A physiological crisis drives the coral recruitment bottleneck

Recruitment failure is a leading cause of population decline for tropical
corals. Because the causes of death for small corals are unclear, it is
challenging to predict how recruitment bottlenecks will change in the
future. We tested the hypothesis that depletion of biomass causes high
mortality of small corals under thermal stress. The biomass of small
colonies (< 30 mm diameter) of genetically identified broadcast
spawning Pocillopora from Moorea, French Polynesia, was manipulated using
elevated temperature to increase respiration, and reduced day length to
decrease photosynthesis. Corals with high or low biomass were incubated at
ambient summer (28°C) and elevated (31°C) temperatures. Small P. meandrina
with high biomass were six times more likely to die at 31°C versus 28°C,
but corals with low biomass were 48 times more likely to die at 31°C
versus 28°C. When small Pocillopora were grown in seawater augmented with
bicarbonate to reduce the energetic expenditure on skeletogenesis, growth
rates were not affected but energy expenditure was reduced by 20%.
Resource-limitation of small corals therefore can affect their response to
elevated temperatures, supporting the hypothesis that a physiological
crisis initiated by resource limitation mediates the stringency of
recruitment bottlenecks and the rate of coral community recovery. Data in
support of this publication are supplied in 11 files.