Seawater carbonate chemistry and dissolution rates by boring microflora during ex situ experiments with dead corals (Porites lobata), 2009

Eight-month-old blocks of the coral Porites lobata colonized by natural Hawaiian euendolithic and epilithic communities were experimentally exposed to two different aqueous pCO2 treatments, 400 ppmv and 750 ppmv, for 3 months. The chlorophyte Ostreobium quekettii dominated communities at the start and at the end of the experiment (65-90%). There were no significant differences in the relative abundance of euendolithic species, nor were there any differences in bioeroded area at the surface of blocks (27%) between pCO2 treatments. The depth of penetration of filaments of O. quekettii was, however, significantly higher under 750 ppmv (1.4 mm) than under 400 ppmv (1 mm). Consequently, rates of carbonate dissolution measured under elevated pCO2 were 48% higher than under ambient pCO2 (0.46 kg CaCO3 dissolved m2/a versus 0.31 kg /m2/a). Thus, biogenic dissolution of carbonates by euendoliths in coral reefs may be a dominant mechanism of carbonate dissolution in a more acidic ocean.将定植有夏威夷本土石内生物（euendolithic）与石表生物（epilithic）群落的8月龄叶状滨珊瑚（Porites lobata）块状样本，置于两种不同水体二氧化碳分压（pCO₂）条件下开展为期3个月的实验暴露处理，两组处理的水体pCO₂分别为400ppmv与750ppmv。实验起始与结束阶段，绿藻（chlorophyte）凯氏旋丝藻（Ostreobium quekettii）均为群落优势类群，占比达65%-90%。不同二氧化碳分压处理组间，石内生物物种的相对丰度无显著差异；珊瑚块状样本表面的生物侵蚀面积占比（27%）同样未出现显著差异。然而，凯氏旋丝藻菌丝的侵入深度在750ppmv处理组中显著高于400ppmv组，分别为1.4mm与1mm。由此，升高二氧化碳分压条件下测得的碳酸盐溶解速率较环境背景组高出48%，二者分别为0.46千克碳酸钙每平方米每年（kg CaCO₃·m⁻²·a⁻¹）与0.31 kg·m⁻²·a⁻¹。综上，珊瑚礁生态系统中石内生物介导的碳酸盐生物溶解过程，可能成为未来酸性海洋中碳酸盐溶解的主导机制。