Anthropogenic Disturbance Can Determine the Magnitude of Opportunistic Species Responses on Marine Urban Infrastructures

Background: Coastal landscapes are being transformed as a consequence of the increasing demand for infrastructures to sustain residential, commercial and tourist activities. Thus, intertidal and shallow marine habitats are largely being replaced by a variety of artificial substrata (e.g. breakwaters, seawalls, jetties). Understanding the ecological functioning of these artificial habitats is key to planning their design and management, in order to minimise their impacts and to improve their potential to contribute to marine biodiversity and ecosystem functioning. Nonetheless, little effort has been made to assess the role of human disturbances in shaping the structure of assemblages on marine artificial infrastructures. We tested the hypothesis that some negative impacts associated with the expansion of opportunistic and invasive species on urban infrastructures can be related to the severe human disturbances that are typical of these environments, such as those from maintenance and renovation works. Methodology/Principal Findings: Maintenance caused a marked decrease in the cover of dominant space occupiers, such as mussels and oysters, and a significant enhancement of opportunistic and invasive forms, such as biofilm and macroalgae. These effects were particularly pronounced on sheltered substrata compared to exposed substrata. Experimental application of the disturbance in winter reduced the magnitude of the impacts compared to application in spring or summer. We use these results to identify possible management strategies to inform the improvement of the ecological value of artificial marine infrastructures. Conclusions/Significance: We demonstrate that some of the impacts of globally expanding marine urban infrastructures, such as those related to the spread of opportunistic, and invasive species could be mitigated through ecologically-driven planning and management of long-term maintenance of these structures. Impact mitigation is a possible outcome of policies that consider the ecological features of built infrastructures and the fundamental value of controlling biodiversity in marine urban systems

Diversity patterns and long-term changes in the benthic macroalgal vegetation of the Northern Adriatic Sea

The northern Adriatic Sea is a shallow, semienclosed basin characterized by oceanographic features considerably different from the rest of the Mediterranean. The northern Adriatic was recolonized by marine biota in the last 20,000 years, after its emersion at the time of the Last Glacial Maximum. Despite of such recent hydrogeological origin, it hosts a relatively diverse seaweed flora consisting of approximately 500 species (with the highest diversity recorded for the Lagoon of Venice, over 310 species). Literature information and surveys carried out in the last two decades allow to highlight some changes in the composition of its seaweed vegetation. The most evident change is a remarkable loss of fucoid brown algae, which have decreased in distribution and abundance throughout the basin in the last 50-60 years. Fucus virsoides, the only endemic Mediterranean species of Fucus, has suffered the most dramatic decline and is now relegated to a few sites in the Lagoon of Venice, Slovenia and northern Croatia; unfortunately, this species appears now a strong candidate for extinction. Concurrently, a substantial increase in the number of introduced species took place in the last few decades, particularly in the Lagoon of Venice; many alien species are now well-established and some (Caulerpa cylindracea, Gracilaria vermiculophylla, Agardhiella subulata, Hypnea cervicornis, Sargassum muticum) have become locally very abundant. At the same time, recent surveys discovered a previously unappreciated diversity in some habitats, namely the offshore reefs scattered in the northernmost part of the basin (Tegnue and Trezze). At least 173 species have been reported from these biogenic concretions and molecular investigations are now unraveling a great diversity in the number of encrusting coralline algae. We suggest that future investigations on the northern Adriatic seaweed vegetation should focus on detailed assessments of species diversity in poorly-studied areas and continued monitoring of ecologically important/floristically interesting species

Regional environmental conditions determine tolerance to future warming of a marine macroalgae forests

Peer reviewe

Distribution, health and threats to Mediterranean macroalgal forests: defining the baselines for their conservation and restoration.

The worldwide decline of macroalgal forests is raising major concerns for the potentially negative consequences on biodiversity and ecosystem functions, pushing for the definition of specific conservation and restoration measures. Protecting and restoring these habitats requires detailed information on their distribution, ecological status, and drivers of decline. Here, we provide the most updated available information on the distribution of Mediterranean Cystoseira s.l. forests by conducting a comprehensive bibliographic survey of literature published from 2009 to 2021, complemented by unpublished data. We also provide insights into the ecological status of these forests and the stressors affecting them across the Mediterranean basin. Our results show that most Mediterranean coasts remain un(der)studied and that the available information is concentrated in spatially limited coastal areas, restricted to very few species. When the ecological status is reported, data is highly heterogeneous, making any comparisons problematic, what claims for the description and use of easy and standardized monitoring methods for comparative purposes. Drivers of decline of Cystoseira s.l. forest have been even less investigated and, therefore, still poorly characterized. Our results highlight that our current knowledge is still insufficient to implement effective conservation and restoration strategies at the basin scale but also regionally. We call for the urgent need for mapping and standardized monitoring of Cystoseira s.l. forests to obtain baseline information for future management strategies involving their conservation, the mitigation of the stressors threatening them and the restoration of the degraded forests