The research, published in Proceedings of the National Academy of Sciences (PNAS), used fossils to reconstruct global oceanic biodiversity patterns for the last ice age (approximately 20,000 years ago) and the pre-industrial period, i.e. before 1950, and used the results to make projections for the near future (2090s). The equatorial "dip" in diversity that is observed today existed already during the pre-industrial period but it was not present during the last ice age. The decline of tropical diversity is the result of warming after the ice age, and it appears that anthropogenic warming will worsen the tropical diversity decline further. By the end of the 21st century, tropical diversity may decrease to levels not seen for millions of years if our future aligns with the "business-as-usual" CO2 emission scenario.
The pelagic ocean covers the vast majority of Earth’s surface and is the largest biome on Earth. It is home to phytoplankton that play a key role in global oxygen production, top predators and economically important species that are increasingly under threat from climate change.
To reconstruct the past state of tropical marine diversity, the researchers used tiny shells of fossil plankton called foraminifera. These shells are preserved in marine sediments and act as sentinels of changes in past pelagic ecosystems.
“Biodiversity is usually high in the tropics and low at the poles. We call this important pattern the ‘latitudinal diversity gradient’. Yet, recent studies have found that global marine biodiversity patterns often show an equatorial 'dip' of diversity. We wanted to explore what caused this, and whether it was a recent pattern,” says lead author Moriaki Yasuhara from the University of Hong Kong (China).
"These clear links between warming and reduced tropical biodiversity mean that by the end of this century oceanic diversity at the equator may dip to a level unprecedented in human history,” co-author Derek P. Tittensor, associate professor at Dalhousie University, concluded.
“This research shows furthermore how data on past marine ecosystems preserved in marine sediments provide scenarios of diversity change relevant to the assessment of global change policies,” adds co-author Michal Kucera from MARUM.
Moriaki Yasuhara, Chih-Lin Wei, Michal Kucera, Mark J. Costello, Derek P. Tittensor, Wolfgang Kiessling, Timothy C. Bonebrake, Clay Tabor, Ran Feng, Andrés Baselga, Kerstin Kretschmer, Buntarou Kusumoto, and Yasuhiro Kubota (2020): Past and future decline of tropical pelagic biodiversity. Proceedings of the National Academy of Sciences of the United States of America. DOI: 10.1073/pnas.1916923117
School of Biological Sciences and Swire Institute of Marine Science, The University of Hong Kong (China)
Institute of Oceanography, National Taiwan University(Taiwan)
MARUM– Center for Marine Environmental Sciences and Faculty of Geosciences, University of Bremen
School of Environment, The University of Auckland(New Zealand)
Department of Biology, Dalhousie University, Halifax (Canada)
UN Environment Programme World Conservation Monitoring Centre, Cambridge (Great Britain)
GeoZentrum Nordbayern, Department of Geography and Geosciences, Friedrich-Alexander Universität Erlangen−Nürnberg
Center for Integrative Geosciences, University of Connecticut, (USA)
Departamento de Zoología, Genética y Antropología Física, Facultad de Biología, Universidad de Santiago de Compostela(Spain)
Faculty of Science, University of the Ryukyus,Okinawa (Japan)
MARUM produces fundamental scientific knowledge about the role of the ocean and the ocean floor in the total Earth system. The dynamics of the ocean and the ocean floor significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, and create unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society and the marine environment, and in accordance with the Sustainable Development Goals of the United Nations. It publishes its quality-assured scientific data and makes it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperates with commercial and industrial partners in accordance with its goal of protecting the marine environment.