Pioneering study shows that climate played a crucial role in changing the location of ancient coral reefs: coral reefs until 250 million years ago extended much farther outside the tropics

The study, published in Nature Communicationshows how temperature changes and plate tectonics, where the positions of the Earth’s continents were in very different positions than they are today, have determined the distribution of corals through the ages.

Although climate has often been considered the primary driver of coral reef location, this had not yet been proven due to the limited fossil record. Now, for the first time, a team of international scientists have used habitat modeling and reconstructions of past climates to predict the distribution of suitable environments for coral reefs over the past 250 million years.

The researchers, from the University of Vigo in Spain, the University of Bristol and University College London in the UK, then checked their predictions using fossil evidence from warm-water coral reefs . They showed that corals in the past, around 250 to about 35 million years ago, existed much farther from the equator than they do today, due to warmer climatic conditions and a more even distribution. shallow ocean floors.

“Our work demonstrates that warm-water coral reefs track tropical to subtropical climatic conditions on geologic timescales. In warmer intervals, coral reefs have expanded poleward. However, in cooler intervals, they became constrained to tropical and subtropical latitudes,” the first author said. Dr. Lewis Jones, researcher in computational paleobiology at the University of Vigo.

Suitable coral habitats were restricted to tropical regions around 35 million years ago, due to global cooling and increasing shallow oceans resulting from tectonic changes in the Indo-Australian archipelago, recognized as a hotspot warm marine biodiversity.

While this suggests warm temperatures have enabled long-term poleward expansions of corals in the past, the researchers say coral reef ecosystems are unlikely to keep up with the rapid pace of human-induced climate change.

“Current anthropogenic climate change will cause suitable habitat for coral reefs to expand poleward. In fact, we are already seeing the expansion of some tropical reef corals. However, if coral reef ecosystems – and all the biodiversity they support – can keep up with the current rapid pace of anthropogenic climate change is another question,” Jones said.

“Limiting global warming is fundamental to saving coral reefs, as well as the biodiversity they support. Yet, perhaps even more important is reducing the rate of global warming.”

Warm-water coral reefs, also known as the “rainforests of the sea”, are home to the greatest biodiversity of marine organisms on Earth. In today’s oceans, these biologically rich ecosystems, including reef fish, are restricted to tropical and subtropical regions, where ocean surface temperatures generally do not fall below 18°C. A significant part of this modern biodiversity is found in the Indo-Australian archipelago. However, in the geological past, coral reef ecosystems also existed outside the tropics and subtropics, with their fossil remains found much further from the equator.

Co-author Dr Alex Farnsworth, Senior Research Associate in Meteorology and Climate Modeling at the University of Bristol’s Cabot Institute for the Environment, said: “Climate has changed dramatically over geological time. , but understanding its impact on coral reef ecosystems has been difficult. a lack of quantifiable data that has significant gaps.

“Using this new combined data model approach, we can begin to better understand the evolution and behavior of reef ecosystems.”

Previous work has failed to find a strong relationship between temperature and coral reef distribution because the fossil record is incomplete and biased. For example, not all remains of organisms or ecosystems that existed in the past are recorded in the fossil record, and the most important factor explaining the sampled distribution of ancient reefs has been shown to be gross domestic product. , with the majority of known resources. fossil reef data from wealthy countries, simply because those are the areas where we have looked the most.

Co-author Dan Lunt, Professor of Climate Science at the University of Bristol’s Cabot Institute for the Environment, added: “This work highlights that climate and ecosystems have been intimately linked in the Earth’s past history. This has crucial implications for ecosystems today, given current global warming.”

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