New species assemblages cause local extinctions

As the world is transformed by climate change, identifying new assemblages of species is critical for protecting them from extinction. In a new study led by John Pandolfi and Dr. Timothy Staples of the ARC Centre of Excellence for Coral Reef Studies, scientists looked at how the assemblages of plankton species have changed over the past 66 million years across the world’s oceans.

The researchers have used the findings of their study to develop the first-ever method for detecting new communities of species in all types of ecosystems.

“A novel ecological community is one with combinations of species that are different to any past observations from that site,” said Professor Pandolfi. “These different species combinations can be due to new species arriving in the community, existing species leaving, or species becoming rarer or more common.”

“We found that when novel communities formed, existing species were twice as likely to disappear from the community permanently, representing a ‘local’ extinction. Species in the novel community were also more likely to be new arrivals that had never been observed in the community before.”

One place where new assemblages have appeared is across communities of coral reefs in the Caribbean. Two types of branching coral that once dominated the region are now rare, and new coral species have emerged in their place. 

Branching corals were lost due to the impacts of overfishing, changes in water quality, and climate change. The transformation of reef assemblages leads to different inhabitants and functions. 

“The challenge is to manage at risk or vulnerable areas like this where novel communities exist, or where they’re in the process of forming,” said Professor Pandolfi.

“To do this we need to understand the changes in species composition we see in novel communities, as well as what is driving these changes. To achieve these goals, we need to be able to reliably identify when a novel community has emerged.”

The study has produced the first standardized, quantitative methodology for determining the existence of novel ecological communities based on a database of marine plankton over millions of years.

“We came up with a measure of novelty that can be used with community data from any time scale, organism or ecosystem, so comparative approaches to the study of novelty are now possible,” said Dr. Staples. “In this study, we applied our methodology to the past 66 million years, but it would work just as well on much shorter time frames.”

Using a global set of microfossil data from deep sea drilling cores, the researchers examined the marine plankton record. Professor Pandolfi said that while novelty was rare, extinction was an important component. Furthermore, after novel communities emerged, subsequent communities were more likely to transform into new assemblages.

“Novelty begets novelty,” said Professor Pandolfi. “And the likelihood of extinction was higher when novel communities emerged.” He said the pressures that cause communities to become novel in the first place need to be relieved. “Otherwise we may end up with cascading novelty, where the emergence of novel communities drives further novelty, including the loss of existing, native, species.”

According to Professor Pandolfi, this means when a novel community is identified it needs attention and effective preventive management. He noted that future studies need to identify novel communities within vulnerable ecosystems, such as the Great Barrier Reef. “At the end of the day that’s where we want to go to test this.”

“Modern novel ecological communities may need to be managed effectively to prevent the propagation of subsequent novel communities, because of the associated risk of increased extinction,” said Professor Pandolfi. “We can’t just throw in the towel and let those ecosystems degrade, we need to arrest this progression.”

The study is published in the journal Science.

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By Chrissy Sexton, Earth.com Staff Writer