A non-native species is a species not naturally found in an environment. An invasive species is a species that causes economic or ecologic harm. All invasives are non-natives, but not all non-natives are invasives. Invasive species are a major concern for the Great Lakes because of the numerous implications from their presence. Invasive species disrupt an ecosystem, and alter the relationships among organisms and the system. As of now, there are more than 185 non-native species in the Great Lakes. Some of the most well known invasives are the Sea Lamprey (Petromyzon marinus), Round Goby (Neogobius melanostomus), Zebra Mussels (Dreissena polymorpha) and Quagga Mussels (Dreissena rostriformis).
Sea Lamprey are native to the Atlantic coast and were first discovered in Lake Erie in 1921 and had spread throughout the other upper Great Lakes by 1939. When the Welland Canal was opened, the naturally existing barrier between Lakes Michigan, Superior, Huron and Erie and the Atlantic Ocean was bypassed, and a pathway into this new habitat was created. The introduction into this system had significant negative implications on native predator fish populations, particularly the lake trout because of the lamprey’s preference for lake trout over other predator fish species.
In their adult stage, sea lamprey are parasites. Their jawless mouths have rows of teeth, which suction to the side of a fish. Their rasping tongues remove the scales, and the suction keeps the lamprey attached to fish while they feed on the blood and tissues of the host. In lake trout, 40-60 percent of all attachments result in death of the host. A single sea lamprey can be responsible for 15-40 pounds of fish biomass loss, largely due to blood loss as a result of the lamprey’s attachment.
Round Gobies were first found in the Great Lakes in the early 1990s, after being brought over in the ballast tanks of shipping vessels coming from the Caspian and Black Seas. Round gobies consume zebra and quagga mussels, of which there is an endless supply in the Great Lakes. This endless food supply provides an advantage over other forage fish species. In addition to the mussels, round gobies also consume the eggs of predator fish such as lake trout and whitefish and other benthic macroinvertebrates (small bottom dwelling organisms). In addition to food competition, round gobies also compete with native species for habitat.
Zebra mussels and quagga mussels are similar organisms in that both are bivalves from the Black and Caspian Sea region and both organisms are filter feeders and are able to remove the plankton from large volumes of water. Zebra mussels were first seen in Lake St. Clair in 1988, and have spread to all five Great Lakes in ten years. Quagga mussels were discovered in the Great Lakes in the early 2000s and have quickly out-competed zebra mussels in most areas. The spread of both organisms was easy largely because these organisms are planktonic in their larval stage. They are transported by water currents and can drift for miles before settling.
Zebra mussels require a solid substrate to attach to and warmer water temperatures to reproduce. Quagga mussels on the other hand, do not need to attach to a solid substrate and can survive and reproduce in deeper, colder water. Quagga mussels have a longer siphon (feeding tube) that allows them to be settled in the sediment on the bottom, and still be able to draw in water to filter. This combined with their wider temperature tolerance means quagga mussels can be seen along the bottom of all but the very deepest points in the lakes.
The implications of these filter feeders is clearer water. Since the early 1990s, water clarity has steadily increased. This alteration is increasing the photic zone, or the area in the water where photosynthesis can take place. This means a larger habitat for algae, which leads to algal blooms that can negatively impact the ecosystem.
Overall, non-native species have wide ranging implications. All are introduced into the system and initially find ideal habitat conditions, surplus food supplies and no predators. Species that are considered a non-native assimilate into the ecosystem and cause no significant problems. Invasive species do not assimilate into the system, and instead have population explosions that contribute to dramatic ecological changes. There is no way to tell what consequences will result due to the introduction of non-native species; therefore it is important to prevent their movement into the Great Lakes as opposed to managing them once they are already in the system. This approach is cheaper and will help protect the resiliency of the Great Lakes.
- Emily Shaw, Contributing Writer