Zoological Studies

Vol. 58, 2019

(update: 2020.05.12)

Latitudinal Difference in the Species Richness of Photosymbiotic Ascidians Along the East Coast of Taiwan

Euichi Hirose1,* and Yoko Nozawa2


1Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan. *Correspondence: E-mail: euichi@sci.u-ryukyu.ac.jp (Hirose)
2Biodiversity Research Center, No. 128, Academia Road Sec. 2, Nankang, Taipei 115, Taiwan

(Received 29 January 2020 / Accepted 5 May 2020)
Communicated by Benny K.K. Chan

Some didemnid ascidians harbor cyanobacterial symbionts, and this is the only obligate photosymbiosis system known in chordates. These photosymbiotic ascidians are found only in tropical and subtropical waters, probably because the photosymbionts are vulnerable to low temperatures. We surveyed the photosymbiotic ascidian fauna on the east coast of Taiwan. Present and previous reports show that 13 species have been recorded in Taiwan, and the species richness and composition is different in 5 areas along the east coast. On the middle-east, southeast, and south coasts, 5 or more species have been recorded, whereas only 1 species has been found on the northeast coast, and no species have been recorded on the north coast. The gap in species richness is probably related to the course of Kuroshio Current that goes from south to north along the east coast of Taiwan but changes to an easterly direction off the northeast coast. Increase in water temperature due to global warming could cause northward expansion of the distribution ranges of these ascidians in future. Hence, the photosymbiotic ascidian fauna could be an environmental indicator in subtropical, shallow water, and the present study provides a basic dataset of the current status of photosymbiotic ascidians in Taiwan.

Key words: Biogeography, Coral reef, Didemnid ascidians, Cyanobacterial symbiosis, Latitude, Species diversity.

Citation: Hirose E, Nozawa Y. 2020. Latitudinal difference in the species richness of photosymbiotic ascidians along the east coast of Taiwan. Zool Stud 59:0t. doi:-.