QEIB: Energetic Cost of Burrowing

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Marine sediments (mostly mud) cover 70% of Earth's surface and are inhabited by a diverse community of animals (including worms, clams). These animals are important links in marine food webs and are eaten by many commercially important fish. They also affect the fate of carbon in the ocean, not only because they process it metabolically, but also because their burrowing activities mix the sediment and affect the transport of materials between the water and the sea bottom. Therefore, burrowing animals play an important role in the global carbon cycle, and also affect the fates of nutrients and pollutants in marine habitats. In spite of the abundance of burrowing animals and their ecological importance, burrowing is surprisingly poorly understood compared to other forms of locomotion.This study investigates the physics and metabolism of how animals burrow through mud, focusing on polychaete worms, the abundant and ecologically-important marine relatives of earthworms. Dorgan recently modified a technique called "photoelastic stress analysis" for use with burrowing worms that will be employed in this study to measure the forces worms exert on the sediment while they burrow. Dorgan's work revealed that animals burrow by cracking mud rather than deforming it, leading to the prediction that metabolic costs of burrowing are much lower than previously believed. This study combines such mechanical analyses with measurements of metabolic rates of burrowing worms and of flux of materials through the sediment to elucidate how the mechanics of burrowing affects these processes for animals of different sizes burrowing in various types of sediments.These results will provide important information about the mechanisms and rates that burrowers affect the flux of materials such as carbon or pollutants through the muddy sea floor, and will also increase our understanding of the mechanisms by which animals (and biomimetic robots) can move through sediments. The PI will continue to recruit and encourage young scientists, especially women, and will continue to teach courses on professional development for young scientists. She is a great communicator to the public, and will actively participate in outreach and education based on this research. She will also continue her mentoring students with learning disabilities; she has dyslexia and is able to share techniques that help young scientists with similar and other disabilities.