Abstract
Crustose coralline red algae (CCA) play a key role in the consolidation of many modern tropical coral reefs. It is unclear, however, if their function as reef consolidators was equally pronounced in the geological past. Using a comprehensive database on ancient reefs, we show a strong correlation between the presence of CCA and the formation of true coral reefs throughout the last 150 Ma. We investigated if repeated breakdowns in the potential capacity of CCA to spur reef development were associated with sea level, ocean temperature, CO2 concentration, CCA species diversity, and/or the evolution of major herbivore groups. Model results show that the correlation between the occurrence of CCA and the development of true coral reefs increased with CCA diversity and cooler ocean temperatures while the diversification of herbivores had a transient negative effect. The evolution of novel herbivore groups compromised the interaction between CCA and true reef growth at least three times in the investigated time interval. These crises have been overcome by morphological adaptations of CCA.
Highlights
Crustose coralline algae (CCA) play a key role in the consolidation of many modern tropical coral reefs
Using data from the PaleoReefsDatabase (PARED), a comprehensive compendium of geological and paleontological data of Phanerozoic reef sites as described previously[18,19,20], we evaluate the role of CCA in coral reef development at the level of geological
We highlight alternative explanations for the correlation between CCA occurrences and the formation of true reefs. This includes the impact of herbivore radiation on corals rather than on CCA directly and ecological niches for CCA provided by increased reef growth
Summary
Crustose coralline algae (CCA) play a key role in the consolidation of many modern tropical coral reefs. Even though there are examples of true reefs that grow successful without this CCA ridge under wave-exposure[12,13], CCA are still considered as “the glue that holds coral reefs together”[9] in many cases Another key factor for the success of modern coral reefs are grazing organisms such as echinoids and parrot fish, because they remove fleshy algae from the reef surface[14,15]. We highlight alternative explanations for the correlation between CCA occurrences and the formation of true reefs This includes the impact of herbivore radiation on corals rather than on CCA directly and ecological niches for CCA provided by increased reef growth
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