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The sea area of Dongsha Atoll National Park consists of rich marine resources, but the marine life 「on the land」-Coenobita plays an important role in marine and terrestrial ecosystems in Dongsha Atoll National Park!

In terms of terrestrial ecosystem, Coenobita are amazingly good partners of beachfront terrestrial plants! Coenobita usually forage for fruits or seeds, thus they are categorized as herbivorous terrestrial crabs. They are also responsible for spreading seeds of terrestrial plants. In addition, the biggest population on Dongsha Island-Coenobita rugosus』 ploughing behavior during foraging can fertilize the soil and thus is helpful for plant growth. Moreover, their scavenger role is also helpful to accelerate the decomposition of organic debris.

In terms of marine ecosystem, every year from May to September during the Summer season is the fertilization season of Coenobita. They will migrate from the inland to the beachfront for their 「release of larva」 (i.e. release larvae instead of ova in the sea). These tens of thousands of plankton also nourish the sea area of Dongsha Island. Considering Spring and Summer are also fertilization seasons for many marine lives, the simultaneous release of larvae increases the opportunities of survival for each other as well.

In Dongsha Island, the biggest population among Coenobita is Coenobita rugosus. Their traces are almost all over the whole island. Especially a cluster of Coenobita rugosus can be found foraging about in the seagrass debris nearby the stele and South coast in Summer time on Dongsha Island. Recently we found that the body size of Coenobita rugosus on Dongsha Island is significantly larger than the same species of Coenobita in Taiwan main island and some surrounding islands. The underlying ecofactors contribute to the differences of body size are still under investigation.

Coenobita rugosus foraged about in the seagrass debris. (Photoed by Chia-Hsuan Hsu) A cluster of Coenobita rugosus foraged along with the shore in summer time.(Photoed by Chia-Hsuan Hsu)
Coenobita rugosus foraged about in the seagrass debris. (Photoed by Chia-Hsuan Hsu) A cluster of Coenobita rugosus foraged along with the shore in summer time.(Photoed by Chia-Hsuan Hsu)


In addition to Coenobita rugosus, the traces of Coenobita violascens, Coenobita brevimanus, Coenobita cavipes and Birgus latro were also found in Dongsha. However, the amount of other types of Coenobita is greatly different from the amount of Coenobita rugosus.

The color of Coenobita violascens is more like royal blue, and their numbers in the region of Taiwan main island are quite rare. They often become the targets of businessmen due to their rarity and beauty. However, the population in Dongsha Atoll National Park, a natural environment without artificial disturbances remains stable. The size of Coenobita brevimanus is the 2nd largest among Coenobita in addition to Birgus latro. Coenobita brevimanus is rather ferocious. There was a researcher who was injured by its claws and required to be sent to hospital for treatment. Hence, do not overlook the threat of this pair of claws! Coenobita cavipes usually inhabits in the deep inland forest; however, only a few were also found in Dongsha Island. In addition, Birgus latro is also an occasional visitor that you can only obtain with luck on the island.

Coenobita violascens is often found on Pandanus tectorius. The natural background can bring out its beauty.
Coenobita violascens is often found on Pandanus tectorius. The natural background can bring out its beauty.

Coenobita violascens in royal blue Coenobita brevimanus

Coenobita violascens in royal blue

Coenobita brevimanus

Therefore, we not only realized the importance of Coenobita on the ecosystem, but also discovered the beauty of them. Even though there are many Coenobita existing on Taiwan's main island and the surrounding islands, we tend to go pass rapidly and ignore their existence. Next time, try to stay still and observe it carefully, I believe that there will be more discoveries.


This article was written by Master's student Chia-Hsuan Hsu from National Sun Yat-sen University College of Marine Sciences.

 

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