Search

Macrophytes play an important structural and functional role in marine ecosystems but are experiencing a considerable decline in many areas of the Mediterranean Sea. Despite the long tradition of studies on vegetated marine habitats in the Gulf of Naples (Italy), a gap of knowledge on their long-term dynamics has recently been highlighted, mainly in the most anthropised areas. This work aimed to provide insights from the historic industrialised coastal area of the Site of National Interest (SIN) Bagnoli-Coroglio (Gulf of Pozzuoli, Italy), after decades of chemical contaminations and coastal transformation, to build a baseline for the next remediation and restoration programs. Historical occurrence of macroalgae and seagrasses before, during and after the industrial period was assessed; in particular, we focused the attention mainly on habitat-forming species, due to the vital function played in the trophic net. We observed no differences in the macroalgal diversity between the SIN district and the other parts of the Gulf of Pozzuoli, except for the Gulf of Pozzuoli during the industrial period, where the biodiversity showed a decreasing trend. However, a substantial regression of the largest macrophytes (Fucales) on rocky coasts and of marine monocots on sandy bottoms, all over the area, has been recorded. A loss of about 70% has concerned seagrass cover, mainly Posidonia oceanica, in the contaminated area of the SIN: at present, this engineering species is missing on the bottom, facing the industrialised area. The human-made coastline transformation, the lack of natural substrates and the spatial remoteness among donor populations seem to be the leading causes of the significant decrease, over time, of marine forests in this study area. These factors should be taken into account to establish conservation priorities and for plant restoration.

Corallinales (Rhodophyta) are high Mg-calcite macroalgae and are considered among the most vulnerable organisms to ocean acidification (OA). These sensitive species play fundamental roles in coastal systems as food source and settlement promoters as well as being involved in reef stabilization, and water carbonate balance. At present only a few studies are focused on erect calcifying macroalgae under low pH/high pCO2 and the contrasting results make difficult to predict the ecological consequences of the OA on the coralline algae. In this paper the physiological reasons behind the resistance of Jania rubens, one of the most common calcareous species, to changing ocean pH are analysed. In particular, we studied the photosynthetic and mineralogical response of J. rubens after a three-week transplant in a natural CO2 vent system. The overall results showed that J. rubens could be able to survive under predicted pH conditions even though with a reduced fitness; nevertheless physiological limits prevent the growth and survival of the species at pH 6.7. At low pH (i.e. pH 7.5), the maximum and effective PSII efficiency decreased even if the increase of Rubisco expression suggests a compensation effort of the species to cope with the decreased light-driven products. In these circumstances, a pH-driven bleaching phenomenon was also observed. Even though the photosynthesis decreased at low pH, J. rubens maintained unchanged the mineralogical composition and the carbonate content in the cell wall, suggesting that the calcification process may also have a physiological relevance in addition to a structural and/or a protective role. Further studies will confirm the hypotheses on the functional and evolutionary role of the calcification process in coralline algae and on the ecological consequences of the community composition changes under high pCO2 oceans.

Ocean Acidification (OA) is likely to affect macroalgal diversity in the future with species-specific responses shaping macroalgal communities. In this framework, it is important to focus research on the photosynthetic response of habitat-forming species which have an important structural and functional role in coastal ecosystems. Most of the studies on the impacts of OA involve short-term laboratory or micro/mesocosm experiments. It is more challenging to assess the adaptive responses of macroalgal community to decreasing ocean pH over long-term periods, as they represent the basis of trophic dynamics in marine environments. This work aims to study the physiological traits of a population of Sargassum vulgare that lives naturally in the high pCO 2 vents system in Ischia (Italy), in order to predict the species behaviour in a possible OA future scenario. With this purpose, the photosynthetic performance of S. vulgare was studied in a wild, natural population living at low pH (6.7) as well as in a population transplanted from native (6.7) to ambient pH (8.1) for three weeks. The main results show that the photochemical activity and Rubisco expression decreased by 30% after transplanting, whereas the non-photochemical dissipation mechanisms and the photosynthetic pigment content increased by 50% and 40% respectively, in order to compensate for the decrease in photochemical efficiency at low pH. Our data indicated a stress condition for the S. vulgare population induced by pH variation, and therefore a reduced acclimation capability at different pH conditions. The decline of the PS II maximum quantum yield (F v /F m ) and the increase of PARP enzyme activity in transplanted thalli further supported this hypothesis. The absence of the species at ambient pH conditions close to the vent system, as well as the differences in physiological traits, suggest a local adaptation of S. vulgare at pH 6.7, through optimization of photosynthetic performance.