New studies have uncovered how small damselfish living in coral reefs utilize ‘motion dazzle’ and behavior adjustments to mislead potential threats.
When we think about how animals disguise themselves, we often picture them being still and seamlessly blending into their environment. However, being motionless isn’t always practical; many animals are active and continuously move about in search of food.
Recent research indicates that the bold patterns on the bodies of certain animals may serve two functions: providing camouflage when they are not moving and creating a ‘motion dazzle’ effect while they swim, which can deceive predators into misjudging their position, thereby helping them escape being caught.
This research, conducted by Dr. Louise Tosetto, Professor Nathan Hart, and Dr. Laura Ryan from the School of Natural Sciences at Macquarie University and published in PeerJ on September 26, marks the first instance of demonstrating that humbug damselfish, recognized for their vivid black and white stripes, employ motion dazzle as a defense mechanism.
“Our research further indicates that humbug damselfish adjust their behavior according to their surroundings,” Dr. Tosetto explains.
“In their natural environment, when they encounter backgrounds similar to their striped patterns, such as branching corals, they tend to swim closer and minimize their movement. This likely aids them in blending into their surroundings to evade predators.
“However, when they are feeding outside the coral colony, where camouflage is less effective, they increase their activity and depend more on the startling effects of their stripes, which we refer to as motion dazzle.”
Rigorous Research
Humbug damselfish are small coral reef fish characterized by their striking stripes, often found in social groups sheltered by branching corals. While their stripes provide concealment when they are still, these fish frequently swim to feed, placing them at risk of predator attacks.
The research group examined how various backgrounds impacted the fish’s ability to confuse predators through motion dazzle by recording humbugs swimming in tanks set against different striped backgrounds and then using computer models to predict how predators like coral trout perceive this movement.
They also analyzed retinal data from humbug damselfish to understand the clarity with which the fish could view different striped patterns in their environment.
The findings revealed that when positioned against backgrounds that made it difficult for predators to see them clearly, the humbugs typically swam closer to that background and increased their overall movement, which allowed their stripes to create deceptive motion cues—an anti-predator action.
Conversely, when the background presented wider, more defined stripes that predators could easily perceive, the fish enjoyed two key benefits. First, the outlines of their bodies became less recognizable, making them harder to detect. Second, the blend of their stripes and the background patterns produced confusing motion signals (motion dazzling), causing predators to misjudge the speed and direction of the humbug fish.
“This suggests that humbugs can recognize different backgrounds and may adapt their behavior to enhance their safety from predators,” Dr. Tosetto states.
Lead author Dr. Ryan adds that this research highlights the sophisticated anti-predator tactics of these fish.
“This foundational study offers fresh insights into the motion dazzle concept,” Dr. Ryan says.
“Future investigations should consider how elements like the light-filtering characteristics of water and interactions with other damselfish might influence motion dazzle. The humbug damselfish serves as an excellent model for addressing these significant questions.”
