Chiang Mai Journal of Science

     Territorial damselfish are herbivorous fish that help maintain algal diversity and abundance by aggressive territorial defense and algal farming. We investigated the effect of territorial damselfish on algal diversity and abundance on a reef at Ko Taen, Surat Thani Province, Thailand. Ten permanent patches (20 × 20 cm²) were set up inside and ten outside damselfish territory and monitored bimonthly. We found 22 macroalgal species with five dominant species: Polysiphonia sp., Padina minor, Ulva compressa, Gelidium pusillum, and Lobophora variegata. The abundance of Polysiphonia sp. was significantly higher inside damselfish territory than outside. In contrast, the abundances of Gelidium pusillum, Padina minor, and Ulva compressa were slightly higher outside the territory. It might be perhaps because their feeding behavior, territorial defense, and farming activities altered the benthic community. These damselfishes exclude other herbivorous fishes from their territories and remove unpalatable algae and maintain their algal food crop. For species diversity, there was no significant difference between algal species diversity outside and inside damselfish territories. Our results indicated that damselfishes have a strong effect on algal abundance and composition.