Friend or foe? The bloody-red shrimp invasion may not be so bad for the Great Lakes
By Liz Pacheco
With a name like “bloody-red shrimp,” the invasive species might seem like the Great Lakes’ worst nightmare. But it’s a misnomer for this miniature invader. First found in 2006, bloody-red shrimp have proliferated in the Great Lakes. However, researchers are still trying to determine what effects, if any, the species will have on the ecosystem.
Like many other Great Lakes invasives, this mysid (a small shrimp type that carry young in a pouch on their body) hitched a ride in ballast water. First found in waters connected to Lake Michigan, the species has spread to every Great Lake, except Superior, as well as the St. Lawrence River.
Despite the name, bloody-red shrimp (Hemimysis anomala) aren’t very red, more a pink, said Lars Rudstam, a natural resources professor at Cornell University and director of the Cornell Biological Field Station.
“We don’t know why they have that color. We thought maybe it has to do with swarming during mating time,” Rudstam said. “Some people think it has to do with UV protection during the day.”
But the color is innocuous since the shrimp measure less than one-half inch at full size. When matured in the summer, the shrimp are less than a quarter-inch long. They’re approximately double that length in the winter.
Instead of size, the species gets its strength in numbers.
“The species is known for a swarming habit,” said Yves de Lafontaine, the acting director for Environment Canada’s Division of Research for the Protection of Aquatic Ecosystems. “[They] can create huge densities in a restricted zone.”
A study led by de Lafontaine and published this October in the Journal of Great Lakes Research, assesses the presence of bloody-red shrimp in the “restricted zone” of the Montreal Harbour on the St. Lawrence River. While the river’s ecosystem is different than the Great Lakes’, de Lafontaine’s study revealed an important aquatic habit of the bloody-red shrimp.
“We found the species fairly abundant with densities over 1000 animals per square meter,” said de Lafontaine, who described this as a high number. The Montreal Harbour is an ideal home for the shrimp, which thrive in rocky areas or tight spaces where they can hide during the day from predators. Samples taken in the open channel showed densities closer to five shrimp per square cubic meter.
A high density in a shipping area increases the risk of bloody-red shrimp spreading via ballast water. There are no prevention measures in place and de Lafontaine said the only immediate solution would be treatment of ballast water to eliminate the shrimp.
But reducing the population isn’t a major initiative, since scientists are still unsure what affect bloody-red shrimp have on the Great Lakes’ ecosystem.
“In Europe, the Hemimysis was introduced deliberately as a food item for fish,” de Lafontaine said. While European research and studies on similar species can give some idea as to what could happen in the Great Lakes, more research in North American waters is needed.
De Lafontaine is now studying the shrimp’s potential impact on food webs. The species is omnivorous, typically feeding on zooplankton (small organisms) and algae. They’re also potential prey for small fish. What’s unique is they don’t have specific competition in the food web.
“[They’re] going to graze and going to utilize a lot of sources that are particularly used by other species,” de Lafontaine said.
Rudstam sees this lack of competition as evidence for why they’re not a major concern.
“During the time when larval fish need the zooplankton the most, this animal isn’t abundant yet,” Rudstam said. “The timing and its restrictions to really rocky habit, suggest to me it’s not going to have a really big affect.”
Other scientists see things differently.
Tony Ricciardi, an invasive species biologist at McGill University, doesn’t see the bloody-red shrimp wreacking havoc like the quagga mussel, but cites the lack of mysid shrimp competition in shallow waters as a potential issue.
“This is a warning sign, because invaders (especially predators) that cause the most disruption tend to be those that have no functional equivalent in the recipient habitat,” Ricciardi wrote in an e-mail. These invasives can fill a previously undefined niche in the ecosystem where there’s no species to keep them in check.
Rapid reproductive rates and a history of mysid shrimp altering food webs are also concerns, wrote Ricciardi, who elaborates on these predictions in a paper to be published by the Journal of Great Lakes Research.
Perhaps equally important, although more complicated, is the question Ricciardi raises about the bloody-red shrimp’s place among the Great Lakes’ invasives.
“What are the collective impacts of the growing conglomerate of invasive species?” he wrote, citing round gobies and zebra and quagga mussels. “And how do these species interact?”