Invasive species threaten marine biodiversity on a global scale.
To test whether marine reserves provide resistance to invading species, the abundance of two conspicuous invaders, a seaweed and an oyster, were measured inside marine reserves and in comparable areas outside reserves in north-western Washington State.
Densities of both invaders were significantly higher in marine reserves than in comparable unprotected areas outside reserves. Although the causal mechanisms have not yet been identified, differential rates of human harvest do not appear to be responsible for the patterns observed.
It is provisionally suggested that physical or biological aspects of the reserves themselves may directly or indirectly facilitate biological invasion.