Marine Bioinvasions: Conservation Hazards and Vehicles for Ecological Understanding

The old ocean is gone. Life in today's seas is changing in an alarming rate. While many species are dwindling due to overfishing and habitat destruction (Roberts 2007), others invade new regions using anthropogenic vectors (Carlton 1996). These changes are rooted in human activities more than a thousand years old, but have accelerated dramatically in the past few decades due to new technology and increased connectivity (Carlton 1989; Carlton et al. 1999; Crooks and Suarez 2006). Huge fleets extract fish and shellfish with deadly efficiency, and at the same time the growth of trade facilitates the dispersal of organisms attached to the hulls of ships and, more recently, carried within ballast water. Aquaculture, live marine seafood and bait, and the aquarium trade have also become important vectors for the invasion of exotic marine species.

Invasions, in and of themselves, are rated high as a cause of native biodiversity loss and economic damage (Primack 2004; Mooney et al. 2005). But invasions also interact with other factors compromising the integrity of marine ecosystems, including habitat destruction, pollution and climate change. Habitat destruction causes disturbance which opens up space for newcomers such as invaders. Pollution can make environmental conditions less tolerable for native species, and perhaps provide opportunities for opportunists, among them exotic species. Climate change will also play a large role in the invasion process (Mooney and Hobbs 2000). Modifications to ocean temperature, biogeochemistry, salinity, sea level, and current circulation patterns have all been detected within the last few decades, and are expected to continue (IPCC 2007). The ecological ‘footprint’ of these changes has been observed both in terrestrial and marine ecosystems worldwide (Walther et al. 2002, 2005). Documented ecological changes in the oceans include modifications to the phenology of pelagic organisms resulting in trophic “mismatches” between predators and prey (Edwards and Richardson 2004), severe events of coral bleaching that negatively influence the structure of coral reef communities (Hughes et al. 2003), and a mostly northward shift in fish distributions in the North Sea presumably in response to warming temperatures (Perry et al. 2005). Evidence has also started to show shifts in the distributional limits of benthic organisms in temperate coastal environments (Sagarin et al. 1999; Helmuth et al. 2006). Apart from range extension of native species due to climate change, increasing temperatures at medium and high latitudes have the potential to facilitate the establishment of species invading from warmer waters, thus affecting community structure and potentially function.