We just finished the last collection site of the cruise and are heading back to Alpena. The rumor on the ship is there will be a swim call when we reach Thunder Bay. The lesson of the day is Brandon’s story of the ship. The Guardian is welded, pinned and bolted together. Should a small crack appear in a weld seam and a small amount of water is taken on there might not be a great concern. However, at some point when the wrong weld, or a dozen bolts or a hundred pins are removed, the ship begins to sink; now there is a problem. Our ecosystems are like a ship. They are made up of hundred if not thousands of organisms. The loss of one or two may not create a serious problem. However, at some point the removal of one critical species or a larger group of organisms will cause the destruction of the ecosystem. The Great Lakes have shown themselves to be a very resilient set of ecosystems. They have withstood many different attacks by many different organisms. They have weathered the loss of dozens of native species. How do we know, however, if the next invasive or the next extinction will cause the ship to sink?