在大滅絕造成浩劫之後生物仍持續使海洋生態系運作

原文網址：http://www.leeds.ac.uk/news/article/4121/life_goes_on_for_marine_ecosystems_after_cataclysmic_mass_extinction

在大滅絕造成浩劫之後生物仍持續使海洋生態系運作

科學家發現史上最重大的全球滅絕事件之一並未從基礎層面改變整個海洋生態系。

包括里茲大學的Alex Dunhill博士的國際科學家團隊，發現二疊紀末的大滅絕雖然殲滅了絕大部分的物種，但海洋生態系的運作方式似乎沒有太過劇烈的改變。

主要作者，里茲大學地球和環境學院的Dunhill博士表示：「雖然三疊紀末的大滅絕事件對海洋物種的整體數目有重大影響，但是倖存物種的多樣性仍足以讓海洋生態系的運作方式維持得跟之前一樣。」

「我們並非指說一切安好。」共同作者，德州大學奧斯汀分校地質科學院的古生物學家William Foster表示。「而是滅絕事件過後的全球海洋變得有點像是由骷顱船員掌舵的幽靈船――雖然所有的崗位都在運作，但是僅由少數物種來操縱。」

三疊紀末期的大滅絕事件發生在2億100萬年前。當時火山活動造成大氣的溫室氣體濃度飆升，導致相當迅速的全球暖化，地球將近50%的生物因而死亡。這場火山爆發事件也和盤古超大陸的分裂以及大西洋的形成有關。

團隊檢視了從三疊紀中期至侏儸紀中期7000萬年間的化石紀錄，以比較三疊紀末期滅絕事件發生前後海洋生態系的改變。他們將居住在海洋的動物依據其移動方式、棲息場所和飲食習慣來分類出不同的生活類型。

接著他們確定沒有一種生活類型因為滅絕事件而完全消失，代表海洋生態系完整地保存下來。

他們今日發表在《古生物學》(Palaeontology)的結果顯示雖然滅絕事件並未顛覆全球海洋生態，但它對個別區域和環境卻有深遠的影響，並對特定類型的海洋生態系造成重大衝擊。

Dunhill博士表示：「三疊紀末期死傷最慘重的海洋生物之一便是固定不動，居住在礁體的生物，像是珊瑚。當我們檢視化石紀錄，我們看到雖然海洋生態系整體來說仍然持續運作著，但熱帶珊瑚礁生態系卻耗費超過2000萬年的時間，才從這場環境浩劫中回復過來。」

「礁體生態系對迅速發生的環境變遷最為敏感。三疊紀末期溫室氣體對海洋生態系造成的影響，跟今日我們見到因為海洋溫度升高而死亡的珊瑚礁所經歷的情況並沒有多大差異。」

共同作者，倫敦自然史博物館的Richard Twitchett表示：「瞭解過去大滅絕事件中珊瑚礁的崩毀程度，或許有助於我們預測現在海洋生態系將會遭遇的情況。」

「過去每當溫室氣體迅速增加時，熱帶生態系就會有大範圍地區受到摧殘，儘管各次事件的溫室氣體變化速率和罹難物種不盡相同。雖然(造成二氧化碳增加的)起因有所差異，當看見過往事件一再造成類似的後果，便可以推論類似情形在未來也可能會再度重演。」

Life goes on for marine ecosystems after cataclysmic mass extinction

One of the largest global mass extinctions did not fundamentally change marine ecosystems, scientists have found.

An international team of scientists, including Dr Alex Dunhill from the University of Leeds, has found that although the mass extinction in the Late Triassic period wiped out the vast proportion of species, there appears to have been no drastic changes to the way marine ecosystems functioned.

Lead author Dr Dunhill, from the School of Earth and Environment, said: “While the Late Triassic mass extinction had a big impact on the overall number of marine species, there was still enough diversity among the remaining species that the marine ecosystem was able to function in the same way it had before.”

“We’re not saying nothing happened,” said co-author Dr William Foster, a palaeontologist from the Jackson School of Geosciences at the University of Texas at Austin. “Rather, global oceans in the extinction’s aftermath were a bit like a ship manned by a skeleton crew – all stations were operational, but manned by relatively few species.”

The Late Triassic mass extinction occurred 201 million years ago. Nearly 50 per cent of life on Earth died out as a result of huge volcanic eruptions. The volcanic activity created high levels of greenhouse gases in the atmosphere which led to rapid global warming. The eruptions are also associated with the break-up of the super-continent Pangaea and the opening of the Atlantic Ocean.

The team compared marine ecosystems across the late Triassic mass extinction event by examining fossils from the Middle Triassic to Middle Jurassic —a 70 million-year span. They classified the lifestyle of different ocean-dwelling animals by how they moved, where they lived and how they fed.

They were then able to determine that none of these lifestyles had completely disappeared due to the extinction event, which preserved the marine ecosystem.

Their results, published today in Palaeontology, showed that while the extinction did not result in a global marine ecological shift, it had profound regional and environmental effects and had an extreme impact on specific ocean ecosystems.

Dr Dunhill said: “One of the great marine casualties of the Late Triassic were stationary reef-dwelling animals, such as corals. When we examined the fossil record we saw that while the marine ecosystem continued to function as a whole, it took over 20 million years for tropical reef ecosystems to recover from this environmental cataclysm.

“Reef ecosystems are the most vulnerable to rapid environmental change. The effect of the Late Triassic greenhouse gases on marine ecosystems is not so different from what you see happening to coral reefs suffering from increasing ocean temperatures today.”

Co-author, Professor Richard Twitchett, from the Natural History Museum in London said: “Understanding the extent of reef collapse during past extinctions may help us predict what is in store for our modern marine ecosystems.

“Tropical ecosystems suffered widespread devastation each time that greenhouse gases rose rapidly in the past, despite differences in the rates of change and species involved. When you see similar responses occurring time and time again in the past, despite different starting conditions, it follows that similar responses will likely occur again in the future.”

原始論文：Dunhill, A; Foster, W; Sciberras, J; Twitchett, R. Impact of the Late Triassic mass extinction on functional diversity and composition of marine ecosystems. Palaeontology, 2017 DOI: 10.1111/pala/12332

引用自：University of Leeds. "Life goes on for marine ecosystems after cataclysmic mass extinction."