North Atlantic shrimp fishery may be vulnerable to climate change

Shrimp Said At Risk From North Atlantic Warming
Alister Doyle, PlanetArk 8 May 09;

OSLO - A $500 million North Atlantic shrimp fishery may be vulnerable to climate change that could disrupt the crustaceans' life cycle and mislead them into hatching when food is scarce, scientists said.

Any damage to stocks of the northern shrimp -- a small, sweet-tasting variety popular in salads -- could have knock-on effects in the ocean food chain ranging from algae to cod, according to a Canadian-led team of experts.
Northern shrimp are hauled aboard a shrimp boat. (Credit: Aldric D'Eon)

"The shrimp is the marine equivalent of the canary in the mine shaft. It's an indicator of climate change," Peter Koeller, the lead author of the study at the Bedford Institute of Oceanography in Canada, told Reuters.

Writing in Friday's edition of the journal Science, the scientists said that the shrimp timed mating so that their eggs hatch when algae that shrimp larvae feed on are most abundant.

"They have evolved to mate the previous year at just the right time to take advantage of spring blooms," said Koeller. Eggs carried by the females take between 6 and 10 months to incubate over the winter.

"But climate change could decouple the match" between seabed temperatures and food, he said of findings with colleagues in the United States, Britain, Denmark, Iceland and Norway.

The scientists found that the crustaceans, which live from the Gulf of Maine to Arctic waters north of Norway, time their mating according to water temperatures on the seabed where the adults live. Warmer waters could disrupt that timing.

Previously, one theory had been that the larvae hatched in direct response to a chemical trigger from the blooms, for instance cued by dead algae drifting down from the surface.

The shrimp make up about 70 percent of the 500,000 tons of cold-water shrimp harvested annually from the world's oceans. Koeller said the fishery was worth about $500 million.

Koeller said shrimp were an important link in the food chain -- they feed on algae and are in turn eaten by fish. Overfishing of cod has helped a sharp rise in shrimp populations.

The U.N. Climate Panel says that a build-up of greenhouse gases in the atmosphere, caused mainly by mankind's use of fossil fuels, could push up world temperatures and cause more heatwaves, more powerful storms and rising ocean levels.

(Editing by Angus MacSwan)

Shrimp tuned to ocean temperature
Victoria Gill, BBC News 7 May 09;

Stocks of northern shrimp, the essential ingredient in the ubiquitous prawn cocktail, could be badly affected if ocean temperatures rise.

Researchers report, in the journal Science, that shrimp eggs hatch within days of each spring phytoplankton bloom - the main food source for the larvae.

They conclude that shrimp are adapted to local temperature, which determines how long eggs take to develop.

If seas warm, as predicted, shrimp stocks could decline, the team says.

The international team of scientists found that, throughout the north Atlantic - from Cape Cod in the US to to Svalbard in Norway - northern shrimp ( Pandalus borealis ) eggs hatched, on average, in time with the bloom.

This is the period when food is abundant, so the larvae have a far better chance of survival.

But to get the timing right, 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."

This means it would be impossible for the shrimp to adapt to a rapid change in temperature at the seafloor, where they live.

Shrimp boats

Dr Koeller's team collected samples of shrimp daily and counted the proportion of females that were still carrying their eggs. With satellite imaging, they were able to compare the timing of the algal blooms to the release of the larvae.

As Dr Koeller pointed out, 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."

For Northern Shrimp Populations In North Atlantic, Timing Is Everything
ScienceDaily 7 May 09;

Even for Northern shrimp (Pandalus borealis), which support commercial fisheries worldwide, timing is everything in life. The tiny creatures, eaten in shrimp rolls and shrimp salad, occupy a pivotal role in the oceanic food chain and may serve as early indicators of changing climate due to their sensitivity to temperature. Northern shrimp also seem to have an uncanny sense of reproductive timing, releasing their larvae to match the arrival of food and thus maximizing larval survival.

In a study to be published May 8 in the journal Science, Anne Richards of NOAA’s Northeast Fisheries Science Center (NEFSC) laboratory in Woods Hole, Mass. and international colleagues evaluated the timing of the annual shrimp hatch between 1998 and 2007 in 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 - the major source of food for the shrimp larvae - in each location using satellite images that show biological productivity in surface waters, commonly called ocean color.

“In the Gulf of Maine we have seen years when there is a good match in timing between when shrimp larvae are released and when the annual spring bloom begins. In these years larvae tend to have high survival rates, resulting in large year classes and a very successful fishery,” said Richards, who has been studying Northern shrimp for almost two decades. “In other years that timing is off, leading to lower survival rates and a poorer fishery. The match or mismatch between the larvae and their food appears to be a key factor in shrimp production.”

The Science study looked at stocks of Northern shrimp, also called pink shrimp, in the Gulf of Maine, on the Scotian Shelf and in the Gulf of St. Lawrence, off Newfoundland and Labrador, on the Flemish Cap, off western Greenland and Northern Iceland, in the Barents Sea and off Svalbard, a group of islands between Norway and the North Pole.

The spring phytoplankton bloom occurs at different times in different latitudes because sunlight and sea surface temperatures, the primary triggers for onset of blooms, vary among regions. The researchers found a surprising tendency in each location for the shrimp eggs to hatch and the larvae to appear just as the bloom arrived.

“The interesting thing is that the timing of the hatch is strongly dependent on temperature on the ocean bottom, but the timing of the bloom is a function of several factors, including temperature throughout the water column and available sunlight,” Richards said. “Yet, on average, in most of these locations, there is a close match between the hatch and the bloom. It makes perfect sense from an evolutionary perspective, but it is still surprising. Before the advent of satellite imagery, it would have been very difficult to be able to demonstrate this phenomenon across a wide geographic area.”

The time it takes for shrimp eggs to develop into young shrimp, or larvae, varies significantly depending on local bottom water temperatures. In the southern Gulf of Maine off Cape Cod, the waters are relatively warm and shrimp eggs take six months to hatch, while in the cold waters off Northern Iceland the eggs take 9-10 months to hatch. This suggests that the time of mating must have evolved so the larvae are ready to hatch near the time of the bloom under average temperature conditions for each area.

Northern shrimp may serve as an early indicator of the impact of climate change since their life cycle is very temperature dependent. The species breeds once a year, usually in the summer/fall, with the female carrying eggs on her abdomen much like lobsters do until they hatch the following winter/spring. Although the shrimp live most of their life in colder bottom waters, once the eggs hatch the young shrimp live near the surface for several months feeding on phytoplankton and larger zooplankton.

The authors say changing climate may increase bottom water temperatures, resulting in shorter development times for the eggs. If so, the eggs may hatch too early and be too far ahead of the spring bloom for optimum survival. However, they also say this “mismatch” in timing might not occur if warmer sea surface temperatures result in earlier spring blooms.

Richards is testing the “match-mismatch” hypothesis suggested in this study in more detail in her own research on the Gulf of Maine shrimp stock. So far, she has found a strong relationship between water temperatures, the timing and amount of plankton in surface waters, and shrimp survival rates.

“The warming trends evident in the waters in the Northeast U.S. are likely to have an impact on shrimp recruitment and survival," Richards said. "Shrimp production may be much more variable in the future as the Gulf of Maine warms. The population there may ultimately decline if temperatures continue to increase unless the shrimp can adapt.”

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.