Anthropogenic modification of estuaries: disturbance and artificial structures influence marine invasions

Abstract

Estuarine environments are threatened by the synergistic effects of anthropogenic disturbance and bioinvasion. The construction of artificial structures (such as pilings and pontoons) provides a habitat resource in close proximity to vessel hulls that may be carrying a wide range of non-indigenous fouling species. In addition, the release and accumulation of toxicants from antifouling (AF) paints on vessel hulls creates a chemical disturbance that may reduce the invasion resistance of native communities. This thesis examines how shipping-related disturbances affect sessile communities, and in particular what role AF paints and artificial structures play in the invasion of estuaries.

Using a series of field-based experiments, I found that copper and tributyltin have the potential to influence both the transport of species to a new region, via the application of AF paints on vessel hulls, and their subsequent establishment, via the accumulation of AF biocides in estuaries. Temperature, pH, salinity and turbidity were also related to species distributions. During subtidal surveys of artificial and natural structures I found more non-indigenous species (NIS) on pilings and pontoons than on rocky reef, and shallow floating structures were identified as hotspots for invaders. These findings suggest that artificial structures play an important role in the initial establishment of sessile non-indigenous species in new regions. A subset of NIS were also present on the reefs sampled during the survey and I conducted manipulative experiments to determine factors affecting the invasibility of turf and canopy-forming algal assemblages. The resident assemblage provided a barrier to most invaders, particularly when light and sedimentation levels were also high (i.e. on horizontal substrate). My results suggest that the areas of reef most susceptible to invasion are vertical rock walls and those subjected to disturbances that release space.

In summary, this is the first study to relate copper and tributyltin contamination in the field to NIS distributions. My research has also highlighted the potential role of artificial structures in facilitating the establishment of NIS in estuaries and identified invasion threats to rock wall communities and disturbed reefs in estuarine systems.