Physical-Biological Interactions in the Fertilization Ecology of Broadcast Spawners: The Role of Gamete Traits and Turbulence Structure

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The goal of this research is to determine the role of key biological and physical factors on fertilization rates in broadcast spawning, the reproductive strategy used by many benthic invertebrates. The objectives are to quantify the effect of gamete traits, instantaneous turbulence structure, and unsteady flow phenomena on subsequent gamete coalescence processes and fertilization rates. Fertilization is typically modeled as a bimolecular reaction, with the fertilization rate proportional to concentrations of gametes. Conventional thought has been that since turbulence produces efficient dilution of gamete concentrations, it hinders fertilization success. However, this conclusion is based on consideration of average turbulent dispersion. Recent work has provided evidence that instantaneous turbulence structure promotes local coalescence at shorter timescales, before dilution takes place, thus enhancing fertilization rates. This work will extend idealized numerical and laboratory studies to include ecologically relevant factors specific to the broadcast spawning process. It integrates numerical simulations and laboratory experiments to investigate process-level effects of individual biological and physical factors. The numerical simulations will consider the effects of gamete viscosity, rheology, and taxis, for 2D pseudo-turbulent flow, unsteady obstacle wakes, and 3D chaotic mixing scenarios. The laboratory experiments will model the effects of gamete viscosity, rheology, morphology, and buoyancy, using 3D boundary layer turbulence, obstacle wakes, and surface waves. A novel two-color planar laser-induced fluorescence system will be used to quantify concentrations of gamete surrogates, including those regions where they overlap. Surrogates made using dyed solutions of glycerol and a biopolymer will model the viscosity and rheology of sea urchin gametes, and fluorescent particles will be used to investigate size and inertial effects. Floating particles will be used to study the effect of convergence zones in free-surface turbulence on fertilization rates for species with buoyant gametes. The educational and outreach goals are to integrate research methods into the PI's teaching curriculum as an effective tool for learning fluid mechanics, and to use the topic of broadcast spawning to get K-16 students interested in engineering and science. A numerical simulation platform will be integrated into a course; students will use the simulation environment and their knowledge of the Navier-Stokes equation to model an unsteady cylinder wake. Likewise, a simplified version of the obstacle wake experiment will be developed as a teaching tool. The PI will also develop an interactive laboratory demonstration to use with visiting groups. The demonstration will include a removable benthic seascape for the bed of the teaching flume, complete with sea urchin mimics that spawn viscous gamete surrogates. Visitors will be able to experiment with hands-on props such as flow obstacles and a removable bed-roughness section. Several permanent posters and a short video about broadcast spawning in nature will enhance the demonstration. Finally, the PLIF system will be used to make educational movies for dissemination via a digital library of the American Physical Society.