Evading Predators: Lessons from Under the Sea

Photo Story Published : Jun 03, 2022 Updated : Sep 29, 2023

Disguises, poison strikes, impersonation, or just lying low — marine creatures adopt a great variety of tactics to stave off attacks and survive dangers in the deep blue seas

The web of life is so diverse and dynamic that every ecosystem has its own set of survival challenges. A particularly critical one is avoiding predation. There are potential predators in every corner, habitat, and ecosystem and their presence shapes how other animals are built, what they may eat, and where they choose to rest.

Animals must constantly evaluate the risk of predation in their surroundings and act accordingly. Even something as seemingly straightforward as when to graze, where to display from, or how far from the cave to explore, requires vigilance and preparedness. While avoiding predation directly benefits survival, it also comes with costs. It takes away energy that would otherwise be allocated to other important life tasks like feeding, resting, socialising, and breeding.

Diving into the marine world, we uncover some efficient and fashionable anti-predator adaptations at play in the evolutionary game of hide-and-seek. In response to the risk of being eaten, animals have employed a range of strategies to deal with every stage of the struggle — avoid being seen, fight back, and escape upon capture.

Some creatures stay buried in the sand, and others live in burrows; still others take shelter in crevices — going wherever they think will be challenging for a potential predator. Hiding is a good low-risk strategy, but it could limit movement. Then there’s disguise, widely practised in the animal kingdom in many different styles. Administering venom is not an uncommon defensive approach either, entering the bloodstream through bites, stings, fangs, or spines. Poisons, quite different from venom, begin to act once ingested or inhaled, sometimes when absorbed through the skin. But that’s not all, marine creatures have a host of other tactics to deter an attack. Here are ten strategies that walk a tightrope between effectiveness, investment, risk, and reward.

**LAY LOW:** Microscopic zooplankton prefer avoidance over confrontation and stay deep in the ocean during the day when shallow-water-predators are most active. After dark, millions of plankters swim up towards the surface to feed, making this daily vertical movement the largest migration on Earth. Photo: Umeed Mistry
Cover photo: Umeed Mistry

MOVING HIDEAWAY: The coconut octopus has found a way to hide and still get around. It gathers empty shells and coconuts and fashions them into mobile homes. With a coconut covering its entire body, the octopus proceeds to literally walk on two arms (bipedal locomotion), mimicking a coconut drifting through the ocean. Hiding may be useful to keep away predators that rely on visual cues, but several predators in the ocean can detect vibrations and smells, so like most anti-predator strategies, this is not foolproof. Photos: Umeed Mistry

MASQUERADE IN PLAIN SIGHT: Animals more vulnerable to predation choose disguises that allow them to go about their day hiding in plain sight. They do this by masquerading as something inanimate or inedible. Decorator crabs (left) allow their carapaces to be taken over by other sessile (stationary) forms of life that help them blend with the underwater scenery.

Ornate ghost pipefish (right) strikingly resemble in colour and movement the delicate-looking arms of feather stars (crinoids). They are typically found upside down or at a slight diagonal, and the movement of their fins and style of swimming mimics the gentle sway of feather star arms in a current. Photos: Dhritiman Mukherjee (left), Sahil Khanna (right)

**STOWAWAY HITCH-HIKER:** How does riding piggyback keep an animal concealed? Will the host come to its rescue when a predator shows up? This strategy is usually effective for very small animals that hitch-hike on larger creatures. (Top) Juvenile gold trevallies swim rapidly along with a host of animals — groupers, sharks, manta rays, even dugongs. Hitch-hiking provides them safe passage through the vast and dangerous parts of the ocean. Host animals are mostly unaffected by hitch-hikers as they pose no evident harm and are unlikely to steal their food. It might, however, stop being a feasible strategy when the hitch-hiker grows to be the appropriate meal size for its host.
A hair-raising version of this interaction is when hitch-hikers seek shelter in the folds of a jellyfish. The more venomous the jellyfish, the higher the risk, but also higher the reward for guests. Small crabs and juvenile fishes are often seen hiding on or within the umbrella of jellies, carefully swimming and navigating the tentacles of their host. As long as hitchhikers can take care of themselves around the jellyfish, most of their predators will stay far away. Photos: Umeed Mistry

**INK SMOKESCREEN:** When a predator gets much too close for comfort, with no other escape routes in sight, a highly effective last-ditch effort is to create a smokescreen to buy extra time to leave the scene. Cephalopods like the octopus, cuttlefish, and squid are known for their ability to do this by releasing ink into the water.
Cephalopods have a highly specialised organ called the ink sac that produces, stores, and expels ink turning the water murky. This clouds the predator’s sight and lets the creature flee. The ink contains melanin which imparts the dark colour we see, along with enzymes, amino acids, metals, etc. Inking is a fantastic escape strategy when a predator gets too close, but the ability remains limited to a handful of animals. Photo: Vardhan Patankar

**VENOM ATTACK**: Administering venom by injecting, puncturing, or biting is a very effective mode of self-defence. Urchins, the herbivorous relatives of sea stars and sea cucumbers, have mouths on their underside, to graze on algae growing on the ocean floor. A menacing (and beautiful) heap of venomous spines pointing in all directions deters most predators and makes their lifestyle viable. Photo: Sahil Lokhandwala

**PACKING POISON:** Predators of pufferfish have to get past its three-stage defence system. Keeping up with its sudden swimming sprints, avoid getting thrown off by its rapid puffing up with water, and finally escape poisoning. Pufferfishes store a potent neurotoxic poison called tetrodotoxin, produced by symbiotic bacteria. When consumed, they cause paralysis and even death in humans and many fish species. Photo: Umeed Mistry

**YOUTHFUL IMPERSONATOR:** In many marine species, juvenile and subadult life stage animals bear little to no resemblance to adults. Sometimes they also inhabit separate habitats, have different diets, and need to be wary of a different set of predators. Harlequin sweetlips are large polka-dotted, carnivorous fish that patrol coral reefs day and night for invertebrates and small fish. As juveniles, however, they are vulnerable to predation and are thought to have evolved to resemble poisonous flatworms. By hovering nearly upside down and rapidly oscillating their bodies to mimic the undulating movements of swimming flatworms, juvenile sweetlips are less likely to become a hungry predator’s target. Photo: Umeed Mistry

PARTNER UP: For an animal in the wild facing constant stress of predation, having a partner can be helpful: To watch your back as you work, complement your weaknesses, and strengthen your chances of survival. As the name suggests, the watchman goby stands guard as its partner, an Alpheus shrimp, carefully feeds, finds broken shells, and digs out sand. This is not altruism; it is a mutualism where the shrimp pays the goby back by providing a secure burrow to call home.

Some animals have evolved to scale up from one-on-one partnerships to live in large groups. We see this best in the way fish school. Schooling makes swimming easier and betters the chances of finding food. It is also a fantastic defence strategy as it makes it easier for fish to detect predators through constant communication. Schooling confuses predators who get overwhelmed by the numbers, lowering the probability of an individual being caught. Photos: Umeed Mistry (left), Sahil Lokhandwala (right)