Jaruwan Mayakun and Anchana Prathep

pp. 653 - 663

Abstract

Diversity and abundance of macroalgae at Samui Island, Surat Thani Province, Southern Thailand
was investigated during rainy and dry seasons. Five study sites were chosen around the Island on the basis of
its high species richness and abundance. Applying a “Visual Census Method”, the abundance of macroalgae
in terms of percentage cover could be estimated. Thirty-four taxa of marine algae were found from the five
sites around the Island: Phra Yai, Sila-ngu, Hua-tanon, Ban Pang-ga and Taling-ngam. A total of thirty-four
taxa were identified during this study, comprising 1 Cyanophyta, 9 Chlorophyta, 10 Phaeophyta and 14
Rhodophyta. The brown alga, Sargassum polycystum, was widely distributed and found at all sites, while
Padina and Acanthophora were the most abundance species throughout this study. Sila-ngu and Hua-tanon
sites had the richest diversity of macroalgae during the dry season; 22 species and 20 species were found
respectively. This high diversity might be the result of greater habitat complexity, while only 2 species of macroalgae were found on the soft-bottom substrate at Phra Yai. A greater abundance of macroalgae was
found during the dry season which might be due to the combination of increasing light intensity and the
accumulation of nutrient run off during the rainy season. The algae, therefore, could have greater photosynthesis and grow later in the early part of dry season. Diversity of macroalgae, however, was 35 % less in
the last 18 years. This might be the result from increasing tourist activities in Thailand. Thus, marine conservation and management are urgent issues for the island. In addition, further intensive studies on macroalgae are also needed because they have received less attention when compared to other marine organisms
such as corals and fishes.