that many species of seabirds breed on these islands and feed in the surrounding
waters. Some species of the birds, such as the kittiwake, get their food from
the waters surface. With wings outstretched they hover above the coastal
waters. When they see their prey, they glide down and pick up the prey with
their beaks. Other species, such as the Alaskan murre, dive as much as 180
meters into the ocean, grab their prey and reemerge at the surface.
During the two large coccolithophore blooms, the Pribilof Islands were surrounded by coccoliths. The white scales reflected most incoming sunlight and in doing so cast a shadow on the depths below, Hunt said. Both the murre and kittiwakes foraged for food in these waters. The researchers studied the two birds as they hunted during the coccolithophore blooms. "For the birds chasing food under the water, the coccoliths made it harder to find prey. In contrast, the surface feeders prey was easier to find with the coccoliths present, because the coccoliths highlighted the prey for them," said Hunt. Unexpectedly, the birds that fed off the surface had more offspring than usual, and the birds that dove for their prey had fewer offspring than usual.
|This true color image (a detail of the April 25, 1998 image) from the SeaWiFS instrument shows the bright reflection caused by billions of coccoliths. The Pribilof islands (in the lower left of this picture) are a breeding ground for migratory birds. The bird populations there began to change with the appearance of the coccolithophores. (Image courtesy Norman Kuring, SeaWiFS project)|
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