Sex and the Coral Polyp


Story by Shannon Wianecki

coral spawns

Few people think of corals as animals — which they are — and fewer folks contemplate the sex lives of these tiny creatures ensconced in stony casings. But for those in the know, coral spawns are magical events not to be missed.

Corals belong to the Cnidaria phylum, which includes sea anemones and jellyfish. Unlike their soft-bodied relatives, coral polyps secrete carbonate exoskeletons and cement themselves to the ocean’s floor. Reefs may look like rock, but they are actually colonies of living corals.

Hawaiian waters are home to numerous coral species, named for the shape of their colonies: cauliflower, antler, lobe, mushroom, finger, and rice. Throughout the year, our resident corals engage in a flurry of sexual reproduction linked to the lunar cycle. How do these immobile animals mingle their DNA? Each species responds differently to environmental clues. When the time is ripe, they simultaneously release their eggs and sperm.

Rice coral predictably spawns a few days after the new moon, June through August, between 8 and 10 p.m. In the nascent moon’s wan light, the corals release bundles of gametes by the thousands. Most bundles float to the surface, where they break apart, releasing eggs and sperm. Ideally, eggs will be fertilized by sperm from neighboring colonies and develop into larvae that drift in the currents to establish new populations elsewhere.

Biologists tracking a spawning event from a reef on Maui were surprised to discover just how far and fast coral larvae travel: they reached Lana‘i within twenty hours. After a spawning, a strong-scented slick lies on the ocean’s surface. People often report it as pollution, not knowing that it’s evidence of reef regeneration.

“It smells kind of fishy,” says marine biologist Pauline Fiene, who guides dive trips during spawns. “It’s really wonderful to smell because you know that spawning occurred that night.”

To witness this year’s rice-coral spawn from dry land, contact the Maui Ocean Center: (808) 270-7000; On the designated evening, the aquarium hosts an after-hours underwater peep show.


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