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August 2013 Issue

Krill Die-Off on US West Coast
Millions of krill, which are food for salmon, whales and other large marine species, have been washing up on beaches from Bodega Bay, California, to Newport, Oregon, in recent weeks.

Joe Tyburczy, a California Sea Grant coastal specialist in Eureka, California, is trying to figure out why, with colleagues from NOAA, Humboldt State University and Oregon State University.

Possible explanations currently under study include winds—mating swarms of krill at the surface may have been pushed ashore by strong storm winds. Low-oxygen waters may have contributed to the mortality event by driving masses of krill to shallower-than-normal waters, where oxygen levels are higher, but the animals are also more vulnerable to wind-driven currents.

A krill pathogen or parasite could have played some role. Some krill have washed up alive, and there have been many reports of surprisingly little predation by birds.

Tyburczy has been gathering a variety of data from colleagues to help assemble a coherent picture of the conditions that might explain the krill deaths.

“The krill die-off is a puzzle,” Tyburczy said. “We can solve it only if we make use of ongoing, long-term monitoring data. It’s the monitoring data that can tell us what the ocean conditions were before, during and after the krill die-off.”

Glass Sponges Proliferate in Weddell Sea
The breakup and collapse of the Larsen-A ice shelf in the western Weddell Sea in 1995 has resulted in fundamental changes to life on the seabed.

As reported by biologists from the Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research in Current Biology, Antarctic glass sponges (Hexactinellida) have been the prime beneficiaries of the disappearance of the ice shelf. The density of these archaic filter feeders has increased threefold between 2007 and 2011 despite only low plankton food supply and water temperatures of -2° C. The sponges have grown remarkably quickly and completely supplanted competitors for food.

The study results show that communities at the bottom of the western Weddell Sea react considerably more quickly to climate-related changes than previously thought.

During a Polarstern expedition to the former Larsen-A ice shelf, biologists succeeded in demonstrating that glass sponges can grow rapidly within a short period of time, which contradicted scientists’ previous assumption that communities on the Antarctic seabed only change very slowly because of the very low temperature and patchy supply of food in pack-ice-covered waters. The study shows that glass sponges may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats in a short period of time.

Marine biologists at the Alfred Wegener Institute will continue to monitor the changes to communities in the western Weddell Sea. In January 2013, the planned dives in the area of the former Larsen-A ice shelf were canceled due to the solid pack ice in the Weddell Sea.

The hope is for better pack-ice conditions during future Polarstern trips to this part of the Antarctic to discover more about the life cycle of the glass sponges.

Blue Whales Found to React to US Navy Sonar Sounds
Some blue whales off the coast of California change their behavior when exposed to the sort of underwater sounds used during U.S. military exercises, according to the Southern California Behavioral Response Study funded by the U.S. Navy Chief of Naval Operations Environmental Readiness Division and the U.S. Office of Naval Research.

The whales may alter diving behavior or temporarily avoid important feeding areas, according to the study, published in July in the Proceedings of the Royal Society B.

The Southern California Behavioral Response Study exposed tagged blue whales in the California Bight to simulated midfrequency (3.5 to 4 kilohertz) sonar sounds significantly less intense than the military uses.

“Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced,” said lead author Jeremy Goldbogen. “But overall the responses are complex and depend on a number of interacting factors,” including whether the whales were feeding deep, shallow or not at all.

The scientists tagged the whales with noninvasive suction cups, which recorded acoustic data and high-resolution movements as the animals were exposed to the controlled sounds.

The scientists found that some of the whales engaged in deep feeding stopped eating and either sped up or moved away from the source of the noise. Not all of the whales responded to the noise, and not all in the same way.

Blue whales, whose populations are decreasing globally, appear regularly off the southern California coast, where they feed. That area is also the site of military training and testing exercises that involve loud midfrequency sonar signals. Such sonar exercises have been associated with several unusual strandings of other marine mammal species, typically beaked whales, in the past. Until this study, almost no information was available about whether and how blue whales respond to sonar.

These are the first direct measurements of individual responses for any baleen whale species to these kinds of midfrequency sonar signals. The findings help to understand risks to these animals from human sound and inform timely conservation and management decisions.

BOEM, USFWS and NOAA to Survey Protected Species
Teams of marine scientists will head out to sea this summer on the largest survey of Atlantic marine protected species on the U.S. East Coast.

From July through September, they will be studying whales, porpoise, dolphins, turtles, seals and seabirds from Maine to Florida to learn more about their population sizes and migratory patterns. 

  The research is part of a five-year study developed and funded by the Bureau of Ocean Energy Management (BOEM), the U.S. Fish and Wildlife Service (USFWS) and NOAA.


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