How can patterns in the marine biodiversity of the past help us to understand how it may change in the future? A recent research by Drs Moriaki Yasuhara and Timothy C Bonebrake (School of Biological Sciences and Swire Institute of Marine Science, The University of Hong Kong) and numerous international collaborators finds that the tropical diversity decline now seen in the ocean is not purely human induced, but nonetheless will worsen considerably if we do not limit anthropogenic climate warming.
如何鑒往知來，預測熱帶海洋生物多樣性的未來？香港大學生物科學學院及太古海洋科學研究所副教授安原盛明博士、Timothy Bonebrake博士，以及其國際團隊近日的研究發現，熱帶海洋生物多樣性局部下降的趨勢，可能不單單來自人類活動。儘管如此，人類若不能有效控制二氧化碳的排放量，全球暖化將會加劇熱帶海洋生物多樣性的喪失。
The research, published in Proceedings of the National Academy of Sciences of the United States of America, used fossil records to reconstruct global oceanic biodiversity patterns of the last ice age (~20,000 years ago) and the pre-industrial period (before 1800s), and used these to build ecological models for projecting global marine biodiversity in the near future (2090s). Using fossil protozoan foraminifera (Images 1, 2) as a “window” to see into past pelagic ecosystems through their rich fossil records, the authors discovered an equatorial “dip” in diversity during the pre-industrial period and projected for the end of this century, but not during the last ice age (Image 3).
研究利用化石記錄重建末次冰盛期（約20,000年前）及前工業革命時期（西元1800年）全球海洋生物多樣性的分佈模式，並以該模式來預測至本世紀末前（約2090年）全球海洋生物多樣性的變化，研究成果於《美國國家科學院院刊》發表。作者們透過研究有孔蟲（圖一及二）豐富的化石記錄去了解過去的遠洋生態系統，發現不論在前工業革命時期或本世紀末，赤道的海洋生物多樣性均比亞熱帶低，但在末次冰盛期，這情況卻不存在（圖三）。
“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 patters often show an equatorial ‘dip’ of diversity. We wanted to explore what caused this, and whether it was a recent pattern,” said lead author Dr Moriaki Yasuhara.
主作者安原盛明博士指出：「生物多樣性在熱帶地區通常較高，在兩極地區較低，這樣的生態模式稱為『生物多樣性隨緯度變化的梯度』。然而，近期多項研究發現全球海洋生物多樣性隨緯度變化，呈現雙峰分佈，意即赤道多樣性呈現局部性『下降』的趨勢。因此，我們希望利用化石紀錄來探究這種現象的成因，以及可能出現的時間點。」
The modern decline of tropical diversity likely started during post-ice-age warming around 15,000 years ago. However, the magnitude of decline is projected to be amplified by anthropogenic warming. 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.
近代赤道多樣性的局部性『下降』，可能自後冰河時期（約15,000年前）開始；但人類活動導致的海洋暖化，將加劇多樣性下降的幅度。若按經濟如常的碳排放量，到本世紀末，熱帶海洋生物多樣性可能會減少到過去數百萬年來從未經歷的水平。
“By using fossil records we discovered that the diversity ‘dip’ in equatorial regions of the ocean is caused by species distribution shifts driven by post-ice-age ocean warming,” continued co-lead author Dr Chih-Lin Wei, Associate Professor at Institute of Oceanography, National Taiwan University. The pelagic ocean covers the vast majority of Earth’s surface and is the largest ecosystem on Earth (Images 4, 5). It is home to planktons that play a key role in food chain, top predators and economically important species that are increasingly under threat from climate change.
台灣大學海洋所副教授魏志潾表示：「利用化石記錄，我們發現赤道多樣性的局部性『下降』，可能源自後冰河時期海洋暖化時物種分佈的改變。」上層海洋覆蓋了地球超過70% 的表面積，是地球上最大的生態系統（圖四及五），亦是在食物鏈中擔當重要角色的浮游生物的家園；可惜浮游生物作為頂級掠食者和重要經濟物種的主要食物來源，其生存卻越受氣候變化的威脅。
“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 Dr Derek P Tittensor, Aassociate Professor at Dalhousie University, concluded.
另一位作者加拿大達爾豪西大學副教授Derek Tittensor作出總結：「海洋暖化與熱帶生物多樣性下降之間的明確關聯意味著到本世紀末，海洋生物多樣性可能下降至人類歷史上前所未見的水平。」
About the journal paper
Citation: 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.
Link of journal paper: http://www.eurekalert.org/s/pio/pnas
For more information about Dr Moriaki Yasuhara’s research, please visit: https://moriakiyasuhara.com
For media enquiries, please contact Ms Naussica Lau, External Relations Officer of HKU Faculty of Science (tel: 3917 7897; email: nauslau3@hku.hk) or Dr Moriaki Yasuhara (email: yasuhara@hku.hk).
Images download and captions:
Image 1: A living planktonic foraminifera 浮游有孔蟲, Globigerinoides sacculifer. Photo credit: Katsunori Kimoto.
Image 2: Scanning electron microscopy image of a planktonic foraminifera species 浮游有孔蟲, Globigerinella adamsi. Photo credit: Briony Mamo.
Image 3: Biodiversity patterns with latitudes in three different time periods. Note the equatorial “dip” in the pre-industrial time (green) and 2090s (red), but not in the last ice age (blue). 生物多樣性隨緯度的變化（上圖）。在前工業革命時期（綠色）或是本世紀末（紅色），生物多樣性皆較亞熱帶低（呈雙峰分布），但末次冰盛期（藍色）則不然。
Image 4: An example of pelagic ocean ecosystem 1. 遠洋生態系統範例 Photo by Max Gotts on Unsplash
Image 5: An example of pelagic ocean ecosystem 2. 遠洋生態系統範例 Photo by Jet Kim on Unsplash