DoE monitors infected stony corals during annual spawn

Hard corals on Cayman's reefs spawned on the nights of 26 and 27 Sept. - Photo: Liz Wyatt

Over a couple of nights a year, usually a few days after a September full moon, Cayman’s coral reefs explode with activity as entire colonies spawn, emitting eggs and sperm into the water column.

The natural phenomenon is eagerly awaited by divers each year who swap notes on the exact timing of the spawning and which coral species will “go”. This year’s spawning held another level of suspense as observers monitored corals infected with stony coral tissue loss disease to see if they managed to spawn.

Members of the Department of Environment’s Stony Coral Tissue Loss Disease Response Team dived in East End with Ocean Frontiers and in West Bay with Divetech to see if SCTLD had impacted spawning.

In a social media post, the DoE said, “The purpose of these observations was to monitor multiple species of stony corals to see if there was a difference between apparently healthy corals and ones infected with SCTLD.”

Tammi Warrender, lead coordinator on the DoE’s SCTLD response project, inspects a large colony of mountainous star coral for gamete setting and spawning potential on 26 Sept. – Photo: Katie Ebanks, DoE

Some divers reported back that they had observed spawning from the parts of individual corals that remained healthy, right up to the disease line of the lesion on the coral.

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The most obvious sign of SCTLD is a circular white lesion that stands out in stark contrast to the healthy part of the coral. It can quickly spread to the entire coral if it’s not treated. The DoE’s response teams have been trying to combat the spread of the disease by using a syringe to place antibiotic paste at the outer edge of individual lesions, which stops them from infecting the rest of the coral.

The disease was first spotted in Grand Cayman, at the Penny’s Arch dive site off Rum Point, in June last year. Since then, it has spread along almost the entire coastline of the island. So far, no evidence of it has been seen on Little Cayman or Cayman Brac.

The Department of Environment is continuing to collate data gathered on the two nights of the coral spawning, on 26 and 27 Sept., and says it plans to share its findings in the next few weeks.

SCTLD targets at least 25 species of hard coral, many of which spawned over those two nights.

The spawning

Eggs on the verge of erupting from a hard coral in East End on 26 Sept. – Photo: Liz Wyatt

On each night, the spawning event – when millions of eggs and sperm erupt from corals in what resembles an underwater snowstorm – lasts about 20 minutes. This is how corals – which are animals – reproduce, and expand and rebuild their colonies.

Divers who are lucky enough to witness this spectacle keep an eye on the corals that are “bundling”, when the peach-coloured eggs are visible inside the individual polyps, getting ready to pop. Then, the first one squeezes out, and suddenly that’s followed by a flurry of eggs that waft gently in the current for a few seconds before starting to float upward to the surface.

It is on the surface of the sea where the fertilisation happens, when a coral egg and sperm join together as an embryo. This develops into a coral larva, or a ‘planula’, which can float in the ocean for days or even weeks before dropping to the ocean floor.

Then, if the conditions are right, these can eventually, and very slowly, grow to form new coral colonies. Hard corals grow at a rate of 0.2 to 1 inch a year, according to coral.org

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