Friday, November 1, 2013
Microscopic Suspension Feeders Near Boundaries: Feeding Restrictions and Strategies Due to Eddies
Rachel Pepper, Miller Inst. Research Fellow, Integrative Biology and Civil & Environmental Engineering, University of California, Berkeley
Microscopic sessile suspension feeders (organisms that live attached to surfaces and consume organic particles and bacteria) are a critical component in aquatic ecosystems ranging from puddles, wetlands, and lakes to the ocean. In these disparate environments, sessile suspension feeders provide a key trophic stage intermediate between bacteria and larger organisms and perform the vital ecological function of removing bacteria and debris from the water. They may also be important for natural cleanup of contaminants, as sessile suspension feeders can consume the bacteria that break down oil and sewage released into bodies of water. Suspension feeders survive by creating a feeding current that draws fluid towards them, and from which they filter their food of interest. A better understanding of this feeding current will enhance our understanding of the contributions of sessile filter feeders to the ecology of the systems where they live and possibly to the effective cleanup of human-introduced contaminants. I will discuss theory, simulations, and experiments that show that eddies form near these feeders as a result of fluid forcing near a boundary. The extent of these eddies, and their effect on the nutrient uptake of the organism depend on the angle of fluid forcing relative to the boundary. I will also discuss calculations that show feeding at an angle greatly increases the feeding efficiency of model filter feeders with perfect nutrient capture efficiency in the absence of diffusion, experimental data that cultured filter feeders feed at an angle to the substrate, the effects of nutrient diffusion and inefficient nutrient capture on our model, and a possible mechanism for filter feeders to change their orientation.