The equator might already be too warm for some marine species to survive, according to a new study published in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS). Marine biodiversity is responding to the warming global temperature by moving away from the equator as the oceans heat up, according to the study that examined 48,661 marine species.

The area around the equator was considered stable and ideal for life due to the density of species found there. Increasing evidence suggests that this is changing. While earlier studies have predicted such an impact, this is the first such study to quantify it at a global scale and across marine species.

The research was led by the University of Auckland in New Zealand and is the culmination of lead author Chhaya Chaudhary’s PhD.

“Our work shows that human-caused climate change has already affected marine biodiversity at a global scale across all kinds of species. Climate change is with us now, and its pace is accelerating,” said Mark Costello, the study’s co-author and one of the lead authors on the current sixth assessment report of the International Panel on Climate Change (IPCC). IPCC is a United Nations body set up to assess science related to climate change. 

Marine species moving northwards

The study found that while the species diversity was reducing around the tropics, it was rising around the sub-tropics since the 1950s. This was true of all the 48,661 species studied. They included seabed (benthic), open water (pelagic), fish, molluscs and crustacean species. 

Pelagic species had shifted poleward in the northern hemisphere more than benthic. The lack of a similar shift in the southern hemisphere was because ocean warming has been greater in the northern than southern hemisphere, the study found.

“The decrease in numbers of species at the equator doesn’t mean that sea life is becoming extinct from the planet. Instead, it means extirpation, or local loss of those species,” said co-author David Schoeman, USC Australia Professor of Global-Change Ecology. “It also puts the livelihoods of our tropical-island neighbours at risk, both in terms of seafood resources and tourism attractions.”

Uncertainty around future change

Climate change is set to disproportionately impact agriculture and fishing but there is plenty of uncertainty around how the patterns will change. “We can predict the general shift in species diversity, but because of the complexity of ecological interactions, it is unclear how species’ abundance and fisheries will change with climate change,” said Costello. 

Researchers cautioned that the planet had so far endured only a fraction of the warming that is expected by 2050. 

There is a ongoing push to reduce global carbon emissions in an effort to avoid some of the worst-case scenarios predicted due to climate change. Extreme weather events are already rising with small-island nations and developing countries worst-hit. There is also evidence that high temperatures are affecting diet diversity across countries. This latest study only reinforces the extent of the impact climate change will have on people and their livelihoods.