Statolith morphometrics as a tool to distinguish among populations of three cubozoan species

Abstract

Little is known on cubomedusae population structure, and what is known for many species is mostly from rare occurrences or from a metapopulation perspective. Knowledge on population units is critical for understanding population dynamics as well as predicting potential risk to swimmers. Otolith shape analysis is a proven stock identification technique in fishes; here, we applied shape analysis to cubomedusae statoliths. Medusae of three species were collected from three distinct populations around the coastline and nearshore islands of northern Queensland, Australia. Canonical discriminant analysis was performed on normalised elliptical fourier coefficients for statolith proximal, oral and lateral faces and combinations of statolith faces for each species. Significant discrimination of sampling populations was achieved in two species (Copula sivickisi statolith proximal face and Chironex fleckeri oral + lateral faces). Differences in statolith shape, therefore, were capable of successful discrimination among sampling locations but was not capable for one species. The ecological niche, and associated ecological pressures, of some cubozoan species (e.g. Carukia barnesi) may not vary enough for differences in statolith shape among locations to occur. Statolith shape in combination with other stock identification techniques, such as genetics and/or elemental chemistry, will help to discriminate the spatial scales of cubozoan populations.