Invertebrate resting stages in residual ballast sediment of transoceanic ships

Abstract

Ballast water has been the primary vector of nonindigenous species (NIS) to the Laurentian Great Lakes over the past 45 years. Although ballast water exchange regulations were implemented in 1993 to reduce propagule loads, new NIS continue to be discovered. A possible explanation for this trend is the importance of alternative vectors, such as residual ballast of ships claiming "no ballast on board". We investigate resting stages of invertebrates in residual ballast sediments of transoceanic ships as a possible vector of NIS to the Great Lakes. To model the introduction effort potentially associated with this vector, we collected sediment samples from 39 ships entering the Great Lakes and measured the density, viability, and species richness of resting stages contained therein. Viable resting stages of NIS were found in 32% of ships, at a mean density of 3.0 × 105·ship–1. Temperature, salinity, and removal of eggs from sediment during incubation had a significant impact on total abundance and species richness of hatched taxa. A total of 21 NIS were identified, consisting exclusively of rotifers and cladocerans. Salinity of residual ballast water and geographic region of ballast uptake were predictive variables for profiling invasion risk due to ships, although explained variability was low.