一沙一世界——劉烘昌與螃蟹

:::

1993 / 7月

文‧張靜茹 圖‧劉烘昌


當人為因素造成海岸不斷流失,各種開發計畫又在海岸加緊推動,新竹海邊,卻有一位年輕的學子,一步一腳印地從事著海岸生態的調查。

在香山海邊,許多人注意的是開發成工業區、住宅區後的利益,他卻看到了不一樣的東西。


靠近新竹香山,名為「海山船澳」的小海彎內,退潮時,逐浪人的每一步都在泥濘的沙地上,留下了深深的印痕,但平緩的沙地上,卻早有許多小腳印捷足先登。

邊緣動物

在遠遠傳來的海浪聲中,靜觀看來單調的這一片淨土,卻是充滿生機,棲息著許多五色的小螃蟹。紅、黃相間的招潮蟹,稍有動靜即一溜煙鑽回洞中;幽靈蟹微微露出小足於洞緣,昭示著它的地盤;像一顆顆珍珠般的小兵蟹,常不顧一切地由微小的沙洞中湧出,在陽光下泛著銀藍色光芒,又被稱為「海和尚」。

兩年來,新竹清華大學研究生劉烘昌在這塊人跡罕至的土地上,記錄到卅幾種螃蟹。而其中身體不時發出銀樣色澤的海和尚,更是數量眾多。退潮時常成群結隊,幾十群,甚至上百群蜂擁而出。在此觀察螃蟹,一待幾個小時的劉烘昌,常常不覺就被海和尚十面埋伏地團團包圍。

但是,這種「螃蟹雄兵」的景象,不久後卻可能逐一消失。

「念中興大學時,我在台中山上的草湖溪進行溪蟹調查。溪澗裡,蝦、蟹眾多,一個晚上,可以記錄到五百多隻溪蟹。燈光一照,水潭裡都是蝦子發出的亮點,像銀河系般煞是好看。結果不久水利局在草湖溪規劃建民水壩,準備做為大台中未來的飲用水源,以後河川生態改變,溪裡蝦蟹的命運難卜」,劉烘昌述及生態觀察的歷程,「等我到清華大學念博士班,就到香山進行潮間帶蟹類的研究,如今又傳出香山將填海造陸的開發計畫。我的研究對象就像自然環境中的邊緣人,人為開發的觸角極易侵入它們的領土。」

螃蟹海岸

香山海埔地是近來政府一連串海埔地開發計畫之一,省府將在此填海造陸近一千公頃。

但香山海岸五百公尺到兩公里寬的潮間帶上,也是全省特有的「台灣招潮蟹」數量最多之處。根據海洋大學與劉烘昌對海岸進行的生態調查發現,西海岸潮汐區裡原本廣泛分佈著各種螃蟹,隨著海岸土地流失與海灘污染,許多豐富的海岸生物正急遽銳減。以中部海岸鹿港、大肚溪、到後龍溪為例,鹿港如今已幾乎沒有潮間帶;大肚溪口因為興建火力發電廠,破壞嚴重,如今要看成群結隊的招潮蟹,與族群最大的海和尚,恐怕只有到香山了。

今年初,一位研究沙地生物的韓國學者來台灣做調查,省立博物館的工作人員帶著他全省採集,其他地方的沙地動物寥寥可數,到了新竹海岸,他才轉悲為喜,見到了豐富的海岸生物。

解開生命之謎

螃蟹起源於海洋,許多螃蟹則演化、遷移到陸、海交接的潮間帶生活。由於人類也由海中演化成為陸生動物,基於對自我生命起源的好奇與探索,使人們急欲了解在海、陸間過渡的沙蟹,在生理、生化上的適應情形,因此目前國際上對陸生螃蟹的研究很多。

在清大生命科學研究所就讀的劉烘昌,卻不只為解開生命之謎而研究螃蟹;大學時,他已開始對生物行為產生興趣,曾跟著魚類與植物學者上山、下海做調查,更選擇螃蟹做為自己長期的觀察對象。

人們看來景色一致,略帶蒼涼的海岸,對劉烘昌或對螃蟹,卻極其豐富與多樣。

潮間帶的沙土,質地是易積水,或顆粒較細,還是黏性高,螃蟹分的可清楚,「兵蟹棲息在較潮濕的沙質地裡,招潮蟹在較乾燥的泥地上挖洞,幽靈蟹則在高潮線以上活動」,劉烘昌如數家珍說,螃蟹領域分明。

兩頭「圓圓」海和尚

在劉烘昌眼裡,每一種螃蟹性情不同,行為互異,長相也各具特色。幽靈蟹行動如風;雄性招潮蟹兩螯一大一小,比例極端懸殊;海和尚行進舉止卻不太像螃蟹,不四處橫行,卻直來直往。「不是所有的螃蟹都橫著走路」,長期觀察螃蟹的劉烘昌說,也不是所有的螃蟹都長得一副「兩頭尖尖,這麼大個口」的模樣。

劉烘昌推測,在潮汐區的螃蟹中,海和尚可能是較早由海洋性演化成陸棲性動物的一種。因為最早上陸,鰓的構造具有像肺一樣的功能,以輔助在陸地上呼吸,體形維持著圓球形,以供鰓室擴充,與其他螃蟹扁平的身材極不相同。

四到六月時,沙地上會出現一個個像小煙囪的泥球,「由此就可以知道海和尚的幼蟲上岸了」,劉烘昌解釋,生活在河川的溪蟹,因為卵較大,整個幼蟲發育過程可在卵中完成。潮汐區裡的螃蟹,幼蟲必需回到海洋生活,經過多次脫殼後,再一隻隻回到海岸,鑿洞定居,它們挖出的泥,就堆置在洞穴外,像個小煙囪,小螃蟹經過一年就可以長為成蟹。

「但是螃蟹的年齡比女人的歲數還要神秘」,劉烘昌說,螃蟹幾個月就脫一次殼,而且是徹底地全身換新,「重新做人」,連身上的器官,如胃、腸的內壁都會更新,因此很難由螃蟹身上看出他們的年齡與歷經的風霜。「對螃蟹,我們不知道的生態行為還很多。」

蟹溺己溺

但劉烘昌還有多少時間可以瞭解台灣的螃蟹?根據地方政府的規劃,未來將有容納三百萬遊客的遊憩設施,和新竹飛機場等「壯觀」的結構物,矗立在平坦無垠的香山海灘上。由於市府估計未來新竹縣、市合併後,人口將會成長到一百萬人,在開發藍圖上,住宅區、污水處理廠、垃圾場也已一一搶佔海岸。

如果此處填海造陸,對螃蟹有何影響?「沒有了沙灘,海水上不來,缺乏養分、食物和水,漲潮時仍須回到潮線上濡濕鰓穴的螃蟹,哪還活得下去?」充滿「蟹溺己溺」心情的劉烘昌說。他更擔心此地開發後,會變成新竹目前唯一的南寮海水浴場——「垃圾遍佈,海水黃濁,空氣中滿布濃煙!」

新竹是台灣海峽最窄處,地形上的原因,使之成為台灣風速最快之處。冬天,海岸常吹砂瀑,縣政府曾在香山海岸背後山坡上蓋住宅區,結果因為風太大而蓋不成,冬天東北季風一吹,更令人受不了。曾仔細研究工業區環境影響評估的劉烘昌,不解地說:「此地蓋住宅區不曉得會有誰願意來住?」他認為,海岸開發利基不多,可是卻很適合做生態教室。

一沙一世界

專一研究螃蟹生態、皮膚被陽光烤得紅褐的劉烘昌說,人們也許覺得這樣的地方,若保持自然面貌,既無生產力,又不能幫地方政府賺錢;「可是小朋友卻覺得螃蟹可愛極了」,新竹許多小學常在此進行生態教學,劉烘昌是最佳的生態老師,「帶小朋友來此看螃蟹,要回去了,連叫都叫不動,好久都無法將他們集合起來。」

但螃蟹卻不只是好玩而已,在潮間帶,由於鹽份高,適合生存的生物種類不多;但由上游沖刷而下的有機質源源不絕,食物豐富,生存其間的生物往往數量龐大。尤其成千上萬的小螃蟹,迴游到大海上,大部分都成為其他海洋生物的食物來源。

潮間帶的螃蟹,是食物鏈中重要的初級消費者,在生態系裡扮演著重要角色。他們將污染物質分解、轉化為無機物,再隨著潮水回到大海供藻類食用,進而餵養魚類,人們遂能享用豐富的漁業資源。

雖然在香山海埔地開發的公聽會上,劉烘昌仍努力為螃蟹請命,提出螃蟹對人類的意義,但他卻已不奢望大人們還會留下一塊天然海岸,讓下一代自己決定怎麼使用。

海角一樂園

「以後我就到沒有人的荒島上做研究好了」,他說,有很多陸蟹都分佈在海島上。例如澳洲聖誕島上有一種陸蟹,多到上億隻,每年大遷移,壯觀至極,「如果可以在荒島上做研究,螃蟹的天敵就我一個人。」

果真如此,劉烘昌也是最瞭解螃蟹,卻最沒有殺傷力的「天敵」了。

〔圖片說明〕

P.18

新竹香山海岸今年底將填土造陸一千公頃,若潮間帶消失,圖中海和尚成群結隊的景象,也將盛況不再。

P.20

景緻看來單調的沙地,其實充滿生機,研究螃蟹的劉烘昌,常在此一待幾個小時。(鄭元慶攝)

P.22

直來直往,「兩頭不尖」的海和尚,不畏生人,常成群由洞中湧出,如「螃蟹雄兵」一般。圖中的螃蟹幼蟲,還需蛻殼一次,才會出落成小螃蟹的模樣。

P.24

劉烘昌在新竹香山海岸調查,記錄到卅幾種螃蟹,退潮後的沙地,布滿螃蟹鑿洞後遺留的泥球。圖左上至下為白扇招潮蟹、兵蟹、臺灣厚蟹,,右圖為幽靈蟹,螯上有一磨擦頭部即會出聲的發聲器,與背上有一笑臉的網紋招潮蟹。

相關文章

近期文章

EN

The World in a Grain of Sand: Liu Hung-chang and Crabs

Chang Chin-ju /photos courtesy of courtesy of Liu Hung-chang /tr. by Jonathan Barnard

While man has caused a steady loss of coastal land and has numerous development plans in the works for the shorelines, along the coast of Hsinchu a young scholar has been taking one step at a time in his research on coastal ecologies.

Many people see the benefits of developing the Hsiangshan coastline with industrial and residential zones. But he sees something else.


When the tide is receding in Haishanchuan Ao, a small bay near the Hsiangshan coast of Hsinchu, people leave deep impressions of their footprints on the soft and level sands--but only after little creatures have already left a myriad of their marks.

Creatures on the edge:

With the peaceful sound of distant waves, this stretch of land seems so featureless and tranquil. It is in fact teeming with life, full of colorful small crabs. With red and yellow bodies, fiddler crabs vanish back into their holes when sound or movement announces the approach of other creatures. Ghost crabs put their feet on the edge of their holes to stake out their realms. Known as "sea monks" in Chinese, soldier crabs, which look like pearls, recklessly rush out of their small holes in the sand, flickering silver-blue under the sun.

For the past two years, Liu Hung-chang, a graduate student at National Tsing Hua University has come to this piece of land rarely visited by people to record some 30 kinds of crab. Among these are silver-colored soldier crabs, whose numbers are greatest. When the tide is out, they band together into dozens--even hundreds--of groups. Here for hours at a time, Liu sometimes feels as if they are ambushing him on all sides.

But these "crab armies" may be marching on their last campaigns.

"When I was in National Chunghsing University, in the mountains near Taichung along the Tsaohu River, I conducted investigations on river crabs. In the mountain streams, there are numerous shrimps and crabs. I could record more than five hundred river crabs a night. Ponds would be full of the light emitted from shrimps' eyes. It was beautiful, like the Milky Way. But now the Water Conservancy Bureau is planning to build a dam on the Tsaohu River, preparing it to be used as Taichung's future source of drinking water. In the future, as the river ecologies change, it will be hard to predict how this will affect the river shrimps and crabs," Liu explains. "Then when I enrolled in the doctoral program at National Tsing Hua University, I came to Hsiangshan to perform research on eulittoral zone crab species, and now there is a plan to make new land from the sea with land fill. The targets of my research are like the natural environment equivalents of people on the edge; their space is easily disturbed by the tentacles of development."

Crabs by the seashore:

The tidal land at Hsiangshan is one of a string of areas that have recently been targeted for development by the government. In all, the provincial government hopes to wrest some 1000 hectares of land from the sea.

But the eulittoral zone, a 500 to 2000 meter strip along the seashore, is the area with the most Taiwan fiddler crabs, a species unique to Taiwan. According to research carried out by National Taiwan Ocean University and Liu Huang-chang, many species of crab were spread widely throughout Western Taiwan's tidal flats, but as the shores have been eroded and the beaches polluted, the once abundant seashore creatures have been rapidly declining. Among such rivers in central Taiwan as the Lukang, Tatu and Houlung, the Lukang has almost no eulittoral zone left. Because of a newly built thermal power station, the mouth of the Tatu river has been severely damaged. If you want to find groups of fiddler crabs and soldier crabs, whose numbers are the largest of all, you'll have to go to Hsiangshan.

At the beginning of this year, a Korean expert in shoreline animals came to Taiwan to do research. Staff of the Taiwan Provincial Museum brought him all over the province to carry out research. In other places the animals living in the sand were few and far in between, but when he got to the coast by Hsin- chu, he happily found abundant shoreline wildlife.

Resolving the secrets of life:

Crabs originated from the ocean but many have evolved and now live on the eulittoral zone where the land and sea meet. Because man also evolved from out of the sea, our interest in sand crabs and their physical and biochemical adaptability stems from an interest in ourselves. And so there is a lot of research being conducted around the world on land crabs.

Studying at the Life Sciences Research Center of National Tsing Hua University, Liu's interest in crabs extends beyond a search for the secrets of man's development. When he was in college, he had already become greatly interested in animal behavior. He climbed mountains and delved into the sea with researchers of fish and plants and selected crabs as his own long-term target for observation.

When others come to this coast, it may seem dreary and desolate. But for Liu Hung-chang and crabs, it holds an abundance of treasures.

There are different kinds of sand in the eulittoral zones: sand that easily absorbs water, fine sand, sticky sand, etc. Crab species have clear preferences. "Soldier crabs live in relatively wet sandy areas, and fiddler crabs dig their holes in relatively dryer mud, whereas ghost crabs live above the high tide line," says Liu Hung-chang, as if he is listing his family treasures.

The "rounded" sea monks:

In the eyes of Liu Hung-chang, each crab species is special. They all differ in behavior and appearance. Ghost crabs whisk along quick of foot. Male fiddler crabs have one small claw and one large one, giving them unusual proportions. In their movement and behavior, soldier crabs simply don't look like crabs. Rather than scurrying everywhere sideways, they move straight. "Not all crabs move sideways," says Liu, a long-time observer of crabs. "And not all of them have sharp double claws and a large mouth."

Liu conjectures that among the crabs of the seashore, soldier crabs were perhaps one of the earliest to leave the sea for the land. The earliest to get on dry land, their gills have changed, taking on some of the functions of lungs and allowing them to breathe on land. Their round shape has allowed for the expansion of the gill chambers; in this they differ markedly from the flat bodies of other crabs.

From April to June, clumps that look like small round chimneys appear on the sands. "This means that the baby soldier crabs have come on land," Liu explains. Because their eggs are bigger, a young river crab can develop entirely within the egg. For crabs in tidal zones, the young must return to the sea to live. After they shed their shells several times, they return to land where they dig holes to live in. They pile the excavated sand outside, and the result looks like small chimneys. A young crab develops into an adult in a year.

"But the age of a crab is more of a mystery than the age of a woman," Liu says. Crabs shed their shells every several months, and they thoroughly change their entire bodies, "completely making themselves over." Even their organs, such as the inside wall of their stomachs and intestines, are completely remade. And hence it is hard to tell the age of a crab by looking at its body. "We are ignorant about a lot of crab behavior."

Making a last stand with the crabs:

But how much more time does Liu have to try to under stand the crabs of Taiwan? According local government plans, in addition to such facilities as the Hsinchu airport, the shore will be the site of a tourist area that can hold 3 million visitors. Because the government estimates that the population will approach 1 million after Hsinchu County and City are merged, in the blueprints for development of residential areas, sewage treatment plants and garbage dumps have all been planned for the coast.

What effect would the landfill project have on the sand crabs? "Without the beach, the sea water won't be able to come up, and they will lack nutrients, food and water. How can the sand crabs, which need to go to the tide line to get their gills wet when the tide is rising, live on?" says Liu, feeling that the loss is as much his as the crabs. He is even more worried that after this land is developed, it will become like Nanliao, Hsinchu's only operating seaside amusement park, "covered with litter, its water yellow and dirty, its air full of thick smoke!"

Hsinchu is at the narrowest point of the Taiwan Strait. Because of topographical reasons, it is the windiest spot in all of Taiwan. In the winter, there are often sand storms along the coast. Once the county government began building a residential development on the mountain slopes, but the wind was so strong it couldn't be completed. In the winter, people simply can't stand the northeast winds. Liu, who has carried out detailed research on estimating the environmental effects of the industrial area, is baffled and says, "Who would be willing to live here?" While the profits to be made by building along the coast are few, the site is well suited to be an ecological classroom.

The world in one grain of sand:

Specializing in crab ecologies, Liu, whose skin has been tanned a deep brown, says people may feel that this place left in its natural state would be unproductive, unable to help the county raise money. "But little kids feel that crabs are extremely cute." Many Hsinchu elementary schools come here for their ecological studies programs. Liu is the best ecological teacher. "If you bring kids here to look at crabs, when you want to leave, you can shout all you want, but you won't be able to get the kids to line up."

But crabs are more than just fun. Because of a high salt content, few species are suitable for living in eulittoral zones. But because there are many organisms being washed out of the river mouths, the food is plentiful, and the populations of the species that do exist here are always large. This is especially the case for the countless number of small crabs. When they return to the sea, most of them become a major source of food for marine life.

The crabs in eulittoral zones are an important base-level consumer in the food chain. They play an important role in the ecological system. They break down pollutants, turning them into inorganic substances, which flow out with the tide to become food for algae, which become food for fish, which in turn end up on our dinner tables.

At the hearing for the landfill development plans at Hsiangshan, Liu did, of course, do his best to beg for mercy for the crabs, explaining the meaning they hold for people. But he knows it's beyond his power to get people to leave behind this chunk of natural coastline for the next generation to decide how to use.

Paradise by the sea:

"In the future, I'll go to some uninhabited island to do my research," he says. A lot of land crabs live on such islands. On Christmas Island off Australia, for instance, there is a colony of more than 100 million crabs of one species. Every year, during their migration, the sight is magnificent. "On an uninhabited island, I would be the crabs' one and only enemy."

Liu, though understanding crabs best, would make a pushover of a predator.

[Picture Caption]

p.18

At the end of this year along the Hsiangshan Coast of Hsinchu, landfill will be used to create 1000 hectares of new land. If the tidal areas are lost, so will the sight of solider crabs gathering together in their battalions.

p.20

A sand beach, which may seem like a dull and dreary place, is actually teeming with life. Liu Hung-chang, a researcher of crabs, can spend hours at a time here. (photo by Cheng Yuan-ching)

p.22

Marching back and forth, soldier crabs are rounded on both sides. Not in awe of men, they often gather in groups and stand guard in their holes, like "courageous crab soldiers." The crab larva in this picture still has to shed its shell one time before it looks like a young crab.

p.24

In carrying out his investigations on the Hsiangshan coast of Hsinchu, Liu Hung-chang has recorded more than 30 kinds of crabs. After the tide recedes, the beach is littered with the small clumps of sand that crabs have removed from their holes. On the left from top to bottom, there is a "white-fan" fiddler crab, a soldier crab, and a Helice formosensis. On the right is a ghost crab, which can create noise by rubbing its antennae against its head, and a "net" fiddler crab, with a characteristic"smiling face" on its back.

X 使用【台灣光華雜誌】APP!
更快速更方便!