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

Coral reef disturbances Rise in seawater temperatures Outbreak of crown of thorns starfish (Acanthaster planci) Destruction by typhoons Widespread of coral diseases Soil run off Nutrient enrichment Pesticides Heavy metals

Coral reef disturbances 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

Study area 104 study sites in the Ryukyu Islands Sampling periods Sep. to Oct. 2009 Nov. to Dec. 2009 Feb. to Mar. 2010 Jun. to Jul. 2010 Nov. to Dec. 2010 Feb. to Mar. 2011 Kume Island 5 study sites Kerama Islands 3 study sites Okinawa Islands 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 Tidal area Channel Beach River mouth Branching coral Seagrass beds Seagrass Coral beds Moat Reef crest study site (coral reef area)

Parameters water quality Nutrient parameters Total Nitrogen TN Total phosphorus TP Nitrate and Nitrite (NO 3 +NO 2 ) Phosphate DIP Turbid parameter Water turbidity Horizontal transparency Coral condition Coral coverage (%)

Parameters water quality Nutrient parameters What is horizontal transparency? Total Nitrogen TN Total phosphorus TP Nitrate and Nitrite (NO 3 +NO 2 ) Phosphate DIP Secchi disk Turbid parameter Water turbidity Horizontal transparency Coral condition Usual method of transparency has some defects such as difficulties in measuring at shallow and clean waters in coral reefs. Coral coverage (%) Horizontal transparency is the method of measuring horizontal distances keeping the Secchi disk perpendicular to seabed.

Results Summery of the analyzed water quality data Mean Min Max n Achievement 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 transparency (m) 7.3 0.1 43.0 1781 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