25 November 2020
Modern taxonomy illuminates the Red Sea ecosystem
Published online 15 October 2015
New studies in the region lift the veil on a coral ecosystem, thriving with biodiversity.
The 2,000-km long stretch of coral reef system in the Red Sea ranks among the most significant five reefs in the world. It is home to approximately 1,100 species of fish, 300 species of hard corals and countless invertebrates – but remains one of the most understudied ecological systems on the planet.
Researchers at the King Abdullah University of Science and Technology (KAUST) are working to change that. Focussing on the Saudi Arabian coastline, Michael Berumen, is looking at coral reef ecology, larval connectivity, movement ecology, biogeography and the impact of climate change on coral reef ecosystems.
A knowledge foundation of the Red Sea ecosystem still in its infancy and the number of species being discovered is growing enormously, says Berumen. “In the past three years, we have more or less identified one hundred new species, the possibility for which has long passed in a system like the Great Barrier Reef in Australia.”
New species from the old
Traditional taxonomy methods relied on macromorphological traits to classify different species. But this flood of fresh knowledge brings the need for new methods to avoid the risk of misclassification which was so endemic in the past. Morphological traits may be misleading, explains Berumen, because most corals are characterized by high plasticity and fish species sometimes resemble each other closely.
Now, “the emergence of molecular taxonomy offers genetic evidence of dissimilarities between species that were once thought to be one and the same,” he says.
Molecular taxonomy can decipher a species’ DNA. A case in point is Berumen’s current research on Plectropomus pessuliferus, or “roving coralgrouper”, a fish species whose dispersion was believed to span from the West Pacific to the Red Sea.
Their proliferation was debunked when Berumen and his team took an intricate look at its genetic information and identified the truth. In fact, this ‘new’ Red Sea specimen is completely different from its West Pacific brethren. “I would not even call them sister species,” says Berumen, who believes they should be better described as branches on the same tree.
“It is incredible that a species as well known as the Plectropomus pessuliferus is almost surely going to be described as a new species [from now on],” he says.
Berumen's research has not yet been published, and so is yet to scrutinised by peers. But he is confident that the scientific community will agree that this grouper is not only a different species that will eventually need renaming, but that it is also endemic to the Red Sea, which makes its conservation a priority.
“We are now quite certain that the Red Sea is the only area where this fish lives, and no population outside would help recover it if we mismanage it.”
Gustav Paulay is a curator of marine malacology – the branch of invertebrate zoology that studies molluscs – at the Florida Museum of Natural History. He has conducted field studies in the tropical Indo-Pacific and Oceania and recently has started collating information from other locations, including the Red Sea.
“[Berumen] contacted me because he needed help surveying invertebrates' biodiversity in the Red Sea, a category which has been even less studied than the fish and the corals,” he says.
Paulay ended up joining four expeditions with Berumen on KAUST's research vessel and collected many new species and records of sea slugs, sponges and molluscs. He screened his finds via a 'triple documenting’ process. He would collect a couple of specimens from a species, photograph the live animal, take tissue samples for DNA barcoding, and then preserve the specimen so it could be looked up using traditional morphological taxonomic methods.
“It turns out a lot of species are very difficult to distinguish morphologically, and without the genetic data and the live image data we are really missing a lot,” he explains.
Reef structures are considered a fragile form of ecosystem, requiring efficient protectorates for certain species to be conserved and well shielded.
While correctly identifying species is a first step in defining conservation priorities, movement ecology is primarily concerned with establishing marine protected areas – in other words, scrutinizing larval movement across generations. Knowing the perimeters of adult fish movement within and among reefs is critical for designing the boundaries of a no-fishing zone, for managing fisheries and for conserving reef health and function.
Studying fish larval dispersal pattern is critical; you need to know where the babies of the population you want to protect go.
“Studying fish larval dispersal pattern after a spawning event is also critical,” says Berumen, “because you need to know where the babies of the population you want to protect end up, specifically when you are trying to rebuild a species' population or make a fishery more sustainable.”
Surprisingly, currents are not the only force at work determining where larvae will go.
While studying larval movement patterns in the lab, Berumen realised that larvae are more than capable of swimming against most ocean currents, or to use the currents to control the depth they are in.
Depending on species, the sites of larvae three days after being spawned can be very different from where they end up two weeks later.
“The larvae have to avoid becoming food, and at that size there are a million things out there that want to eat you,” says Berumen.
Scientists can use a fluorescent chemical called tetracycline to track the movement of larvae by staining the eggs after they are born. They first experimented on the Red Sea clownfish, Amphiprion bicinctus, whose habits are easy to anticipate.
To identify particular individuals among larvae, confirming their parentage, KAUST scientists injected mothers with isotopes of barium, a chemical that would produce a particular signature in her eggs and larvae before they were born.
“We used this technique to confirm genetic parentage analysis, which forced us to sample large pools of mums, dads and offspring, and then undergo a massive mathematical exercise to go through all possible combinations.”
In the last couple of years, they have found some examples of populations where the offspring don't stay close to home and all disperse from their parents' reef.
Berumen says that he does not have much information about the Plectropomus pessuliferus' larval dispersion pattern but that there are proposals in the work to study it.
“This would help us figure out what should be the appropriate scale of the marine area meant to protect this endemic species,” he says.
Ensuring the sustainability of reefs at a species-level scale is a difficult feat, but an essential one. According to Berumen, deciding whether it would be enough to conserve a couple of reef systems or hundreds of thousands of square kilometers to save the corals is not only a good start but also possibly a key to the survival of this species.