Abstract
The photosymbiotic ascidian fauna at Changi Beach, Pulau Semakau, Sentosa and St. John’s Island, Singapore were surveyed. A total of five species, Diplosoma simile, Lissoclinum bistratum, Lissoclinum punctatum, Lissoclinum timorense and Trididemnum cyclops, were recorded, with Lissoclinum timorense and Trididemnum cyclops being newly recorded in Singapore. However, no photosymbiotic species were found at Changi Beach probably due to the polluted waters in the region. Coastal development has caused Singapore waters to become turbid, leading to decrease in suitable habitats for photosymbiotic ascidians. Clean waters in Pulau Semakau probably provide a better environment for the growth of photosymbiotic ascidians and this area has a greater variety of these ascidians than the other areas in Singapore. Each of the five species has also been recorded in the Ryukyu Archipelago (Japan) and three species (Diplosoma simile, Lissoclinum bistratum and Trididemnum cyclops) have also been recorded in Taiwan.
Highlights
Photosymbioses have been known in some colonial ascidians of the family Didemnidae in tropical and subtropical waters
Five photosymbiotic ascidians were recorded in the present survey, including three species previously observed by Kott (1982) and two new records in Singapore
John’s Island and two species in Sentosa, but no photosymbiotic species were found at Changi Beach
Summary
Photosymbioses have been known in some colonial ascidians of the family Didemnidae in tropical and subtropical waters. Photosymbionts such as Prochloron and Synechocystis are cyanobacteria (see Parry and Kott 1988; Lewin and Cheng 1989; Hirose et al 2009b). The biogeographic survey of photosymbiotic didemnids in Ryukyus has recorded the current distribution range for each species. Taiwan (21°-25°N) is positioned close to the southernmost island group of the Ryukyu Archipelago (i.e., the Yaeyama Islands), and 10 species in total were recorded from Kenting (southern Taiwan) and Lyudao (off the southeast coast of Taiwan), but no photosymbiotic species were found in Keelung (located in northern Taiwan), probably due to the cold surface water in winter Five photosymbiotic didemnid species were reported as additions to the marine benthic fauna of Singapore
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