Quantitative Analysis of Flow through Free-swimming Appendicularians

Appendicularians are pelagic tunicates (Phylum: Chordata, Subphylum: Tunicata) that frequently dominate the mesozooplankton community and are key grazers in both coastal shallow seas and oligotrophic environments. Understanding of their feeding mechanisms, specifically selective feeding, has important ramifications for predicting their impact on particle distributions in the upper ocean. The goal of the current study was to determine the role of flow morphology in regulating particle capture within the houses of free-swimming appendicularians (Oikopleura dioica). We used two methods— standard Particle Image Velocimetry (PIV) with laser sheet illumination and bright field micro-PIV— to gain unprecedented spatial and temporal resolution of body kinematics and fluid motion through the mucous-mesh house. Analysis of small-scale fluid interactions at various parts of the house provided insight into factors that influence particle capture and selection in these important grazers.