Physiology & physiological ecology
Research study 1

photograph of cup corals Balanophyllia eleganshistogram showing planulation rate of cup corals Balanophyllia elegans in relation to pH and food levelA group of researchers from the University of California Santa Cruz investigates planulation (release of larvae), and growth, calcification, and survival of the newly settled juveniles of cup coral Balanophyllia elegans under 3 levels of simulated ocean acidification1 and 2 levels of nutrition2.  The authors note that cup corals in areas of the west coast are currently exposed to upwelling waters of high CO2  and low pH, and predicted increases in atmospheric CO2 will lead to greater chronic levels ocean acidity.  histogram showing percentage mortality of juvenile cup corals Balanophyllia elegans in relation to pH and food levelThe research protocol is designed for long-term exposure to enhanced pCO2 levels, a more realistic approach than short-term, acute exposures commonly used by many current experimenters.  Results after 8mo in culture show that planulation rates are significantly lower at low food ration (see histogram upper Right), but are unaffected by pCO2 (pH) levels.  Juvenile mortality is significantly greater under conditions of high pCO2 and low food (see histogram lower Right).  Growth (calcification) of juveniles is significantly affected by ration level, but calcification is nevertheless positive even in the high pCO2 treatment.  Skeletons in high-food-treatment individuals are up to 7 times larger in volume and 5 times heavier than those in low-food treatments.  Interestingly, the crystal morphology of the aragonite3 comprising the skeleton is squatter at high pCO2 level than at low level.  Cup corals derive all their nutrition heterotrophically, that is, from food and not from symbiotic microorganisms as do other corals.  The authors conclude that as long as abundant food is available, impending degree of ocean acidification may not be a critical factor in their survival.  Crook et al. 2013 Biogeosci 10: 7599.

NOTE1  adults are maintained under 3 carbon-dioxide treatments (pCO2) of “low” (410uatm, pH equivalent to about 8.0; i.e., similar to current levels), “medium” (770uatm, equivalent to pH 7.8), and “high” (1220uatm, equivalent to pH 7.6).  The high-level treatment is equivalent to 3 times the current level of atmospheric pCO2.  Actual measured pHs in the culture jars, averaged over the 8mo experimental period, are 8.0, 7.8, and 7.6, exactly as intended

NOTE2  nutritional levels are “high” (feeding every 3d) and “low” (feeding every 21d) during the 8mo study period.  Food provided at each feeding session consists of a single 50ml bolus of concentrated brine-shrimp nauplii larvae (Artemia salina) injected into each 4-liter jar used to culture the cup corals.  The food is left in the jars for “several hours”, thought to be sufficient for each individual coral to eat its fill, and then the jars are flushed clean

NOTE3  one of 3 common forms of calcium carbonate, occurring naturally in most molluscs, corals, and tubeworms.  Most mollusc shells are purely aragonite, but some have degrees of admixture of calcite, another common form of naturally occurring calcium carbonate.  Calcite is the principal component of limestones, chalk, and marble and, as just mentioned, is present in some mollusc shells, and found in spicule form in some sponges.  It is also the principal component of skeletons of echinoderms, brachiopods, bryozoa, and many planktonic microorganisms

Photographs provided by the authors of their work: photo series showing developmental and growth views of cup corals Balanophyllia elegans  
  Planula larvae seeking spots on which to settle Newly settled larva and a juvenile Skeleton of 8mo juvenile with measurements indicated, top view Same skeleton. longitudinal view from the side  
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