Biodiversity Conservation

Session 2

Nutrient Concentration and Water Turbidity on Coral Reef Areaand their Effects on the Living Coral

Koichi KINJOOkinawa Prefectural Institute of Health and Environment

Coral reef disturbancesCoral reef disturbances

Rise in seawater temperatures

Outbreak of crown‐of‐thorns starfish(Acanthaster planci)

Soil run‐off

Nutrient enrichment

Pesticides・Heavy metals

Destruction by typhoons Widespread of coral diseases

Coral reef disturbancesCoral reef disturbancesIncreasing 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.

Nutrient enrichment

Soil run‐off

Sedimentation

Coral death

Overgrowth of algae

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.

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

Topics

Study areaStudy area

Okinawa Islands70 study sites

Kerama Islands3 study sites

Kume Island5 study sites

Miyako Island6 study sites

Yaeyama Islands20 study sites

104 study sitesin 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

River mouth

Tidal area†

Seagrass beds

Coral beds

Investigation points ・3 or 4 points set for each study site

Water samples were collected under normal conditions.

study site(coral reef area)

Reef crestMoat

River 

Beach  Branching coral

Seagrass 

Channel 

Parameters water quality

•Total Nitrogen（TN）•Total phosphorus（TP）•Nitrate and Nitrite (NO3

－+NO2－)

•Phosphate（DIP）

Coral condition

•Water turbidity•Horizontal transparency

Nutrient parameters

Turbid parameter

•Coral coverage (%)

Parameters water quality

•Total Nitrogen（TN）•Total phosphorus（TP）•Nitrate and Nitrite (NO3

－+NO2－)

•Phosphate（DIP）

Coral condition

•Water turbidity•Horizontal transparency

Nutrient parameters

Turbid parameter

•Coral coverage (%)

What is horizontal transparency?

Secchi disk

Usual method of transparency has some defects such as difficulties in measuring at shallow and clean waters in coral reefs. Horizontal transparency is the method of measuring horizontal distances keeping the Secchi disk perpendicular to seabed.

Parameters water quality

•Total Nitrogen（TN）•Total phosphorus（TP）•Nitrate and Nitrite (NO3

－+NO2－)

•Phosphate（DIP）

Coral condition

•Water turbidity•Horizontal transparency

Nutrient parameters

Turbid parameter

•Coral coverage (%)

Results

※ 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

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 1666Horizontal transparency (m) 7.3 0.1 43.0 1781

Summery of the analyzed water quality data

Results（Water quality data for each monitoring period）

・Each water quality parameters  tended to be the maximum in summer and to be the minimum in winter.

median

25 percentile 

75 percentile 

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 ）

・In the coral reef area adjacent to the urban area, each water quality parameters became comparatively high. 

Urban area Natural areaAgricultural area

Results（Relation between coral coverage (%) and each water quality parameter）

50% 50%

50% 50%

0.08 0.01

0.11 14.0

・When nutrients concentration or turbidity decreased or horizontaltransparency increased, coral condition became better.

Environmental guidelines for coral reef conservation

Thank you very much for your attention