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Vermetid reefs are distinctive bioconstructions of the Mediterranean and other warm temperate and subtropical seas. In the Iberian Peninsula the vermetid endemism Dendropoma lebeche Templado et al., 2016 and the coralline alga Neogoniolithon brassica-florida (Harvey) Setchell & Mason are the main biogenic engineers of this natural heritage. However, very few empirical studies deal with their early patterns of succession. We installed two sets of colonization plates in spring (May) and autumn (November) along a healthy vermetid reef on the island Nueva Tabarca (Alicante, SE Iberian Peninsula), to study the early succession patterns of assemblages. Taxonomic composition and the Shannon diversity index were considered over a 1–2 year period. The seasonal month of installation had a detectable effect on taxonomic composition during the first nine months of immersion, also conditioning the diversity pattern. The succession proceeded faster for the May installation set, where both engineering species showed higher cover values from the beginning. Even though there was hardly any three-dimensional accretion on the plates during this study, those that remained well over a year reached Dendropoma densities close to those reported for healthy Mediterranean vermetid reefs. The use of colonization plates as recruitment enhancers could be a potential tool for restoration procedures, because of the minor impact of their installation and the relatively short time required to achieve high vermetid densities. This research received financial assistance from the project “Seguimiento de macroalgas sobre el litoral rocoso y Posidonia de la Comunidad Valenciana, dentro de la Directiva Marco del Agua” of the Generalitat Valenciana.

Vermetid reefs are a key intertidal habitat in the warm-temperate part of the Mediterranean Sea and in some subtropical and tropical regions in the Atlantic and Pacific oceans. This unique and highly diverse ecosystems is under siege due to both the high anthropogenic pressure and the global climate change, with documented local population declines in the Eastern Mediterranean. This study aims at evaluating the conservation state of vermetid reefs along the Lebanese coast (Eastern Mediterranean), where seawater warming, habitat degradation and coastal urbanization likely threaten their presence. In order to assess the conservation status of vermetid reefs in Lebanon, five sites were randomly selected among those belonging to three impact classes: i) not impacted (i.e. protected), ii) moderately impacted, and iii) impacted. Two different non-destructive methods were applied to assess the presence of living vermetids Dendropoma anguliferum (Monterosato, 1878) and Vermetus triquetrus (Bivona-Bernardi, 1832) which shape the reef, and the associated communities. Our results highlight that no living vermetid reefs were recorded in the impacted sites where evident signs of bio-physical erosion of the reef are already underway. Living individuals of Vermetus triquetrus were found in some not impacted and moderately impacted sites, while living individuals of the endemic reef-builder Dendropoma anguliferum were found only at very low densities at the not impacted (protected) site. Such findings corroborate preliminary observations of population decline in the Eastern Mediterranean, and of vermetid reefs vulnerability to human disturbances. This raises concerns about the near future persistence of vermetid reefs in the region, and represents a call for management and conservation actions to preserve this reef-building species in the Mediterranean Sea.

Este artículo contiene 8 páginas, 4 figuras., Experiments have shown that increasing dissolved CO2 concentrations (i.e. Ocean Acidification, OA) in marine ecosystems may act as nutrient for primary producers (e.g. fleshy algae) or a stressor for calcifying species (e.g., coralline algae, corals, molluscs). For the first time, rapid habitat dominance shifts and altered competitive replacement from a reef-forming to a non-reef-forming biogenic habitat were documented over one-year exposure to low pH/high CO2 through a transplant experiment off Vulcano Island CO2 seeps (NE Sicily, Italy). Ocean acidification decreased vermetid reefs complexity via a reduction in the reef-building species density, boosted canopy macroalgae and led to changes in composition, structure and functional diversity of the associated benthic assemblages. OA effects on invertebrate richness and abundance were nonlinear, being maximal at intermediate complexity levels of vermetid reefs and canopy forming algae. Abundance of higher order consumers (e.g. carnivores, suspension feeders) decreased under elevated CO2 levels. Herbivores were non-linearly related to OA conditions, with increasing competitive release only of minor intertidal grazers (e.g. amphipods) under elevated CO2 levels. Our results support the dual role of CO2 (as a stressor and as a resource) in disrupting the state of rocky shore communities, and raise specific concerns about the future of intertidal reef ecosystem under increasing CO2 emissions. We contribute to inform predictions of the complex and nonlinear community effects of OA on biogenic habitats, but at the sametime encourage the use ofmultiple natural CO2 gradients in providing quantitative data on changing community responses to long-term CO2 exposure., This work contributes to the University of Palermo FFR-A project and the EU-FP7 MedSeA project (grant agreement no. 265103) to M.M.

Vermetid reefs in the Mediterranean Sea are increasingly affected by both anthropogenic actions and global climate change, which are putting this coastal ecosystem at risk. The main species involved in building these reefs are two species of intertidal vermetid gastropods and the crustose calcareous alga, Neogoniolithon brassica-florida, which cements the gastropod shells and thus solidifying the reef edges. In the present study, we examined the pattern of distribution in the field and the environmental sensitivity (thermal tolerance, resilience to low pH, high light intensity and desiccation) of N. brassica-florida along the coasts of Sicily and Israel by means of chlorophyll fluorescence and total alkalinity measurements in situ and in the laboratory. Tidal regimes did not affect photosynthesis of N. brassica-florida but light intensity in the intertidal did. Sensitivity to increased light intensity was amplified by elevated temperature and reduced pH. Winter temperature above 16 °C caused a decrease in the photosynthetic performance of photo-system II. Similarly, a decrease in pH resulted in decreased maximum photosynthetic yield and electron transport rate. Calcification was significantly lower at pH 7.9 as compared with ambient (8.1) pH. In fact, dissolution at pH 7.9 at night was higher than net calcification during the day, suggesting that N. brassica-florida may not be able to contribute to reef accretion under the levels of seawater warming and ocean acidification projected by the end of this century.