February 9, 2017
Warming Alaska waters are luring all kinds of new creatures – and some of the smallest can potentially be the biggest troublemakers. In the eastern Gulf of Alaska tiny filter feeders called salps are appearing. The inch-long tubes never stop feeding on phytoplankton, the foundation of the ocean’s food chain.
“Just the fact that they are here is different from the usual. “
Wesley Strasburger is a fishery research biologist based at the NOAA Auke Bay lab in Juneau. He’s chief survey scientist for the eastern Gulf that began last year. Salps can asexually bud off clones and form long feeding chains of several hundred.
“They are very efficient feeders, constantly filtering. Have muscle bands around the outside of their tunicate and rhythmic pulsing move water constantly and trap food in a mucous web. Anything in their path they eat. They are not selective. Anything in their path they will eat it.”
That means all the microscopic crustaceans and other larvaes that small fish depend on. Salp abundance made a big increase in 2015 based on takings in tiny mesh surface trawls on surveys that expanded from 100 miles out to 200 miles. And they made up a big part of many fishes diet.
“In the diet data, juvenile pink salmon, chums, sockeye, juvenile rockfishes and juvenile sablefishes were all eating these salps. That is not typical, their diets are usually copepods, euphausiids, and larvaceans – which seem to have been at least in part, displaced by these salps.”
Strasburger says salps are not an energetically dense diet; the trade off is that there are a lot of them. Another plankton vacuum cleaner called gymnosomes also are appearing in Southeast waters.
“These were very abundant this years and ubiquitous. So not only do we have these salps filtering all the primary productivity out of the waters; we also have this other gymnosome doing the same thing and they also are very abundant. “
Researchers have a seven year time series of various zooplanktons which will show measurable impacts when salp or gymnosome blooms appear. Strasburger says they will be closely watching the impacts on Southeast’s juvenile fish.
“That’s kind of where we’re at. They are squarely on our radar and we will monitor to see how it affects the ecosystem.”