Tue. May 17th, 2022

Corals that were once thought to be a single species are really two, the study concludes

A female colony of the coral Plexaura homomalla releases eggs into the water (seen as bright white spots). Male colonies of this species release semen. In contrast, colonies of the closely related species Plexaura kükenthali release fully formed larvae called planulae, a new study finds. Credit: Mary Alice Coffroth

On a night dive at St. John’s coast in the US Virgin Islands in 2016, two coral reef researchers saw something unexpected: A coral colony with slender, waving branches released larvae into the water.


Although this method of reproduction is not unusual, the behavior in question was surprising because the coral was named Plexaura kükenthali.

For decades, researchers had debated whether P. kükenthali was its own species or the same species as another coral called Plexaura homomalla. Because P. homomalla was known to send sperm and eggs into the water – not fully formed larvae – the 2016 observation added a new dimension to the conversation.

“Although I had always wondered if the two forms were really two species, that was the moment we realized they should be different,” said University at Buffalo professor and coral researcher Howard Lasker, who conducted the 2016 observation with UB Ph.D. .D. student and coral researcher Angela Martinez Quintana.

However, a more definitive call would require further evidence.

So are these corals a species or two?

It seems like an esoteric question: What is a species really?

“You never get a good answer and different people will tell you different things,” says Jessie Pelosi, a 2019 UB graduate in environmental geoscience and biological science. “With P. kükenthali and P. homomalla, there has been this conflict as to whether they are different species, or are they just one and the same in reality? They were described as separate species, then fused together and then separated again.”

Corals that were once thought to be a single species are really two, the study concludes

A colony of the coral Plexaura kükenthali in the US Virgin Islands. Credit: Howard Lasker

Pelosi set out to learn more after hearing about this story from Mary Alice Coffroth, another UB professor and coral researcher, and Lasker. Both encouraged Pelosi to explore the subject further through a bachelor’s research project at UB with the aim of more comprehensively assessing whether the two corals were really two different species, as people now say.

With Coffroth and Lasker as advisors, Pelosi assembled an interdisciplinary team from UB, the University of Rhode Island and Auburn University to take a closer look at P. kükenthali and P. homomalla.

The result is a new study published September 20 in the journal Coral reef.

Yes, these are two species, researchers say

“I think all the data suggests that they are two separate species,” says Pelosi, the first author to complete his research at UB and now pursue a PhD. in Biology from the University of Florida. “We looked at a lot of different factors, including morphological, genomic, reproductive, and symbiotic differences.”

  • Corals that were once thought to be a single species are really two, the study concludes

    Calcium carbonate structures called clubs and spindles isolated from Plexaura homomalla, seen under a microscope. This visual is a composite that combines focus-stacked microscope images of individual sclerites. Areas of light and shadow have been improved to better visualize the structures. A new study finds variation in the shape and size of sclerites produced by P. kükenthali and P. homomalla. Credit: Jessie Pelosi, adapted from a photo posted in Coral Reefs.

  • Corals that were once thought to be a single species are really two, the study concludes

    A colony of the coral Plexaura homomalla in the Florida Keys. Credit: Mary Alice Coffroth, as published in Coral Reefs.

Morphologically, the team saw variation in the shape and size of calcium carbonate structures called clubs and spindles that each species produces. In addition, the researchers identified “strong genetic differences across the genome between the two species” and observed differences in timing and method of reproduction, Pelosi says. Finally, he adds, P. kükenthali and P. homomalla tend to host different types of algae as symbionts.

The research is based on a 1998 paper in the journal Avicennia by Pedro García-Parrado and Pedro M. Alcolado, who characterized P. kükenthali and P. homomalla as separate species after examining some aspects of their morphology and depth preferences.

Pelosi points out that “there are some interesting intricacies,” with some overlap between the features of the two species. For example, some clubs and spindles on P. kükenthali and P. homomalla are very similar, although the overall trends in shape and size point to a difference in morphology. Researchers also discovered a coral colony that appears to be a hybrid between P. kükenthali and P. homomalla, suggesting that interference between these closely related species still occurs, although the frequency of this phenomenon is unknown.

Yet the evidence suggests that P. kükenthali and P. homomalla are distinctive species, Pelosi and Lasker say.

“It’s a really nice study because it cuts across so many different conditions,” says Lasker, Ph.D., professor of geology and environment and sustainability at UB College of Arts and Sciences, and senior author on the new paper. “It just points in some ways to how little we know about these animals.” (Yes, corals are expensive.)

Pelosi notes that in addition to simple curiosity, understanding the biology of soft corals such as P. kükenthali and P. homomalla is important for practical reasons: “We see that octocorals or soft corals in some areas seem to be able to better withstand the effects of “Climate change than rocky corals or hard corals. So soft corals are really important players in the conservation of the reef’s biological diversity and the provision of habitats for reef fish and small invertebrates such as snails and shrimp.”


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More information:
Jessie A. Pelosi et al. Coral reef (2021). DOI: 10.1007 / s00338-021-02175-x

Provided by University at Buffalo

Citation: Corals that were once thought to be a single species are really two (2021, October 7) retrieved October 8, 2021 from https://phys.org/news/2021-10-corals-thought-species.html

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