Spatial differences in the growth rates of Pocillopora damicornis associated with sedimentation rate and light intensity at Polhena patchy reef, southern Sri Lanka

Abstract

Near shore patchy reef located at the leeward side of the fringing reef at Polhena was surveyed to evaluate spatial patterns of growth rates of Pocillopora damicornis. This study was carried out at three locations of the reef; front, side and back from June to November in 2004. Three sites were selected from each location considering the depth (surface, middle, and bottom). Forty five colonies of P. damicornis which were approximately of the same size were studied. Temperature, dissolved oxygen, BOD5, salinity, pH, soluble reactive phosphorous, turbidity and light intensity of each site were measured fortnightly and their mean values were 28.06 ± 0.24 °C, 8.78 ± 0.15 mg L -1, 1.40 ± 0.32 mg L -1, 31.91 ± 3.49 mg L -1, 8.12 ± 0.04, 8.12 ± 0.01, 20.21 ± 2.05 μg L -1, 5.78 ± 1.20 NTU, and 49.17 ± 1.97 Lux respectively. Sediments in each site were collected using traps and mean overall sedimentation rate for the experimental period was 45860.6 ± 3364.2 ml m -2 day -1 (2620.6 ± 192.2 g m -2 day -1) (n = 36). Growth of coral colonies, which was measured as linear skeletal extension rate (LSER), was 0.15 ± 0.01 mm day -1. Significant differences in mean light intensity, mean sediment volume, and LSER of coral colonies were observed among different sites. The highest sedimentation rate 94818.2 ± 6981.5 ml m -2 day -1 (5418.2 ± 398.9 g m -2 day -1) and the lowest LSER of the colonies (0.05 ± 0.01 mm day -1) were observed at back bottom site. The highest LSER was observed at front surface (0.23 ± 0.01 mm day -1). LSER showed a significant negative correlation (R 2 = 0.59) with increased sedimentation rate and low light intensity. Back bottom site of the patchy reef was having comparatively unfavorable conditions for the growth of corals that were subjected to more environmental stress than the corals in other sites of the reefs. Sri Lanka J. Aquat. Sci. 20 (1) (2015): 47-58