Attached and free-living crustose coralline algae and their functional traits in the geological record and today

Crustose coralline algae (CCA) are important ecosystem engineers and carbonate producers today and in the geological past. While there is an increasing number of publications on CCA every year, it is evident that there are many misunderstandings and inconsistencies in the assignment of CCA to taxonomic and functional groups. This is partly because CCA are treated by biologists, ecologists and palaeontologists as well as covered by studies published in journals ranging from geo- to biosciences, so that there is often a mixture of terminology used and differing scientific focus. In this review, a comprehensive overview is given on what is known about CCA, their functional traits and their roles in environments from the present and the past. In this context, some bridges are built between the commonly different viewpoints of ecologists and palaeontologists, including suggesting a common and straightforward terminology, highlighting and partially merging different taxonomic viewpoints as well as summarizing the most important functional traits of CCA. Ideally, future studies should seek to quantitatively analyse potential implications for CCA and their associated organisms under ongoing global change.