Meeting Abstract
Many types of zooplankton have spines but their functional consequences are debated. Using naupli larvae of barnacles, we studied the hydrodynamic effects of spines and their impact on swimming, sinking, and feeding performance of these microscopic animals operating in a size and speed range at which the fluid dynamics is poorly understood. Barnacle nauplii are unique among crustaceans by having frontal horns and some have long tail spines. Naupliar form can range from parasitic species whose naupli have globular bodies with small horns and tails, to gooseneck species whose nauplii have slender bodies and long, fine horns and tail spines. Such diverse forms enable us to study the effects horn, tail, and body shape on hydrodynamic performance. By measuring hydrodynamic forces and torques on, and flow fields around dynamically-scaled physical models of nauplii for which morphology can be altered, we tested the hypothesis that long body extensions (horns and tail spines) increase drag on and resist tumbling by nauplii, These model experiments and our high-speed, micro-Particle Image Velocimetry analysis of live larvae showed that a globular body with small horns and tail spines (the parasitic Polyascus plana) experience lower drag and disturb the water less when they move than does a slender body with long tail spines and horns (the gooseneck Lepas sp.).Low-drag shapes can enhance swimming performance, whereas high-drag shapes can reduce sinking rates and enhance feeding by acting as sea anchors so flapping appendages can sweep through the water to filter particles. Thus, tradeoffs between different ecological functions impose constraints on the evolution of larval forms.
