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Underwater forests of Antarctica

Scientists dive deep into unlocking mysteries of unique marine ecosystem

 

There are mighty forests in Antarctica. Just don’t expect to see them poking through the ice and snow.

The forests are underwater, composed of several species of huge brown algae, or seaweed, which blanket the ocean floor on the western side of the Antarctic Peninsula. These macroalgae dominate the local ecosystem in ways no other seaweed does anywhere else in the world.

This unique marine forest — comparable to the great kelp forest off the coast of California in terms of sheer biomass — and the marine organisms that inhabit it has drawn a team of researchers from the University of Alabama at Birmingham (UAB) and University of South Florida (USF) down to the U.S. Antarctic Program’s Palmer Station for more than a decade.

“We’ve learned that the community at Palmer is structured very differently than lots of other communities that look similar superficially,” said Charles Amsler aboard the ARSV Laurence M. Gould a day before he and the rest of a seven-member team headed south for Antarctica from Punta Arenas, Chile, on a diving research expedition that will stretch into June.

A professor at the UAB and one of three principal investigators on the project, Amsler explained that the team’s previous work has shown that the major brown algae and some of the other marine organisms in the ecosystem use chemical defenses to thwart predators. Much of scientists’ earlier work involved studying the function and evolution of these chemical defenses. Some of the compounds they have isolated in the past show promise as cancer therapies or even pesticides.

Now, Amsler, James McClintock, also a professor at UAB, and organic chemist Bill Baker from the University of South Florida, are diving deeper into the connections within the ecosystem. They want to understand the ecological relations between the macroalgae, the smaller algal species that seek refuge within the poisonous seaweed, and the vast numbers of small crustaceans called amphipods that swarm the ecosystem.

“This project is really about understanding how this community works, and through understanding this unique community, understanding more about how a kelp forest works, other marine communities work, in contrast,” Amsler said.

For example, the amphipods are essentially the marine equivalents of insects. Normally, they would feast on the brown algae — but that’s not the case because of the evolutionary chemical defenses of the polar seaweeds.

“So imagine a forest or grassland at home with 100,000 plant-eating insects per meter squared, and yet the big macrophytes [aquatic plants] that dominate the system aren’t edible,” Amsler explained.

Aside from their ongoing work since the 1999-2000 field season, there’s been little characterization of the marine community around Palmer, according to McClintock. “That makes it very exciting for us because it is a frontier in that sense,” he said.

The study also establishes an important baseline to monitor future changes to the environment, noted McClintock, a marine invertebrate zoologist whose interests also range to ocean acidification and the impacts of invasive subpolar species in the Antarctic.

The Antarctic Peninsula is undergoing rapid evolution from climate change, and it is one of the fastest-warming regions on the planet. The average winter temperature is about 6.5 degrees Celsius higher in the winter than it was in the 1950s — a rate of increase more than five times the global average.

Delving into this unique and quickly changing ecosystem involves scuba diving in near-freezing waters. The seas around Palmer are also home to leopard seals, a predator dangerous enough to require an alarm system to alert divers in the water if someone topside in the dive boat spies one of the sharp-toothed critters.

The divers head into the murky coldness to collect samples for lab work at Palmer Station and back at their home universities, as well as for in situ studies. One experiment headed by PhD graduate students Kate Schoenrock and Ruth McDowell from UAB involves studying the relationship between the large algae and smaller, filamentous algae (referred to as endophytes) that live off the dominant seaweeds.

The scientists already know how the endophytes benefit from previous research: “You see them growing inside the large, chemically defended macroalgae,” Amsler said. “They’re living in there as a refuge from all these amphipods.”

McClintock said that in an earlier experiment, which excluded the amphipods in a controlled environment, that “after several months, these [macro] algae look like they’re covered with hair. … The amphipods are like these mini-lawnmowers that are keeping the macroalgae nice and clean and happier than they would be otherwise.”

The next question is what effect do the endophytes have on the macroalgae? Maybe the relationship is one-sided, and the endophytes inhibit growth of the macroalgae by limiting the surface area available for photosynthesis. Perhaps they act as pathogens.

To test such hypotheses, the divers transplant specimens from the ocean onto a concrete substrate — a square block of concrete secured to the bottom — which they lower into the water with the help of lift bags filled with air. [Link to UAB blog post for detailed description.] The researchers then monitor the growth and health of the brown algae attached to their artificial reef.

USF graduate students Alan Maschek and Jason Cuce are heading up some of the chemistry work, studying compounds in other marine organisms that appear to inhibit the amphipods’ ability to molt, which prevents them from growing.

“That sort of thing has never been seen in a marine environment,” Amsler said, adding that such a finding would represent a significant discovery in marine chemical ecology.

McClintock said that so far a sponge and a tunicate have both shown these potentially molt-inhibiting compounds

“They are very differently phylogenetically, and yet to both have evolved a compound that may be involved in tricking crustaceans in terms of their ability to molt would be very interesting,” he said.

Both Amsler and McClintock have a long history of working in Antarctica dating back to the 1980s. Amsler’s wife, Maggie Amsler, a research assistant at UAB and member of the dive team, first went to the ice in 1979. Her mentor was Mary Alice McWhinnie, one of the first women to work in the U.S. Antarctic Program, at the time called the U.S. Antarctic Research Program.

Despite the collective years they share of living and working in Antarctica, the veteran scientists seem no less enthusiastic about their latest adventure than when they were graduate students. It’s a passion they seem eager to pass on to the younger members of their team firsthand.

“We believe it’s very important for the students to see the [marine] communities they’re working on. So many of our ideas come from being in these really special communities,” Amsler said.

Now on his third deployment, Maschek said he was inspired to be certified to dive after his first visit to the Ice.

“Diving down there is like no other experience I’ve ever had. It truly is mind-numbing as you drop down,” he said.

Added Maggie Amsler on the day of her 52nd birthday, some three decades after her first trip to the Ice: “It’s actually pretty wonderful that I’m doing this and keep getting opportunities to come down. … You never know where life is going to take you. For me, it seems that it takes me back here.”

NSF-funded research in this story: Charles Amsler and James McClintock, University of Alabama at Birmingham, Award No. 0838773; and Bill Baker, University of South Florida, Award No. 0838776.

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Curator: Peter Rejcek, Antarctic Support Contract | NSF Official: Winifred Reuning, Division of Polar Programs