The symbiotic relationship between corals and their photosynthetic partners, algae (photosymbionts), dates back to at least the Devonian period (385 million years ago), according to a new study.
Dendroid Porites Coral Dendrostella trigeum tab-shaped coral fragments Romerolite Brevis Riphaeus. Image credit: Chong others., doi: 10.1038/s41586-024-08101-9.
All modern corals belong to a group called scleractinians, which evolved during the Triassic period.
These corals may provide habitat for symbionts (such as photosymbionts) that play a role in nutrient recycling, which is especially beneficial in nutrient-poor waters.
However, it is not clear whether earlier extinct forms of coral had photosymbionts.
“The Devonian period (419 to 359 million years ago) was a time when sea surface temperatures and atmospheric carbon dioxide were higher than they are today,” said Jonathan Jung, a researcher at the Max Planck Institute for Chemistry, stated in their paper.
“Unlike today, its carbonate chemistry is dominated by calcite precipitation, likely due to the low magnesium-to-calcium ratio in seawater.”
“The Middle Devonian was the period of greatest expansion of metazoan reefs in the Phanerozoic era, and well-preserved reefs from this period span what is now Europe, North America, North Africa, Australia, Siberia, and China.” explained the researchers.
“In the Devonian period, these reefs bordered the lake seas on the southern margin of Lorsia and the northern boundary of Gondwana.”
“Along the southern margin of Lorsia, these ancient reef communities reached their greatest extent and highest diversity during the Givetian period of the Devonian period (approximately 387 to 382 million years ago).”
“These thriving metazoan coral reefs became diachronically extinct during the course of the Kerwasser crisis in the Late Fraznian (372.2 million years ago).”
“Then, coral reefs were built primarily by cyanobacteria/algae, which were present in very small numbers until the end of the Famenian period (Devonian-Carboniferous boundary).”
“The ability to host photosymbionts was paramount to the ecological success of ancient coral reef communities during the Givetian period, and the subsequent collapse of coral reefs in the Late Devonian was associated with a gradual loss of photosymbiotic relationships. It is suggested that
“However, there is still no clear consensus as to whether photosymbiosis was prevalent in now-extinct coral groups during the Paleozoic era.”
In their study, Dr. Jung and his co-authors examined fossils of two extinct reef coral groups from the mid-Devonian period: the tabula corals and the shibo corals.
They measured nitrogen isotopes bound to corals (15no/14N), can be used to distinguish whether corals obtain energy from photosynthetic symbionts.
Their results suggest that symbionts were present in the tabular corals they studied, but not in most civet corals.
This discovery provides definitive geochemical evidence of the oldest known example of symbiosis in corals.
“Wide-spread oligotrophy during the Devonian may have promoted coral photosymbiosis, and its occurrence may explain why Devonian reefs were the most productive reef ecosystems of the Phanerozoic.” the researchers wrote in their paper.
“These early signals of photosymbiosis in mid-Devonian corals indicate that it supported coral productivity under warm climate conditions.”
“The Late Triassic and Early Miocene (the subsequent period when coral photosymbiosis was reconstructed using nitrogen isotopes) were also warmer than today.”
“In contrast, under modern global warming caused by anthropogenic greenhouse gas emissions, coral bleaching and associated mass mortality events are likely the greatest threat to the future of coral reefs, with the disruption of coral symbiosis due to warming.” It shows that there is.”
“The strength of coral photosymbiosis in past warm climates suggests that the failure of coral symbiosis under ongoing global warming will not be due to an increase in ocean surface temperatures reached, but rather an increase in ocean surface temperatures.” This shows that the rate of increase is greater than the adaptive capacity of the symbiotic relationship.
team's paper appear in the diary nature.
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J. Jung others. Coral photosymbiosis on mid-Devonian coral reefs. naturepublished online October 23, 2024. doi: 10.1038/s41586-024-08101-9
Source: www.sci.news
