Favorable conditions offer hope for endangered elkhorn coral

Coral reefs, known as the rainforests of the sea, play a pivotal role in the world’s ecosystems. The elkhorn coral, a species of branching coral that has dramatically declined over the last few decades due to numerous environmental challenges, has found a surprising lifeline in the waters of Florida.

A groundbreaking study led by researchers at The Ohio State University reveals the key ingredients for restoring the critically endangered elkhorn coral. The revival of this particular coral depends heavily on its location, the surrounding environmental conditions, and the intricacies of its microbiome.

Focus of the study 

The researchers discovered a beacon of hope for the elkhorn coral in Florida’s Dry Tortugas National Park. This area’s unique oceanographic conditions have resulted in an environment where corals can prosper. 

The findings showed a direct correlation between these conditions and the growth and survival of elkhorn coral, including an observable positive impact on the coral’s microbiome – the diverse array of microbes that naturally associate with them.

Speaking about the study, senior author Professor Andréa Grottoli explained that elkhorn coral is now “functionally extinct” in Florida, despite being once a major architect of the reef ecosystem in the Caribbean. 

Environmental stressors

Professor Grottoli explained that the coral is highly sensitive and has suffered from environmental stressors such as marine disease and climate change, resulting in drastic population decline. Even though there are still some colonies, “there aren’t enough of them to effectively reproduce,” she said.

The survival and revival of the coral population is of utmost importance, particularly for regions like the Florida Keys. Coral reefs in this region provide protection against coastal erosion and significantly contribute to the local economy through tourism and federally managed fisheries. 

The decline of such an integral species can be a major blow to the ecosystem and economic stability, hence necessitating the study to determine the best strategies for its restoration.

Previous research 

In 2018, the researchers collaborated with the United States Geological Survey (USGS) and placed replicated elkhorn colonies in five different locations along Florida’s offshore coral reef. 

After two years of observation, the team was ready to sample the coral’s physiology and compare the fate of the colonies. They looked at a range of physiological traits vital to the coral’s survival, such as biomass, fat content, and indicators for coral feeding.

What they found was striking. Of the five sites, only the samples from Dry Tortugas National Park showed significant signs of thriving. As Grottoli noted, “certain biological traits indicated that the Dry Tortugas corals were eating more zooplankton,” a critical nutrient source for the corals, playing a crucial role in tissue building and repair.

This observed abundance of food can be credited to the phenomenon of periodic upwellings that frequently occur in Dry Tortugas. These are wind-driven events that cause nutrient-rich water from the colder, deeper parts of the ocean to surge to the surface. This process stimulates zooplankton production and brings ample food for the elkhorn coral, creating a true oasis for the endangered species.

Potential restoration site

The study makes a strong case for the Dry Tortugas as a potential location for elkhorn coral restoration, adding to the increasing body of evidence advocating for this. Grottoli notes that the restored corals here could potentially provide a source population for new coral recruits throughout the Florida Keys. However, she also cautions that more research is needed to ascertain if other at-risk species could flourish in the same location.

Despite the optimistic outlook of their findings, Grottoli is clear that the study is not a panacea for all problems facing endangered coral populations. It’s about making smart decisions, she says, but the core issues of climate change and local stressors like overfishing and pollution need to be addressed.

“We’re trying to make smart conservation and restoration decisions, but at the core of this work is that coral reefs are declining because of climate change and local stressors like overfishing and pollution,” said Grottoli. “Until we address those two things, no matter how smart we are about coral restoration and conservation, we’re always just putting a band-aid on it.”

The research is published in the journal Nature Communications Earth and Environment.

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