Intertidal Seashell and Land Snail survey of Dongsha Island

Project Duration	2011-12-31 ~ 2012-12-30
Research Title	Intertidal Seashell and Land Snail survey of Dongsha Island
Contracted Organization	Kaohsiung Medical University
Principal Investigator	Chiu Yu-Wen
Co-Principal Investigator	Hsieh Pao-Sen
Project Participants	Tsai Cheng-Da, Huang Yen-Ming, Yen Yi-Chun, Su Chun-Yu, Lin Yi-Ju, Cheng Tzu-Yun, Hung Yun-Hsuan
Keywords	Dongsha Island, intertidal zone, habitat, mollusks, terrestrial snails
Abstract	1. Background Previous studies on Dongsha Island mainly focused on birds, corals, and fishes, particularly within the atoll and lagoon areas. Although extensive seagrass beds occur around Dongsha Island, surveys of mollusks in seagrass habitats and on land have been relatively limited. Therefore, this study focused on intertidal and terrestrial molluscan resources and produced ecological map brochures and survey manuals to support environmental interpretation and conservation education in the national park. 2. Results Quantitative and qualitative surveys were conducted in five types of intertidal marine habitats and two types of terrestrial habitats over five field surveys. A total of 141 mollusk species from 60 families were recorded. Among them, 123 species from 51 families were found in marine intertidal habitats, and 19 species from 9 families were recorded in terrestrial habitats. Two terrestrial species—the African giant snail (Achatina fulica) and Macrochlamys hippocastaneum—were identified as invasive species. In terms of relative abundance per unit area, the three most dominant species were: - Saccostrea mordax (20.72%) - Euplica scripta (20.60%) - Littoraria undulata (11.07%) Among habitat types, seagrass beds supported the highest species richness (65 species from 37 families), while mangrove habitats had the lowest richness (6 species from 3 families). Breakwater block habitats exhibited the highest abundance (224 ind./m²) and biomass (1938.03 g/m²), whereas mangrove habitats had the lowest abundance (6 ind./m²) and biomass (2.67 g/m²). ABC curve analysis of abundance and biomass indicated that mollusk communities in seagrass beds and sandy habitats experienced significant disturbance during the year, gradually becoming dominated by one or a few small-sized species. In terms of diversity indices, seagrass habitats had the highest richness but lowest evenness; sandy habitats had the highest overall diversity; mangrove habitats had the lowest richness and diversity but the highest evenness. For terrestrial snails, Macrochlamys hippocastaneum showed seasonal variation in size distribution: individuals with shell widths of 0.5–1.99 cm were more abundant in winter (December), while larger individuals (1.5–2.49 cm) were more common in late spring (May). An ecological map brochure and a basic survey manual for intertidal and terrestrial mollusks of Dongsha Island were produced as appendices. 3. Major Recommendations Immediate Recommendation (1) Initiate planning for a biological specimen collection repository within Dongsha Atoll National Park. Physical specimens should be preserved and linked to species databases for research and educational display purposes. Long-Term Recommendations (1) Designate intertidal seagrass beds as priority long-term monitoring habitats. The dominant and widely distributed species Euplica scripta is recommended as an indicator species. (2) With potential future public access and implementation of ecological education and guided tours, continuous long-term qualitative and quantitative monitoring of habitat communities is essential to understand seasonal population dynamics and ecological trends.