--------- Scientific report, 2015 UNESCO/MAB Young Scientists Awards, Vietnam --------- SCIENTIFIC REPORT MAB YOUNG SCIENTISTS AWARDS Outbreak of the Coral Eating Snails (Drupella spp.) in the Cat Ba World Biosphere Reserve, Vietnam – Looking at the habitat utilization and prey selection Prepared by: Nguyen Duc The Vietnam, November 2016 Outbreak of the Coral Eating Snails (Drupella spp.) in the Cat Ba World Biosphere Reserve, Vietnam – Looking at the habitat utilization and prey selection 1 --------- Scientific report, 2015 UNESCO/MAB Young Scientists Awards, Vietnam --------- TABLE OF CONTENTS LIST OF TABLES ........................................................................................................ 3 LIST OF FIGURES ...................................................................................................... 3 ACKNOWLEDGEMENT ............................................................................................ 4 ABSTRACT .................................................................................................................. 5 I. INTRODUCTION ..................................................................................................... 6 II. MATERIAL AND METHODS ............................................................................... 8 1. Time of study ......................................................................................................... 8 2. Area of study ......................................................................................................... 9 3. Fieldwork ............................................................................................................ 10 3.1. Preparatory work for the survey.................................................................. 10 3.2. Method of survey, field sampling ................................................................. 11 3.3. Method of specimen analysis in laboratory ................................................. 13 III. RESULTS AND DISCUSSION ........................................................................... 14 1. The coverage percentage of the bottom components at surveyed sections ........ 14 2. Species composition and density of Drupella in survey areas ........................... 15 2.1. Species composition ..................................................................................... 15 2.2. Density of Drupella ...................................................................................... 16 2.3. Age structure of Drupella population .......................................................... 17 2.4. Spatial structure of Drupella populations ................................................... 20 3. Discussion on dangerous changes in choice prey of coral-eating snails (Drupella) ............................................................................................................... 25 IV. CONCLUSION .................................................................................................... 28 REFERENCES ........................................................................................................... 29 Outbreak of the Coral Eating Snails (Drupella spp.) in the Cat Ba World Biosphere Reserve, Vietnam – Looking at the habitat utilization and prey selection 2 --------- Scientific report, 2015 UNESCO/MAB Young Scientists Awards, Vietnam --------- LIST OF TABLES Table 1. The geographic coordinates of the survey sites ............................................ 10 Table 2. Coverage percentage of bottom components on the reef in survey ............. 14 Table 3. Density of Drupella (individuals/m2) at surveyed sites ................................ 17 LIST OF FIGURES Figure 1. The map showing the study area and the location of sample collection at Cat Ba Island, Vietnam ................................................................................................. 9 Figure 2. The equipment for fieldwork ....................................................................... 11 Figure 3. The placement of transects surveyed .......................................................... 11 Figure 4. Sampling in the quantitative squares placed on the transect line ................ 12 Figure 5. Sample analysis in the laboratory................................................................ 13 Figure 6. Measure the length of shells ........................................................................ 13 Figure 7. External morphology of coral-eating snails (Drupella) in Cat Ba .............. 16 Figure 8. The density of Drupella as per surveyed area on the reef flat and the reef slope zones .................................................................................................................. 16 Figure 9. Size groups (shell length - L) of the Drupella populations ......................... 18 Figure 10. Distribution of Drupella group on the living coral .................................... 20 Figure 11. The correlation between the density of Drupella with the coverage of living corals on reef zone at survey locations ............................................................. 21 Figure 12. Chart of Drupella density distributed on reef flat and reef slope at survey locations ...................................................................................................................... 22 Figure 13. Drupella density distributed on reef flat and reef slope at closed and open areas ............................................................................................................................ 23 Figure 14. The percentage of Drupella distributed on the substrate components ...... 24 Figure 15. The number of live coral colonies were occupied by Drupella/transect 100m ........................................................................................................................... 25 Figure 16. The acroporids are being occupied by Drupella, observations in 2002 (Resource: Nguyen Văn Quan, 2002) ......................................................................... 26 Figure 17. The living coral are being occupied by Drupella are coral blocks, observations in 2016 ................................................................................................... 26 Outbreak of the Coral Eating Snails (Drupella spp.) in the Cat Ba World Biosphere Reserve, Vietnam – Looking at the habitat utilization and prey selection 3 --------- Scientific report, 2015 UNESCO/MAB Young Scientists Awards, Vietnam --------- ACKNOWLEDGEMENT The author would like to thank especially UNESCO MAB Young Scientist Award 2015 for support. This research will be not possible also without great support of Prof. Nguyen Hoang Tri (President & Secretary General, MAB National Committee of Vietnam-Unesco). I would like to express my profound gratitude to Dr. Tran Dinh Lan and Dr. Nguyen Van Quan (Institute of Marine Environment and Resource, Vietnam) for their help and comments regarding the common approach for my project. Field work for this work was made thanks to the providing necessary facilities during field works support by The Institute of Marine Environment and Resource - Vietnam Academy of Science and Technology (VAST). Also, I am very much grateful for collaboration from the Management Board of Cat Ba Archipelago Biosphere Reserve was very important for all the help provided. I am thankful for all member of the project: Mr. Chu The Cuong, Mr. Pham Van Chien and Mr. Dang Do Hung Viet for supporting research activities and collection of samples. Contact address: Nguyen Duc The Department of Marine Biodiversity and Conservation, Institute of Marine Environment and Resource (IMER), Vietnam Academy of Science and Technology (VAST) No. 246 Da Nang Str. Hai Phong City, VIETNAM Tel: +84 31 376 0601 (office) Fax: +84 31 376 1521 E-mail: [email protected]; [email protected] Outbreak of the Coral Eating Snails (Drupella spp.) in the Cat Ba World Biosphere Reserve, Vietnam – Looking at the habitat utilization and prey selection 4 --------- Scientific report, 2015 UNESCO/MAB Young Scientists Awards, Vietnam --------- ABSTRACT This project aimed to be the breakdown study about biological and ecological characteristics of coral-eating snails (Drupella spp.) on the coral reefs in the Cat Ba World Biosphere Reserve of Vietnam, that focused on observing the natural distribution-density specific, prey choice on the coral colonies to the density of coral eating snail populations. The study area is the Cat Ba reef areas, which is location have unique characteristics represent for the eastern reef of North Vietnam, unlike the other reefs in the Indo – Pacific, the coral communities are very abundant in term of species diversity and reef morphology (Poritidae, Faviidae). Six reef sites were proposed and observed to collect basic information of the Drupella on the coral reefs in the two area of the Cat Ba (the open area and close area). The methods used for research were modified according to English et al. (1997), Hodgson (2000), and Cumming, RL (2009). For all reef sites, the coverage percentage of the bottom components at surveyed sections are proposed and discussed. Also, the species composition, density, size group, distribution characteristics and choice prey of coral-eating snails (Drupella) monitored at each reef sites for two transects (reef flat and reef slope). The results show that virtually the monitored points have the coverage of live coral is low (<40%), the dominant coral species on the reefs belong to genus Galaxea, Goniopora