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A coral reef in waters around Orchid Island (Lanyu, 蘭嶼) is expanding, but rampant growth of excavating sponges could endanger its existence, an environmental group said.
Taiwan Environmental Information Association members and volunteers on June 9 and June 10 dived near the island to document the conditions of the reef.
Living coral along the island’s eastern and northern coastlines cover between 43.75 percent and 65 percent of the reef, association member Lin Yu-chu (林育朱) said, adding that when coral coverage surpasses 50 percent, the environment can be regarded as a beneficial habitat.
However, the group found that excavating sponges of the genus Cliona have expanded their coverage to 17.5 percent in waters near Beauty Rock (玉女岩), a popular attraction in the island’s north.
Ubiquitous in the Caribbean, the excavating sponges compete with coral for living space on the sea floor, Lin said.
Sponges’ coverage around Orchid Island was less than 5 percent, but has been growing quickly as of late, particularly the excavating sponges, she said.
Excavating sponges used to only be found near Green Island (綠島) to the north, Lin said, adding that this is the first time they have been found near Orchid Island.
Sponges live on microorganisms and organic particles, and they prosper in waters with high salinity, National Penghu University of Science and Technology associate professor Huang Yu-sheng (黃俞升) said.
Excavating sponges ooze an acidic substance that can erode the calcium carbonate in coral reef, he said, adding that the phenomenon is part of nature’s biogeochemical cycle.
If the activities of the coral and excavating sponges can achieve a balance, the sponges will not affect the area’s ecology, he said.
The association expressed concerns about the potential effects of excavating sponges on coral and the area’s ecology, but said that long-term observation is needed before any conclusions can be reached.
