Impacts of food availability and <i>p</i>CO<sub>2</sub> on planulation, juvenile survival, and calcification of the azooxanthellate scleractinian coral <i>Balanophyllia elegans</i>

Abstract

Abstract. Ocean acidification, the assimilation of atmospheric CO2 by the oceans that decreases the pH and CaCO3 saturation state (Ω) of seawater, is projected to have severe adverse consequences for calcifying organisms. While strong evidence suggests calcification by tropical reef-building corals containing algal symbionts (zooxanthellae) will decline over the next century, likely responses of azooxanthellate corals to ocean acidification are less well understood. Because azooxanthellate corals do not obtain photosynthetic energy from symbionts, they provide a system for studying the direct effects of acidification on energy available for calcification. The solitary azooxanthellate orange cup coral Balanophyllia elegans often lives in low-pH, upwelled waters along the California coast. In an 8-month factorial experiment, we measured the effects of three pCO2 treatments (410, 770, and 1220 μatm) and two feeding frequencies (3-day and 21-day intervals) on "planulation" (larval release) by adult B. elegans, and on the survival, skeletal growth, and calcification of newly settled juveniles. Planulation rates were affected by food level but not pCO2. Juvenile mortality was highest under high pCO2 (1220 μatm) and low food (21-day intervals). Feeding rate had a greater impact on calcification of B. elegans than pCO2. While net calcification was positive even at 1220 μatm (~3 times current atmospheric pCO2), overall calcification declined by ~25–45%, and skeletal density declined by ~35–45% as pCO2 increased from 410 to 1220 μatm. Aragonite crystal morphology changed at high pCO2, becoming significantly shorter but not wider at 1220 μatm. We conclude that food abundance is critical for azooxanthellate coral calcification, and that B. elegans may be partially protected from adverse consequences of ocean acidification in habitats with abundant heterotrophic food.

Peer Review #1 of "Effects of low pH and feeding on calcification rates of the cold-water coral Desmophyllum dianthus (v0.1)"

“…In this particular study, high food conditions also seemed to alleviate some of the stress associated with high pCO 2 in the CWC solitary species Balanophyllia elegans. Better nutrition not only favoured calcification, but also increased the number of larvae released and reduced juvenile coral mortality by 5-15% (Crook et al, 2013). A possible role of energy expenditure for reproduction is supported by our observation that, after this experiment was completed, reproduction was observed in 8 polyps, and that this occurred mostly in D. dianthus polyps reared under HF (7 out of 8).…”

Effects of low pH and feeding on calcification rates of the cold-water coralDesmophyllum dianthus

“…In this particular study, high food conditions also seemed to alleviate some of the stress associated with high pCO 2 in the CWC solitary species Balanophyllia elegans. Better nutrition not only favored calcification, but also increased the number of larvae released and reduced juvenile coral mortality by 5-15% (Crook et al, 2013). A possible role of energy expenditure for reproduction is supported by our observation that, after this experiment was completed, reproduction was observed in eight polyps, and that this occurred mostly in D. dianthus polyps reared under HF (7 out of 8).…”

“…The variability observed in HF treatment could be explained by the different morphological features of the polyps (size, calyx diameter, tentacle crown size), that would allow some corals to feed more efficiently than others. In addition, a food-replete environment may allow corals to reorganize energy allocation in order to increase inter-polyp competition for resources and reproductive success as observed in Crook et al (2013). In this particular study, high food conditions also seemed to alleviate some of the stress associated with high pCO 2 in the CWC solitary species Balanophyllia elegans.…”

Differential responses to ocean acidification between populations ofBalanophyllia eleganscorals from high and low upwelling environments

“…The upwelling mosaic of the CCLME combined with B. elegans' nonplanktonic larval stage, which restricts gene flow, creates the potential for population variation through local adaptation or phenotypic plasticity when exposed to low pH (Sanford & Kelly, ). Previous research has shown B. elegans to be sensitive to low pH, with juvenile mortality 10%–20% higher under pH 7.6 compared to ambient conditions (pH 8.0) (Crook, Cooper, Potts, Lambert, & Paytan a., ). However, only a single population from Monterey Bay, California, was investigated, where exposure to pH < 7.8 is rare (Evans, Pespeni, Hofmann, Palumbi, & Sanford, ; Kroeker et al, ).…”