The hydrodynamic costs of spination in zoea

Abstract

The benefits of spines in zoea and other crustaceans have been documented in numerous studies as a form of anti-­‐predatory behavior. This study examined the potential costs of having spines using three different methods. Drag forces on spines were calculated using hydrodynamic equations and compared between zoea models with long and short spines; clay models were used in corn syrup sinking rate experiments to measure drag coefficients; and zoea models were created in FreeCAD and ran through a shear simulation in MATLAB to examine their stabilities. The study found that the presence of spines increased the drag forces on the models both through calculations and through direct measurements in corn syrup. Moreover, the presence of spines made models more susceptible to tumbling under shear when the spines were flared. However, if long spines were held in typical positions, the zoea models were actually more stable than the short spined model. This study highlights some of the plausible costs associated with spines and further studies are needed to examine the relative importance between hydrodynamic costs in spines versus decreased risk in predation.