Habitat Distribution and Heterogeneity in Marine Invasion Dynamics: the Importance of Hard Substrate and Artificial Structure

Abstract

Biological invasions by non-native species are common in coastal marine communities in many global regions, and the rate of documented invasions has increased dramati- cally in recent time (e.g., Por 1978 ; Cohen and Carlton 1995 ; Reise et al. 1999 ; Ruiz et al. 2000 ; Orensanz et al. 2002; Hewitt et al. 2004 ; Castilla et al. 2005 ; Kerckhof et al. 2007) . It appears, however, that not all habitats are equally important as sites for colonization. For example, most invasions in marine systems are known from temperate latitudes (Ruiz and Hewitt 2008) . Non-native populations are usually found in bays and estuaries, and relatively few non-native species have been reported from exposed outer coasts and offshore locations (Carlton 1979 ; Wasson et al. 2005) . Furthermore, within bays and estuaries, it appears that hard bottom communities and especially artificial hard substrata, such as docks and pilings, are often foci for colonization (Cohen and Carlton 1995 ; Wasson et al. 2005) . Patterns of habitat utilization may have significant implications for the dynamics of marine invasions, and efforts to curtail their establishment, spread and impacts. Here, we evaluate the known distribution of non-native species in coastal habitats, using North America as a model. Our goal is to provide a summary of available information on distributions of non-native marine invertebrates and algae according to habitat, highlighting the relative importance of hard substrata. We also examine the potential role of artificial (anthropogenic) hard substrata for marine invasions, and consider some possible implications of observed distributions of habitats for invasion dynamics