Award: PLR-0944511

Description. This project investigated the importance of top predators on oceanic food webs. The relatively pristine Ross Sea includes large populations of upper-level predators such as minke and killer whales, Adélie and Emperor penguins, and Antarctic toothfish. We focused on food web interactions of Adélie penguins, minke whales, and the fish-eating Ross Sea killer whales (type-C), all of which exert foraging pressure on their main prey, crystal krill and silver fish, in McMurdo Sound. We quantified the abundance and distribution of phytoplankton, sea ice biota, prey, and predators, and relevant habitat information in McMurdo Sound. The sampling area encompassed "hot spots" discovered during the first year of fieldwork for fish eating killer whale, minke whale, and Adélie penguin feeding. At each station, data were collected using a remotely operated vehicle (the SCINI ROV) and a tow package (FATTI), which was developed specifically for this project. The sampling suite addressed 4-dimensional mapping of all levels of the pelagic food web, including, primary producers, intermediate consumers, and meso- and top-predators. We constructed a "map" of sea ice patterns, and added successive layers of the water column, distribution of phytoplankton, prey distribution, and predator foraging to search for interacting responses in the ecosystem. Sea ice patterns: Fast ice (sea ice attached to land or ice shelves) plays important physical and ecological roles as a barrier to wind, waves, and radiation, as both a barrier and a safe resting place for air-breathing animals, and as a substrate for microbial communities. While sea ice has been monitored for four decades using satellite imagery, only recently is resolution sufficient to distinguish fast ice from mobile pack ice. We found that fast ice retreat dates have not changed over the last 37 years, but fast ice reaches its minimum extent later and begins to refreeze earlier in the year, in partial agreement with increases in Ross Sea pack ice extent and duration. Phytoplankton primary producers: Maximum concentrations of fast ice algae occurred during November, with higher concentrations on the east side of McMurdo Sound and lower concentrations on the west side in the cold water outflow from under the Ross Ice Shelf. In early to mid-December, warming surface water ablated the undersurface of the fast ice and ice algae sank rapidly out of the water column to provide fuel for the benthos. Also in early to mid-December, the system transitioned to a phytoplankton bloom at the fast ice edge and under the ice. The bloom sustained relatively high chlorophyll concentrations into January, providing food web support for the large abundance of top predators in this region. Prey Distributions: The distribution of prey, crystal krill and silverfish, were assessed using an acoustic echosounder towed by the ROV under the fast ice. Prey had low abundances in spring (November), but increased when the summer phytoplankton bloom was carried under the ice by currents from open water. Subsequently, ice edge distributions of krill and fish reflected the timing of increased predation along the ice edge, with higher concentrations observed > 1km under the fast away away from air breathing predators. Thus, fast ice habitat likely provides a refuge from most large predators, potentially effecting trophic relationships in polar shelf waters. Growing evidence indicates that the Ross Sea, Antarctica, food web is structured as a ?wasp-waist? ecosystem, where the abundances of krill and fish constitute the potential restriction of energy flow. The abundances of these prey appear to be strongly influenced by top-down predation, and to have only a minimal coupling with phytoplankton and primary production. Predator patterns: Antarctic minke whales and type-B (seal eating) and type-C killer whales arrive in early-mid December. The arrival of whales coincides with the decrease in sea ice cover below 80%, consistent with results from other studies. Despite primary productivity in the Ross Sea being the richest in the Southern Ocean, results indicate that a relatively small number of cetaceans, along with other abundant mesopredators (e.g., penguins, seals), alter food availability in specific regions to the extent that they force alterations in the foraging behavior of competitive predators. Broader impacts: This project has emphasized the integration of science and engineering. We developed novel tools for biological oceanographic studies in ice-covered seas. Incorporation of the latest mature yet inexpensive "commercial off the shelf" technology with standardized science instruments specifically built for this project enhanced transfer from engineering to science. The proliferation of remotely operated vehicles following the SCINI footprint (SCINI-Deep, MSLED, IceFin) is a testament to how initial transfer of engineering expertise has quickly spread to benefit the science community. Our educational efforts especially emphasized global environmental awareness, and promoted questioning and problem-solving mindsets. Project personnel have been successful at obtaining other employment in engineering and education fields. Last Modified: 03/07/2017 Submitted by: Kendra L Daly