REPORT Spatial variability of UVR attenuation and bio-optical factors in shallow coral-reef waters of Malaysia V. S. Kuwahara • R. Nakajima • B. H. R. Othman • M. R. M. Kushairi • T. Toda Received: 1 October 2009 / Accepted: 22 March 2010 / Published online: 8 April 2010 Ó Springer-Verlag 2010 Abstract Biologically diverse coral-reef ecosystems are both directly and indirectly susceptible to changes in the spectral ultraviolet radiation (UVR) distribution. The pur- pose of this study was to (1) measure the variability of UVR and photosynthetically active radiation (PAR) pene- tration in the water above coral reefs around the Malaysian peninsula, (2) measure the variability and distribution of UVR-specific biogeochemical factors, and (3) determine the impact of biogeochemical variability as it affects the UVR:PAR ratio. Downwelling UVR and PAR irradiance and bio-optically derived biogeochemical factors were measured at 14 coral survey stations around the Malaysian peninsula from August 10–29, 2007. The West Coast was characterized by relatively shallow mean 10% UV-B (320 nm) penetration (1.68 ± 1.12 m), high chlorophyll (3.00 ± 4.72 lgl -1 ), high chromophoric dissolved organic matter (CDOM; 6.61 ± 3.31 ppb), high particulate organic carbon (POC; 190.65 ± 97.99 mg m -3 ), and low dissolved organic carbon (DOC; 1.34 ± 0.65 mg m -3 ). By contrast, the East Coast was characterized by relatively deep mean 10% UV-B penetration (5.03 ± 2.19 m), low chlorophyll (0.34 ± 0.22 lgl -1 ), low CDOM (1.45 ± 0.44 ppb), low POC (103.21 ± 37.93 mg m -3 ), and rela- tively high DOC (1.91 ± 1.03 mg m -3 ). The UVR:PAR ratio was relatively higher on the East Coast relative to the West Coast, suggesting variable concentrations of UVR- specific absorbing components. At all sites, UVR attenua- tion coefficients showed significant correlations with CDOM, but were spatially dependent with regard to chlo- rophyll a, POC, and DOC. The results suggest that bio- optically significant CDOM and DOC factors are uncou- pled in coral-reef communities of Malaysia. Furthermore, the results support prior studies that show chromophori- cally active concentrations of DOM and POC are signifi- cantly altering the amount of UVR penetration above coral reefs and may be notable factors in regulating intricate biogeochemical cycles around benthic coral communities in Malaysia. Keywords Ultraviolet radiation (UVR)  Chromophoric dissolved organic matter (CDOM)  Dissolved organic matter (DOC)  Inherent optical properties (IOP) Introduction The intensity of solar ultraviolet radiation (UVR) received at the Earth’s surface is more dependent on the solar zenith angle through the atmosphere than on variability in the ozone layer. Coral-reef ecosystems are generally situated in the smaller zenith angle regions of the tropical and subtropical oceans, exposing them to the highest levels of solar UVR Communicated by Environment Editor Prof. Rob van Woesik V. S. Kuwahara (&) Faculty of Education, Soka University, 1-236 Tangi-cho, Hachioji-shi, Tokyo 192-8577, Japan e-mail: victor@soka.ac.jp R. Nakajima  T. Toda Department of Environmental Engineering for Symbiosis, Faculty of Engineering, Soka University, Tokyo, Japan B. H. R. Othman Marine Ecosystem Research Centre, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia M. R. M. Kushairi Faculty of Science and Environmental Technology, Universiti Industri Selangor, Shah Alam, Malaysia 123 Coral Reefs (2010) 29:693–704 DOI 10.1007/s00338-010-0618-1