Environmental conditions, like temperature and ocean chemistry, influence the development of many marine creatures in their earliest stages of life, including the ratio of male to female offspring. For example, when the temperature at sea turtle nesting beaches is warmer than usual, more female hatchlings result!
So the big question is: Will the environmental effects of climate change shift sex ratios in the future? And could this spell trouble for the future of some species?
New research has found that the green sea turtle population from the northern Great Barrier Reef has an extremely female-biased sex ratio – showing that 99.1% of juvenile, 99.8% of subadult, and 86.8% of adult-sized turtles are female. Great Barrier Reef green turtle rookeries have been producing primarily females for over 20 years now and the complete feminization of this population is possible in years to come. More on this study can be found here: http://www.cell.com/current-biology/fulltext/S0960-9822(17)31539-7
Temperature isn’t always the driving force behind skewed sex ratios in the sea. Ocean acidification, which results from the uptake of carbon dioxide by our oceans, has recently been shown to affect the sex ratio of Sydney rock oysters. The researchers who undertook this study, including Associate Professor Patti Virtue from the Institute for Marine and Antarctic Studies, found that after just one reproductive cycle there were 16% more females than males when oysters were exposed to increased ocean acidification. More on this study can be found here: http://rspb.royalsocietypublishing.org/content/285/1872/20172869