The ingenuity of white oval squid camouflage brought to light

White oval squid (Sepioteuthis lessoniana sp. 2), known locally as shiro-ika, are medium-sized squids naturally distributed in the Indian and western Pacific oceans, flittering in and out of a wide range of different habitats – from shallow seagrass beds, over coral reefs, to depths of 100m along coastal environments. In such biodiverse zones, the squids encounter predators of all sizes and shapes, from seabirds flying overhead to sharks, tuna, and other cephalopods prowling under the sea.

Such a variety of threats calls for a large repertoire of survival strategies. Researchers from the Okinawan Institute of Science and Technology (OIST) have previously discovered how shiro-ika change color when moving between different shades of substrate – and now, the same team has painted a full picture of how the cephalopod employs a sophisticated range of camouflaging strategies to adapt to different environments and threats. “The wide variety of visual strategies used by the squid is surprisingly complex, especially considering that squid have traditionally been regarded as spending most of their lives in the open water column,” explains former OIST Visiting Researcher Dr. Ryuta Nakajima, “This discovery suggests that squid have a deeper behavioral relationship with the ocean floor than previously thought.”

The natural predators of shiro-ika often have sharp but monochrome vision that is tuned to spot symmetry in the otherwise asymmetric substrates in reefs. To counter this, the squid selects color patterns are highly irregular to perfectly match their surroundings – whether they are mimicking algae-covered rocks, blending into the shadows under rocks, or turning transparent to stay invisible against sandy seagrass beds.

The team also described a specific coloration pattern dubbed ‘disruptive’, which, like the dazzle-patterns that were painted on warships during WW1, is not meant to conceal the squid but might instead confuse predators about the true shape, size, and location of the squid, making it easier for them to escape in a pinch. “The squids' ability to change their appearance is stunning,” adds Dr. Wee Hin Boo from the Institute of Climate Change at the National University of Malaysia, who contributed to the research. “By analyzing the underlying mathematical patterns in their behavior, we were able to confirm the different strategies they use to vanish into the background. It was a fascinating challenge to quantify what the eye sees.”

As part of their strategy, the squids select different arm positions to minimize symmetry, like casting them off to the side or letting them flop chaotically in front. And a well-known defensive strategy of oval squid is schooling, forming groups of up to 200 individuals. OIST researcher Dr. Zdenek Lajbner continues: “We found that the squids synchronize their camouflaging strategies, like stacking on top of one another to masquerade as a rock, showing the ability to coordinate their camouflage.”

“These squid have recently been observed in the Mediterranean Sea, which they’ve entered through Suez Canal. As they appear in more varied ecosystems, their diverse camouflaging strategies become increasingly relevant to science,” says former OIST researcher Dr. Michael Kuba, who’s now at the University of Naples Federico II in Italy. Dr. Nakajima adds that “shiro-ika is a commercially important species in Okinawa, yet its annual catch has declined by 98%. I hope this study will provide valuable insights into the ecological interdependence between squid and their ecosystem, ultimately contributing to the development of more effective conservation strategies.”

The squid featured in this study are part of the successful research aquaculture project led by Dr. Lajbner at OIST, which has shown the feasibility of raising healthy and active squid over several generations – something which has proven exceedingly difficult for cephalopods in general. Dr. Lajbner summarizes: “Oval squid are a viable candidate for future research into cephalopod cognition, as well as a potential model animal for studying visual perception and motor control through the central nervous system. It’s a remarkable animal.”