鳥類在長程遷徙巡航的時候，是透過感知到地球的磁力線和和太陽光線的角度來控制方向的。那麼，珊瑚幼蟲(coral larvae)和珊瑚礁的幼魚苗(fish larvae)，又是透過什麼方式，從茫茫的大海之中，可以找到出生的棲息地的方向來游回去生長呢？
答案是透過珊瑚礁所發出來的音頻的引導，很神奇吧！
有科學家做了實驗，把健康珊瑚礁的聲音錄下來，然後找一些定點播放，結果這些地點珊瑚幼蟲和珊瑚礁的幼魚苗回游的比例比沒有播音的地方高上很多(幼魚苗回游的比例高上67%)。
Healthy coral reefs, Gordon knew, are lively with sound; the unfolding waves of sound are like an underwater orchestra or the endless improvisation of a jazz band. On the Great Barrier Reef, the humpback whales sing the soprano melody. Fish supply the chorus: whooping clownfish, grunting cod, and crunching parrotfish. Sea urchins scrape, resonating like tubas. Percussion is the domain of chattering dolphins and clacking shrimp, who use their pincers to create bubbles that explode with a loud bang. Lobsters rasp their antennae on their shells like washboards. Rainfall, wind, and waves provide the backbeat…
科學家Gordon深知，健康的珊瑚礁是充滿動感的聲音的。一波波湧動的聲音，有若水中的交響樂，或有若不間斷的爵士樂團即興演奏。在大堡礁，座頭鯨唱女高音的曲調。魚類的大合唱包括：小丑魚的吶喊聲、鱈魚的咕嚕聲、鸚鵡魚的嘎吱聲。海膽刮擦，發出有若低音大喇叭的聲音。打擊樂的領域，則是海豚的喋喋不休和蝦子的啪噠聲，它們用蝦鉗弄出泡泡爆裂的聲音。龍蝦用它的觸鬚刮殼，像刷洗衣板一般。降雨、陣風和海浪，則是提供了這些聲音的背景基調。
…scientists can decode spectrograms to detect the presence and estimate the biomass of herbivores and planktivores, and even distinguish different types of corals inhabiting the reef. Specific events—like schools of fish suddenly fleeing a predator-have distinctive sound signatures, allowing researchers to follow events on the reef acoustically. Since sound travels better and farther than light underwater, digital bioacoustics is a powerful, reliable, noninvasive way to capture the complexities of the underwater world.
……解譯聲音的頻譜，科學家就可以偵測並估計，草食性動物和食浮游生物動物存在的生物量，甚至可以分辨出，珊瑚礁上不同珊瑚的種類。特定的狀況，譬如一群魚突然驚逃掠食者的追逐，所形成特別的聲紋，研究者可以循聲來追蹤珊瑚礁裏發生的事情。在水中，聲音比光線的傳播要容易，數位錄音的技術，就成為掌握複雜的水底世界，一種非常有力、可靠而且是非侵入式的蒐集資料方式。
Recordings of marine soundscapes can also serve as a proxy for assessing coral reef health. The soundscape of a degraded ecosystem is usually missing sounds found in a healthy ecosystem; its spectrogram looks like a puzzle missing various pieces —or, if invasive species are present, one with odd-looking pieces from a different puzzle. Much as a radiologist assesses your health by looking at an X-ray, a trained scientist can assess the health of a coral reef, or any ecosystem, by looking at its spectrogram over time. The degradation of a reef may reveal itself in sound before its decline is visible to the human eye.
錄製海洋的聲景(soundscapes) ，也可以間接用來評估珊瑚礁的健康程度。退化生態系統的聲景，往往是缺乏在健康的生態系統中發現的各種聲音，它的聲音頻譜看起來猶如少了解答謎題的各種不同拼圖一般。或者，如果有入侵的物種存在，看起來就會像是另外一個謎題的奇怪拼圖一樣。很像放射科的專家，透過研究一個X光片來評估你的健康，訓練有素的科學家，可以透過長期觀察聲音頻譜的變化，評估一個珊瑚礁或其他任何生態系統的健康狀況。
When corals are stressed by changing ocean temperature, they commit a form of mass suicide. Healthy corals— tiny, translucent, soft-bodied animals related to jellyfish and anemones — depend on symbiotic algae, known as zooxanthellae, which live within their tissues. The microscopic, brightly colored algae provide corals with oxygen and other vital nutrients; in return, the corals provide the algae with a protected environment for photosynthesis. This symbiosis enables coral colonies to thrive and reproduce; the relationship between plants (algae) and animals (corals) is so intimate that some refer to reefs as “planimals.” When ocean temperatures are stable, coral colonies can live for hundreds or even thousands of years. But warmer water disturbs the delicate symbiosis; the algae begin producing chemicals that threaten the corals, which expel their colorful plant symbionts. Without the algae, corals lose their color and begin to starve, a phenomenon referred to as bleaching. When the underlying calcium carbonate skeleton is revealed, the color of coral death manifests as a dull yellowish-white.
面臨海水溫度變化的挑戰(變暖)，珊瑚大量自殺死亡。健康的珊瑚，是細小、透明的、身子柔軟的動物，類似水母和阿米巴原蟲。它們仰賴住在它們體內共生的藻類，亦稱為蟲黃藻(zooxanthellae)。微小亮色的藻類，提供珊瑚氧氣及其他重要的養分，而作為回報，珊瑚則提供了一個保護的環境，供藻類進行光合作用。這種共生的結構，使得珊瑚群得以繁衍興盛。這種植物(藻類)和動物(珊瑚)的關係是如此密切，因此有些人稱之為「植動生物」(planimals)。當海洋的溫度穩定的時候，珊瑚群可以活上數百年，甚至長達數千年。但是，暖化的海水，干擾了微妙的共生關係。藻類開始產生危及珊瑚的化學物質，以致珊瑚開始排斥它的共生夥伴。沒有了藻類，珊瑚因而失色且開始挨餓，產生一種我們稱為白化的現象。當珊瑚原本隱藏在下面的碳酸鈣骨骼顯露出來的時候，珊瑚的死亡就呈現出白而泛黃的單調顏色。
……
在全球暖化，海水的酸度變高的情況下，全世界的珊瑚礁已經陸續出現有大量死亡白化的現象。
The disappearance of corals is a death knell for many other species. Corals are like the rainforests of the marine world: although reefs occupy less than a tenth of a percent of the ocean floor, they support one-third of all known ocean species…
珊瑚的消失，將敲響許多其他物種滅絕的喪鐘。珊瑚有若海洋世界的雨林。棲息地雖然僅佔少於海床總面積千分之一中的十分之一，但是珊瑚卻庇護著所知海洋生物種類數的三分之一…
……
珊瑚白化死亡的區域，少了生物多樣性，發出的音頻和健康的珊瑚礁不同，珊瑚蟲不再游回來固著，珊瑚礁的小魚苗也不再游回來了，白化珊瑚區最後成為生態的死區。
有些比較強韌的珊瑚存活了下來，但是接下來長出來的珊瑚都顯得特別低矮，庇護生物的空間變小，生物多樣性的降低是可以預期的。
科學家試著在白化珊瑚的區域播放健康珊瑚的音頻，發現有些魚是游回來了，但是長期的效應會如何，還有待更長期的觀察。畢竟，生態系統環環相扣，是很複雜的。
由於珊瑚對聲音是如此敏感，因此在珊瑚卵大量噴發受精直到珊瑚幼蟲由大海游回棲地定著的這段繁殖的期間，人類在附近活動可能會產生干擾的聲音，那是要絕對避免的，其理甚明。
*：Karen Bakker, “Sounds of Life,” 2022, Princeton University Press
P.S. 白化珊瑚的照片來自維基百科
2024/5/28 Reef Lullaby 珊瑚搖籃曲 Damakey
