Predator and prey

Researchers hunt for answers to dynamics of Ross Sea ecosystem

There are few places left in the world where the big predators — think lions, tigers and bears (oh my) — still naturally dominate their ecosystem. That’s even true of the world’s oceans — except one.

The Ross Sea , which has been dubbed the Last Ocean , is still relatively pristine. Whales, penguins and seals gather in large numbers every austral summer — a wildlife scene that seems only possible in Pixar cartoons these days.

They feast on a host of prey, from shrimp-like krill to herring-sized silverfish. In turn, these small critters — scientifically classified as zooplankton — graze on the Southern Ocean’s version of flora such as phytoplankton and smaller zooplankton such as copepods.

This intact marine food web offers benthic ecologist Stacy Kim and her colleagues an opportunity to challenge scientific orthodoxy. Researchers have assumed that ecosystems pulse from the bottom up, that it’s the small stuff in the food web that structures the system.

“I don’t think that’s strictly correct,” explains Kim, a researcher at Moss Landing Marine Laboratories , from the lowest floor of the Alfred P. Crary Laboratory at McMurdo Station on a December day last year.

She notes that the bottom-up hypothesis is based on terrestrial ecosystems — but 70 percent of the world is covered by water. In addition, previous ecosystem studies generally began after humans had already rearranged the natural order of things.

“The ecosystems we’ve studied don’t have natural populations of top predators,” Kim says. “Of course, they’re going to have a lesser impact on the food web and ecosystem structure.”

Kim is overseeing a two-year field project to understand the food web interactions between top predators — particularly Adélie penguins, killer whales and minke whales — and the pressures they exert on specific types of prey.

Her team occupies one of several labs attached to a chilly aquarium room containing tanks of hulking Antarctic toothfish and other marine vertebrates and invertebrates. Just a few hundred meters away, down the rocky volcanic slope of Ross Island, the iced-over waters of McMurdo Sound, which opens to the Ross Sea, offer a natural laboratory to test Kim’s hypothesis.

“Out here we have this great opportunity — this Ross Sea opportunity — that is unique to look at these populations of top predators and how they’re influencing things,” Kim says enthusiastically.

Photo Credit: Peter Rejcek

Researchers prepare to deploy SCINI and FATTI through a hole in the sea ice.

In the aquarium room, engineers Eric Stackpole and Laughlin Barker are carrying what appear to be a couple of torpedoes in various states of assembly. In fact, one of the projectile-sized instruments is SCINI . The other is FATTI.

SCINI (Submersible Capable of under Ice Navigation and Imaging) has become one of Kim’s primary tools over the years. A custom-built, remotely operated vehicle (ROV), SCINI carries a couple of cameras that the marine biologist and her team have used to explore the seafloor of McMurdo Sound.

However, on this project, SCINI flies through the water column, pulling its newly built companion, FATTI, for Fluorometer and Acoustic Transducer Towable Instrument. FATTI’s acoustics help find schools of krill and fish. The fluorometer provides a type of flashlight to see phytoplankton, small plant cells, in the water.

The researchers are particularly interested in the pressure that predators put upon a couple of wee-sized marine animals: a species of krill called Euphausia crystallorophias, commonly referred to as crystal krill, and Antarctic silverfish, Pleuragramma antarcticum.

“It’s pathetic the amount of information known about crystal krill. It’s like they don’t exist,” laments David Ainley from his outpost at Cape Royds, a rocky outcrop of Ross Island that’s home to the southernmost breeding colonies of Adélie penguins in the world.

All the glory and research is devoted to crystal krill’s popular cousin, Euphausia superba, a pelagic species that is also a target of krill fisheries that supply the omega 3 supplements market. Crystal krill prefers to hug coastal waters, offering a tasty meal for predators hunting along the receding sea ice edge during summer months.

Photo Credit: Peter Rejcek

Penguins march across ice floes near Cape Royds.

“We’re hoping to learn more about crystal krill than necessarily penguins,” adds Ainley, who is a co-principal investigator on the project, senior ecologist with ecological consulting firm H.T. Harvey and Associates in California. He and research assistant Jean Pennycook outfit Adélies with satellite tags to track their movements when they leave the colony to forage to feed their hungry, downy-feathered chicks.

Previous research with collaborators Walker Smith of the Virginia Institute of Marine Science and Vernon Asper at the University of Southern Mississippi used an autonomous glider to study the foraging behavior of Adélie penguins from another Ross Island colony at Cape Crozier. The glider also carried acoustic instruments to locate krill and fish.

While good data exist about penguin ecology, less is known about the bigger players in the food web — the whales. That’s where Robert Pitman and John Durban , with NOAA’s Southwest Fisheries Science Center , come into the project.

They are studying minke and killer whales.

“There’s been an increasing realization, not only in the Ross Sea but around the world, that killer whales are important in these food webs,” notes Durban, a population ecologist.

How important is one of many questions to be answered.

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