Transition of Species Composition, Abundance and Distribution of the Gracilarioid Seaweeds (Rhodophyta) in Coastal Areas of the Upper Gulf of Thailand Observed from 2004 to 2007

Abstract

Observations of red gracilarioid seaweeds were performed between 2004 and 2007 in several areas along the upper Gulf of Thailand at Ang Sila, Sri Racha harbor and Ko Si Chang in Chonburi, Ban Phe in Rayong, Laem Tien, Laem Sok and Ao Cho in Trat, Bangra Noi in Phetchaburi, Ta Mong Lai and Wanakorn beach in Prachuap Khiri Khan and at Thung Wua Laen beach in Chumphon Province. Changes in species diversity and biomass, as well as environmental factors, were investigated at three-month intervals covering both the monsoon and dry seasons. Eight species of gracilarioids that are distributed on west and east coasts of the upper Gulf of 7KDLODQGZHUHLGHQWLÀHG_x005F_x000F_LQFOXGLQJHydropuntia edulis,*UDFLODULDFKDQJLL_x005F_x000F_*_x005F_x0011_ÀUPD_x005F_x000F_*_x005F_x0011_VDOLFRUQLD_x005F_x000F_ *_x005F_x0011_UKRG\PHQLRLGHV_x005F_x000F_*_x005F_x0011_UXEUD, G. tenuistipitata, and *_x005F_x0011_PLQXWD_x005F_x0011_7ZRXQLGHQWLÀHGVSHFLHVZLWK IRUPVVLPLODUWRNQRZQVSHFLHVZHUHDOVRIRXQG_x005F_x0011_7KHÀUVWZDVVLPLODUWRGracilaria (and named Gracilaria sp.) and was collected from Trat Province, while the second was similar to Gracilariopsis sp. (cf. EDLOLQLDH) and was collected from Chonburi Province. The gracilarioids occurred mostly in Chonburi and Trat Provinces. G. salicornia was dominant among the collected specimens. The present observations suggest that there have been remarkable changes in the coastal environment along the upper Gulf of Thailand. Most of the study sites had highly turbid and nutrient-rich seawater. The algal biomass decreased when the concentration of dissolved inorganic nitrogen (DIN) and turbidity were extremely high during the dry season. A decrease in seaweed species diversity was observed: in particular species of Gracilaria have disappeared from Ban Phe and decreased at Laem Tien, Laem Sok and Ao Cho. The loss of seaweed beds, particularly in Trat Province, was caused by deterioration of the coastal environment.