Corals - mouths and mayhem
Extracted from The Sea That Never Sleeps by Douglas David Seifert, read the full feature in the DIVE night diving special edition
Stony coral species are invertebrate animals with a body form known as a polyp. With a few notable exceptions of standalone species – such as the mushroom corals (Cycloseris, Herpolitha, and Fungia) and the cup corals (Tubastrea) and the walking dendro corallite – corals are collective colonies made up of multitudes of tiny, individual, yet interconnected, polyps that are clones of each other, each one following the relatively simple design of a sack-shaped body called a coelenteron with a ring of tentacles at the open end surrounding an orifice that brings food in and delivers waste out.
At night, when witnessed feeding in aggregate, the base limestone exoskeleton structure secreted by the individual polyps and the generations that preceded them is obscured by an opaque, pulsing, mass of swollen and extended polyps, with their elastic tentacles waving en masse and grasping blindly about the water column for planktonic prey unlucky enough to be carried within reach.
The corals are hyperactive at night – a lush collection of animals, with their tentacles a gelatinous carpet flowing in constant sinuous motion. Only viewed at night can a coral reef be truly seen as what it is: a living panorama of tentacles and mouths and mayhem.
The diversity and colours are especially apparent at night.
The tubastrea cup corals are a vivid yellow or orange, with their long tentacles outstretched. The mushroom corals and Herpolitha coral that look like bleached coral skeletons by day are pulsing with life and colourful pastel-tinged opaque tentacles at night.
Gorgonian corals – the sea fans and sea whips – and other species of soft corals are alive with tumescent tissues in vibrant colours and grasping tentacles or cilia as they join in the plankton-feeding windfall.
One of the reasons coral is so active at night is not solely the availability of food, for plankton passes with the current incessantly, but at night the majority of grazing fish predators are inactive, hiding from their own nocturnal predators.