Coral reefs are among the most diverse, complex and productive ecosystems on the planet. Most of the biodiversity of coral reefs is made up of tiny organisms living deep within the three-dimensional matrix of the reef. Although largely invisible, this diversity is essential to the survival and functioning of coral reef ecosystems, and many fear that climate change will lead to a dramatic loss of this diversity.
New research by scientists from University of Hawaii at MÄnoa reveals that the species that dominate experimental coral reef communities are changing due to climate change, but that total biodiversity does not decline under future oceanic conditions of warming and acidification predicted by the turn of the century.
The study was published in the Proceedings of the National Academy of Sciences.
“Rather than the predicted collapse of biodiversity under warming and acidifying oceans, we have seen significant changes in relative abundance, but not species occurrence, resulting in a reshuffle of community structure. coral reefs, “said Molly timmers, lead author who conducted this study during her doctoral research at Hawaiian Institute of Marine Biology (HIMB) at UH MÄnoa School of Earth and Ocean Science and Technology (SOEST).
Important but neglected organizations
âThe tiny organisms living in the structure of the reef are known as the cryptobiota, which are analogous to insects in a rainforest,â Timmers said. “They play a vital role in reef processes such as nutrient cycling, cementation and food web dynamics – they are an important diet for many fish and invertebrates that make coral reef ecosystems so vibrant.”
Despite their critical importance to coral reef ecosystems, these cryptobiotics are often overlooked in climate change research due to the challenges associated with investigating them using a visual census and identifying this very diverse community. and under-researched.
“As a result, our perception of coral reef biodiversity across marine gradients and how biodiversity will respond to climate change is primarily based on a handful of observable surface-living taxa, such as corals and fish,” Timmers said.
To assess the responses of the under-studied cryptobiota to future ocean conditions, Timmers and colleagues at HIMB designed an experiment in which staged sedimentation plates were placed in experimental circulating reservoirs. These mesocosms received unfiltered seawater from a nearby reef slope off the HIMB coast and were processed under conditions of warming and / or ocean acidification predicted at the turn of the century. After two years of exposure, the team examined the clusters of organisms that had grown on the population plates using DNA meta-bar coding techniques.
“This two-year experimental mesocosm study is unprecedented for climate change research and is the first to examine the diversity of the entire coral reef community, from microbes and algae to corals and fish.” , said Jury Chris, the author who developed and maintained the mesocosm system.
While the total number of species did not change between current and future ocean-conditioned combination treatments, study results revealed that the composition of the coral reef community differed significantly between treatments. The end result of this reshuffle in response to climate change will critically depend on the ecological roles that the winners and losers play.
However, “we lack sufficient information on ecological functions, life cycles and distributions (not to mention names) for most members of the cryptobenthic coral reef community to be able to adequately predict ecosystem responses or outcomes. changes in this community, âsaid Timmers. .
This study highlights the importance of including these under-studied organisms in future work that seeks to predict the consequences of climate change on coral reef ecosystems.