By Steven Maier
Macroscopic residents of the Great Lakes get all the attention. But smaller creatures play a larger role than size would suggest.
Pictured here are zooplankton collected from Lake Ontario. The man who collected them (with some help) is Curtis Karboski, a biologist working for the Lower Great Lakes Fish and Wildlife Conservation Office in New York.
Zooplankton are invertebrate animals and the second step in the food chain, surviving on often-microscopic plant life. Some can be large, like the jellyfish. Some can be as small as a single cell. Most are not visible to the naked eye.
The ecosystem in Lake Ontario is experiencing some big changes right now, though most would never know it.
“Nothing is evident looking at the lake,” Karboski said.
The zooplankton are experiencing an invasion. Native zooplankton like the daphnia (lower-left and middle-right) are increasingly preyed upon by newcomers like the Fishhook waterflea (lower-middle) and the Spiny waterflea (middle-left).
They affect the lake like any other invasive species, Karboski said, just at a lower level. He likened it to the arrival of the round goby in the 1990s, which changed the Lake Ontario ecosystem as it competed for resources with native fish.
These changes work their way up the food chain. Zooplankton are an important food source for smaller forage fish. What starts with daphnia eventually affects salmon. One worry is that the invasives will eat the natives out of extinction, then die of starvation themselves.
A similar situation took place in Lake Huron 14 years ago. The Chinook salmon, an introduced species, preyed on the alewife population to the point of collapse. Once the alewives were gone, the salmon followed suit.
Scientists aren’t sure how invaders like the waterfleas will change the lake, Karboski said. Until that becomes apparent, preparing responses will be difficult.