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有聽過Salp嗎？～（小小生物將能改善地球溫室效應唷）

作者：Jessica的老公│2010-08-13 18:29:55│巴幣：18│人氣：10589

The Salp: Nature's Near-Perfect Little Engine Just Got Better

樽海鞘（海樽）：

近乎完美的天然小發動機是更好的選擇

文章選自ScienceDaily (Aug. 9, 2010)，加上個人翻譯。

(馬丁博士與薩瑟蘭研究員看著Salp)

ScienceDaily (Aug. 9, 2010) — What if trains, planes, and automobiles all were powered simply by the air through which they move? Moreover, what if their exhaust and byproducts helped the environment?

每日科學（2010年8月9日） - 如果火車，飛機和汽車的動力都僅僅是通過周遭的空氣來推動？此外，如果他們的廢氣和副產品又能幫助環境呢？

Well, such an energy-efficient, self-propelling mechanism already exists in nature. The salp, a smallish, barrel-shaped organism that resembles a kind of streamlined jellyfish, gets everything it needs from the ocean waters to feed and propel itself. And, scientists believe its waste material may actually help remove carbon dioxide (CO2) from the upper ocean and the atmosphere.

那麼，這樣的高能源效率，自我推進的機制已經存在於自然界。salp，中文名為樽海鞘或海樽，外觀短小，桶型的有機體，類似於一種簡單的水母，它從海洋水域可獲取需要的一切，如食物和推動自身。而且，科學家們相信樽海鞘產生的廢料可能實際上有助於消除來自上海洋和大氣層的二氧化碳（CO2）。

Now, researchers at the Woods Hole Oceanographic Institution (WHOI) and MIT report that the half-inch to 5-inch-long creatures are even more efficient than had been believed. Reporting in the current issue of the Proceedings of the National Academy of Sciences, they have found that the ocean-dwelling salps are capable of capturing and eating extremely small organisms as well as larger ones, rendering them even hardier -- and perhaps more plentiful -- than had been thought.

現在，伍茲霍爾海洋學研究所（WHOI）和麻省理工學院的研究人員指出，半英寸到5英寸長的這類生物比原來認為的更有效率。在國家科學院的報告中，他們已經發現，居住於海洋的樽海鞘能夠捕捉和攝取非常小的生物體或略大的，使他們超乎人們想像的更強壯或許更豐富。

"We had long thought that salps were about the most efficient filter feeders in the ocean," said Laurence P. Madin, WHOI Director of Research and one of the investigators. "But these results extend their impact down to the smallest available size fraction, showing they consume particles spanning four orders of magnitude in size. This is like eating everything from a mouse to a horse."

伍茲霍爾海洋研究所研究主任和一名調查員，馬丁說：『我們早就認為 salps在海洋中最有效的濾食性動物。但這些結果令人訝異這麼小的體型，卻能吞吃跨越4個數量級大小的顆粒。這就像吃了從老鼠到馬這樣顯著的差距。』

(樽海鞘有著讓海水從進水孔流入由出水孔排出過著濾食的生活)

Salps capture food particles, mostly phytoplankton, with an internal mucous filter net. Until now, it was thought that only particles as large as or larger than the 1.5-micron-wide holes in the mesh.

Salps捕獲食物顆粒，主要是浮游植物，其內粘膜濾網，到現在為止，人們認為只有粒子一樣大或大於 1.5微米（mm）範圍內的網孔。

（注意其濾食行為）

But a mathematical model suggested salps somehow might be capturing food particles smaller than that, said Kelly R. Sutherland, who wrote the paper as part of her PhD thesis at the MIT/WHOI Joint Program for graduate students. In the laboratory at WHOI, Sutherland and her colleagues offered salps food particles of three sizes: smaller, around the same size as, and larger than the mesh openings.

但是，數學模型推測salps某種程度上可能捕捉更小的食物顆粒。凱利河薩瑟蘭，她在麻省理工學院 /伍茲霍爾海洋研究所研究生聯合方案，寫的博士論文的一部分，薩瑟蘭和她的同事們提出salps食物顆粒三種尺寸：小，大約在同一大小，和大於網孔。

"We found that more small particles were captured than expected," said Sutherland, now a postdoctoral researcher at Caltech. "When exposed to ocean-like particle concentrations, 80 percent of the particles that were captured were the smallest particles offered in the experiment."

現在是加州理工學院博士後研究員的薩瑟蘭指出：『我們發現，高於預期更小的顆粒被捕獲，當暴露在海洋般的粒子濃度下，八成以上被抓獲的粒子都是最小的粒子。』

This finding is important for a number of reasons. First, it helps explain how salps -- which can exist either singly or in "chains" that may contain a hundred or more--are able to survive in the open ocean, their usual habitat, where the supply of larger food particles is low. Madin, who served as Sutherland's advisor at WHOI, adds: "Their ability to filter the smallest particles may allow them to survive where other grazers can't."

這一發現有許多理由使其很重要。首先，它有助於解釋salps可以單獨或以上百串鏈在一起的方式生存棲息在開放的海洋，那裡供應較少大顆粒的食物。在伍茲霍爾海洋研究所擔任薩瑟蘭的顧問，馬丁補充道：『他們的能力，可以過濾最小的微粒，讓他們能夠生存在其他食草動物不能生存的地方。』

（Salp生活史中也可以群聚的方式生活）

Second, and perhaps most significantly, it enhances the importance of the salps' role in carbon cycling. As they eat small, as well as large, particles, "they consume the entire 'microbial loop' and pack it into large, dense fecal pellets," Madin says.

第二，也許是最重要的是，它增強了salps在碳循環作用中的重要性。當他們吃小，以及大粒子，他們能消費整個微生物循環，並將其包裝成為較大的，密度高糞粒。

The larger and denser the carbon-containing pellets, the sooner they sink to the ocean bottom. "This removes carbon from the surface waters," says Sutherland, "and brings it to a depth where you won't see it again for years to centuries."And the more carbon that sinks to the bottom, the more space there is for the upper ocean to accommodate carbon, hence limiting the amount that rises into the atmosphere as CO2, explains co-author Roman Stocker of MIT's Department of Civil and Environmental Engineering .

體積大與高碳密度的顆粒形成的越早，其顆粒就越快沉到海底。這樣能從海洋表面消除碳源，而這些顆粒將沈的更深，在未來的幾個世紀都不會再看到它。”而當碳聚集至海底底部，這代表海洋上層將有更多的空間來容納碳，因而限制了二氧化碳上升到大氣中的數量。

（生物性碳循環）

"The most important aspect of this work is the very effective shortcut that salps introduce in the process of particle aggregation," Stocker says. "Typically, aggregation of particles proceeds slowly, by steps, from tiny particles coagulating into slightly larger ones, and so forth.

最重要的方面是，salps聚集顆粒的過程非常有效率，斯托克說。在自然情況下，從微小的顆粒凝結成稍大的過程是非常緩慢的。

"Now, the efficient foraging of salps on particles as small as a fraction of a micrometer introduces a substantial shortcut in this process, since digestion and excretion package these tiny particles into much larger particles, which thus sink a lot faster."

現在，salps有效率的覓食過程能將顆粒小到1微米的粒子變成大顆粒，藉由消化，排泄讓這些微小顆粒聚集成更大顆粒，從而更快地沈降至海底。

This process starts with the mesh made of fine mucus fibers inside the salp's hollow body. Salps, which can live for weeks or months, swim and eat in rhythmic pulses, each of which draws seawater in through an opening at the front end of the animal. The mesh captures the food particles, then rolls into a strand and goes into the gut, where it is digested.

這一過程開始於salp中空身體內的網狀纖維所製成粘液中。 Salps，可以活數週或數月，並且有規律地游泳與攝食，salp讓海水從前端進入。其布滿黏液的網狀纖維可以網捕獲食物顆粒，將其滾成長絲，並進入腸道，在那裡繼續消化。

（海樽構造示意圖）

It had been reasoned that the lower limit of particles captured by a salp was dictated by the size of the openings in the mesh (1.5 microns) In other words, particles smaller than the openings were expected to pass through the mesh. But the new results show that it can capture particles as small as 0.5 microns and smaller, because the particles stick to the mesh material itself in a process called direct interception, Sutherland says.

根據推測，salp捕獲粒子的下限應該還是決定於網狀開口的大小（1.5微米）。換言之，小於1.5微米的顆粒應該可以通過網格。但新結果顯示，它能夠捕捉小至0.5微米或更小的粒子，瑟蘭說：『因為這個網狀構造能執行被稱為『直接攔截』的行為。』

（形形色色的海樽）

"Up to now it was assumed that very small cells or particles were eaten mainly by other microscopic consumers, like protozoans, or by a few specialized metazoan grazers like appendicularians," said Madin. "This paper indicates that salps can eat much smaller organisms, like bacteria and the smallest phytoplankton, organisms that are numerous and widely distributed in the ocean."

直至目前的認定，非常小的細胞或微粒主要是由其他微生物攝食，如原生動物，或某些特殊的多細胞食草生物。這篇論文表明，salps可以吃更小的生物，如廣泛分佈於海洋的細菌和最小的浮游植物。

（手繪海樽構造圖）

The work -- funded by the National Science Foundation and the WHOI Ocean Life Institute--"does imply that salps are more efficient vacuum cleaners than we thought," says Stocker. "Their amazing performance relies on a feat of bioengineering -- the production of a nanometer-scale mucus net -- the biomechanics of which still remain a mystery, adding to the fascination for and the interest in these animals."

國家科學基金會和伍茲霍爾海洋研究所海洋生命學院指出，salps是比我們想像更有效的真空吸塵器，salp的能力來自於一個生物工程的壯舉，就是能夠產生納米級的粘液網。在生物力學來說，仍然是一個謎，從而增加salp的魅力與無限的價值。

樽海鞘

樽海鞘(Salps)，一種類似海蜇的動物，以水中的浮遊植物(海藻等)為食，通過吸入噴出海水完成在水中的移動。他們身體呈桶狀，且幾乎完全透明，身長在1厘米到10厘米之間。它是具有類似於水母的半透明、稍扁平桶狀的海洋生物。作為部分生殖周期，它們形成環狀結構。

樽海鞘尾索動物亞門(Urochordata)海樽綱(Thaliacea)紐鰓樽科(Salpidae)海樽科(Doliolidae)的一類小型遠海膠質脊索動物。見於暖海，南半球常見。體桶狀，透明，有環狀肌帶，兩端開口，身長一般在1到10厘米。濾食微小的浮遊生物。生活環複雜，有性和無性時期交替。無性時期許多個體連成長鏈。許多種能發光。

（種類繁多的海樽）

“樽海鞘”是一種半透明的類似水母的海洋生物,它們在海洋食物鏈中的位置並不重要，但是卻是為海洋減少溫室氣體的重要成員，這一觀點大大提升了樽海鞘在海洋動物中的地位。在海洋中成群存在的樽海鞘每個只有人的拇指大小，它們上十億的聚集在一起，生活在海洋中的“熱區”，每天可以將海洋中成噸的碳從海洋表面運輸到海洋深處。樽海鞘是半透明的類似水母的海洋生物，它們通過從前面吸進海水然後從後面排出的噴氣式方式運動。當水通過其粘膜的時候，樽海鞘就將其中的可食用成分吸收的一幹二凈。

海洋從大氣中吸收多余的二氧化碳——一部分來自石油等燃料的燃燒。在有陽光照射的海面，浮遊植物利用這些二氧化碳生長。動物則吃掉浮遊植物，並制造出碳。但是在動物死亡以後，這樣的碳大部分溶解並重新進入海洋，被植物或細菌再次利用，或者返回大氣層。美國國家海洋學院的 Laurence Madin和他康涅尼格大學的同事Patricia Kremer對大西洋中部進行了四次探索。每一次他們都發現，有一種特殊種類的樽海鞘，大量成群成倍的增長，並能持續幾個月。

（海樽幫助海中二氧化碳的集中與沈降，減少二氧化碳在大氣與海水中的濃度）

科學家對一群面積大約10萬平方千米的樽海鞘進行研究。據科學家統計計算，樽海鞘大約消耗由浮遊植物產生的碳總量的74%，同時利用自己的“排泄小球”向深海轉運大約四千噸碳。它們將零散的碳聚集到一起，使之沈降的更快。在以前的研究中樽海鞘的排泄小球一天大約下降一千米。即使是死亡了，它們每天也能以475米的高速沈降。如果樽海鞘真的處在食物鏈的末端並在沈降的過程中不被吃掉的話，他們能給海洋中運輸進更多的碳。樽海鞘白天向下遊很遠，而夜里又向上遊回去，這一過程被稱作垂直運動。像這樣，樽海鞘向深海中釋放排泄小體，令很少有動物能在那吃掉它們。這也大大增加碳從大氣中轉移出去的機會。