Carbon cycling in the Caribbean reef-building coral Orbicella: Quantitative evidence for enzymatic control of skeletal density banding and coral-endosymbiont physiological plasticity during seasonal environmental change.

摘要

Although modern Metazoan corals construct Earth's wave-resistant coral reefs, serve as a cornerstone of marine ecology, and may help mitigate the accumulation of greenhouse gases by building a skeleton (composed of a calcium carbonate mineral called aragonite) that functions as a carbon sink, the mechanisms of coral health, growth, and survival have not been fully elucidated. This study demonstrates that corals, found on the leeward coast of Curacao in the Southern Caribbean Sea, manipulate cellular and protein expression of a versatile ectodermal cell, the chromatophore, specifically and plastically, to facilitate or inhibit light-capture by the coral's photosynthetic endosymbiont, the unicellular dinoflagellate zooxanthellae. Quantitative image analyses show that both the cellular density of zooxanthellae and the density of the chromatophores change according to positioning on the reef tract, and therefore levels of irradiance to which the host and endosymbiont are exposed. These results are correlated to the measured change in density articulated in the coral skeleton as sub-annual density banding. Results from this study are considered in the context of recent work by the author and Piggot et al. 2009, which indicate a measureable, cyclical, and complex geobiological response by the coral organism to seasonal changes in SST and ecological differences in irradiance experienced by neighboring colonies on the same reef tract. Foremost, it is hypothesized here that low-density regions of the coral skeleton are formed during the steady-state coral-symbiont existence and are thusly recommended as the targets of isotopic analyses for paleoclimatological studies.