Coralline Algae in a Changing Mediterranean Sea: How Can We Predict Their Future, if We Do Not Know Their Present?

Abstract

In this review we assess the state of knowledge for the coralline algae of the
\nMediterranean Sea, a group of calcareous seaweeds imperfectly known and considered
\nhighly vulnerable to long-term climate change. Corallines have occurred in the
\nMediterranean area for ∼140 My and are well-represented in the subsequent fossil
\nrecord; for some species currently common the fossil documentation dates back to
\nthe Oligocene, with a major role in the sedimentary record of some areas. Some
\nMediterranean corallines are key ecosystem engineers that produce or consolidate
\nbiogenic habitats (e.g., coralligenous concretions, Lithophyllum byssoides rims, rims of
\narticulated corallines, maerl/rhodolith beds). Although bioconstructions built by corallines
\nexist virtually in every sea, in the Mediterranean they reach a particularly high spatial
\nand bathymetric extent (coralligenous concretions alone are estimated to exceed 2,700
\nkm2 in surface). Overall, composition, dynamics and responses to human disturbances
\nof coralline-dominated communities have been well-studied; except for a few species,
\nhowever, the biology of Mediterranean corallines is poorly known. In terms of diversity,
\n60 species of corallines are currently reported from the Mediterranean. This number,
\nhowever, is based on morphological assessments and recent studies incorporating
\nmolecular data suggest that the correct estimate is probably much higher. The responses
\nof Mediterranean corallines to climate change have been the subject of several recent
\nstudies that documented their tolerance/sensitivity to elevated temperatures and pCO2.
\nThese investigations have focused on a few species and should be extended to
\na wider taxonomic set.