Analysis of invertebrate resting eggs and other biota in ballast tank sediment of domestic Great Lakes cargo ships

Abstract

Domestic shipping in the Laurentian Great Lakes may be a vector of secondary spread for non-native species, but research has not yet assessed the role of ballast tank sediment. Here, ballast tank sediment was collected from three domestic ships (M/V American Century, M/V Edwin H. Gott, and M/V Mesabi Miner) during 2011 and 2012 at Lake Superior harbors in the USA and analyzed for invertebrates. Samples contained evidence of active life stages of Bivalvia, Cladocera, Copepoda, Gastropoda, Hydracarina, Nematoda, Oligochaeta, and Ostracoda as well as dormant life stages of some species including ones hatched in the laboratory from Cladocera, Copepoda, Ostracoda, and Rotifera. Excluding resting eggs, the groups Bivalvia, Copepoda, and Ostracoda comprised 83% of individuals recovered. The mean density of resting eggs per ballast tank ranged from 16.0 to 24.8 eggs/g wet sediment for samples collected during November and from 0.2 to 2.7 eggs/g wet sediment for samples collected during December to March. The mean viability (percentage hatched) of resting eggs per ballast tank ranged from 31.2% to 75.8% for samples collected during November; December to March samples were not assessed for egg viability. Bosminidae (Cladocera) were the most commonly hatched taxa and comprised 548 of 819 hatchlings (or 67%). Hatched eggs included Eubosmina coregoni and Bythotrephes longimanus which are non-native to the Great Lakes. Densities of resting eggs and other biota were comparable to, or greater than, published densities of organisms in ballast tank sediment of foreign ships entering the Great Lakes and ballast tank water of domestic ships operating within the Great Lakes.