Thirty years since the coral reef CO<sub>2</sub> sink/source debate

In the late 1990s, a debate emerged over whether coral reefs are net sources or sinks for CO2. The prevailing consensus held that coral reefs, through calcification, act as short-term sources of CO2. However, Kayanne et al. (1995) challenged this view by presenting observations that the Shiraho Reef on Ishigaki Island was, in fact, absorbing CO2. Despite further surveys, research, and discussions—both directly and indirectly related to the debate—the consensus that coral reefs are CO2 sources remained in place, and by the 2000s, the debate was considered settled. Nonetheless, the discussions significantly advanced our understanding of the relationship between coral reef community metabolism and the marine carbon cycle. Additionally, the measurement techniques and models developed during this period continue to play a key role in current ocean acidification research.