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Tabitha Hui - Marine Invasions

University of Tasmania, Australia

The impact of Ballast Water Discharge and Environmental Conditions
on the Incidence of Marine Invasive Species

Biological invasions are a potent force for ecological and evolutionary change. Introduced species compete with and prey on native species, and act as vectors or reservoirs of diseases. They may also cause direct economic damage to human activities such as farming, forestry and aquaculture. During the past century, the use of ballast water by commercial ships has created a highly efficient transfer mechanism for entire plankton communities. Ships take on ballast water from coastal areas, entraining diverse planktonic assemblages that inhabit these areas, which are then discharged en masse at subsequent ports of call. The US receives more than 100,000 commercial ship arrivals per year, and approximately 79m tons of ballast water from overseas each year. Despite a clear role of ships in coastal invasions, the relationship between ballast water discharge and the incidence of marine invaders remains poorly understood. The overall aim of my research, therefore, was to examine the possible links between ship arrivals/discharge, and environmental conditions, and the occurrence of invasive species. Specifically, I studied the impact of ballast water discharge, the number of ship arrivals and environmental conditions on the fouling communities of San Francisco Bay. The proportion of invasive species in a community was found to be highest at moderate salinities (~27ppt) and at warmer temperatures (~20oC). As ballast water discharge or the number of ship arrivals increased, total species richness was found to increase. However, the proportion or number of invasive species appeared to be unaffected by shipping activity. Several possible reasons exist for this: (1) oyster-mediated invasions may have boosted the number of invasive species in the southern part of the bay, which is away from any major ports; (2) the invasive species may have been around for long enough to spread around the bay; (3) management strategies to reduce the number of invasions may be effective. It is envisaged that as more complete and better quality data becomes available, the impact of shipping and environmental conditions on marine invasive species will be more clearly understood.

Funding provided by the Smithsonian Institution Women’s Committee