‘Knight in spiny armor’: could lobsters help save Florida’s dying corals?

An unexpected champion has emerged in the increasingly grave battle to save Florida’s imperiled coral reefs: spiny lobsters that urinate in the water and scare off predatory worms and snails seeking to feast on the delicate organisms.

The finding is one of the more bizarre conclusions of a three-year study by scientists from the Florida fish and wildlife conservation commission (FWC), who are also warning it may already be too late for some species of coral to survive without significant human assistance.

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Last summer’s record ocean heat further accelerated a 90% decline in healthy coral in the Florida Keys since the 1970s. The National Oceanic and Atmospheric Administration (Noaa) confirmed last month that ongoing high temperatures meant the world was experiencing its fourth global bleaching event of all time, and second in 10 years.

The reef-dwelling lobsters, the researchers say, could act as “knights in spiny armor” as the fight continues to save reefs in various states of degradation from collapsing completely. Not only does the scent of their urine appear to scare off corallivorous snails and fireworms that like to munch on live coral, but the spiny spotted lobsters are partial to themselves eating any of the smaller creatures unaffected by the odor.

“Lobsters urinate quite frequently, it’s part of how they communicate with each other, and they’re social animals so they’ll seek out the odor of other lobsters and aggregate shelters together. Prey can smell that odor and avoid it,” said Casey Butler, associate research scientist and head of the lobster research program at FWC.

In places where nursery-grown coral was planted as part of restoration programs, Butler said, the lobsters had an equally important role in devouring the creatures that harm it.

“Those little nuggets of corals that are out-planted are tasty and as soon as you put them down, the snails and the worms go right for them,” she said.

“But lobsters are also great universal predators themselves, especially spotted spiny lobsters that live and forage directly on the reef their whole lives. It’s like eating off a buffet.”

The study, funded by a grant from the Fish & Wildlife Foundation of Florida, combined field and laboratory research. It also looked at how the “food web” around fragile coral reefs was changing by studying the gut contents of two species, the spotted spiny lobster, and its closest relative, the Caribbean spiny lobster, which leaves the reef at night to feed.

“We were interested in trying to understand if lobsters can work as some sort of bio-control of these coral predators when the corals are facing so much struggle in order to survive, and the other part of the question was how are food webs shifting?” Butler said.

“In the better-quality, or less-degraded reefs, the lobsters were eating things higher up on the food web, benthic [bottom dwelling] fish, mollusks, fireworm and even lionfish.

“At more degraded reefs, you see more diversified gut contents, they eat whatever happens to be available, things with lower trophic profiles, so lower in the food web, like worms, brittle stars, detritivores, things like that. So the whole coral reef food web is really shifting with this degradation as well.”

The study comes, as Butler acknowledges, during a particularly depressing time for coral reefs globally amid a worsening climate emergency. A succession of storm surges, cyclones and flooding have turned Australia’s Great Barrier Reef into a “coral graveyard”; and some 54% of ocean waters containing coral reefs worldwide have experienced heat stress high enough to cause bleaching, Noaa’s Reef Watch said last month.

In Florida, pillar coral has almost entirely disappeared, and other species will struggle to recover without robust and diverse replanting programs from land-based nurseries, alongside other protective measures, she said. And lobsters, she believes, can play at least a small part.

“Unfortunately, it doesn’t seem like a silver bullet. But if it was applied in a way that was thought out well, you could potentially use them alongside coral restoration because they’re eating things that are corallivores and things like that at the higher quality reefs,” she said.

“We don’t have any pristine reefs in the Florida Keys, all our reefs are to some degree degraded, so out-planting occurs to increase live coral cover of different species at the reefs. If the out-planting is at the higher-quality reefs then perhaps those spotted spiny lobsters would be beneficial in keeping the corallivores down.”

Ultimately, Butler said, it will require an all-round effort to rescue the reefs.

“There’s a lot of smart people working on this, like looking at genetics and which types of genes result in more resilience to things like bleaching and disease,” she said.

“So it’s going to take some of that stuff, as well as just a lot of willpower and hope. Some species are going to be harder to rehabilitate without the help of humans. Corals can survive to some degree, but it’s been a downward slope for quite a while now.”