DNA analysis reveals submarine ecosystem engineers


They look like pink chewing gum on the rocks off the coast of British Columbia, the one indistinguishable from the other.

But a new DNA analysis of coralline algae led by researchers at UBC and the Hakai Institute revealed a wealth of different species, a diversity that could be the key to protecting critical underwater habitats such as algae forests .

"Corallines play a very important role in their ecosystem, from cementing together coral reefs to emitting scents that attract other species such as sea urchins, abalone, corals and algae in the area", said Patrick T. Martone, professor of botany at UBC. who supervised the research. "Some coral species are better suited to attracting organisms than others and respond to climatic stresses such as rising ocean temperatures in different ways. But they all look the same, so it's hard to say how the changes in their environment are really affecting them . "

Coralline algae appear to be among the only species to benefit from the loss of sea otters, an endangered species native to the northern Pacific Ocean. When sea otters are lost, sea urchins bloom and mow forests of algae, which provide an important habitat for many marine organisms. The resulting "sea urchins" salt marshes are largely lifeless, with the exception of coral algae that seem to thrive in the landscape.

Coral algae in a forest of algae

Coral algae in a forest of algae Credit: Jenn Burt

Coral algae in a sterile sea urchin

Coral algae in a sterile sea urchin. Credit: Jenn Burt

"The fact that the corals do better in this environment would represent an exception to our understanding of the impact of losing" keystone "species such as sea otters, which usually cause an overall loss of biodiversity", said Martone.

To find out if the coral reefs are really improving in the absence of furry creatures, the researchers examined coral diversity in both sea urchin salt marshes and kelp forests. They counted how many were present, took samples and sequenced DNA in the laboratory.

"What we've discovered is that there are many species there," said Katharine Hind, lead author and former post-doctoral researcher at Hakai. "And while some coral grows more abundantly in salt marshes, we found more species and greater diversity in algae forests."

The researchers also found that while the coral communities at different algae forest sites were similar to one another, they were different in the sterile hedgehog sites, which were dominated by a few species.

"So what we start to see is actually a loss of coral diversity, despite the apparent increase in abundance. This greater understanding changes our interpretation of the ecological model – a lesson that should be applied to cryptic species in other biological systems, such as fungi, insects or plants on earth, "said Hind. "It is possible that we could lose some sort of ecosystem function as a result of this loss of diversity."

The researchers hope to understand what role each of the coral species will play.

"We are witnessing a decline in algae forests along the coast as they are replaced by these sea urchin-dominated salt marshes," said Martone. "We think that the corals can be the key to understanding the maintenance of hedgehogs – some species on which hedgehogs prefer to settle could give positive feedback to bring more hedgehogs to the area. In contrast, the corals that push spores they respond in a more positive way could help bring back the forests of kelp in underground barriers. "

The study was published in Proceedings of the National Academy of Sciences (PNAS).

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