Temperature effect over ontogenetic patterns of feeding structures in scyphozoan ephyrae: functional and ecological implications

Abstract

Jellyfishes of the class Scyphozoa (~200 spp.) have a wide morphological diversity apparently associated with their habits and feeding modes. Their early development imply a drastic morphological change from the ephyrae stage (juvenile) to the adult body form. It is not yet known if environmental factors (e.g. temperature, and consequently viscosity) could determine functional shapes/dimensions of feeding structures of these medusae. In filter-feeding organisms, depending on the distance between consecutive filtering elements, as well as fluid regime, an eventual superposition of boundary layers around adjacent structures could reduce/inhibit the flux through filtering spaces. In this way, even a porous structure could act as an almost continuous barrier, with low filtering efficiency. An environmental factor that affects such type of interaction is the ratio of importance between viscosity and inertial forces, expressed by the Reynolds number (Re). Changes in temperature modify water viscosity, in one hand at low temperatures (low values of Re) the thickness of the boundary layer increases, on the other hand at higher temperatures (higher values of Re), the boundary layers retreat which can increase the filtering performance. Although some organisms can compensate changes in the fluid environment through morphological and behavioural responses, nothing is known if filtering organisms can perform such responses. This project will describe the early developmental stages of three Rhizostomeae species (Lychnorhiza lucerna, Cassiopea andromeda, and Cotylorhiza tuberculata), and of one 'Semaeostomeae' (Aurelia sp.) focusing on the development of the filtering oral arms. It will be tested the hypotheses that different temperatures promote a different development of the oral arms, that would compensate the variations in viscosity. The species will be submitted to cultivation in different temperatures and will be documented from the early ephyra stage to adulthood morphology. Oral arms structures will be measured, compared, and analysed between the different experimental designs. Additionally, quantification of the interaction features between fluid and animal (e.g. velocity of feeding currents) during swimming and feeding of the different specimens under distinct experimental treatments.