This research project identified how an animal community is able to survive the food-poor winters in the High Antarctic by using an unexpected food source: bacteria. As a result we advanced both our understanding of marine ecology and the factors that control the fate of carbon on the planet.

Intellectual Merit: The scientific advances of this project fall into three categories: methodological, ecological, and global carbon-cycle implications.

Methodological advances: In many systems the importance of top-down forcing (grazing, predation) can determine the community composition and metabolic rate of prey with important implications to the functioning of an ecosystem. We also know that bacterial metabolisms are critical to the overall functioning of the globe. However, we do not know how grazing of bacteria by animals impacts the rate and type of bacterial mediated processes that occur. Part of this understanding is limited by methodology, we do not know whether currently used approaches to quantify an animal’s diet work when dealing with bacteria or Archaea. Two potential, and employed techniques are stable isotopic and fatty acid analyses. As part of this research, we showed that many of the basic assumptions for these techniques are either violated or are inherently more variable when dealing with bacterial and archaeal food sources than the paradigms constructed around plant and animal diets would suggest. These results will improve the accuracy and applicability of future studies that aim to constrain the role of microbial food sources in animal diets.

Ecological understanding of polar systems: Polar habitats experience short term periods of high food availability and long periods of no food during winter; however one potential food resource that is active throughout the winter are bacteria. Bacteria can degrade resources that animals cannot digest. Through this research we showed that when food becomes scarce, bacteria that are active become the food source by the animals that live in the mud. Further, we demonstrated that if microbial activity is inhibited when food is scarce the entire food web starts to fail. This identified a mechanism by which this community is able to survive and a previously hypothesized but never demonstrated role of bacteria as critical food resource for animals.

Advances in Carbon Cycling – The vast majority of the world’s seafloor occurs at depths that get only episodic inputs of food, making the intensely seasonal High Antarctic a perfect model system to understand global processes. This food is formed in the surface water by phytoplankton and as the plankton sinks it brings down with it carbon from the atmosphere, minimizing the impact of human CO₂ release on our climate. A portion of this food that falls to the seafloor is consumed by bacteria or animals meaning that the carbon is released back into the water. This released carbon will resurface within approximately 1000 years. However, the portion of the carbon that is not consumed by biology is buried for geologic time periods (>10,000s of years), making it one of the few long term sinks of carbon on the planet. While most of the carbon that makes it this deep is not digestible by the animals, bacteria can consume it and through their own growth facilitate the transfer of this carbon into the animal food web. Thus, through identifying the routing of carbon through bacteria into animal food webs in this research, we have identified a mechanism that alters the total amount of carbon that is buried within the seafloor. As part of this research we have synthesized these concepts within an Ecosystem Service review article to facilitate their use by resource managers.

Broader impac...