Some crabs carry anemones on their backs to protect themselves from predators. The anemones release stinging substances that deter potential attackers.
The behavior of crabs that carry anemones dates back to a story of evolutionary adaptation. Some crabs, faced with numerous predators, began to grasp anemones to benefit from their defensive system thanks to stinging cells. This initially accidental "evolutionary tinkering" favored the survival of these clever crabs. Over time, with these obvious advantages, the species exhibiting this behavior became more numerous. Today, it has even become instinctive in some species: from a young age, they start to seek out and attach these living shields.
The crab carries the anemone, providing it with mobility and access to food-rich areas. In exchange, the anemone protects the crab with its stinging tentacles, deterring potential predators like octopuses or certain fish. Thus, the crab enjoys a sort of mobile defense system, while the anemone benefits from a prime location to easily capture its prey. A win-win exchange, where each benefits from the other's presence without too much effort.
Crabs choose their anemones like one chooses a good jacket: just the right size and practical. They spot the anemones based on their shape, size, or defensive abilities. The crab gently grabs the anemone with its claws to detach it from its substrate without damaging it. Then, it positions it directly on its shell. The anemone firmly attaches itself with its adhesive foot, allowing for a solid and durable attachment. Over time, the anemone even slightly adapts its shape, fitting the crab's shell like a second skin. Crabs know how to care for their anemone, regularly handling it to ensure optimal maintenance, and can even replace a sick or weakened anemone with another that is better suited.
For example, there is the boxer crab (also known as the pom-pom crab), from the family Lithodidae, which carries small anemones in each of its claws, like boxing gloves. The crab uses these anemones to defend itself, waving them in front of predators, while the anemones benefit from the food particles that circulate when the crab eats.
Another common case is the crab Dorippe frascone, which chooses its own anemone and places it directly on its shell. Here too, both parties benefit. The anemone provides protection against attacks, thanks to its stinging tentacles, and in return, it travels for free, accessing new food sources along the way.
The decorator crab, typical of the genus Camposcia, takes decoration to the extreme by attaching several small anemones to its body. As a result, the crab achieves near-perfect camouflage, and the anemone enjoys a constant flow of water and fresh nutrients.
This partnership gives a significant boost to both creatures: the crab benefits from top-notch protection thanks to the stinging tentacles of its anemone, which deters many potential predators. The anemone, on the other hand, gets to travel without tiring, easily accesses more food, and enjoys a living space with less competition. As a result, both live overall better, thus increasing their chances of survival and reproduction. It also boosts local biodiversity, as their combined presence creates a particular ecological niche that is beneficial to other marine species nearby. In short, these two buddies effectively strengthen their ecosystem, simply by one serving as a mobile home and the other as a bodyguard.
The stinging property of the anemone's cells generally does not harm the host crab, as its claws and shell are often protected by a particularly thick layer or a specific biochemical substance that partially neutralizes the anemone's toxins.
Anemones carried by crabs benefit from increased mobility. This allows them to access new food sources while avoiding the accumulation of sediment debris on their bodies.
Once a crab chooses a specific anemone, it is able to recognize and reuse the same anemone if it happens to be temporarily lost or detached.
Some species of anemones refuse to be carried by crabs by intentionally secreting an extremely irritating substance to deter potential crab transporters.
Yes, several other similar relationships exist in the marine environment. One of the most well-known associations is that of the clownfish living among the tentacles of sea anemones to benefit from their protection against predators, in exchange for regular cleaning of the anemone and increased aeration due to the fish's movements.
Yes, anemones gain several significant benefits from being carried by crabs. They mainly benefit from the mobility provided by their host, which allows them to access more food and better environmental conditions, as well as dispersion that promotes their proliferation.
Yes, the crab can survive without anemones, but its survival capacity is significantly reduced. Without this symbiotic protection, the crab is more vulnerable to predators, and its access to food resources may also be limited.
No, not all marine crabs exhibit this behavior. Only certain specific species, such as crabs of the genus Lybia or some hermit crabs, display this symbiotic association, due to evolution which allows them to benefit from enhanced protection provided by anemones.
Crabs have adapted claws that allow them to gently grasp the bases of anemones and carefully position them on their carapace. Some species also secrete specific substances that facilitate the lasting attachment of the anemone to their exoskeleton.
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