few days are able to entrain recruits to a vessel hull. The study presented in Chapter Three showed that there was high survivorship of B. neritina recruits during 12 translocation scenarios tested. In particular, the juvenile short-residency recruits (1-8 days) survived voyages of 8 days at a speed of 18 knots; the longest and fastest voyage simulated. Interestingly, variation in voyage speed and voyage duration had no effect on the survivorship of recruits, but did have legacy effects on post-voyage growth. Again, B. neritina which recruited over very short residency periods of 1 day continued to perform well after translocation and had the highest level of reproductive output after the voyage scenarios (Chapter Four). Recruits that were older (32-days) and reproductively mature at the commencement of the scenarios failed to release any propagules. Even though the number of ‘at sea’ and ‘port residency’ days were equal, reproductive output was higher after short and frequent voyages than after long and infrequent voyages. Finally, the study presented in Chapter Five examined transgenerational effects of B. nertina. Results showed that although the environmental history of the parent colony had a carry-over effect on offspring performance, it was the offspring environment that was a stronger determinant of success (measured by reproductive output and growth). Although cross-vector spread is possible (i.e. parent and offspring both fouling an active vessel), offspring released from a hull fouling parent into a recipient environment will perform better. In combination, these studies have provided new insights into NIS transport via vessel biofouling. Although shipping pathways are dynamic and complex, these results suggest that juvenile stages that recruit over short residency periods and are then translocated on short voyages, may pose a higher risk for NIS introduction than originally assumed. This has implications for marine biosecurity management as short residency periods are common and short, frequent voyages are typical of domestic vessel movements which are largely unmanaged.