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Department of Earth Sciences


As our climate warms Britain’s weather is becoming ever more extreme: with heatwaves and heavy rainfall events increasingly frequent and severe. In Scotland, winter precipitation has increased by 20% since the 1960s, and this upward trend looks set to intensify.

A group of scientists from the University of Cambridge and British Antarctic Survey investigated how extra rainfall pouring into Scottish lochs could impact sea urchins by diluting the salty seawater they live in. Urchins are slow moving bottom feeders, making them vulnerable to changing seawater conditions because they cannot evade rapid influxes of floodwater.

For the new study, Nicholas Barrett, who is jointly based at Cambridge’s Department of Earth Sciences and the British Antarctic Survey, undertook research on a colony of sea urchins housed at the Scottish Association for Marine Science in Oban. The research team included Professor Liz Harper from Cambridge Earth Sciences and Professor Lloyd Peck from the British Antarctic Survey.

Barrett plunged the urchins into water of varying salt contents and monitored their response over an initial 24-hour period, then over a month to check for protracted outcomes. The study differs from previous investigations, which only looked at impacts of short-term, shock-changes, in salinity.

“Climate change is happening faster than some animals with long generation times and slow growth rates are able to adapt,” said Barrett. “The question for us was whether they could acclimatize within their own lifetime to rapid salinity changes induced by climate change,” said Barrett. Acclimatisation can leave animals more able to cope with future periods of stress. Take, for example, elite runners who train at high altitude — their bodies produce more red blood cells, meaning they perform better when they return to lower altitudes.

To establish how the urchins coped with changes to seawater, Barrett monitored the urchin’s oxygen consumption (indicating their metabolic rate), their activity levels and feeding rate. He also tested the urchin’s ability to flip themselves if they toppled over. Healthy urchins use their tube-feet to manoeuvre and right themselves, but also to respire and gather food.

His findings showed that the urchins showed clear signs of stress when immersed in the most dilute water — replicating an extreme and drawn out flood event, “we saw that they were sluggish, ate less and moved slowly, and at the same time they respired more quickly,” said Barrett. Barrett also noted signs of physical deterioration, including a loss of body mass and scarring of the urchin’s tube feet — compromising their ability to feed, respire and manoeuvre.

The picture was more rosy for the urchins held in only slightly diluted water, which showed signs of adjustments and tolerance — suggesting they could survive over the long term in less drastic conditions.

Previous research, including earlier work by Barrett, Harper and Peck, has shown that the impact of climate change on marine life can be complex and unpredictable when multiple environmental changes interact. The latest study reveals the direct impact of a single stressor — rainfall induced freshening on urchins — and is one example where clear consequences for specific marine animals can be predicted.  


Barrett, N. J., Harper, E. M., Last, K. S., Reinardy, H. C., & Peck, L. S. (2023). Behavioural and physiological impacts of low salinity on the sea urchin Echinus esculentus. Journal of Experimental Biology, jeb-246707.

Feature image: Sea urchin Echinus esculentus, credit: N. Barrett.