Spatial variability of UVR attenuation and bio-optical factors in shallow coral-reef waters of Malaysia

Biologically diverse coral-reef ecosystems are both directly and indirectly susceptible to changes in the spectral ultraviolet radiation (UVR) distribution. The purpose of this study was to (1) measure the variability of UVR and photosynthetically active radiation (PAR) penetration 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 μg l⁻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 μg l⁻¹), low CDOM (1.45 ± 0.44 ppb), low POC (103.21 ± 37.93 mg m⁻³), and relatively 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 attenuation coefficients showed significant correlations with CDOM, but were spatially dependent with regard to chlorophyll a, POC, and DOC. The results suggest that bio-optically significant CDOM and DOC factors are uncoupled in coral-reef communities of Malaysia. Furthermore, the results support prior studies that show chromophorically active concentrations of DOM and POC are significantly 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.