With the ocean temperature expected to rise 3℃ by 2100, marine biologists are scrambling to understand how warming waters affect marine life in shallow ecosystems. That is especially true for octopuses, who play a crucial role in these delicate reef and tidal pool habitats. They are both predator and prey, which means the effects of warmer water on their life cycles could be devastating.

“Cephalopods [which include octopus, squid, and cuttlefish] are an important taxon for our oceans,” explains Bret Grasse, the manager of Cephalopod Operations at the Marine Biological Laboratory (MBL), in Woods Hole, Massachusetts. “They are not only highly voracious predators, so they consume a lot of prey, but they’re also heavily relied on as prey for other species. They are a very high-protein, low-fat meal, like the swimming Cliff bar of the sea.”

Previous studies have examined the influence of temperature on the octopus life cycle, but they used stable warm water temperatures. Now, for the first time, in research published in Science of the Total Environment, scientists from Ocean University, in China, looked at how temperature affects octopus embryo development. They did this by fluctuating the temperature by 6° C during the 47-day development period, which more accurately mimics oceanic environments, where waves of warmer water can create temperature variations where octopuses live.

The more extreme temperature shifts disrupted octopus embryo development, leading to premature hatching, embryo deformations, and bacterial infections. While these findings seem bleak for octopus survival, they could still recover long-term. Several marine biologists believe that thanks to the octopus’ short life cycle, they might adapt better than other oceanic animals.

In their experiments, the Ocean University researchers separated 24 clutches of gold-spot octopus (Amphioctopus fangsiao) into four different groups, including a control group with a stable warm water temperature of 18℃; a ramping group, whose temperature fluctuated between 18℃ and 24℃ by one degree every five days; an oscillating group, whose temperatures oscillated between 18℃ and 20℃ every twelve hours; and an acute group, which started with an 18℃ environment only to have the water increase to 24℃ when the embryos were in the final stage of development. Each variation mimics heat fluctuations observed 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 unaffiliated with this study. “But this occurs as spikes of many degrees in highest temperatures that last just hours, and the temperatures cycle daily, vary over weeks, and cycle seasonally. So the temperature variation is closer to something the animals will actually experience — a hot summer day baking at low tide in the sun followed by a cool night under water or a warm current returning later to a more normal cool current.”

The Ocean University researchers found that the groups with the most drastic temperature change, the oscillating and acute groups, experienced the most negative effects. The acute group had the lowest successful hatching rate, as many embryos prematurely hatched, dying almost immediately with underdeveloped organs. In contrast, the oscillating temperature changes made the embryos unviable when bacterial infections spread throughout the clutch of eggs.

Out of the 400 eggs in the experiment (100 for each experimental group), only 36 embryos successfully hatched into juveniles. While most juvenile octopuses learn to swim and eat independently, these 36 juveniles were stuck at the bottom of the tank, the heavy yolk of the embryo still attached to their bodies. Suffering from incomplete development or premature hatching, none of the juveniles survived beyond 11 days, all of them starving to death.

While these results present a bleak picture for the future of the gold-spot octopus and its relatives, not all experts believe that warmer temperatures will bring such negative effects. This is mainly due to the octopus’ ability to adapt.

“We do know that cephalopods are very adaptive, because they have that short-lived lifespan,” Grasse says. “They have RNA editing capabilities, which allow them to [acclimate to] temperatures over time.” And while we don’t know exactly how they’ll react, “it could be theorized that with the short lifespan and the plastic nature of their biology, they could potentially be better conditioned to sort of rapidly evolve and deal with these types of changes more so than maybe other organisms that take a lot longer to reach reproductive maturity and have much longer lifespans.”

Some of these adaptations seem to be happening. Eli Eisenberg, a professor of physics and astronomy at Tel Aviv University who is studying large-scale RNA expression data in octopuses, notes that cephalopod habitat ranges have expanded in recent years, partly due to temperature fluctuations, as many species are moving to cooler waters.

Even with these adaptations, other climate change effects, such as ocean acidification, may eventually cause more negative influences on octopus life cycles and ranges. And that could have wide-ranging effects.

“Octopuses are both a predator and a 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 effect on octopus development. “An impact on them would also be an impact across the food web and on ecosystem functioning, not just within the marine world but also globally.”