A correlation between larval size and spat growth and development in coral species Porites astreoides : an approach to understanding the effects of ocean acidification on calcifying organisms

Abstract

Ocean acidification poses an extreme threat to coral colony survival. The rise of carbon dioxide in atmospheric pressure decreases the seawater carbonate ion concentration resulting in lower rates of calcium carbonate deposition in coral skeletons. If this rise continues, rates of coral erosion will exceed coral accretion, causing coral reef systems to significantly decline. Coral calcification rates could decline by 20% to 80% of modern values by the end of this century. Porites astreoides from Bermuda’s Rim Reef release larger planulae than P. astreoides from Bermuda’s Patch reefs, so adult P. astreoides colonies were collected from two Patch Reef sites and two Rim Reef sites in Bermuda. Planulae were settled in three target pCO2 levels (420, 1200, and 1670 ppmv) and reared in experimental conditions for two weeks. My objective was to determine whether there is a species-specific differential response to CO2. I am focusing on answering whether 1) larval sizes across the north lagoon differ, and 2) larvae differ in their response to CO2 variations. I predict that if Rim Reef larvae are larger than Patch reef larvae of the same species, they will be more resistant to ocean acidification effects. Rim planulae were significantly larger. Rim and Patch corals differed significantly for both total calcification and settlement proportions, with higher rates of calcification under ambient CO2 conditions, but no significant difference among CO2 conditions in settlement proportions. This study provides suggestive evidence to support the hypothesis that increased larval size leads to increased resistance to enriched CO2 in P. astreoides recruits.