Latitudinal patterns of biological invasions in marine ecosystems : a polar perspective

Biological invasions in coastal ecosystems have occurred throughout Earth’s history, but the scale and tempo have increased greatly in recent time due to human-mediated dispersal. Available data suggest that a strong latitudinal pattern exists for such human introductions in coastal systems. The documented number of introduced species (with established, self-sustaining populations) is greatest in temperate regions and declines sharply at higher latitudes. This observed invasion pattern across latitudes may result from differences in (1) historical baseline knowledge, (2) propagule supply, (3) resistance to invasion, and (4) disturbance regime. To date, the relative importance of these mechanisms across geographic regions has not been evaluated, and each may be expected to change over time. Of particular interest and concern are the interactive effects of climate change and human activities on marine invasions at high latitudes. Shifts in invasion dynamics may be especially pronounced in the Northern Hemisphere, where current models predict not only an increase in sea surface temperatures but also a rapid reduction in sea ice in the Arctic. These environmental changes may greatly increase invasion opportunity at high northern latitudes due to shipping, mineral exploration, shoreline development, and other human responses.