Photosynthetic and respiration responses were measured in situ at different depths and under a variety of light regime for seagrass Thalassia hemprichii from coastal area of Teluk Kemang, Port Dickson, Malaysia. The photosynthesis and respiration rate was measured from evolution of oxygen from the seagrass enclosed in glass cuvet. The photosynthetic rate at 0.5 m was higher (0.429 ▒ 0.086 mg O2/hr/g fr wt.) than at 2.0 m depth (0.289 ▒ 0.034 mg O2/hr/g fr wt.). Respiration rate was not significantly different at two depths. In laboratory study, the light saturation of T. hemprichii was reached at 400-800 Ámol/m2/sec, whereas, the compensation point was around 20 Ámol/m2/s. The photosynthesis was relatively constant at light intensity up to 1600 Ámol/m2/s. Comparing these results to in situ light measurement from the seagrass bed (1095.430▒5.803 Ámol/m2/s at surface water and 115.00▒1.512 Ámol/m2/s. at 2.0 m depth), this species depth distribution should not be light limited to a depth of about 2.0 m i.e. T. hemprichii could penetrate a depth of more than 2.0 m in this study area. However, the present field observation indicated that this species could only be found at intertidal area (1.5 - 2.0 m High Water Level) and assumed that other environmental factors i.e. current movement, water visibility and sediment status may affects the depth distribution of this seagrass in this costal water.
M.K. Abu Hena , K. Misri , B. Japar Sidik , O. Hishamuddin and H. Hidir , 2001. Photosynthetic and Respiration Responses of Dugong Grass Thalassia hemprichii (Ehrenb) Aschers. at Teluk Kemang Seagrass Bed, Malaysia. Pakistan Journal of Biological Sciences, 4: 1487-1489.