Previous studies have investigated the influence of temperature on the life cycle of octopuses, but using stable warm water temperatures. Now, in a study conducted in Science of the entire environment, Scientists at Ocean University in China studied how temperature affects the development of squid embryos by allowing the temperature to fluctuate by 6°C during the 47-day development period. This more accurately simulates the marine environment, where waves of warmer water can cause temperature fluctuations in the squid’s environment.

The more extreme temperature fluctuations disrupted the development of the octopus embryo, leading to premature hatching, embryo deformations, and bacterial infections. Although these results seem grim for the survival of the octopus, they could still recover in the long term. Several marine biologists believe that the octopus could adapt better than other marine animals thanks to its short life cycle.

In their experiments, the researchers at Ocean University separated 24 clutches of goldspot octopuses (Amphioctopus fangsiao) were divided into four different groups, including a control group with a stable warm water temperature of 18 °C; an increasing temperature group whose temperature fluctuated by one degree every five days between 18 °C and 24 °C; an oscillating group whose temperature fluctuated between 18 °C and 20 °C every twelve hours; and an acute group that started with an ambient temperature of 18 °C and then increased the water temperature to 24 °C when the embryos were in the final stages of their development. Each variation mimics temperature fluctuations seen in reef environments.

“We often talk about climate change as small changes in annual or global average temperature,” says David Scheel, a professor of marine biology at Alaska Pacific University who is not involved in this study. “But this occurs as multi-degree spikes in maximum temperatures that last only hours, and temperatures fluctuate daily, over weeks and seasonally. So the temperature variation is more closely approximating what the animals actually experience – a hot summer day baking in the sun at low tide, followed by a cool night underwater or a warm current that later changes to a more normal cool current.”

The Ocean University researchers found that the groups with the most drastic temperature fluctuations, the oscillating and acute groups, had the most negative effects. The acute group had the lowest successful hatching rate, with many embryos hatching prematurely and dying almost immediately with underdeveloped organs. In contrast, the oscillating temperature fluctuations rendered the embryos unviable if bacterial infections spread throughout the clutch.

Of the 400 eggs in the experiment (100 for each group), only 36 embryos successfully hatched into young. While most young octopuses learn to swim and feed on their own, these 36 young remained stuck at the bottom of the tank with the heavy yolk of the embryo still clinging to their bodies. Because they suffered from incomplete development or premature hatching, none of the young survived for more than 11 days; all of them starved to death.

These results paint a bleak picture for the future of the golden octopus and its relatives. However, not all experts believe that higher temperatures will have such negative effects. This is mainly due to the octopus’ adaptability.

“We know that cephalopods are very adaptable because they have such a short lifespan,” says Grasse. “They can edit RNA, which allows them to change temperature over time.” And while we don’t know exactly how they will respond, “one could theoretically assume that because of their short lifespan and the plastic nature of their biology, they may be better conditioned to evolve quickly and deal with such changes better than perhaps other organisms that take much longer to reach reproductive maturity and have much longer lifespans.”

Some of these adaptations do indeed appear to be happening. Eli Eisenberg, a professor of physics and astronomy at Tel Aviv University who studies large-scale RNA expression data in octopuses, notes that cephalopods’ habitats have expanded in recent years, partly due to temperature changes as many species move to cooler waters.

Even with these adaptations, other impacts of climate change, such as ocean acidification, may ultimately have more negative effects on octopuses’ life cycles and ranges. And that could have far-reaching consequences.

“Octopuses are both predators and prey. They are food for animals such as dolphins, whales, eels and other fish, while they feed on animals such as crabs, lobsters, mussels and snails,” says Qiaz Hua, a PhD student at the University of Adelaide who studies warmer temperatures and their impact on octopus development. “An impact on them would also have implications for the entire food web and the functioning of ecosystems, not just in the marine world but also globally.”