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

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. Corallines have occurred in the Mediterranean area for ∼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. 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). 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). Overall, composition, dynamics and responses to human disturbances of coralline-dominated communities have been well-studied; except for a few species, however, the biology of Mediterranean corallines is poorly known. In terms of diversity, 60 species of corallines are currently reported from the Mediterranean. This number, however, is based on morphological assessments and recent studies incorporating molecular data suggest that the correct estimate is probably much higher. The responses of Mediterranean corallines to climate change have been the subject of several recent studies that documented their tolerance/sensitivity to elevated temperatures and pCO2. These investigations have focused on a few species and should be extended to a wider taxonomic set

Importance du choix des échelles de temps pertinentes pour l'étude du fonctionnement d'écosystèmes marins littoraux

Semi-continuous (1/30 min) records of physicochemical parameters (T, S, DO and pH) have been measured at 1.50 m in Mediterranean coastal waters (Marseilles) from 1998 to 2000, together with meteorological parameters. Physicochemical data were studied in order to synthesise the information at different time scales (inter-annual, season, day, hour), particularly the semi-conservative DO and pH response to hydroclimatic variables. At a daily time scale, important circadian dynamic has been measured under all circumstances with a strong reactivity to irradiance change under the influence of biological activity. This work may contribute to the definition of new tools for coastal waters observation. (C) 2004 Academie des sciences. Publie par Elsevier SAS. Tous droits reserves.Des enregistrements semi-continus (1/30 min) de paramètres physico-chimiques (T,S, OD et pH) ont été réalisés de 1998 à 2000, à 1,50 m de profondeur dans des eaux littorales méditerranéennes (Marseille), associés à des enregistrements d'irradiance et de vitesse et direction du vent. Les données physico-chimiques ont été traitées pour en synthétiser l'information à différentes échelles de temps (inter-annuel, saisonnier, quotidien et horaire) et, en particulier, examiner la réponse des paramètres semi-conservatifs OD et pH aux variables hydroclimatiques. À l'échelle de la journée, des variations circadiennes importantes résultent d'une activité biologique variant avec l'éclairement, avec un fort couplage OD–pH. La réflexion menée sur ces données peut contribuer à la définition d'enregistreurs automatiques, outils d'avenir pour l'observation des eaux côtières