MCR LTER: Coral Reef: Effects of Flow and Temperature on Growth and Photophysiology of Scleractinian Corals in Moorea, French Polynesia

To test for threshold effects in the response of coral physiology to increasing
seawater flow, field and laboratory experiments were conducted in Moorea. First, the
growth of juvenile massive Porites spp. and branching P. irregularis was compared among habitats differing in water
motion. Growth of massive Porites spp. responded to flow in a
pattern consistent with a threshold effect, whereas growth of P. irregularis increased linearly with flow. Second, a
recirculating flume was used to test the effect of flow on photophysiology (ΔF⁄Fm'),
effective photochemical efficiency) for massive Porites spp.;
ΔF⁄Fm' displayed a threshold response at 23 cm/sec and 28 °C, but not at 31 °C.
Finally, intra-colony variation in the response of ΔF⁄Fm' to flow and temperature
was explored to evaluate the functional significance of colony shape in small
corals. ΔF⁄Fm' on the top and upstream surfaces of massive Porites spp. responded with a threshold effect of flow at 28 °C
(but not 31 °C), but ΔF⁄Fm' on downstream surfaces was unresponsive to flow. ΔF⁄Fm'
for P. irregularis was less responsive to flow than for massive Porites spp., suggesting that the photophysiological response
of corals to varying flow speeds may differ between species and morphologies.
Together, these results emphasize that flow can have diverse effects on the
physiology of corals, with the outcome depending on flow speed, temperature,
location on the colony, and perhaps morphology. These data were published in The Biological Bulletin and were part of the masters thesis of W.
Goldenheim (2011).