Award: PLR-0944694

Food webs are structured both by the amount of production at the base and the amount of predation at each trophic level above the base. In terrestrial food webs we know about this structuring, e.g. the growth of grass at the base and the predation of wolves at the top, with various intermediate organisms in between, such as insects, songbirds and ground squirrels. In marine food webs, though, it is much more difficult to quantify the ‘top down’ (predation) compared to the ‘bottom up’ (production) forces, essentially owing to the ocean not being the usual environment in which researchers (or other humans) exist without difficulty. In our project we attempted to determine whether penguins and whales altered the prey (fish, krill) available to them by their very acts of foraging. In other words, was their foraging intense enough to deplete prey or cause it to move to where it would be more difficult to obtain? We investigated the foraging habitat and preyscape experienced by Adélie Penguins (ADPE) breeding at Cape Royds, Ross Island, using tags that allowed investigation of foraging trip extent and diving depth, coincident with an ROV (Remotely Operated Vehicle) equipped with acoustics, CTD and fluorescence measurement capabilities. At the same time we logged ADPE diet by observing the food passed from parents to chicks. We found that the whales and penguins depleted the krill, or caused it to flee to deeper depths, where they were foraging most intensely. Curiously, the penguins began to forage beneath the really dense portion of phytoplankton blooms, probably to increase visibility of prey thus to facilitate capture. In summary, we found that penguins, aided by baleen whales, did alter their preyscape, i.e. the distribution and abundance of their prey.

Last Modified: 12/13/2015
Modified by: David G Ainley