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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.

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.

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.

Vermetid reefs are a key intertidal habitat in the Mediterranean. Despite recent evidence of local extinction in the Eastern Mediterranean, their role as habitat engineers and the high numbers of ecosystem services they provide, vermetid reefs are among the least known marine habitats of the Mediterranean. Here we present a literature-based study to assess for the first time their distribution inside the basin and provide evidence of a general lack of protection at Mediterranean scale.