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A krill and a calanus together.

A krill and a calanus together.
A krill and a calanus together.
A krill and a calanus together.
A krill and a calanus together.
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348314
Linder, Christopher L.
A krill and a calanus together.
Still Image
05/04/2009
graphics/PD5_dailys/cl_20090504144156.jpg
Image of The Day caption:
Marine mammals, fish, and seabirds all depend on abundant tiny planktonic animals for food, especially krill and copepods, little drifting crustaceans that in turn eat much tinier single-celled organisms. WHOI biologist Carin Ashjian led a 2009 research cruise to study the Arctic Ocean ecosystem, chronicled as a Polar Discovery expedition. Shown here are a krill (upper animal, about an inch long) and two copepods (a larger Calanus and a smaller Pseudocalanus, bottom center) collected on that expedition.
For size comparison, here's a Calanus next to a krill. The krill is about two centimeters long. The zooplankton team uses some smaller krill like this one in their grazing experiments, but they aren't doing egg-laying experiments with krill. The other two tiny copepods-one at the bottom and one at left-are Pseudocalanus. The Metridia were probably swimming too fast to get caught in this picture. Just think-an animal as big as a 60-foot bowhead whale can support itself on animals this teeny. But then, these animals are pulling off a similar trick, eating microzooplankton 1/1000th their size.
Photo by Chris Linder
© Woods Hole Oceanographic Institution
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