Award: PLR-1141948

Marine food webs are structured or organized by top-down (predation) and bottom-up (production) forces, but while bottom-up processes are often studied the effects of predation in open-water systems have rarely been assessed. It is much easier to determine how much food there is than it is to assess how predators change the availability of their prey either by consuming it or chasing it out of reach. In the Ross Sea, Antarctica, we used an acoustically equipped autonomous glider (a 3m long torpedo with wings that propells itself, and possesses a recording 'fish finder') to assess changes in the preyscape and environment; that is, availability of crystal krill and silverfish, the two main prey species of penguins and whales in that area. The glider was controlled via satellite link from a location in the USA, as its position was continually plotted on a chart showing the coast and sea ice (we didn't want it to crash into the beach, nor become lost under an iceberg or sea ice). At the same time, miniature satellite-linked time-depth recorders were attached to Adélie penguins, which along with censuses of co-foraging cetaceans, assessed foraging pressure (depth and distance from the colony). Simultaneously the glider also assessed food availability for the prey species, using chlorophyll concentration as a proxy, i.e. the krill fed on diatoms. Our results indicated that this is "wasp-waist" food web, apparently controlled in the middle food web levels by the availability of krill and fish. While there was more than enough food for krill and fish to eat, their depth and abundance were uncoupled from the phytoplankton, but were strongly altered by the level of predation. This was a collaborative effort among engineers, biological oceanographers and wildlife ecologists; several beginning investigators were involved. Last Modified: 09/17/2015 Submitted by: David G Ainley