Coral skeletal extension rate: An environmental signal or a subject to inaccuracies?

Abstract

Coral skeletal extension rate has been widely used to assess coral growth characteristics across environmental gradients and as an environmental proxy. Herein, the potential sources of errors when measuring skeletal extension rates are identified and discussed, and it is demonstrated that measurements of this growth parameter do not necessarily reflect an annual time scale and can result in substantial miscalculations. Instead, it is dissepiment spacing and number that best reflect the time scale. On the other hand, calcification rate is the growth parameter that appears to better reflect the environmental controls that regulate physiological processes in symbiotic corals. Nonetheless, any error associated with measuring extension rate would result in under- and overestimation of calcification rate values, which could lead to huge errors if this growth parameter is used as an environmental proxy. The aim is to promote further discussion, avoid future misuse of extension rate as an environmental proxy, and encourage future research about how to accurately measure extension rate and the use of calcification rate as an environmental proxy.