Cup Corals: In Praise of Orange-Cup Corals

WHEN TRAVEL WRITERS TALK ABOUT UNDERSEA LANDSCAPES OF PRISTINE CORALS, they’re not talking about orange cup corals (Tubastraea coccinea). Which is a shame – they’re one of my favorite corals to see. While orange cups aren’t a familiar, reef-building species like mountainous green star, their personas are larger than life – exuberant vivid patches of bright-orange corallites (or calcium carbonate cups) with thick, fleshy tentacles they extend to troll for the microscopic plankton in the current.

TO ALGASIZE OR NOT TO ALGASIZE   There’s a reason for all this. Reef-building (“hermatypic”) corals occupy our attention because they can in fact build up those mountainous structures that make up a reef. The trick is, they have an advantage that orange cups don’t have – dinoflagellates, the photosynthetic algae that live in symbiotic relationship with them. While reef-building polyps do extend their tentacles to filter plankton for nutrition, they get most of their food – as much as 80 percent of it – and a reef-building boost from their photosynthetic friends.

Algae-lacking orange cups have no such fall-back. Orange cup corals occur in clusters of a hundred or less rather than the thousands that make up a structure of reef-building corals.

DRAMATIC & IMPRESSIVE   But they compensate for this with exaggerated corallites, intense coloration and their thick, fleshy tentacles. Corallite for corallite, they’re dramatic and impressive, and even in patches they embody the phrase marine biologists sometimes use to describe corals: “a wall of mouths.”

Field guides tend to describe orange cups as “preferring shaded areas.” But the algae in hermatypics photosynthesizes solar energy to create nutrition. Reef-builders thrive in sunlight. I would suggest that, rather than preferring the underside of a cavern or pier, those are the places that orange cups and other ahermatypics can thrive without being outcompeted by hermatypics.

In the daylight, the orange cup’s corallites are closed up, as are most other coral species during the daytime. But brain or star corals are dramatic even when closed, perhaps more so in their delicate beauty. Closed up, the orange cups stand out for being so stark and negligible that you’d pass right by them without a serious glance.

THE LESSON:   Don’t judge things by their surface.

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