Ocean acidification (OA), caused by the dissolution of anthropogenic CO2 into the surface waters of the ocean, threatens the fate of calcifying marine organisms. The effects of OA on adult coral calcification have been well-studied over the past decade and generally results in decreased calcification rates with increasing pCO2, although the effects of OA on early life history stages are less well-studied. This thesis addresses the effects of OA on coral recruit physiology with an emphasis on filling key gaps in the ecological relevance of previous manipulative OA coral studies. Chapter I: In March and June 2010, two experiments were conducted exposing newly settled Seriatopora caliendrum recruits to low (440, 456 μatm), high (663, 837 μatm; March,June respectively) and diurnally oscillating pCO2 which mimicked the conditions at Hobihu reef, Taiwan where adult corals were collected. Calcification and survival of coral recruits was elevated in diurnally oscillating pCO2 relative to static ambient and high pCO2, hypothesized to be the result of increased DIC stored in coral tissues at night. Chapter II: In March 2011, newly settled Pocillopora damicornis recruits were exposed to low (493 μatm) and high pCO2 (878μatm) in varying light intensities (226, 122, 70, 41, 31 μmol photons m-2 s-1) to test the effects of light and OA on coral recruit physiology. Coral recruit calcification and survival in both pCO2 treatments was light-dependent, with large differences in calcification at intermediate light intensities (41, 70 μmol photons m-2 s-1) though calcification at high and low light intensities did not differ (226, 31 μmol photons m-2 s-1). Survivorship was not correlated with size and was highest in both ambient and high pCO2 at 122 μmol photons m-2 s-1. Chapter III: Finally, the activity of carbonic anhydrase in S. caliendrum juveniles (< 3 cm ) exposed to ambient, high and diurnally oscillating pCO2 was measured to elucidate the mechanistic basis for increased calcification in diurnally oscillating pCO2. CA activity was decreased in both high and diurnally oscillating pCO2 during the day, which is consistent with the DIC buildup hypothesis proposed in Chapter I. Together these findings provide novel insight into the physiology of corals exposed to OA under ecologically relevant seawater chemistry and light conditions. Coral recruits are biologically quite different than their adult counterparts therefore further work is needed to determine the extent to which these results apply to adult corals.
Thesis or Dissertation