Abstract
Pelagic jellyfish blooms are increasing worldwide as a potential response to climate-change. However, virtually nothing is known about physiological responses of jellyfish to e.g. sudden changes in water temperature due to extreme weather events. When confronted with a sudden decrease or increase in water temperature by 6°C, medusae of Cassiopea sp. exhibited a strong response in locomotor activity (i.e., bell pulsation increased and decreased by ca. 37 and 46% in hot and cold acute (2h) treatments, respectively) relative to control. Although medusae significantly gained in body mass (wet weight) upon chronic (2weeks) heat treatment, their body size (e.g., bell diameter) did not change over this time interval. In contrast, chronic cold treatment resulted in both significant shrinking (reduced diameter) and mass loss. Measurements of mitochondrial electron transport system (ETS) activities and rate of respiratory oxygen uptake (MO2) are good estimates of energy consumption and the potential aerobic metabolic rates of an organism. While both acute treatments significantly increased ETS-activities, acclimation over two weeks resulted in a drop in activities to the control levels. Whereas acute heat treatment significantly increased MO2, chronic exposure resulted in significant MO2 decrease compared to control; however no changes in MO2 could be observed in both acute and chronic cold treatments. Overall these results suggest an enhanced growth in response to global warming, whereas low temperatures may set the limits for successful invasion of Cassiopea into colder water bodies. Our results provide a framework for understanding the physiological tolerance of Cassiopea under possible future climate changes.
•Acute cold/heat treatment decreased/increased Cassiopea's bell pulsation rate.•Cassiopea sp. medusae seem to acclimate well at 32°C, gain body mass and reduce the aerobic energy consumption.•Chronic cold treatment caused body mass loss, but no apparent change in aerobic metabolism.•Body mass and protein content showed contradicting responses, suggesting watery growth.