The World Beneath. Richard Smith

The World Beneath - Richard  Smith


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are one of the species that exploits corals as a home. Instead of carrying around shells for protection like their non-reef counterparts, coral hermit crabs cozy up in small holes in the coral, filter feeding with specially adapted arms and never departing their safe havens. Likewise, Christmas tree worms depend entirely on corals providing them places to burrow, shelters from which to extend their filter-feeding bristles to trap passing plankton.

      Dot and dash butterflyfish. Fiji.

      Corallivores, those organisms that feed on corals, are easily spotted on healthy coral reefs. I became fixated with one corallivore in particular: a damselfish called the big-lipped damsel. I had only ever seen pictures of the fish and was having a hard time finding them in the wild. Finally, while diving a small marine reserve in the southern Philippines, I spotted one of these superficially unspectacular fish by chance in a rich coral garden. I identified it by the quick glimpse I caught of its preposterously large lips as it fed on a branching coral. These lips are so large that they’re surely the true inspiration for the inflated Hollywood “trout pout.” However, these lips serve a purpose, as does everything in nature. After finding more of these fish a year later in West Papua, I spent an hour or so watching their antics and confirmed the function of the lips. These fish are obligate corallivores, and rather than utilize the approach of the dainty butterflyfish that pluck one polyp at a time, the damselfish instead completely denudes the surface of the coral of tissue, their sensitive flesh meeting the sharp coral skeleton beneath. Their voluptuous lips protect them from cutting and tearing their skin against these edges.

      Spawning

      One evening in mid-November, after spending the twilight hour making observations on the social behavior vswam up into a cut in the reef full of corals, sponges, and crinoids. There was an excitable energy in the water, and before long I started to notice a few little white specks lifting off a coral. Very quickly, several corals and even a crinoid began spawning, releasing great clouds of sperm and eggs. It was magical to witness this event firsthand. The crinoid appeared almost on fire as a smoke of gametes were released. The coral took a subtler approach, releasing visible individual large gametes into the water.

      Spawning barrel sponge. Tubbataha Reef, Sulu Sea, Philippines.

      Spawning Acropora coral. Wakatobi, Sulawesi, Indonesia.

      Sessile Invertebrates

      A huge variety of sessile organisms, in addition to corals, occupy the hard substrates of reefs, including sponges, bryozoans, tunicates, gorgonians, sea anemones, and corallimorphs (large disc-shaped animals, superficially similar to sea anemones). Some of these organisms are so ancient that they haven’t shared a common ancestor since the times of the very earliest animal life on Earth.

      Many other organisms attached to the reef contribute to the diversity of coral reefs. The Anthozoa, which includes not just the corals, but also a wide variety of their relatives such as gorgonians, sea anemones, and corallimorphs are very diverse. Some of these are solitary and consist of a single polyp, such as sea anemones and corallimorphs, which are both known for their noxious stinging tentacles. Gorgonians are considered to be a type of soft coral, and like their closest relatives, do not produce a calcium carbonate skeleton. Gorgonians are largely defined by their fan-like shape, which gives them their common name, the sea fan. Some gorgonians grow to be the size of a car; others form bush-like shapes. Often, the only way to identify them at a species level is to view them under microscopic magnification.

      Sea anemone tentacle detail. Wakatobi, Sulawesi, Indonesia.


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