Study: How Climate Change Affects Sperm Competition in the Sea

A new study revealed that changing global seawater conditions due to climate change could alter the rules of sperm competition among many important marine species.

It is widely accepted that about one third of the carbon emissions produced by human activities is being absorbed by the oceans, resulting to some changes in the seawater chemistry. Since the industrial revolution, scientists measured a 25 percent increase in the acidity of seawater. They also projected that the seawater acidity would continue to increase over the coming century unless drastic measures to cut carbon emissions are made.

The study, published in the journal Scientific Reports, showed that the increasing ocean acidification caused by manmade carbon emissions is decreasing the sperm performance in a species of sea urchin.

Sea urchins, like majority of marine species, reproduce by releasing sperm and eggs directly into the seawater. During reproduction, these species are highly sensitive to environmental stress, including the seawater chemistry. Any changes in the seawater chemistry, like increasing acidity, could affect the reproduction process.

For the study, the researchers used techniques employed by infertility clinics, which measures the health of human sperm, to look at the sperm performance of sea urchins in current and simulated future ocean conditions. The identity of the sperm of "winner" males was also analyzed by conducting a competitive fertilization trial where males were paired up to compete to fertilize a batch of eggs in each seawater condition.

In current ocean conditions, the researchers identified the sperm of winner males as the highest number of fast swimming sperm per ejaculates.

"We know that males rarely gain sole access to a batch of eggs in the sea, and most fertilisation takes place under competition from rival male ejaculates so it's important for a male to produce a highly competitive ejaculate," explained Anna Campbell, a PhD student at the University of Exeter and lead author of the study, in a statement.

However, the number of fast swimming sperms per ejaculates becomes less significant in the simulated seawater condition with high levels of acidity. Their findings suggest that climate change could fundamentally alter reproduction process in the sea.