As coral reefs face threats, UB scientists study the future of soft corals

Mary Alice Coffroth and Howard Lasker.

UB coral researchers Mary Alice Coffroth and Howard Lasker. Photo: Douglas Levere


Published September 16, 2022


This summer, coral researchers from around the world gathered to share their latest findings at a conference devoted to reef science, conservation and management.

One question that looms large in the field: As warming waters, ocean acidification and other pressures threaten corals, what will reefs look like in years to come?

“Much of the conference was focused on the future of coral reefs,” says UB scientist Howard Lasker, who attended the 15th International Coral Reef Symposium in July in Bremen, Germany, with fellow UB coral scientist Mary Alice Coffroth. Both are research professors of geology in the College of Arts and Sciences.

“While it has been a consistent theme that we must reduce CO2 emissions, the focus of many of the papers has been the science behind approaches to facilitate the survival and recovery of reef corals,” Lasker adds.

As part of the symposium, Lasker was honored at a reception for newly named Fellows of the International Coral Reef Society (ICRS), which sponsors the conference. According to the organization, “The status of ICRS Fellow is awarded in recognition of scientific, conservation, or management achievement and service to ICRS over a significant period of time.”

Prior to the conference, Coffroth participated in the fourth of a series of workshops hosted by the National Science Foundation-funded Coral Bleaching Research Coordination Network. The event was geared toward writing a perspective on the future of coral bleaching research. She also attended the first workshop in 2019 to help develop recommendations for coral bleaching experimental design protocols.

Lasker and Coffroth have been studying coral reefs for several decades. Their work has spanned a period where large-scale bleaching events and other dangers linked to climate change have placed many reefs in peril.

The pair recently took time to share with UBNow some of their latest research, focused on “soft corals” in the Caribbean, with implications for understanding the future of reefs.

How has the world’s understanding of the threats facing reefs changed since you began studying corals?

Lasker: When I started studying reefs in the 1970s, we were all focused on complex and fascinating questions about how reefs work. The role of corals, fishes, hurricanes, sea urchins and other organisms were all being studied in systems that seemed to have been around ‘forever’ and which we expected would continue ‘forever.’

While some researchers were already raising the alarm about the effects humans were having, many, including me, thought of those as concerns for specific places with especially large human populations or especially uncaring approaches to using reefs. 

We have steadily seen the effects of humans spread through all of the world’s oceans, and the effects of ocean warming pays no attention to local policies. Now it is the rare scientist who does not have to include our altered environments in their research.

What are soft corals, and why are they important?

Lasker: When people hear the word coral, they usually think of stony corals. Those are corals that produce hard skeletons. Stony corals — called scleractinian corals in the vernacular of researchers — create the framework of the reef.

Soft corals, also known as octocorals, are the sea fans and sea plumes one sees waving to and fro in videos of reefs. Their name, octocorals, comes from each polyp having eight tentacles. Like their scleractinian cousins, they create three-dimensional structure on the reef, which is used by fishes and other small organisms. Unlike their scleractinian cousins, they do not have a solid skeleton, and when they die they break down into sand.

Octocorals have always been present on reefs, but as hard corals have steadily declined in abundance, the octocorals have increasing importance on reefs. And in some places, octocorals, unlike the hard corals, have actually increased in abundance.

Octocoral forest on the south shore of St. John, Virgin Islands.

An octocoral forest on the south shore of St. John, Virgin Islands. Some stony corals are visible in the foreground, but on this reef and many Caribbean reefs, they no longer dominate the reefscape, says UB coral researcher Howard Lasker. Photo: Howard Lasker

Dr. Lasker, some of your recent work has documented the rise of soft coral “forests” in Caribbean reefs. Can you talk about these findings?

Stony corals, also called hard corals, have been in decline for at least the last 50 years, and sadly, many reefs are only a pale shadow of the reefs of 50 years ago.

Octocorals have been more resilient to stresses that have killed stony corals, and some reefs have transitioned from a mix of hard corals and octocorals to predominantly octocorals. The soft corals’ upright, tree-like structure creates a “forest” that provides many, but not all, of the ecosystem services that hard corals provide.

We have been studying this transition with the goal of understanding why octocorals have been resilient and the important question of whether we can expect that to continue.

Dr. Lasker, you co-led a team that was monitoring reefs in the U.S. Virgin Islands when two major hurricanes hit in 2017. What did you observe in the years after?

The first thing to understand is that coral reefs have always been affected by hurricanes, just as fire has been an important component of the dynamics of forests. Historically, hurricanes have caused damage, which over the course of years and decades reefs recover from. The difference now is that stony corals have been reduced to such low numbers that they do not recover.

What we discovered in the Virgin Islands is that while octocorals were adversely affected at our study sites, the damage was not as great as we feared and, more importantly, the following year we saw the development of new colonies which with time should lead to the recovery of the octocorals.

Dr. Coffroth, you recently studied soft corals and their algal symbionts during a bleaching event. What were some of the most useful findings?

Reef corals and octocorals form a symbiosis with single-celled algae that live in the coral tissue. These algal symbionts, in the family Symbiodiniaceae, use energy from the sun to produce nutrients that are passed to the coral, and the coral in return provides the algal symbionts with nitrogen, CO2 and a safe place to live. This symbiosis is a true mutualism where both partners benefit.

Much of the normal coloration of corals and octocorals is due to the brownish algal symbionts that they harbor. Under periods of stress, such as elevated temperatures, the stony corals and octocorals may lose the algal symbionts on which they depend. Then the coral appears white, and this is called coral bleaching.

We have found that, in many cases, octocorals do not bleach as readily as stony corals, and if they do bleach, they generally recover. Given that there are many species of symbiodinian algal symbionts which have different physiologies, we sought to determine if the symbionts harbored by Caribbean octocorals were more thermotolerant. 

Our laboratory studies demonstrated that the symbiont types that are found in Caribbean octocorals can grow at temperatures where many stony corals exhibit bleaching. This suggests that at least some of the resilience seen in octocorals may be due to this symbiosis.

Flasks containing algal symbionts isolated from stony corals and octocorals.

Flasks containing algal symbionts isolated from stony corals and octocorals. These intracellular symbionts provide the corals with nutrients from photosynthesis. Scientists culture these algal symbionts to study a variety of topics, including the symbionts' thermal tolerance and their ability to adapt to the changing climate. Photo: Douglas Levere

What role will soft corals play in the future of coral reefs?

Lasker: This is the big, and unknown, question. If conditions continue as they are, octocoral forests may persist. They will not build the reef the way stony corals have, and in the long run that will lead to changes on the reef. 

Reef scientists refer to ‘flattening of the reef,’ which occurs as the dead skeletons of stony corals erode. However, in the short term, octocoral forests will provide habitat for fishes and other organisms, and if conditions improve, their effects might even facilitate recovery of stony corals. 

However, that requires a big improvement in environmental conditions. If environmental conditions continue to deteriorate due to warming sea temperatures, overfishing, onshore land use policies and other anthropogenic effects, then octocorals too will suffer.

Is there anything else you would like to add?

Lasker: If humans do not reverse CO2 emissions and eliminate other stressors to reefs, then the fate of reefs is rather bleak. Some researchers are working on finding and propagating more resistant corals, but that, too, requires us to stop the decline in environmental conditions.

We cannot simply turn back the clock and recreate the reefs of 50 years ago, but we may be able to set the stage for recovery if we can reverse CO2 emissions, eliminate overfishing and adopt land use policies that will not further degrade reefs.