Sources and movements of Chironex fleckeri medusae using statolith elemental chemistry

Abstract

Chironex fleckeri medusae metamorphose from sessile polyps, possibly in estuarine environments, and migrate into coastal waters. The objective of this study was to critically test the anecdotal paradigm that the medusae originate in lower salinity waters. Laser-ablation inductively coupled plasma-mass spectrometry was used on C. fleckeri statoliths to test the hypothesis that C. fleckeri medusae only originate from low salinity tidal creeks. Statoliths were extracted from C. fleckeri medusae collected from multiple locations around tropical Australia. Strontium:Calcium (Sr:Ca) ratios were used as a proxy for salinity; where salinity remained consistent in the field, the ratio was compared with the elemental chemistry in statoliths. Sr:Ca ratios of the statolith core and edge zones showed some evidence that medusae originated in lower Sr:Ca levels and moved to higher levels as expected under the hypothesis. That pattern was not consistent, however, and sources from multiple oceanographic regimes were indicated. Core-to-edge elemental profiles of statoliths and concentric increments showed high variability in Sr:Ca ratios both within and between individuals. The ratios suggested that many jellyfish had been exposed to a wide range of oceanographic regimes, while others had spent their whole lives in high Sr:Ca ratio waters. Elemental chemistry and concentric increments in the CaSO4 matrix of cubomedusan statoliths provide a tool to study cubozoan ecology.