The ‘taste’ and ‘smell’ of coral reefs provide insight into a dynamic ecosystem

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Coral reefs are biodiversity hotspots and are incredibly productive with a large number of organisms interacting simultaneously. Hundreds of molecules made by prominent members of the coral reef community were recently discovered by a team of scientists. Together, the compounds – modified amino acids, vitamins and steroids – understand the “smell” or “taste” of corals and algae in a tropical reef, and will help scientists understand both the dynamics of the food web and the chemical ecology of these ecosystems. .

The study, led by the Scripps Institution of Oceanography at UC San Diego, the University of Hawai’i (UH) at M?noa and the NIOZ Royal Netherlands Institute for Sea Research, was published today in the Proceedings of the National Academy of Sciences.

Although corals and algae (limu) are attached to the seabed, these organisms interact via chemicals dissolved in the water. Although knowing the importance of these molecules built during photosynthesis and released into the marine environment, their quantity, energy content and structural diversity have always been a mystery to biologists.

thousands of molecules

The team applied a cutting-edge analytical technique, known as untargeted tandem mass spectrometry, to characterize the thousands of small molecules that organisms use for growth, communication and defence.

“We have known for years that organic molecules play a big role in the fate of coral reef systems, but until now we lacked the analytical capabilities to analyze the dynamics of thousands of different molecules that make up the ‘exometabolome’ of coral reefs,” said Andreas Haas, lead author of the work.

In the reefs surrounding Mo’orea, one of French Polynesia’s Society Islands, the team collected specimens of two reef-building corals (block coral and cauliflower coral), a calcified red algae (algae crustacean coral), brown algae and algal turf (a mixture of microscopic filamentous algae). Next, they isolated and analyzed the molecules that each organism releases into seawater during daytime photosynthesis and, separately, at night when photosynthesis stops.

They found that these organisms release large amounts of hundreds of different compounds that ultimately influence seawater chemistry. The compounds determine nutrient concentrations, the growth of decomposers, and the availability of essential vitamins and minerals to plants. and animals that inhabit coral reefs.

Overview of diversity

This study provides the first snapshot of the diversity of dissolved chemicals floating among coral reefs and a window into the interactions between organisms that scientists are only just beginning to understand.

“There were several surprises with our findings,” said Linda Wegley Kelly, co-lead author of the book. “First, very few molecules were universal for the five organisms we studied. Even the two species of coral made few of the same molecules – more than 85% of the molecules we measured were unique to a single specific organism.”

The study demonstrated the release of more than 1000 distinct molecules with diverse structures, paving the way for new explorations in marine natural products.

Another key finding demonstrated that molecules released by corals contained many more nutrients than those produced by algae, which may have strong implications for the availability of nitrogen, phosphorus and sulfur in these reef ecosystems. Perhaps more importantly for reef food webs, the work showed that the combination of molecules released into the water by algae was more chemically reduced.

Haas explained that “algae potentially provide more energy to bacteria in the reef than corals, with implications for how increasing algae on reefs alters energy transfer by microbes to larger organisms. great in the reef ecosystem.”

Reefs around the world are changing and degrading under local pressures from human misuse and overexploitation as well as global threats of ocean warming and acidification.

“A common global change is a change from coral dominance to increased limu biomass, associated with a change in ecosystem structure and function and the amount and types of fish and invertebrates that reside there. thrive,” said Craig Nelson, co-lead. author of the book. “Understanding what such changes mean for the chemistry of an ecosystem is essential for managers, and this work demonstrates differences in the chemical exudates of corals and algae that can help us understand what changes in corals and algae mean for the ecosystem.”

In future work, the team will observe how the diversity of compounds behaves on the reef, including which molecules are rapidly disappearing, which are accumulating, and whether any of the molecules are taken up directly by other plants and animals that make up the reef. the reef community.

Other study co-authors include researchers from the University of Tübingen (Germany), San Diego State University, and the University of California, Santa Barbara.

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