Intertidal invasion patterns in Canadian ports

Abstract

The establishment of non-indigenous species (NIS) in natural ecosystems is a growing concern for preserving biodiversity at global, national, and regional scales. Due to commercial shipping activities, international ports serve as critical entry points for NIS and a source for secondary dispersal. Sixteen international ports in Canada representing both the Pacific and Atlantic coasts were surveyed to characterize intertidal NIS distributions. Intertidal species diversity of both NIS and native species were significantly different between the Pacific and Atlantic coasts, with higher NIS and native species diversity on the Pacific coast. However, our newly developed Invasive Species Index (a measure of the degree of invasion based on NIS and native species relative abundance) suggested that the Atlantic coast was comparatively more impacted by invasion. No direct link was found between commercial shipping activities (number of ship visits or total tonnage) and the distribution patterns of intertidal NIS in these ports. Instead, NIS distributions in port ecosystems were strongly related to latitude, salinity, sediment type, and human population size. In addition to commercial shipping, future research in conservation and management of invaded communities should consider environmental conditions and the risk posed by local anthropogenic activities (i.e. cumulative vector effects) when characterizing invasion dynamics.