According to new research, prehistoric coral reefs dating back up to 250 million years extended much further away from the Earth’s equator than they do today.
The new study, published in Nature Communications, shows how changes in temperature and plate tectonics, when Earth’s continents were in very different positions than they are now, have influenced the distribution of corals over time.
Although climate has long been thought to be the primary driver of coral reef location, this has yet to be proven due to a lack of fossil records. For the first time, an international team of scientists used habitat modelling and climate reconstructions to predict the distribution of suitable environments for coral reefs over the last 250 million years.
The researchers from the University of Vigo in Spain, the University of Bristol, and the University College London in the United Kingdom then used fossil evidence from warm-water coral reefs to validate their predictions. They discovered that corals existed much further from the equator in the past, between 250 and 35 million years ago, due to warmer climatic conditions and a more even distribution of shallow ocean floor.
“Our findings show that tropical-to-subtropical climatic conditions are tracked by warm-water coral reefs over geological timescales.” Coral reefs expanded poleward during warmer intervals. “In colder intervals, however, they became constrained to tropical and subtropical latitudes,” said first author Dr Lewis Jones, a computational palaeobiologist research fellow at the University of Vigo.
Suitable coral habitats became restricted to tropical regions around 35 million years ago, as a result of global cooling and increases in shallow oceans caused by tectonic changes in the Indo-Australian Archipelago, which is recognised as a marine biodiversity hotspot.
Although this suggests that warm temperatures in the past allowed for long-term poleward expansions of corals, the researchers believe coral reef ecosystems are unlikely to match the rapid rate of human-induced climate change.
“Current anthropogenic climate change will result in the poleward expansion of coral reef habitat.” In fact, some tropical reef corals are already growing in size. “The question is whether coral reef ecosystems – and all the biodiversity they support – can keep up with the current rapid rate of anthropogenic climate change,” Jones said.
Reducing global warming is critical to saving coral reefs and the biodiversity they support.” But perhaps more importantly, slowing the rate of global warming.
Warm-water coral reefs, also known as “sea rainforests,” support the greatest diversity of marine organisms on the planet. These biologically diverse ecosystems, including reef fishes, are now restricted to the tropics and subtropics, where ocean surface temperatures rarely fall below 18oC. The Indo-Australian Archipelago is home to a sizable portion of modern biodiversity. Coral reef ecosystems did, however, exist outside of the tropics and subtropics in the geological past, with fossil remains discovered much further from the equator.
Climate has changed significantly throughout geological time,” said co-author Dr. Alex Farnsworth, Senior Research Associate in meteorology and climate modelling at the University of Bristol Cabot Institute for the Environment. “However, understanding how it has impacted coral reef ecosystems has been difficult due to a lack of quantifiable data with significant gaps.”
“With this new combined data-model approach, we can begin to better understand the evolution and behaviour of reef ecosystems.”
Previous research has failed to find a strong relationship between temperature and the distribution of coral reefs due to an incomplete and biassed fossil record. For example, not all of the remains of past organisms or ecosystems are recorded in the fossil record, and it has been demonstrated that the single most important factor explaining the sampled distribution of ancient reefs is Gross Domestic Product, with the majority of known fossil reef data stemming from wealthy countries, purely because these are the regions where we have looked hardest.
This work highlights that climate and ecosystems have been intimately entwined together in Earth’s past history,” said co-author Dan Lunt, Professor of Climate Science at the University of Bristol Cabot Institute for the Environment. Given current global warming, this has critical implications for ecosystems.”
