2.5 TAKE-UP - ORGANISM AND SEDIMENT COLLECTION

2.5.1 Source ballast water and sediment

When water ballast is gravity fed or pumped on-board a ship, organisms present in the water may also be taken on-board. In addition, organisms may also be present in any sediment that is taken up with the ballast water. Depending on the size of the vessel and, therefore, on the size of the ballast water intakes, such organisms can range in size from micro-organisms such as bacteria and viruses to fully grown fish.

The amount of sediment taken up by a vessel will be determined primarily by water depth and turbulence which in turn are influenced by weather and tidal conditions. If a ship is berthed in shallow or turbid water which has been disturbed by dredging, or by wave and wind action, more sediment (and the organisms contained within it) may be taken up. It is not uncommon for vessels to have accumulations of mud in their ballast tanks of up to 10cm in depth¹³

The Committee notes that many species may be transported in ballast tank sediment. In addition to providing a food source, sediments create habitats for potentially viable resting life stages of organisms such as toxic dinoflagellate spores.

2.5.2 Hull/Marine fouling

Organisms may be collected through fouling of ships' hulls and other parts of the vessel such as propellers, and underwater discharge and suction openings and their gratings¹⁴ Fouled wharf pylons provide a source of larvae of sessile fouling organisms in close proximity to berthed ships. These larvae may attach onto vessel hulls forming and adding to hull fouling communities. Mobile organisms such as crabs may nestle in fouling encrustations and be transferred from one place to another.