The effect of fluid viscosity, habitat temperature, and body size on the flow disturbance of Euchaeta

Abstract

Lay AbstractCopepods are small marine invertebrates that are one of the most abundant multicellular organisms on Earth. They serve as an important link in the marine food chain between small oceanic plant life, called phytoplankton, and larger organisms such as fish. As with all organisms, they must adapt to the surrounding fluid environment. Since copepods are small, they inhabit an aquatic flow regime that provides a balance of inertial and fluid viscous forces on the organism. The flow created by copepods controls, to a large degree, the interaction with prey, predators, and other individuals of the same species. Hence, examination of the flow disturbances created during cruise and escape behaviors provides insight into the method and consequences of propulsion in this unique flow environment. The genus Euchaeta includes species that inhabit ocean waters at different latitudes extending from the subtropics to the poles. The body shapes of these species are very similar, with the primary difference being much larger body size in colder waters. Thus, Euchaeta species provide a natural experiment to study adaptation to fluid property variation between habitats. Here, variation in body size, swimming and escape speeds, or viscosity has direct consequences on the hydrodynamic disturbance created by organism motion. We expected that body size and viscosity would work in opposite directions in shaping the spatial and temporal properties of the hydrodynamic disturbances generated by these copepod species. The results reveal an intriguing interplay between body size and the fluid environment that alters planktonic interactions, including the ability to prey on food items and the ability to escape from predators, in a complex manner. The complex interaction for the genus Euchaeta partially explains species adaptations to the local environmental conditions.