Kelly Benoit-Bird, an Oregon State University oceanographer and lead author on the study, said patchiness is not a new concept, but one that has gained acceptance as sophisticated technologies have evolved to track relationships among marine species.

Dense at right depth
“The spatial patterns of the resource ultimately determine how the ecosystem functions,” said Benoit-Bird, who received a prestigious MacArthur Fellowship in 2010. “In the past, ecologists primarily used biomass as the determining factor for understanding the food chain, and the story was always rather muddled. We used to think that the size and abundance of prey was what mattered most.
“But patchiness is not only ubiquitous in marine systems, it ultimately dictates the behavior of many animals and their relationships to the environment,” she added.
Benoit-Bird specializes in the relationship of different species in marine ecosystems. In one study in the Bering Sea, she and her colleagues were estimating the abundance of krill, an important food resource for many species. Closer examination through the use of acoustics, however, found that the distribution of krill was not at all uniform – which the researchers say explained why two colonies of fur seals and seabirds were faring poorly, but a third was healthy.
“The amount of food near the third colony was not abundant,” she said, “but what was there was sufficiently dense – and at the right depth – that made it more accessible for predation than the krill near the other two colonies.”

Same patterns
The ability to use acoustics to track animal behavior underwater is opening new avenues to researchers. During their study in the Bering Sea, Benoit-Bird and her colleagues discovered that they could also use sonar to plot the dives of thick-billed murres, which would plunge up to 200 meters below the surface in search of the krill.
Although the krill were spread throughout the water column, the murres ended up focusing on areas where the patches of krill were the densest.
“The murres are amazingly good at diving right down to the best patches,” Benoit-Bird pointed out. “We don’t know just how they are able to identify them, but 10 years ago, we wouldn’t have known that they had that ability. Now we can use high-frequency sound waves to look at krill, different frequencies to look at murres, and still others to look at squid, dolphins and other animals.
“And everywhere we’ve looked the same pattern occurs,” she added. “It is the distribution of food, not the biomass, which is important.”

Source: Oregon State University News Release

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