Session 2 Biodiversity Conservation Nutrient Concentration and Water Turbidity on Coral Reef Area and their Effects on the Living Coral Koichi KINJO Okinawa Prefectural Institute of Health and Environment CoralCoral reefreef disturbancesdisturbances Outbreak of crown‐of‐thorns starfish (Acanthaster planci) Rise in seawater temperatures Destruction by typhoons Widespread of coral diseases Soil run‐off Nutrient enrichment Pesticides・ Heavy metals CoralCoral reefreef disturbancesdisturbances Increasing nutrient loads and soil run-off have been pointed out as the potential to serious impact on coral reef areas due to urbanization of coastal areas, growth and development agriculture or livestock farming. Soil run‐off Nutrient enrichment Sedimentation Overgrowth of algae Coral death Decrease of habitat of coral Objectives In order to keep the water quality good for coral health, the environmental water quality guidelines are needed. If the water quality exceed the limits of environmental guideline, it is possible to manage the catchment contiguous to the coral reef area, and to maintain the suitable water quality. In this study, the suitable water qualities are examined for conservation and management of coral reef areas. Topics In the coral reef areas around Okinawa・・・ • The range of water qualities • The seasonal variation of water qualities • The difference of water qualities between the areas • The thresholds of water qualities required for conservation of coral reef areas StudyStudy areaarea 104 study sites in the Ryukyu Islands Sampling periods ・Sep. to Oct. 2009 Kume Island ・Nov. to Dec. 2009 5 study sites ・Feb. to Mar. 2010 Kerama Islands ・Jun. to Jul. 2010 3 study sites ・Nov. to Dec. 2010 Okinawa Islands ・Feb. to Mar. 2011 70 study sites Yaeyama Islands 20 study sites Miyako Island 6 study sites Investigation points ・3 or 4 points set for each study site Water samples were collected under normal conditions. River Channel Tidal area† River mouth Branching coral Beach Coral beds Seagrass beds Seagrass Moat Reef crest study site (coral reef area) Parameters water quality Nutrient parameters •Total Nitrogen（TN） •Total phosphorus（TP） － － •Nitrate and Nitrite (NO3 +NO2 ) •Phosphate（DIP） Turbid parameter •Water turbidity •Horizontal transparency Coral condition •Coral coverage (%) Parameters water quality Nutrient parameters •Total NitrogenWhat is horizontal（TN） transparency? •Total phosphorus（TP） － － Secchi disk •Nitrate and Nitrite (NO3 +NO2 ) •Phosphate（DIP） Turbid parameter •Water turbidity •Horizontal transparency CoralUsual conditionmethod of transparency has some defects such as difficulties in measuring at shallow and clean waters in coral reefs. Horizontal•Coral coverage transparency (%) is the method of measuring horizontal distances keeping the Secchi disk perpendicular to seabed. Parameters water quality Nutrient parameters •Total Nitrogen（TN） •Total phosphorus（TP） － － •Nitrate and Nitrite (NO3 +NO2 ) •Phosphate（DIP） Turbid parameter •Water turbidity •Horizontal transparency Coral condition •Coral coverage (%) Results Summery of the analyzed water quality data Achievement Mean Min Max n ※ rates TN (mg-N/L) 0.08 < 0.02 1.66 1684 92.8% TP (mg-P/L) 0.01 < 0.002 0.190 1682 95.4% Nitrate + Nitrite (mg-N/L) 0.005 < 0.005 1.674 1677 Phosphate (mg-P/L) 0.006 < 0.001 0.094 1681 Water turbidity (Degree) 0.448 0.012 39.658 1666 Horizontal (m) 7.3 0.1 43.0 1781 transparency ※ Achievement rates ： The achievement rates of the severest environmental standard values in Japan established by Basic Environmental Law TN＜0.2mg/L, TP＜0.02mg/L Results （Water quality data for each monitoring period） 75 percentile median 25 percentile ・Each water quality parameters tended to be the maximum in summer and to be the minimum in winter. Results （Water quality data for each type of habitat） ・ Each water quality parameters decreased in proportion to distance from the river mouth. Results （water quality data for 6 areas ） Agricultural area Urban area Natural area ・In the coral reef area adjacent to the urban area, each water quality parameters became comparatively high. Results （Relation between coral coverage (%) and each water quality parameter） 50% 50% 0.08 0.01 50% 50% 0.11 14.0 ・When nutrients concentration or turbidity decreased or horizontal transparency increased, coral condition became better. Environmental guidelines for coral reef conservation Thank you very much for your attention.