Salinity has a greater effect on sea star righting time than temperature

ABSTRACT Acute increases in temperature linked with marine heatwaves have been occurring with increasing frequency around New Zealand. Additionally, as rainfall rates vary in association with climate change, the salinity regimes in estuaries are changing, often with more frequent pulses of low salinity events. These physical changes in the environment can lead to sublethal stress and changes in the distribution of marine organisms. Echinoderms play a key role in the structuring of many inter‐ and subtidal ecosystems and can exert top‐down control, which promotes biodiversity and overall ecosystem function. Here, we investigated the impacts of high temperature, low salinity and their combined effect on behavioural responses of Coscinasterias muricata , a keystone predator. We examined how these two climatic variables, individually and together, would affect righting time, a proxy for fitness, over a one‐week period. We found that only salinity significantly affected righting times, with those exposed to ambient salinity treatments righting an average of 47% faster than those in low salinities, across all days. Neither temperature nor duration of exposure significantly affected righting time. These findings suggest, because keystone species may be affected, that future changes in salinity can have drastic effects on coastal ecosystems and should be further investigated.