Fabrizio Gianni

Aim: Climate change affects dramatically biogenic habitats by altering the geographic distribution of the foundational species and the structure of landscapes they form. As a consequence, the associated biotic communities could experience habitat loss and fragmentation. In this paper, we assess how climate change impacts the geographic distribution of Mediterranean seagrass habitats and the cascading effects on the biodiversity of metacommunities they support. Location: Mediterranean Sea. Taxon: Posidonia oceanica and Cymodocea nodosa. Methods: We employ state‐of‐the‐art physical and biogeochemical data for the Mediterranean Sea to model the seagrass distribution in the present climate using Species Distribution Models (SDMs). Based on the identified habitat configuration, we employ a neutral metacommunity model (NMM) to simulate virtual metacommunities structured by stochastic demographic processes and dispersal. Results: SDMs were fitted with acceptable performances. We show a strong range contraction for both seagrass species (with uncertain predictions for the Southern and Eastern Mediterranean), a decrease in alpha diversity of associated communities, and an increase in beta diversity at the Mediterranean scale. Such changes are solely the result of the rearrangement of the landscape caused by climate change and create an offset for any distributional change related to niche effects. For different basins, we show that patterns of alpha diversity under realistic species dispersal are strongly correlated with habitat availability, while beta diversity is largely influenced by the changes in the spatial configuration of seagrass habitats. Main Conclusions: By highlighting hotspots of metacommunity change linked to habitat fragmentation, our method can be useful for planning conservation and restoration measures at local and regional scales. We show that, besides niche effects, climate change can impact species distribution by altering the landscape structure.

The northern Adriatic Sea (NAS) hosts numerous biogenic subtidal reefs that are considered biodiversity hotspots. Several studies have already investigated the origin and biodiversity of these reefs. However, many of them are still unexplored and further knowledge is needed for their conservation. Here, the spatial variability, epibenthic community structure, and environmental features that characterize these habitats were investigated. Fifteen randomly selected reefs were sampled between 2013 and 2017, including some remote sites that have never been studied before. A fuzzy k-means clustering method and redundancy analysis were used to find similarities among sites in terms of epibenthic assemblages and to model relationships with abiotic variables. The results showed that these reefs are highly heterogeneous in terms of species composition and geomorphological features. The results were also consistent with previous studies and highlighted three main types of benthic assemblages defined by the dominance of different organisms, mainly reflecting the coastal-offshore gradient: nearshore reefs, generally dominated by stress-tolerant species; reefs at a middle distance from the coast, characterized by sponges, non-calcareous encrusting algae and ascidians; offshore reefs, dominated by reef builders. However, distance from the coast was not the only factor affecting species distribution, as other local factors and environmental characteristics also played a role. This kind of biogenic reefs in temperate seas are still poorly known. The present work contributed to shed further light on these habitats, by complementing the results of previous studies on their natural diversity, highlighting the specificity of the epibenthic communities of NAS reefs and the need to improve current, still inadequate, conservation measures.

The aim of the present study was to propose a biotic index (North Adriatic Mesophotic BiogEnic Reefs, NAMBER) suitable for assessing the ecological quality of the mesophotic biogenic reefs of the northern Adriatic continental shelf based on photographic sampling. At each of the 20 study sites, the degree of bioconstruction (expressed as percentage cover of crustose coralline algae), the α‐diversity (expressed as the mean number of taxa), and the degree of sensitivity to human disturbance and climate change (based on literature data and expert judgement) of the benthic assemblages were selected as descriptors and combined in the NAMBER index, using the best values that the three metrics can currently achieve in the studied region as a reference. The study highlighted that there was large spatial heterogeneity among reefs and high variability in the ecological quality values obtained by NAMBER, ranging from bad to high. The index indicates that reefs lying furthest from the coast, under substantially lower anthropogenic pressure, have a generally higher status of environmental quality. However, a clear geographical pattern did not emerge, as reefs close together often had different ecological qualities. The NAMBER index, which combines three ecological descriptors, in accordance with the requirements of the European Marine Strategy Framework Directive, represents a specific adaptation to the northern Adriatic Sea of a multimetric index previously developed for the north‐western Mediterranean Sea, capitalizing on previous knowledge and research efforts. This multimetric biotic index provides an effective standardized tool for monitoring programmes and environmental impact assessments in the northern Adriatic mesophotic biogenic reefs and lays the foundation for ecosystem‐based management and conservation in this basin.

Since the adoption of the Habitats and Birds Directives by EU governments, marine Natura 2000 (N2K) sites have been established in the European Mediterranean Sea, creating one of the largest international networks of protected areas. Nevertheless, to date, marine N2K sites are generally scarcely implemented, studied and monitored, and thus their management effectiveness is weak, and their environmental status is often unknown. The Interreg Italy-Croatia ECOSS project aimed at establishing the ECOlogical observing system of the Adriatic Sea (ECOAdS), to integrate the existing research and monitoring activities in the area, and to promote data sharing at international level, for enhancing monitoring and conservation in Adriatic N2K network. In the framework of ECOSS, a conceptual model was developed and applied to selected N2K sites, to review the existing knowledge, assess site effectiveness, and suggest possible improvements in their monitoring and management based on the contribution that ECOAdS can provide to their implementation. Information on social, ecological, and oceanographic elements related to the conservation and management of these case studies was gathered by consulting the project partners involved in the management and monitoring of the sites and through a literature review. The results of this study revealed a discouraging condition with no management plan in most of the sites, while regulatory measures are generally in place but without surveillance. Monitoring activities are performed occasionally, and information on presence and status of protected species is often lacking or outdated. Although the N2K network provides a unique opportunity to advance marine conservation and achieve the 30% conservation target by 2030, the biggest challenge ahead is the proper management and monitoring of N2K sites. The proposed conceptual model may be taken as a framework to properly set up ecological observing systems in the N2K network and help overcome current limitations, integrating scientific research within the N2K conservation strategies.

The role of herbivorous fish in threatening marine forests of temperate seas has been generally overlooked. Only recently, the scientific community has highlighted that high fish herbivory can lead to regime shifts from canopy‐forming algae to less complex turf communities. Here, we present an innovative herbivorous fish deterrent device (DeFish), which can be used for conservation and restoration of marine forests. Compared to most traditional fish exclusion systems, such as cages, the DeFish system does not need regular cleaning and maintenance, making it more cost‐efficient. Resistance of DeFish was tested by installing prototypes at different depths in the French Riviera and in Montenegro: more than 60% of the devices endured several years without maintenance, even if most of them were slightly damaged in the exposed site in Montenegro. The efficacy of DeFish in limiting fish herbivory was tested by an exclusion experiment on Cystoseira amentacea in the French Riviera. In a few months, the number of fish bite marks on the seaweed was decreased, causing a consequent increase in algal length. The device here presented has been conceived for Mediterranean canopy‐forming algae, but the same concept can be applied to other species vulnerable to fish herbivory, such as kelps or seagrasses. In particular, the DeFish design could be improved using more robust and biodegradable materials. Innovative engineering systems, such as DeFish, are expected to become useful tools in the conservation and restoration of marine forests, to complement other practices including active reforestation, herbivore regulation, and regular monitoring of their status.

Canopy-forming algae are declining globally due to multiple disturbances. This decline has recently been on the increase due to the spread of some tropical herbivorous fishes. This new phenomenon has drawn attention to the effects of fish herbivory in temperate areas, which have been assumed to be negligible compared to that of invertebrates, such as sea urchins. In this study, the impact of a Mediterranean native herbivorous fish (Sarpa salpa, salema) was assessed on the canopy-forming seaweed Cystoseira amentacea var. stricta. Cystoseira amentacea forms belts in the infralittoral fringe of wave-exposed shores, which has so far been considered a refuge from fish herbivory. To test the effects of salema feeding on natural C. amentacea belts, an innovative herbivore deterrent device was conceived. Salema had a significant effect on C. amentacea by decreasing algal size, biomass and fertility, by up to 97%. The results suggest that the contribution of salema feeding to the loss of Cystoseira forests in the Mediterranean may have been overlooked. In addition, the analysis of temporal and spatial patterns of salema landings in the Mediterranean Sea suggests that salema abundance may have increased recently. Thus, along with invertebrate herbivory and anthropogenic stressors, fish herbivory may also represent a potential threat to algal forests in temperate areas.

Cystoseira species are some of the most important marine ecosystem-engineers, forming extended canopies comparable to land forests. Such forests are sensitive to human disturbances, like the decrease in water quality, the coastal development and the outbreak of herbivores. Conspicuous historical declines have been reported in many regions and several Cystoseira species are presently protected by European Union (EU) environmental policies. The aim of this work was to synthesize the conservation perspectives of Cystoseira forests in the Mediterranean Sea, focusing on the opportunities offered by artificial restoration and highlighting the potential role of Marine Protected Areas (MPAs). MPAs give a better protection to healthy forests than non-managed sites and may be a source of propagules for natural recovery and/or for non-destructive artificial restoration of nearby damaged forests. MPAs lacking Cystoseira forests may also represent preferential sites for reforestation. We proposed a flow-chart for the conservation and a reasoned restoration of Cystoseira in the Mediterranean Sea. The successful conservation of Cystoseira forests is still possible, via raising public awareness on the role of Cystoseira and reducing human impacts on coastal ecosystems. Such actions have to be coupled with more specific large-scale management plans, encompassing restoration actions and enforcement of protection within MPAs.

Cystoseira species are some of the most important marine ecosystem-engineers, forming extended canopies comparable to land forests. Such forests are sensitive to human disturbances, like the decrease in water quality, the coastal development and the outbreak of herbivores. Conspicuous historical declines have been reported in many regions and several Cystoseira species are presently protected by European Union (EU) environmental policies. The aim of this work was to synthesize the conservation perspectives of Cystoseira forests in the Mediterranean Sea, focusing on the opportunities offered by artificial restoration and highlighting the potential role of Marine Protected Areas (MPAs). MPAs give a better protection to healthy forests than non-managed sites and may be a source of propagules for natural recovery and/or for non-destructive artificial restoration of nearby damaged forests. MPAs lacking Cystoseira forests may also represent preferential sites for reforestation. We proposed a flow-chart for the conservation and a reasoned restoration of Cystoseira in the Mediterranean Sea. The successful conservation of Cystoseira forests is still possible, via raising public awareness on the role of Cystoseira and reducing human impacts on coastal ecosystems. Such actions have to be coupled with more specific large-scale management plans, encompassing restoration actions and enforcement of protection within MPAs.