Taitung hermit crabs found using plastic waste as shells
三仙台悲情寄居蟹 學者痛心：牠們幾乎都背著垃圾殼
While studying hermit crabs in Taitung County’s Sanxiantai area last month, Professor Chiu Yuh-wen of National Cheng Kung University recorded 14 Coenobita brevimanus — a species of land hermit crab — using discarded plastic as their shells. Even when they were able to find shells, the shells were either broken or too small to provide proper coverage and protection.
Chiu says that this absurd situation is due to a shortage of available shells. Many coastal hermit crabs have similar problems, differing only in degree and the nature of the substitutes available. Some hermit crabs in Tainan, for example, also have trouble finding suitable shells, says Chiu, but they do have those of Achatina fulica — a type of African land snail — available, as they inhabit areas in Tainan near farmland and windbreaks. However, unlike the hard shells of shellfish, snail shells are too thin, fragile and are easily broken.
According to Chiu, hermit crabs have trouble attaching themselves to the smooth inner side of the plastic cover. Also, unlike the natural shells of shellfish, plastic caps and broken shells do not provide effective cover for their pincers, so they have limited defensive effect. As a result, hermit crabs using plastic caps and broken shells cannot effectively defend themselves against predators, and neither do the caps guard against evaporation of body moisture, let alone provide adequate protection for females during the breeding season, Chiu says.
Chiu says that shellfish are used for human consumption, and restaurants are not returning the empty shells of edible shellfish to the shores. Consequently, there is an insufficient supply of shells for hermit crabs.
The most urgent task at the moment, says Chiu, is to find shells for hermit crabs. He says that members of the public could collect shells and place them at the entrance of Sanxiantai, and encourages visitors to do so. The long-term solution, however, lies in sustainable conservation of the habitat, reducing pollution and proper fishery resource management.
(Liberty Times, translated by Lin Lee-kai)
A Coenobita brevimanus, a species of land hermit crab, uses a plastic bottle cap as a substitute for a natural shell.
這隻短腕陸寄居蟹，無殼可背，改背塑膠瓶蓋。
Photo courtesy of Chiu Yuh-wen
照片：邱郁文提供
A land hermit crab carries a broken shell.
短腕陸寄居蟹背著已破損的殼。
Photo courtesy of Chiu Yuh-wen
照片：邱郁文提供
Although this land hermit crab managed to find a natural shell, it is too small to provide adequate coverage and protection.
這隻短腕陸寄居蟹雖有殼可背，卻是無法蔽體的小殼。
Photo courtesy of Chiu Yuh-wen
照片：邱郁文提供
Left: A land hermit crab in Tainan uses a shell from a type of African land snail.
台南的寄居蟹改背非洲蝸牛殼。
Photo courtesy of Chang Yuan-mou
照片：張原謀提供
成功大學教授邱郁文上月到台東三仙台調查寄居蟹生態，記錄到十四隻短腕陸寄居蟹，竟然背的幾乎都是垃圾塑膠殼，而少數有殼可背的個體，不是殘破不堪的破殼，就是無法蔽體的小殼。
邱郁文表示，寄居蟹的殼源不足，造成塑膠製品成為荒謬的替代品，很多海岸的寄居蟹也都有類似的問題，只是嚴重程度及面臨的問題不一樣。他以台南的寄居蟹為例，一樣面臨無合適的殼可背的困境，但台南這裡因靠近農地、防風林，有非洲蝸牛的殼可以代替，但蝸牛殼又薄又脆弱易破，對寄居蟹來說遠不如堅硬的螺殼理想。
他說，塑膠蓋光滑的內側，導致寄居蟹無法以腹肢穩定的勾住；而塑膠蓋和破損的殼，無法讓牠們的大螯如在天然螺殼中一般， 可有效形成密閉的防守位置，因此除了無法有效禦敵外，更無法防止身體水分蒸發，更遑論母蟹在繁殖期可以順利抱卵釋幼。
邱郁文表示，因為螺貝類面臨人類獵捕的壓力，這些可食用的螺貝類送到餐廳後，吃完的殼並不會回到海岸，而造成寄居蟹的殼源不足。
他說，目前最迫切的，就是得先幫牠們找個殼。建議可在三仙台的入口設置貝殼募集點，再鼓勵遊
客送到現場。而治本得做好棲地環境維護，削減污染以及漁業資源管理的永續經營，這得長時期投入才能達成。
（自由時報記者蔡文居）
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