As humans pump more CO2 into the atmosphere, the planet is changing. Not only are temperatures rising, the pH of the oceans is gradually falling; it is expected to drop by 0.4–0.5 units to pH 7.5 by the turn of the century. Rui Rosa and colleagues from Portugal and Germany explain that the majority of studies into the impact that these changes will have on marine species are conducted on adults over relatively short exposure times. But they say, ‘Early life stages (e.g. embryos, larvae) of marine organisms are expected to be the most vulnerable to such climatic shifts…[and] this vulnerability may become a serious bottleneck for species' survival’. Concerned about the impact such environmental changes will have on European squid embryos and hatchlings, Rosa and his collaborators began a large-scale study to look at the effect of future conditions on the young animals (p. 518).
Collecting recently laid squid egg masses from the Atlantic Ocean off the coast of Portugal, the team transported them back to the lab at the Laboratorio Maritimo da Guia, where they installed the eggs in tanks simulating present and future environmental scenarios – present and future winter temperatures (13 and 15°C), present and future summer temperatures (17 and 19°C) and present and future CO2 levels (~430 and 1650 ppm). Then they watched the eggs' progress as they developed.
Monitoring the embryo's survival, the team saw that the youngsters survived well in the present ocean (pH 8) during both the summer and winter, and even the future winter embryos (pH 7.5) survived reasonably well (71%). But when they looked at the survival rates of embryos developing in the future summer scenario (19°C at pH 7.5), the population was decimated, with only 47% of the embryos surviving. And when the team investigated the youngsters' growth rates, they found that the embryos grew faster in the present day (pH 8) summer ocean, but suffered a setback in the lower pH conditions of the future summer seas. The warmer embryos also hatched sooner than their present day siblings, and the team noticed an increase in the number of developmental abnormalities in the embryos reared in the future summer tanks, with deformed eyes, bodies and mantles. The lower pH also reduced the amount of energy that the youngsters could expend and their ability to withstand high temperatures.
Whichever way you look at it, the future is bleak for European squid spawning in the summer, but more encouraging for youngsters born in the winter. Although the team offers a glimmer of hope by pointing out that the squid have already adapted their spawning behaviour in winter to take account of the harsher conditions – they produce smaller eggs in larger numbers – they add, ‘It is hard to predict if in the future they will continue to display these two main spawning seasons or if they will be able to take more advantage of the less-stressful winter prevailing conditions’. We can but hope.