A relationship between two entities (animals, plants, humans, etc.) can only be sustained in the long term if both parties benefit. If a relationship only provides benefits to one side, it will not last. This is the principle of symbiosis.
This species of cleaner shrimp is incredibly daring. They boldly climb into the sharp-toothed mouths of eels, rummaging around their teeth in search of food. This foraging behavior has been a long-established habit of this shrimp species, which specializes in eating the parasites found in the mouths of eels and fish.
Some species of hermit crabs and sea anemones often ride on the backs of larger animals. It’s not that the anemones are tired and want a ride; in fact, both benefit: the hermit crab uses the anemone to ward off predators (as anemones contain toxins in their tentacles), while the anemone benefits by escaping a state of vulnerability and can gather more food while traveling with the crab.
Gobies and hard-shelled shrimp live happily together. Both share a burrow dug by the shrimp, with the fish taking on the role of protector. The eyesight of this shrimp species is quite poor, so they rely on the goby, which has sharp vision, to signal when it is safe to venture outside. In return, the goby gains a “home” to shelter and rest.
Sharks are perhaps the least loved creatures in the ocean. They are large, fierce, and seem cruel. So why do they allow remoras to attach to their bellies? Previously, this relationship was considered commensalism—one species benefits while the other gains nothing. However, it is now clear that not only do remoras scavenge leftover food from sharks, but they also help clean parasites living on the sharks’ bellies; the benefits to the remoras are evident: no creature dares to linger in front of the “death” that is a shark.
The anglerfish has a truly terrifying appearance and is quite cunning in using its own victims to lure in others. Its “fishing rod” is the glowing antenna that dangles from its head. In reality, this species cannot produce light; the glow comes from millions of bioluminescent bacteria—one of the anglerfish’s food sources—that cling to it to avoid being washed into its fearsome mouth below.
These emperor shrimp often ride on animals that are many times larger than themselves and move much faster. When this colossal “transport” moves along the ocean floor, the “emperor” will dangle below to pick up morsels of food mixed in the mud.
Clownfish are perhaps the only species that can withstand the toxins of sea anemones. They can swim freely among the tentacles filled with poison without harm. The anemones eat the leftover food from the fish, and in return, they protect these fish from being eaten by other predators.
