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Invasive seaweeds are listed among the most relevant threats to marine ecosystems worldwide. Biodiversity hotspots, such as the Mediterranean Sea, are facing multiple invasions and are expected to be severely affected by the introduction of new non-native seaweeds in the near future. In this study, we evaluated the consequences of the shift from the native Ericaria brachycarpa to the invasive Asparagopsis taxiformis habitat on the shallow rocky shores of Favignana Island (Egadi Islands, MPA, Sicily, Italy). We compared algal biomass and species composition and structure of the associated epifaunal assemblages in homogenous and mixed stands of E. brachycarpa and A. taxiformis. The results showed that the biomass of primary producers is reduced by 90% in the A. taxiformis invaded habitat compared to the E. brachycarpa native habitat. The structure of the epifaunal assemblages displayed significant variations among homogenous and mixed stands. The abundance, species richness and Shannon-Wiener diversity index of the epifaunal assemblages decreased by 89%, 78% and 40%, respectively, from homogenous stands of the native E. brachycarpa to the invasive A. taxiformis. Seaweed biomass was the structural attribute better explaining the variation in epifaunal abundance, species richness and diversity. Overall, our results suggest that the shift from E. brachycarpa to A. taxiformis habitat would drastically erode the biomass of primary producers and the associated biodiversity. We hypothesize that a complete shift from native to invasive seaweeds could ultimately lead to bottom-up effects on rocky shore habitats, with negative consequences for the ecosystem structure, functioning, and the services provided.

Invasive seaweeds are listed among the most relevant threats to marine ecosystems worldwide. Biodiversity hotspots, such as the Mediterranean Sea, are facing multiple invasions and are expected to be severely affected by the introduction of new non-native seaweeds in the near future. In this study, we evaluated the consequences of the shift from the native Ericaria brachycarpa to the invasive Asparagopsis taxiformis habitat at shallow rocky shores of Favignana Island (Egadi Islands, MPA, Sicily, Italy). We compared algal biomass and species composition and structure of the associated epifaunal assemblages in homogenous and mixed stands of E. brachycarpa and A. taxiformis. Results showed that the biomass of primary producers is reduced by 90% in the A. taxiformis invaded habitat compared to the E. brachycarpa native habitat. The structure of the epifaunal assemblages displayed significant variations among homogenous and mixed stands. The abundance, species richness and Shannon-Wiener diversity index of the epifaunal assemblages decreased by 89%, 78% and 40%, respectively from homogenous stands of the native E. brachycarpa to the invasive A. taxiformis. Seaweed biomass was the structural attribute better explaining the variation of epifaunal abundance, species richness and diversity. Overall, our results suggest that the shift from E. brachycarpa to A. taxiformis habitat would drastically erode the biomass of primary producers and the associated biodiversity. We hypothesize that a complete shift from native to invasive seaweeds can ultimately lead to bottom-up effects in rocky shore habitats, with negative consequences for the ecosystem structure, functioning and the services provided.

Marine and coastal ecosystems are among the most productive environments in the world and their stocks of natural capital offer a bundle of vital ecosystem services. Anthropogenic pressure seriously threatens health and long-term sustainability of marine environments. For these reasons, integrated approaches capable of combining ecological and socio-economic aspects are needed to achieve nature conservation and sustainability targets. In this study, the value of natural capital of the Egadi Islands Marine Protected Area (EI-MPA) was assessed through a biophysical and trophodynamic environmental accounting model. The emergy value of both autotrophic and heterotrophic natural capital stocks was calculated for the main habitats of the EI-MPA. Eventually, the emergy value of natural capital was converted into monetary units to better communicate its importance to local managers and policy-makers. The total value of natural capital in the EI-MPA resulted in 1.12·10 21 sej, equivalent to about 1.17 billion of euros. In addition, using Marxan software, the results of the environmental accounting were integrated with spatial data on main human uses. This integration took into account the trade-offs between conservation measures and human exploitation by means of two different scenarios, with and without considering human uses in the EI-MPA. The comparison between the scenarios highlighted the importance of taking into account human activities in marine spatial planning (MSP), allowing the identification of key areas for natural capital conservation. In conclusion, this study showed the importance of integrating environmental accounting with conservation planning to support effective strategies for ecological protection and sustainable management of human activities. The results of this study represent a first benchmark useful to explore alternative nature conservation strategies in the EI-MPA, and, more in general, in Mediterranean MPAs.

Invasive seaweeds threaten biodiversity and socio-economics values of worldwide marine ecosystems. Understanding to what extent invasive seaweeds can modify local biodiversity is one of the main priorities in conservation ecology. We compared the molluscan assemblage of the invasive Asparagopsis taxiformis with that of the native Ericaria brachycarpa and explore if variation in the molluscan assemblage diversity was related to the substrate attributes (biomass, and thallus, canopy, and interstitial volumes) of the algae. Results showed that A. taxiformis harboured lower diversity and trophic structure of the molluscan assemblage compared to E. brachycarpa. Biomass was the variable that better explained the variation of abundance and number of species as well as the multivariate structure of the molluscan assemblage. Overall, our results suggest that a complete habitat shift from native to invasive species can potentially trigger bottom-up effects in rocky shores habitats, reducing the biodiversity and the services provided by the invaded habitat.

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.

The fan shell P. nobilis (Linnaeus, 1758) is the largest marine bivalve in the Mediterranean Sea which acts as ecosystem engineer, offering an adequate substratum to several associated benthic species. P. nobilis is threatened by the reduction and loss of its natural habitat and by increased anthropogenic inputs into coastal waters. The knowledge on the population of this species are scarce, especially as concerns Sicily and its coasts. This study focused on the density of population, spatial distribution, level of burial and orientation of the population of P. nobilis in the harbour area of Favignana island (western coast of Sicily, Italy). The fan shell surveys were carried out by SCUBA diving using a 50m-transect line perpendicular to the coastline. For each P. nobilis censused, maximum (W) width, minimum width (w) and unburied length (UL) were measured; shell orientation (Or) was determined using an underwater compass and considering the magnitude of the angle formed by the vector and the magnetic north. The specimen status (dead or alive), the depth (by using the electronic depth meter of a diving computer) were recorded. In addition, the geographical coordinates were marked for each individual along the transect by means of a Global Positioning System (GPS). Total shell height (HT) was estimated using a formula considered suitable for the populations of this studied area. The density of P. nobilis was ±11 ind. 100m2, the total height (HT) and the maximum width (W) of the shells was 33 cm and 13,6 cm respectively. In the aim of the "MPA of Egadi Islands" to confirm the need of a new management to protect the biodiversity of the harbour area, more conservation measures are necessary in order to improve the preservation of this endangered species.