A comparison of two methods of obtaining densities of zooxanthellae in Acropora millepora

摘要

Quantification of zooxanthellae densities in tissues of reef-building corals aids in the assessment of the extent and severity of coral bleaching. Various meth-ods are available to quantify zooxanthellae densities; how-ever, a direct comparison of these techniques has yet to been done. Here, we compare estimates of zooxanthellae densities obtained using conventional airbrushing coupled with post-tissue-blasting surface area determination, ver-sus a technique whereby zooxanthellae densities are quantified from a known area (0.25 cm~(2)) of tissue after corals have been fixed and decalcified. Estimates of zoo-xanthellae densities obtained were correlated across re-plicate colonies (R~(2)=0.40, n=81), and both techniques revealed similar patterns of variation among locations. The main benefit of the decalcification technique was reduced processing time, because the technique eliminates the time-consuming process of tissue blasting and re-trospective estimates of surface area. We estimate that decalcification halves the processing time per sample, and produces a more accurate estimate of zooxanthellae density.