The boosting effect of a warmer ocean on the growth rate of baby sea urchins is proving to be a silver lining of a much darker cloud by the time these spikey marine creatures reach adulthood.

Southern Cross University Associate Professor Symon Dworjanyn and University of Sydney Professor Maria Byrne have found that the acidification caused by ocean uptake of carbon dioxide is stunting the gonads – or sex organs – in adult sea urchins which could have significant effects on future population numbers, and a detrimental impact on the ‘uni’ industry in Japan.

Their paper, published in Royal Society B journal today, raises concerns about how changes in ocean acidification and temperatures will impact marine creatures that live along our coastlines as humans continue pumping greenhouse gases into the atmosphere. Especially of concern are animals with shells or other types of hard body parts, like sea urchins, which might find it more difficult to grow structures in an acidifying ocean.

The research was conducted at Southern Cross University’s National Marine Science Centre in Coffs Harbour where Associate Professor Symon Dworjanyn is based.

“This is a really surprising result, given we often think of climate change stressors all working in the same direction – negatively affecting marine animals,” said Dr Dworjanyn.

“This research shows that for a widely distributed and economically important species of sea urchin a warmer ocean may in fact bolster their ability to cope with an acidifying ocean. The sting in the tail is that although we may get bigger urchins in the future they will struggle to reproduce in large numbers.

“Urchins in conditions simulating the turn-of-the-century ocean conditions had smaller gonads meaning they were likely to be less successful in reproducing. This could have significant effects on their future population numbers.”

Tripneustes gratilla, the lamington (also known as collector) urchin involved in the study, along with other species are harvested and grown for their gonads which in Japan is called ‘uni’, a highly-prized sushi.

“If in the future they struggle to produce large gonads it could have direct effects on this industry,” said Dr Dworjanyn.

This is the first study to rear a major marine invertebrate calcifying species from the tiny juvenile through the growth stage transition to the mature adult in near-future and far-future marine climate change conditions, and considering both ocean warming and ocean acidification.

“The results are adding to a story that the fate of organisms under climate change will not be straight forward, but ultimately there appears to be more losing than winning scenarios that are playing out,” Dr Dworjanyn said.

Professor Byrne agreed.

“This study is particularly important because like many ecologically and economically important marine species these urchins make a shell – a structure that is very sensitive to climate change and shows the problems that changing ocean conditions have for many species that we depend on,” said Professor Byrne.

“We found that near-future changes were tolerated by the urchins and favoured growth, indicating some capacity to resist change, while far-future 2100 conditions impaired growth with the poor development of the gonads – the source of future generations being of particular concern.

“Future persistence will depend on some adjustment or adaptation to change, the capacity for which is not known.”