Warm oceans good for fast-growing baby sea urchins but bad for reproduction

Spawning of Tripneustes gratilla, the lamington or collector sea urchin. Photo Steve Dalton.

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 spiky 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.

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.

‘This research shows that for [these] 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,’ said Dr Dworjanyn.

‘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 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 straightforward, but ultimately there appears to be more losing than winning scenarios that are playing out,’ Dr Dworjanyn said.

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