Sea anemones are one of the most exotic and fascinating creatures that inhabit our world’s oceans. Sadly they’re also one of the most exploited, as the current estimated value for the import of marine fish and invertebrates is at US $200-300 million. So what exactly makes this spineless creature so amazing?
The sea anemone is a water dwelling, usually predatory animal named after the terrestrial flower anemone. It’s closely related to jellyfish, and more than a 1,000 species are found throughout the world’s oceans at various depths. They can be as small as an inch or as large as six feet, the Merten’s carpet sea anemone being the largest with a diameter of over 1 meter.
The sea anemone is basically a small sac, and it attaches itself to a surface with the help of an adhesive foot, called a basal disc. It has a cylindrical body which ends in an oral disc, its mouth at the center of this disc, surrounded by tentacles armed with stinging cells. The cells have evolved in such a way that they attach themselves to the organisms that trigger them, and inject a dose of poison into the flesh of the predator or prey. This is also the reason for the characteristic “stickiness” of a sea anemone.
The sea anemone poison is a mix of toxins, including neurotoxins, which paralyze prey, which are then moved to the mouth by the tentacles for digestion. The toxins are also known to act as repellants against other predators when they’re released in water. Clownfish, who share a symbiotic relationship with sea anemones, are not affected by their host’s sting.
The sea anemones are anatomically simple creatures. They have a primitive nervous system, which without centralization, coordinates the processes involved in digestion, as well as biochemical and other physical responses to stimuli. They can have anywhere between as few as ten to as many as hundreds of tentacles.
Although some species are predatory, some anemones form symbiotic relationships with green algae by providing the algae with sufficient exposure to sunlight and protection from herbivores, sea anemones receive oxygen and sugar, the bi-products of the algae’s photosynthesis.
The other more famous symbiotic alliance is with the clown fish, which are covered by a mucus layer that makes them immune to the sea anemone’s stings. The sea anemone protects the clownfish from predators, who in return on undigested and decaying matter that could potentially harm the sea anemone, also the fecal matter produced by the clownfish provides nutrition to the sea anemone. Clownfish are the only species of fish that can avoid the potent sea anemone’s stings.
Most sea anemones spend most of their lives in one place, though some have the ability to move at a pace of about three to four inches an hour. Sometimes they hitch rides on hermit crabs or decorator crabs. The crabs are protected from predators, and the sea anemones get nutrition from bits of uneaten food provided by the crabs.
The sea anemones have long life spans with slow growth rates; also their reproduction rates are considerably lower than those of the resident fish. These are the primary reasons for the exploitation of sea anemones, according to estimates the US amounts to 80% of the $200-300 million industry imports.
The sea anemones play a critical role in the ocean’s biosphere; their overexploitation directly affects the resident fish, crab, shrimp and algae population. The most severely hit organisms are the anemonefish, which primarily depend on the sea anemones for their nutrition and protection.
Did you know that we homosapiens, the most intelligent species in the solar system (for now), share 80% of our DNA with these wondrous creatures. It shows how the complexity in the genome is not connected in any simple way to complexity of the organism.
The research helped us trace our evolutionary roots even further back in time to a pre-animal era. The sea anemones are exceptional relics of our planet’s primitive creatures, and are shockingly more closely related to us than we would have ever thought.
For the natureophille,
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