Despite the limited range and extent of coral reefs (less than 0.1%) across the globe, they support the greatest biodiversity of marine organisms on earth. However, with climate change and ocean acidification, there is no certain future for
coral reef survival.
Coral reefs inhabit waters with a minimum sea surface temperature (SST) of around 18˚C and are limited to equatorial latitudes. It is these tolerances that have long been assumed to be the constraining factor on their distribution, and
therefore marine biodiversity is concentrated in the tropics and subtropics. However, a new study now suggests that this ecological niche so rich in biodiversity once spanned the globe from pole to pole.
Coral reef depiction: ‘The wonderful Paleo Art of Heinrich Harder, 1920.’ | Heinrich Harder / Wikimedia Commons
Climates have changed significantly throughout geological time. Despite this, our understanding of the impact this has had on coral reef systems has been difficult to construct due to a lack of quantifiable data and major gaps in any
available data. This is what Jones et al. (2022) are hoping to close.
This knowledge gap exists because not all ecosystems or remains of organisms are recorded in the fossil record. Most of the data collected come from countries with higher GDPs, which further limits the study of fossil coral reefs.
Previous assumptions of coral reef distribution have been based upon contemporary niche occupation and coral sea water temperature needs. Although the climate was already considered the main driver of coral reef migration, it remained a
hypothesis not yet supported by the fossil record.
Jones’ et al. (2022) study provides data using habitat modelling and climatic reconstructions to predict the distribution of suitable coral environments spanning the last 250 Ma. Jones et al. (2022) found that
prehistoric coral reefs dating from the Permian to the Early Triassic periods suggest that ancient corals extended beyond the equatorial region they predominate today.
‘Ancient corals extended beyond the equatorial region they predominate today.’
Nowadays, cooler temperatures constrain coral geographies to the equatorial bands north and south of warm tropical to subtropical latitudes, with this restriction beginning roughly 35 Ma.
This study confirms previous assumptions on how the distribution of coral throughout geological time has depended on the climate and also highlights the role continental plate migration has had on their distribution.
Contemporary ecological research, therefore, is left with the possibility of using fossil coral distribution as proxies, which allows one to model the future migration trends of corals with our changing climate. The implications of which
suggest that reef distribution may begin to move poleward, mirroring the paleotemperature-coral relationship seen in the Early Triassic.
It might be possible that by employing methods used by Jones et al. (2022), which include habitat suitability modelling, earth system modelling and the 247 Ma Scleractinian fossil record, we may be able to predict the future
suitability of reef planting.
Global map of present coral reef distributions. Red cells contain one coral reef or community, the blue denotes areas of substrate depths less than 200 metres. | Jones et al. (2022) / Nature Communications
When asked about the wider implications of the study, contributing researcher Professor Philip Mannion explained:
‘In addition to better understanding the evolution of the latitudinal biodiversity gradient, whereby species richness is highest in the tropics and declines towards the poles, this study is important for providing a more nuanced view of how
the distribution of biodiversity is affected by long-term climatic changes, with implications for the long-term responses of species to the ongoing climate crisis.’
Professor Mannion’s research focuses on understanding what shapes the spatial distribution of biodiversity, with relevance for understanding the evolutionary driver(s) of the latitudinal biodiversity gradient.
This pattern has long been recognised in the present day, but the mechanisms that underlie it remain uncertain. The fossil record indicates that it has not always been present. Understanding what drives this pattern is important for global
conservation, including how biodiversity will respond to climate change.
Thus, looking to the past may just hold answers to perhaps supporting reefs in adapting to the pace of anthropogenic climate change today.
Featured Image: Marek Okon | Unsplash
Bellwood D.R. and Hughes T.P. (2001) Regional-scale assembly rules and biodiversity of coral reefs. Science. Volume 292, issue 5521, pages 1532-1535.
Descombes P., Wisz M.S., Leprieur F., et. al. (2015) Forecasted coral reef decline in marine biodiversity hotspots under climate change. Global Change Biology. Volume 21,issue 7, pages
2479-2487.
Hoegh-Guldberg O., Poloczanska E.S., Skirving W. and Dove S. (2017) Coral reef ecosystems under climate change and ocean acidification. Frontiers in Marine Science. Volume 4, page 158.
Jones L.A., Mannion P.D., Farnsworth A., Bragg F. and Lunt D.J. (2022) Climatic and tectonic drivers shaped the tropical distribution of coral reefs. Nature communications. Volume 13, issue
1, pages 1-10.
Kidwell S.M. and Holland S.M. (2002) The quality of the fossil record: implications for evolutionary analyses. Annual Review of Ecology and Systematics. Volume 33, Pages561-588.
Paulay G. (1997) Diversity and distribution of reef organisms. Life and death of coral reefs. Pages 298-353.
