Effects of suspended sediments and nutrient enrichment on juvenile corals

Three to six-month-old juveniles of Acropora tennis, A. millepora and Pocillopora acute were experimentally co-exposed to nutrient enrichment and suspended sediments (without light attenuation or sediment deposition) for 40 days. Suspended sediments reduced survivorship of A. millepora strongly, proportional to the sediment concentration, but not in A. tennis or P. acuta juveniles. However, juvenile growth of the latter two species was reduced to less than half or to zero, respectively. Additionally, suspended sediments increased effective quantum yields of symbionts associated with A. millepora and A. tennis, but not those associated with P. acuta. Nutrient enrichment did not significantly affect juvenile survivorship, growth or photophysiology for any of the three species, either as a sole stressor or in combination with suspended sediments. Our results indicate that exposure to suspended sediments can be energetically costly for juveniles of some coral species, implying detrimental longer-term but species-specific repercussions for populations and coral cover.