![]() Although bioconstructions built by corallines exist virtually in every sea, in the Mediterranean they reach a particularly high spatial and bathymetric extent (coralligenous concretions alone are estimated to exceed 2,700 km2 in surface). Some Mediterranean corallines are key ecosystem engineers that produce or consolidate biogenic habitats (e.g., coralligenous concretions, Lithophyllum byssoides rims, rims of articulated corallines, maerl/rhodolith beds). Corallines have occurred in the Mediterranean area for approximately 140 My and are well represented in the subsequent fossil record for some species currently common the fossil documentation dates back to the Oligocene, with a major role in the sedimentary record of some areas. In this review we assess the state of knowledge for the coralline algae of the Mediterranean Sea, a group of calcareous seaweeds imperfectly known and considered highly vulnerable to long-term climate change. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2 it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition it is less diverse today and was the most sensitive to ocean acidification. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Therefore, the coralline algal turf in the lower part of the intertidal zone is not just an extension of the “Photophilous Algae” community but a benthic community its own.Ĭalcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. The occurrence of congeneric species pairs (Tricolia miniata/Tricolia pullus, Nodulus spiralis/Nodulus contortus) which achieve high abundance in one of the levels and are scarce or absent in the other was striking. The species Pisinna glabrata, Skeneopsis planorbis, Nodulus spiralis and Tricolia miniata dominated the mesolittoral stage. ![]() This taxocenosis was compared to that previously studied from the infralittoral level, where the alga Halopteris scoparia was prevailing and 4084 specimens belonging to 66 species of Mollusca were found. ![]() A total of 2520 mollusc specimens belonging to 46 species were identified. The molluscan fauna inhabiting the algal turfs of mesolittoral rocky outcrops, dominated by the coralline alga Ellisolandia elongata, has been quantitatively analysed in a Marine Protected Area of Málaga, southern Spain (W Mediterranean). ![]()
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