Photo Credit: ©Thomas Mueller |
Members
of the Oceanites/Antarctic Site Inventory team hike toward Baily Head,
Deception Island. This past season, the team spent 12 days at the site,
carrying out the most comprehensive survey ever of the world's largest
chinstrap colony.
|
Photo Credit: ©Thomas Mueller |
Steve Forrest of the
Oceanites/Antarctic Site Inventory team conducts a census on a subcolony
of chinstrap penguins at Baily Head, Deception Island. Baily Head is
home to the largest congregation of chinstraps in the world, but their
numbers appear to be in steep decline. |
The big picture
By Peter Rejcek, Antarctic Sun Editor
Posted February 17, 2012
The story of how three little penguin species are coping
with significant changes in climate around the Antarctic Peninsula has
followed a familiar narrative in recent years.
Colonies of ice-dependent Adélie penguins along the
western side of the peninsula are blinking out of existence. A
subantarctic species called gentoos that disdain ice is thriving,
pushing farther south. The third species of brushtail penguin known as
the chinstrap is somewhere in the middle.
All of this is under way in a region considered one of
the fastest warming in the world. It’s where average year-round
temperatures are 3 degrees Celsius higher over the last 60-plus years —
and about double that during just the winter season.
A driving force in the success and failure of the
different penguins revolves around sea ice, its extent and duration
shrinking dramatically in recent decades. Such a scenario means that the
true Antarctic penguin, the Adélie, is losing habitat to the
subantarctic gentoos and chinstraps.
That’s the story. But it’s not the whole picture, according to scientists who have recently published a paper in the journal
Ecology that synthesized penguin census data from a 31-year period at 70 sites around the Antarctic Peninsula.
The findings suggest that site-specific long-term studies
may not accurately reflect regional trends because population responses
to climate change vary spatially. By looking at a large number of
populations along the Antarctic Peninsula, the authors find that they
call the “classic sea ice hypothesis,” while likely still a factor in
the dynamics of the food web, “misses many of the key details that
emerge from a more comprehensive regional-scale analysis.”
Adélie penguins at Torgersen Island, Antarctic Peninsula.
Chinstrap penguins around the Antarctic Peninsula.
Photo Credit: Kris Perry
Gentoo penguins at Biscoe Island, Antarctic Peninsula.
“This study really captures what we’re trying to do,
which is to understand the broad-scale picture of penguin population
dynamics, not necessarily looking at any one site in particular. We’re
trying to get a bird’s eye view of what is going on,” explained
Heather Lynch 
, lead author of the paper.
More than five years ago, while a post-doctoral fellow with
William Fagan at the
University of Maryland, College Park , Lynch joined forces with Ron Naveen and his nonprofit conservation organization,
Oceanites Inc. In 1994, with funding from the
National Science Foundation (NSF) 
,
Naveen had initiated the Antarctic Site Inventory, an ambitious program
to census the seabird populations around the Antarctic Peninsula.
Naveen had the data. Lynch and Fagan had the analytical
tools to create models that would pinpoint trends over time and space.
For the
Ecology paper, the researchers also drew upon other long-term datasets, including those by
National Oceanic and Atmospheric Administration (NOAA) scientists working in the South Shetland Islands off the northwest tip of the peninsula.
The analysis found that Adélies were in significant
decline. No surprise there. Out of 24 breeding sites, Adélies were down
at 18 sites and increasing significantly at only three colonies. But
chinstraps — contrary to some previous research that implied they were
mostly thriving alongside gentoos, as both species are not dependent on
sea-ice like their cousin — are also failing. The 29 chinstrap sites
surveyed found significant declines at 16 sites and increases at seven.
“If you look at the big picture, chinstraps are declining
rapidly and regionally,” Lynch said, even more so than Adélies in the
last decade.
But none of the changes affecting chinstraps or Adélies
appear to be directly related to sea ice, according to the research.
That finding supports a paper published last year by NOAA scientists in
the journal
Proceedings of the National Academy of Sciences.
“We suggest that sea ice no longer drives trends in
penguin populations through direct, physical effects on habitat. Rather,
sea ice is one of several factors that mediate prey availability to
penguins,” wrote the authors, led by
Wayne Trivelpiece , a scientist with NOAA’s
National Marine Fisheries Service .
The work by Lynch, Naveen and their colleagues also
suggest a correlation to food, at least for the peninsula Adélies, which
rely almost exclusively on shrimplike krill. They used chlorophyll a as
a proxy, or as a way to estimate biological activity, because actual
estimates of krill biomass in the Southern Ocean are unavailable on the
scales covered by the research.
Chlorophyll a is a green pigment in phytoplankton,
microscopic plantlike organisms that float in the ocean. Krill feed on
phytoplankton, hence the connection. Scientists believe the little
crustaceans are also reliant on sea ice as both a habitat and source of
food, as juvenile krill feed on algae that grow under the ice. So sea
ice is still in the equation.
The scientists found that neither chlorophyll a nor
changes in spring sea ice were correlated to the spatial pattern of
chinstrap population declines.
In contrast to the other two
Pygoscelis species,
gentoo penguin populations are significantly increasing at 32 of 45
sites and significantly decreasing at only nine sites, the researchers
reported. Lynch and colleagues found that gentoo colonies are restricted
to areas with less than 50 percent sea ice cover in November. Their
southward march has been rapid, thanks to the decline in sea ice at that
time of year.
“I think we have to rethink the paradigm of population change in all three species,” said Lynch, now an assistant professor at
Stony Brook University .
Naveen said the disparate findings suggest that researchers still have much to learn about what is driving the ecosystem.
“We want to try to understand more precisely why we’re
seeing different responses by these three species in what is a vastly
warming ecosystem. It could be food related. It could be oceanography.
It could be something else,” he said.
Both scientists made separate expeditions to the Antarctic
Peninsula this season, the 18th of the Antarctic Site Inventory, which
now includes 142 sites. The current research is partly funded by the
NSF’s
Office of Polar Programs .
Most of Oceanites’ fieldwork is opportunity-based, hitching
rides aboard tourist vessels during the Antarctic summer. This year,
Naveen and his team were able to raise additional funds and charter the
yacht
Pelagic. They spent 12 days at Deception Island, home to world’s largest chinstrap colony at a location called Baily Head.
“Deception Island has never been counted like that in one
season, let alone in a 12-day period. We’re pretty excited about the
results,” Naveen said.
The manuscript describing their findings is still in the
works, but Lynch said the numbers will shock those scientists familiar
with the Baily Head colony.
“We have found a complete collapse of the penguin colony there,” she said. “I was there this year, and it’s like a ghost town.”
Meanwhile, this season Lynch worked aboard the research vessel
Laurence M. Gould , one of two science vessels in the
U.S. Antarctic Program , which is managed by the NSF. She was able to visit several islands where she saw visible signs of change.
“We spend a lot of time chasing ghosts and going to a lot of empty colonies now,” she said.
Photo Credit: ©Thomas Mueller
A sound recorder installed by the Oceanites/Antarctic Site Inventory team at Baily Head, Deception Island.
The chinstrap story has been largely ignored until
recently, according to Lynch. She and Naveen want to focus more
attention to their plight. This year they installed a sound-recording
device at the Baily Head colony that captures 20 minutes of sound per
day. The scientists will be able to hear when the chinstraps return to
their colony in the summer to begin breeding — and even when the eggs
begin to hatch.
“There’s some natural wobble every year when the peak of
egg laying occurs. The better and better we get at understanding that
date and refining our data, we reduce the error in our analyses,” Naveen
explained.
A second device was set up at another location on
Cuverville Island, with a large gentoo population. “It’s just another
tool that we have in the arsenal. We’ll be testing it out over the next
few years to see if it is useful to us, and we’re optimistic,” Naveen
said.
Another very useful tool has been high-resolution satellite
imagery. Lynch and Naveen predict the technology will eventually lend
itself to monitoring penguin colonies around the entire Antarctic. [See
related article —
Eyes in the sky: Scientists use satellites to track health of seal, penguin populations in Antarctica.]
For instance, counts from satellite pictures matched up
closely with previous Oceanites estimates for the Adélie population
breeding on Paulet Island in the Weddell Sea, and a more recent analysis
shows a near perfect match between satellite image-based estimates and
ground counts for chinstraps breeding at Baily Head.
“We’re very clear now that for some of these large
colonies, this is the way to go to measure change, to see if the
colonies are expanding or shrinking,” Naveen said. “The satellite stuff
is going to be pretty amazing.”
Predictions about what might happen to the penguins of the
Antarctic Peninsula are a little harder to come by. The current
population trends will likely continue, assuming the region’s climate
and ecosystem trends also follow their current trajectories.
Regional extinction may be a possibility, unless the
penguins can change their behavior. Naveen noted that previous studies
of tissue samples of eggs from ancient penguin colonies in the Antarctic
Peninsula region show that Adélies once ate a diet similar to gentoos,
one more rich in fish.
Human pressures through whaling 200 years ago removed a
major predator from the peninsula ecosystem for decades, presumably
creating a surplus of krill. Now the whale populations are bouncing
back, and krill are fished commercially for products like omega-3
nutrition supplements. Throw in climate change, and there appears to be
less krill to go around.
A switch to a less krill-centric diet may help. But a
research cruise in 2010 in search of silverfish, a sardine-sized fish
favored by penguins, found little evidence that they were still
available around the peninsula region — another possible casualty of
climate warming. [See previous article —
Fishy business: Climate change may be to blame for disappearance of Antarctic silverfish.]
Naveen sees a lesson here: Can species adapt quick enough to a multitude of changes driven by climate change?
“We’re going to see more and more of that around the globe.
What’s happening in the peninsula may be giving us some clues as to
what we who live in more temperate climates may be facing in the
future,” he said.
NSF-funded research in this article: Ron Naveen, Oceanites Inc., Award No. 0739430 ; and William Fagan and Heather Lynch, University of Maryland College Park, Award No. 0739515 .
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