Non native macroinvertebrates can find their way into a ballast tank. This can cause problems ecologically and economically. Macro-invertebrates are transported by transoceanic and coastal vessels arriving in ports all over the world. Researchers from Switzerland sampled 67 ballast tanks from 62 different vessels operating along geographic pathways, and tested for mid ocean exchange or voyage length that had a high chance of macro-invertebrate relocating to a different part of the world. An assessment was done between the relationship of macro-invertebrate presence, and the amount of sediment in ballast tanks. They discovered a presence of a highly invasive European green crab, mud crab, common periwinkle, soft shell clam, and blue mussel in the ballast tanks of the sampled ships. Although the densities of macro-invertebrate were low, invasion of non-native macro-invertebrates can be worrisome during their mating season. The worst thing that can happen is if a female macro-invertebrate is carrying millions of eggs per animal.