May 8, 2009

Warm Ocean Waters Could Lead To Shrimp Decline

If ocean temperatures rise, researchers report that Northern shrimp will be adversely affected and the population would go into decline.

The Northern shrimp known as Pandalus borealis support commercial fisheries worldwide.

The tiny creatures are an important part of the oceanic food chain and may serve as early indicators of changing climate due to their sensitivity to temperature.

Researchers say Northern shrimp also seem to have an amazing sense of reproductive timing, releasing their larvae to match the arrival of food and thus maximizing larval survival.

In the journal Science, researchers say that shrimp eggs hatch within days of each spring phytoplankton bloom, which is the main food source for the larvae.
Researchers say if seas warm, shrimp stocks could decline.

Anne Richards of NOAA's Northeast Fisheries Science Center laboratory and international colleagues evaluated the timing of the annual shrimp hatch between 1998 and 2007.

They studied the populations or stocks at different latitudes across the North Atlantic Ocean from Maine to Norway.

The researchers also estimated the timing of spring phytoplankton blooms in each location using satellite images that show biological productivity in surface waters.

The international team discovered that throughout the north the shrimp eggs hatched, on average, in time with the bloom. Experts say this is the period when food is abundant, so the larvae have a far better chance of survival.

The team notes that to get the timing correct, the shrimp must mate during exactly the right period during the previous year.

"They don't do this on a year by year basis - deciding to mate a week later because the algal bloom will be a week later," said Peter Koeller, a researcher from the Bedford Institute of Oceanography, who led the study.

"This is on evolutionary time scales - they have adapted to local conditions."

Therefore, Koeller noted it would be impossible for the shrimp to adapt to a rapid change in temperature at the seafloor.

The team collected samples of shrimp daily and counted the proportion of females that were still carrying their eggs.

Koeller said an explosion in the Northern shrimp population in the 1980s and 1990s was linked to a drop in sea temperatures at that time.

He said it was feasible that the opposite could happen "as the climate changes".

"As surface waters warm, this would eventually result in warmer water at the bottom, which would lead to faster development of eggs and earlier hatching," he explained.

"The larvae would be further removed from period of food abundance, which would mean poor survival rates and fewer shrimp."

Lead author of the study was Peter Koeller of the Bedford Institute of Oceanography in Canada. In addition to Richards, other authors were from the United Kingdom, Canada, Iceland, Denmark, and Norway.

Richards work was supported in part by the Fisheries and the Environment (FATE) program at the U.S. National Marine Fisheries Service.


Image 1: A northern, deep-water or Alaskan pink shrimp, Pandalus borealis. (Credit: NOAA)

Image 2: Northern shrimp are hauled aboard a shrimp boat. (Credit: Aldric D'Eon)


On the Net: