The Effects of the 2004 Tsunami on the Seaweed and Seagrass Community at Talibong Island and Nearby Trang province, Thailand Anchana Prathep 1 *, Piyalarp Tantiprapas 2, Bongkot Wichachucherd 1 Ajchara Chotithammo 1 and 1 Seaweeds and Seagrasses Ecology Research Unit, Centre in Biodiversity of Penisular Thailand, Department of Biology, Faculty of Science, Prince of Songkla University, Songkhla, Thailand, 90112 2 Phuket Marine Biological Station, Ao Makham, Amphoer Meung, Phuket, Thailand, 83000 *Correspondence e-mail: anchana.p@psu.ac.th Abstract We assessed the effects of the tsunami on seaweeds and segrasses communities at Talibong island and nearby Trang province, Thailand, 5 days after the 26 th December Tsunami. The assessment showed that the Tsunami directly decreased the abundance of large seaweeds and seagrasses, but the damages were little in the area. However, a greater amount of sediment was likely to cause greater damage to the marine benthic organisms including corals. A 9.0 magnitude earthquake occured on the seafloor near Aceh in northern Indonesia, India Ocean, generating a huge tsunami wave on 26 December 2004. Millions of gallons of water were forced up by the earthquake, creating a massive wave, which then traveled for thousands of kilometers. The tsunami hit the coasts of South Asia, Southeast Asia and even as far as South Africa. The force of the tsunami 1
was great; it flattened buildings along the coast line and carried them miles inland, and overall caused great damage to life and property. We assessed the effects of the tsunami on the seaweed and seagrass communities, at 7 sites around Talibong Island and nearby Trang Province, Thailand (Figure 1). The island was recently designated Ramsar site no. 1182 with connection to Had Chao Mai Marine National Park and Trang River Estuaries (http://www.ramsar.org). Talibong Island supports extensive seagrass and seaweed habitat as well as many marine organisms, including migrating seabirds at Leam Chu Hoi and the important endangered dugong (Dugong dugon). In recent years, the largest group seen was 53 dugongs in the seagrass beds southeast of the Talibong Island (Hines, 2002). The island is known to be the healthiest and most richly diverse seagrass ecosystem in Thailand and is home to eight species of the twelve species seagrasses found in Thailand (Changsang and Poovachiranon, 1994; Poovachiranon and Changsang, 1994). Also, there are various corals such as Porites, Favites, Turbinaria and Acropora, covering an area of 2.38 km 2 along the west to the south coasts of island (Pongsuwan, 1999). In addition, we have been monitoring the seaweed community around the island for almost a year; we found more than 18 species of seaweeds, with Laurencia composita, Padina spp., Turbinaria spp. and Sargassum spp. Caulerpa taxifolia the dominant species (Prathep and Tantiprapaj, 2003). We also recently set up 15 permanent monitoring plots around Talibong Island to monitor the seaweed community there 2
Figure 1. Study sites at Talibong island and nearby Trang province, Thailand Talibong Island was hit by the tsunami; where there were lost of homes, boats and other properties. We assessed the effects of the tsunami on the seaweed community at our permanent plots as well as seagrasses and other marine organisms nearby the study sites, five days after the tsunami catastrophe, from the 31 st December 2004-3 rd January 2005. We found that: 1) where there was no direct hit from the force of the tsunami (sites 1, 2, 5 and 7), the wave force would stir up the sediment from the sea floor. 3
This increased the amount of sediment in the water column, thus increasing the turbidity which decreased the ability of seaweeds and seagrasses to photosynthesize, but this occurred only for a short period of time. The suspended sediment then sank slowly and cover the seaweeds and seagrasses including other marine benthic organisms, but there was less impact on the seaweeds and seagrasses. 2) where an area was directly hit by the Tsunami (site 3, 4 and 6), the very strong wave currents stirred up greater amount of sediment into the water column. The strong current could directly wash the more fragile seaweeds, e.g., Laurencia composita Yamada, Padina spp., Tubinaria spp and some seagrasses, e.g., Syringodium isoetifolium (Ascherson) Dandy, Thalassia hemprichii (Ehrenb.)Aschers. and even some of Enhalus acoriodes (L.F.) Royle onto the shoreline or floating in the water (Figure 2). Often, the other tall macrophytes like Sargassum spp. or Enhalus acoroides (L.F.) Royle were cut and washed up to the shoreline, leaving only the stems on the substrate. The tsunami caused severe damaged to seaweeds community, with a 30% - 60% decrease in seaweeds in our permanent plots; also there were greater sediment within the plots. 4
Figure 2. Many of Enhalus acoriodes (L.F.) Royle plants were washed up to the shoreline. Moreover, where there was a steeper slope (site 3), there was a greater amount of sediment accumulation and damage. The sediment had buried benthic macroalgae, e.g. Peyssonnelia boergesenii Weber Bosse in Børgesen, Gaxaula, Amphiroa, Gelidium, as well as crustose red algae including sponges and corals, causing loss and death of organisms (Figure 3). We observed some marine benthic organisms buried by 20-25 cm of sediment at this site, while some white bacteria colonies were observed covering the anoxic sediment over some dead marine organisms (Figure 4). 5
Figure 3. Peyssonnelia boergesenii Weber Bosse in Børgesen and some red crust algae were buried under the sediment. Figure 4. Great area of white bacteria colonies covered the anoxic sediment over some dead marine organisms. 6
The damage was rather severe at our study sites especially to the benthic marine organisms and fragile seaweeds. The strong rhizome of seagrasses could mostly hold the plants against the force of the tsunami. Thus we found only minor damage to the seagrass community. However, further investigation is still needed over a larger scale and over the long term. Such monitoring would allow us to understand more about the succession and recruitment of marine organisms after catastrophes such as the recent tsunami. Acknowledgements The project was funded by Prince of Songkla University, Thailand. Thanks to all the Seaweeds and Seagrasses Ecology Research Unit, Centre in Biodiversity of Penisular Thailand; thanks also to Professor Larry Liddle and Mr. Charles Benzies. Thanks also to Professor Frederick T. & Cathy Short for help with the manuscript and suggestions and encouragement. References Changsang, H. and Poovachiranon, S. 1994. The distribution and species composition of seagrass beds along the Andaman sea coast of Thailand. Phuket Mar. Biol. Cent. Res. Bull. 59:43-52 Hines, E. M. 2002. Conservation of the Dugong (Dugong dugon) along the Andaman Coast of Thailand: An Example of the integration of conservation and Biology in Endangered Species Research. Ph.D. Thesis. The University of Victoria. 7
Http://www.ramsar.org Pongsuwan, N. 1999. Coral maps in Thai water. Vol. 2 Andaman sea. Coral resources management. Department of Fisheries. World of Set. Phuket. Poovachiranon, H. and Changsang, H. 1994. Community structure and biomass of seagrass beds in the Andaman sea. I Mangrove associated seagrass beds. Phuket Mar. Biol.Cent. Res. Bull. 59:53-64 Prathep, A. and Tantiprapas, P. 2003. Preliminary Study on Seaweeds Diversity at Talibong Island, Trang Province, Thailand. Poster presentation: NRCT-JSPS Joint Seminar on Coastal Ocenography 14-16 December, 2003. Chaingmai, Thailand. 8