Ships have contributed to the spread of scores of invasive species to the Great Lakes.A new study concludes that sediments in ship hulls and fouling on the ships' bottoms harbor scores of invasive species that could adversely impact the Great Lakes.

The study, which was covered in the Buffalo News, investigated 41 ships entering the lakes and found 93 different species in their ballast water. Thirteen of those species had not been observed in the lakes before.

But the fouling on the outside of one ship -- which had traveled in the Mediterranean, Pacific Ocean and Caribbean Sea before dry-docking in Lake Ontario -- contained dozens more potential exotic invaders, including many freshwater species from around the world.

Sediments at the bottom of ballast tanks are also significant because a majority of the ships coming into the lakes from salt water declare that they have no ballast on board and are therefore exempt from inspection. But their tanks do hold sediments that are alive with creatures from all over the world, the study showed.

Click here for a closer look at efforts being made to mitigate ships' impact on the Great Lakes.