Surviving but not thriving: inconsistent responses of zooxanthellate jellyfish polyps to ocean warming and future UV-B scenarios.

Shannon G. Klein,Anthony R. Carroll,Kylie A. Pitt

doi:10.1038/srep28859

Abstract

Complex changes to UV radiation at the Earth’s surface are occurring concurrently with ocean warming. Despite few empirical tests, jellyfish are hypothesised to be increasing in some parts of the world because they are robust to environmental stressors. Here we examine the effects of UV-B and ocean warming projections on zooxanthellate jellyfish polyps. We exposed Cassiopea sp. polyps to three levels of UV-B (future-low (1.43 Wm2), current (1.60 Wm2), future-high (1.77 Wm2)) and two levels of temperature (current-day (25 °C) and future (28 °C)) over 6 weeks. The intensity of UV-B was varied throughout the day to mimic diel variation in UV-B irradiance. Polyp survival, asexual reproduction and YII were measured. In the current and future-high UV-B treatments, more polyps were produced in 25 °C than 28 °C. This pattern, however, was reversed under future-low UV-B conditions, where more polyps were produced at 28 °C. YII was highest under current summer conditions and future conditions of low UV-B and increased temperature. YII, however, was reduced under high UV-B conditions but was further reduced with warming. Our results suggest that although Cassiopea polyps may survive elevated UV-B and warming conditions, they are unlikely to thrive. If, however, UV-B radiation decreases then ocean warming may facilitate increases in Cassiopea populations.

Highlights

Ozone recovery could decrease levels of UV-B radiation at the Earth’s surface, other climate system factors such as ozone chemistry and climate change may strongly influence ozone recovery and make future UV-B radiation levels challenging to model[7]
Polyps in the high temperature, high UV-B treatment began to bud by Day 7, but two polyps died at Day 10 and again at Day 25
If future UV-B levels increase, future ocean warming predictions for the region would probably reduce polyp reproduction, suggesting that rates of asexual reproduction could be much slower in the future

Summary

Introduction

Ozone recovery could decrease levels of UV-B radiation at the Earth’s surface, other climate system factors such as ozone chemistry and climate change may strongly influence ozone recovery and make future UV-B radiation levels challenging to model[7]. Of the studies that empirically examined the effects of elevated UV and increased temperature on marine biota (e.g. refs 19,20), few studies considered the effects on symbioses involving zooxanthellae. High UV-B did not, on its own, affect zooxanthellae densities, E. tourneforti exposed to high temperature and high UV-B simultaneously, experienced 100% mortality[22]. These results suggest that warming temperatures may further increase the susceptibility of zooxanthellae to UV radiation. It is vital to determine the potential interactive effects of future UV-B levels with future ocean warming projections to obtain a realistic understanding of how biota are likely to respond to changing ocean conditions

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