Many marine organisms, including mussels, oysters, and barnacles, have a planktonic (drifting) larval stage and a sedentary (less mobile) bottom-dwelling adult stage. The adults of these organisms release a large number of larvae into the water column, where the larvae develop and grow and often, disperse long distances before settling and changing into adult forms. Larval survival and transport in the water column and larval ability in finding suitable habitat for settlement shape the abundance and distribution of the adult population. All these factors are significantly influenced by the interactions between individual larva and its surrounding fluid. However, current knowledge of larval-fluid interactions, especially at the individual level, is scarce. This project will carry out state-of-the-art observational and modeling studies of larval-fluid interactions. This project provides hands-on training opportunities for undergraduate students. Findings from this highly interdisciplinary project will be incorporated to inquiry-based undergraduate curriculum material that will be taught and evaluated in classrooms and made publicly available through digital libraries.
Interactions between individual larva and its surrounding fluid significantly impact survival and transport in the water column. Examples of these interactions include: 1) generating currents for movement and particle capture, 2) reducing predation risk through minimizing the hydrodynamic signals, and 3) rapidly adjusting swimming patterns in response to fluid movements, such as near-bottom turbulence during settlement. Understanding these key larval-fluid interactions requires observations at fine spatial and temporal scales due to small larval size and rapid viscous decay. Although the overall morphology of larvae is highly diverse there are common shapes shared between taxonomic groups, such as the "armed morphology" of larval molluscs and echinoids whereby larvae use long ciliated extensions for feeding and swimming. It is unclear how morphology influences larval-fluid interactions. This project aims at filling in these knowledge gaps by applying high speed, high resolution micro Particle Image Velocimetry (microPIV) and computational fluid dynamics (CFD) modeling to quantify and mechanistically examine larval-fluid interactions. This project addresses three groups of questions: (1) How do fine-scale larval-fluid interactions differ between ciliated larvae with similar overall morphology? What are the ecological consequences of these differences? (2) How rapidly can larvae vary their influences on surrounding fluid? (3) What are the limitations of microPIV as a way to observe freely swimming larvae at the relevant scale? To address these questions, a series of microPIV observations will be conducted on 3 pairs of related species that have armed larvae. The hypothesis is that despite similarity in overall shape, larval-fluid interactions differ between species and larval performance peaks at ambient condition that the larvae are found. Hypothesis testing will be achieved through comparing the larval-fluid interactions between these studied species through ontogeny and at different temperatures and viscosities. The obtained observational data will be compared against theoretical hydrodynamic models and CFD models to build a mechanistic understanding of how larvae move water around their bodies and the resulting signals.
