Failing food pantry?
Seafloor organisms face possible challenges as climate changes
Posted February 13, 2009
Scientists are well aware that climate change has come to the Antarctic Peninsula in a big way. Ice shelves are collapsing, glaciers are retreating and the duration of winter sea ice is shrinking.
The latter has serious implications for critters like the shrimplike krill, which feed on the ice algae that forms underneath the sea ice, and for Adélie penguins that prey on the krill. Less sea ice means less krill, a biomass deficit that ripples up the food chain. That story is also well known.
But hundreds of meters below the sea ice sits the continental shelf, home to a unique marine menagerie, from sea cucumbers and worms called polychaetes to sea stars and corals and even bacteria, many of which also rely on sea ice algae for dinner. How this community will respond to climate change is a story that interests scientists like Craig Smith, David DeMaster and Carrie Thomas .
“The Antarctic Peninsula is warming faster than anywhere in the world. It can give us insights, advance warning, into what’s likely to happen in polar ecosystems in general as sea ice disappears,” explained Smith, a marine ecologist at the University of Hawaii and a principal investigator for a ship-based project called FOODBANCS2 (Food for Benthos on the Antarctic Continental Shelf 2). “It’s an important time to get a handle on climate change processes and how they’re going to affect these high-latitude ecosystems.”
FOODBANCS refers to a food bank, a pantry of sorts, of the organic material that falls and accumulates on the seabed during the summer as sea ice melts and phytoplankton blooms erupt near the water surface in an area called the euphotic zone. The bottom-dwelling organisms subsist on that short burst of food that falls like breadcrumbs before winter returns, bringing with it sea ice and darkness.
But warming temperatures are disrupting that cycle, shortening the length of winter sea ice, meaning the mix, or composition, of food falling onto the shelf is changing. The question then becomes: How will the benthic fauna respond to that possible change in diet?
“Those animals that rely on ice algae for their nutrition will have a much harder time of it overall,” said DeMaster, a biogeochemist from North Carolina State University and a principal investigator on FOODBANCS2. “We’re already seeing diminished amounts of sea ice during some of our cruises. In the future, it will only get worse.”
Thomas, the project’s third PI from North Carolina State University, is an organic geochemist who is measuring rates of organic matter degradation on the seafloor, conducting feeding experiments on bottom fauna, and using biomarker analyses to unravel changes in the sources of organic matter reaching the seabed.
This month the trio are leading a team of 16 scientists for a month-long cruise aboard the ARSV Laurence M. Gould to retrieve samples from the seafloor along a 500 kilometer, north-south transect just west of the Antarctic Peninsula. This will be the third and final science cruise of the project, which started in February 2008 and included a winter expedition in July and August during the same year.
Over those five degrees of latitude, the scientists expect to see marked differences in the types of material that fall to the seabed and the structure of the benthic communities. That’s largely dependent on the duration of sea ice, which survives longer the farther south one travels, as long as nine months, according to Smith.
“We anticipate seeing a change in feeding strategies as we’re moving along that temperature and sea ice gradient,” DeMaster noted. The idea is that as the climate changes, the southern extreme of the transect will begin to mirror that at the northern end, allowing the scientists to make predictions about how the ecosystem may change.
Smith said, “We do see a substantial shift in community structure from the northern to the southern [ends].”
This project is actually a sequel to an earlier series of five cruises that Smith, DeMaster, and Thomas made along the Antarctic Peninsula from 1999 to 2001 —FOODBANCS1. It was during those five cruises that Smith, DeMaster, Thomas and colleagues developed the food bank hypothesis.
The original FOODBANCS research also clued the scientists into the idea of studying the shelf as a means for looking at the effects of climate change on the peninsula. As Roy Arezzo, an educator who participated in the FOODBANCS2 cruise last austral winter, wrote on his blog , “Due to the build-up of a nutritious food bank layer on the seafloor, the benthic community responds less to seasonal fluctuations, serving as a ‘low-pass filter’ and making it possible to monitor long-term changes in Antarctic production cycles.”1 2 Next