Wetland Ecosystem # 4 : Tidal Flats

Don Hoi Lot Tidal Flats : sustainable harvesting of razor clams

Presented by

Mr. Narong Veeravaitaya

16 November 2007 Tidal Flats • Coastal area is quite important for human being in term of a source of food and aesthetic values. • Anthropogenic effects due to population growth are major impacts to change characteristics of coastal ecosystem i.e. a port construction, pollutants releasing from inland. • Tidal flat is one of important habitats found in coastal area which is consisting of 3 mainly characteristics (sand flats, mud flats and rocky shore. • Tidal flats are intertidal ecosystem often found in the edges of land or near large estuarine. Tidal Flats (cont.)

• Tidal flats are formed by coastal sedimentation processes in which sediment-rich waters enter shallow or sheltered places where the sediments are easily deposited. • Tidal flats usually are without vegetation due to a high degree of morphological dynamism (caused by erosion and deposit processes) and tidal water dynamic. • Tidal flats are quite important for marine habitat; purification of pollutants; fishery resources; feeding habitat for waterbird. • Human activities are the major threats affecting tidal flats. Don Hoi Lot

• Total area of tidal flats in the Inner Gulf of Thailand are about 23,500 ha. • Don Hoi Lot locates at the mouth of Mae Klong River in the Muang District, Samut SongKhram province. • Don Hoi Lot is identified as tidal flat consisting of muddy sand which covers an area of 2,409 ha. • It can be divided into 5 sections of elevated sediment deposits covering 880, 464, 151, 845 and 69 ha. Don Hoi Lot • Don Hoi Lot was declared as Ramsar site since July 5, 2001 in which covers 87,500 ha. • Don Hoi Lot is important as high biodiversity, shorebird stopover site , a vast area of tidal mudflats , a significant habitat of Razor clams, important for tourist area. • Hoi Lot is the Thai name of Razor clam and nowadays its population reduces rapidly due to several causes such as over harvesting, waste water from inland.

Biodiversity in Don Hoi Lot • Bird: found at least 18 species • Invertebrate found at least 42 species • Approximately 9 species of mollusks • Found at lease 16 species of Phylum Arthropoda • a rare type of natural wetland for Thailand, an extremely productive location for the Razor clams. Biology of Razor clams Life history and distribution • Phylum , Class Order Eulanmellibranchia Family • Found several genuses ; Solen, and Solecurtus • Solen has a long, thin and narrow shell • 3 species of Razor clams along the coast of the Andaman Sea (Solen brevis Gray,1832, S. grandis Dunker,1861,and S. exiguous Dunker,1862 ).

Life history and distribution (cont.)

• 6 species were recorded in the Gulf of Thailand : S. corneus Lamarck,1818, S. regularis Dunker, 1861, S. strictus Gould, 1861, S. malaccensis Dunker, 1862, Solen sp.(1) and Solen sp.(2).

• 4 species of razor clams found in Don Hoi Lot; Solen strictus Gould,1861, S. thailandicus Cosel, 2002 (the formal name is Solen sp.(1) ) , S. corneus Lamarck,1818 and S. regularis Dunker,1861 (Tuaycharoen and Kongrabeab ,2005) SolenSolen corneuscorneus LamarckLamarck,, 18181818 SolenSolen strictusstrictus Gould,1861Gould,1861

•• SolenSolen RegularisRegularis Dunker,Dunker, 18611861 Growth and Density • Density of razor clam declined rapidly in 1996- 1997 (4.6±3.7 individual/m2) comparing with their density in 1994-1995 (49.86±37.38 individual/m2) • Biomass of Razor clams in Don Hoi Lot between 1992-1994 had 5,693.87 tons, 5,224.87 tons and 6,503.37 tons respectively. • Average growth rate of Razor clams was 1.2 mm./month. • In case of increment of their weigh aging from 6-9 months was 1.02-1.15 g./month and 10-37 months was 0.07 g./month. Graph 1 Density of Razors clams in Don Hoi Lot from 1980-2004 80 65.51 49.5 60 26.8 26.88 40 18.77 10.2 7.95

individual/m.sq 20 4.1 3.72 0 1980- 1986- 1988- 1990- 1994- 1996- 1999 2000 2003- 1981 1987 1989 1991 1995 1997 2004 year Food and feeding habit

• Razor clams live buried vertically in the sand ranging from 1 – 12 inches deep. • During high tide, they live near soil surface ( 1 inch deep) in order to filter their food such as plankton and detritus suspending in water Reproductive system

• The spawning period were found during December to April and June to October. • the mature gonad were found in the clam length at least 42.4 mm. • The razor clams had the sexual ratio 1:1 • Fertilized eggs had diameter of 56-80 micron Environmental Factors affecting to Razor clams Physical factors • Distribution of Solen regularis is limited within the sandbar where the average sediment grain size was 0.125 mm.

• Distribution of razor clam did not depend on amount of organic matter because they were filter feeder.

• Razor clam could be found at high density when the percentage of sand was more than 80 % in the soil composition and lower density could be found in muddy soil. Chemical factors • Chemical factors that had effects on density and size of Razor clams were amount of dissolved oxygen, nitrite, ammonia, water temperature and pH. • pH reached 9.1 , the clams would died. • Nitrate and phosphate show moderately positive correlation with abundance. Biological factors • Population density of razor clams (Solen regularis and S. vitreas ) and their breeding season were related to abundance of phytoplankton. (Eutetramorus and Teilingia in phylum Chlorophyta).

• Plankton in genus Coscinodiscus, Planktoniella, Nitzchia and Heterothrix found in their stomach Extent of threats

• Encroachment of mangrove forests for aquaculture area • Water pollution from inland. • Excessive harvest of Razor clam and use of quick lime in the harvest which have led to significant reduction in their population. • Impacts from other development projects Existing national plans

• Don Hoi Lot is designated as a Cockle conservation area where use of every fishing tool is prohibited. • Mangrove forests in Muang and Ampawa Districts of Sumut Songkram, covering total area of 10,934 ha have been conserved by Royal Forest Department. Mangrove area Large tidal flats Using lime and stick to catch Razor clams

Video

Horseshoe crab Polychaete or Worm

Other fishery activities in Don Hoi Lot

Tourist

Thank you for your attention