Net calcification rates for coral reef and other calcifiers have been shown to decline as ocean acidification (OA) occurs. However, the role of calcium carbonate dissolution in lowering net calcification rates is unclear. The objective of this study was to distinguish OA effects on calcification and dissolution rates in dominant calcifying macroalgae of the Florida Reef Tract, including two rhodophytes (Neogoniolithon strictum, Jania adhaerens) and two chlorophytes (Halimeda scabra, Udotea luna). Two experiments were conducted: (1) to assess the difference in gross (45Ca uptake) versus net (total alkalinity anomaly) calcification rates in the light/dark and (2) to determine dark dissolution (45CaCO3), using pH levels predicted for the year 2100 and ambient pH. At low pH in the light, all species maintained gross calcification rates and most sustained net calcification rates relative to controls. Net calcification rates in the dark were ~84% lower than in the light. In contrast to the light, all species had lower net calcification rates in the dark at low pH with chlorophytes exhibiting net dissolution. These data are supported by the relationship (R2 = 0.82) between increasing total alkalinity and loss of 45Ca from pre-labelled 45CaCO3 thalli at low pH in the dark. Dark dissolution of 45CaCO3-labelled thalli was ~18% higher in chlorophytes than rhodophytes at ambient pH, and ~ twofold higher at low pH. Only Udotea, which exhibited dissolution in the light, also had lower daily calcification rates integrated over 24 h. Thus, if tropical macroalgae can maintain high calcification rates in the light, lower net calcification rates in the dark from dissolution may not compromise daily calcification rates. However, if organismal dissolution in the dark is additive to sedimentary carbonate losses, reef dissolution may be amplified under OA and contribute to erosion of the Florida Reef Tract and other reefs that exhibit net dissolution.

中文翻译：

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海洋酸化对热带珊瑚礁大型藻类钙化和溶解的影响

随着海洋酸化 (OA) 的发生，珊瑚礁和其他钙化物的净钙化率已显示出下降。然而，碳酸钙溶解在降低净钙化率方面的作用尚不清楚。本研究的目的是区分 OA 对佛罗里达礁区主要钙化大型藻类的钙化和溶解速率的影响，包括两种红藻（Neogoniolithon strictum，Jania adhaerens）和两种绿藻（Halimeda scabra，Udotea luna）。进行了两个实验：(1) 评估总（45Ca 摄取）与净（总碱度异常）钙化率在明/暗条件下的差异，以及 (2) 使用预测的 pH 值确定暗溶解 (45CaCO3) 2100 年和环境 pH 值。在光照下的低 pH 值下，与对照相比，所有物种都保持总钙化率和最持续的净钙化率。黑暗中的净钙化率比光照下低约 84%。与光照相反，所有物种在黑暗中在低 pH 值下的净钙化率较低，叶绿素表现出净溶解。这些数据得到了在黑暗中的低 pH 值下，总碱度增加与 45Ca 从预标记的 45CaCO3 菌体损失之间的关系 (R2 = 0.82) 的支持。在环境 pH 值下，45CaCO3 标记的菌体在绿藻中的暗溶解比红藻高约 18%，在低 pH 值时高约两倍。只有在光照下溶解的 Udota，在 24 小时内也具有较低的每日钙化率。因此，如果热带大型藻类能够在光照下保持高钙化率，在黑暗中溶解后较低的净钙化率可能不会影响每日钙化率。然而，如果黑暗中的有机体溶解会增加沉积碳酸盐的流失，那么在 OA 下珊瑚礁溶解可能会被放大，并导致佛罗里达礁带和其他出现净溶解的珊瑚礁的侵蚀。