Coral Calcification Rates Research Articles

Coral calcification rates by the buoyant weight technique: Effects of alizarin staining

The buoyant weight method has been used in a laboratory experiment over an 18-day period to assess effects of alizarin staining on the calcification rate of the hermatypic coral Diploria strigosa (Dana). Exposure of corals to a concentration of 10 mg/l alizarin for 24 h in a flow-through system caused a significant depression in calcification for a period of up to 6 days. It is suggested that such initial calcification depressions after staining could affect absolute growth measurements and cause synergistic effects with experimental manipulation of environmental conditions unless an appropriate recovery period is allowed.

Coral morphology, diversity and reef growth

The shape of reef corals is affected by light level1,2 and by wave stress3,4, leading to the well-known zonation of coral form associations with exposure and depth3–6. Growth form also seems to be constrained by geometric factors2,7,8. Similarly, coral calcification rate, of importance both for coral form and for net reef growth, is light dependant9,10, and may be affected by other factors such as wave stress and sediment flux. Here the growth structure of raised Pleistocene reefs in New Guinea, of both fringing and barrier types, is explained in terms of variations of coral framework growth rate across the reef profile. A model for growth rate in terms of wave stress, light level and other variables is outlined, first by examining the effects of these factors on coral form and diversity.

ROLE OF SYMBIOTIC ALGAE (ZOOXANTHELLAE) IN CORAL CALCIFICATION

1. In branches of the coral Acropora cervicornis, the abundance of symbiotic algae (zooxanthellae) increases from tip to base, while active calcification decreases. Light enhancement of calcification rates is, paradoxically, greatest in the algae-poor tips of branches.2. Calcium-45 experiments on intact and isolated tips of the coral branches suggest that light enhancement of calcification in the algae-poor tip results from photosynthesis by zooxanthellae farther down in the branch.3. Carbon-14 experiments indicate that organic products of algal photosynthesis are translocated to the coral tip. The main carbon-14 labeled products in the tip are lipids, glycerol and glucose.4. Our data are consistent with the hypothesis that translocated algal products enhance coral calcification rates.

THE PHYSIOLOGY OF SKELETON FORMATION IN CORALS. I. A METHOD FOR MEASURING THE RATE OF CALCIUM DEPOSITION BY CORALS UNDER DIFFERENT CONDITIONS

1. A method is described for the accurate measurement of calcification rates in reef-building corals under various controlled conditions, using calcium-45 as tracer.2. At the temperatures of the experiments, there was a slow but appreciable isotopic exchange between the coral skeleton and sea water. There are indications that this is considerably less in living coral where the tissue forms a barrier against such exchange.3. In many of the reef-building corals tested so far, the calcification rate was significantly lowered by the exclusion of light.4. The calcification rate of reef corals grown in darkness for prolonged periods of time to remove the zooxanthellae is considerably reduced and seems independent of the light intensity.5. Variations in the growth rates of different parts of coral colonies were measured. The existence of growth gradients was demonstrated in a number of species.6. Calcium uptake was greatly reduced on the addition of Diamox, a specific carbonic anhydrase inhibitor. In those species tested, the effect of carbonic anhydrase inhibition and exclusion of light was in the same direction. In the presence of complete inhibition of carbonic anhydrase there was still an uptake, even in darkness.7. It was concluded that the effect of light on reef coral growth is in part mediated through the zooxanthellae. The decreased calcification rates of reef corals in darkness, in the absence of zooxanthellae or in the presence of a carbonic anhydrase inhibitor suggest that the rapid calcification of these corals may be dependent on efficient removal of H2CO3.