Programma della conferenza

Seagrasses are essential to marine ecosystems, where they often play the role of foundation species and provide key ecosystem services, from habitat provision and coastal protection to water purification and carbon sequestration. We collated distribution data for >90% of Mediterranean seagrass species to analyze their vulnerability to climate change using species distribution modeling and climate-niche factor analysis. Our results show that seagrasses generally exhibit narrow ecological tolerances to variations in the environmental variables associated with their current distribution, indicating high sensitivity to climate change. Our study highlights the increasing vulnerability of seagrasses under progressively more severe climate change scenarios and, in particular, identifies significant risks under SSP 8.5. We also find that Posidoniaceae consistently show higher levels of vulnerability than Cymodoceaceae, and that the Adriatic Sea is a regional hotspot of vulnerability compared to other Mediterranean sub-basins. Our study thus highlights the need for targeted mitigation strategies to protect seagrass habitats from the impacts of climate change, and suggests ways to prioritize interventions based on the differential vulnerability projected for different taxonomic groups and/or geographic regions.

Coastal sand dunes are ecologically and economically important habitats but are threatened by multiple factors including climate changes. Climate scenarios predict the intensity and frequency of precipitations will decrease in coastal Mediterranean areas by the end of the century. Water shortage associated with reduced precipitations is a major factor limiting seedling survival in dunes. A greater precipitation reduction is expected in spring, a period favorable for dune plant recruitment. Depositions of Posidonia oceanica wrack can be also present along beaches and embryo dunes. This material can provide essential nutrients to dune plants, but whether it can affect the ability of seedlings to cope with abiotic stressors like water shortage is still largely unknown. Here, the individual and combined effects of precipitation amount (current vs. predicted reduced according to SSP2-4.5 stabilization scenario) and wrack deposition (no wrack vs.wrack alone vs. wrack plus sand) on seedling establishment and growth of three dune species, Cakile maritima, Thinopyrum junceum, and Calamagrostis arenaria, were investigated in mesocosm. Wrack water holding capacity and leachate chemical/physical properties were also evaluated. Neither precipitation nor wrack affected seed germination and seedling emergence success for all investigated species. Reduced precipitation decreased root development while wrack promoted seedling aboveground elongation, regardless of its composition. Reduced precipitation also reduced biomass production in T. junceum and C. arenaria but only in the absence of wrack. Wrack retained water up to five-fold its weight and increase water pH, conductivity, and nutrient content. Our findings indicate that expected reduced precipitations could make dune plant seedlings more vulnerable to additional stressors. But wrack could mitigate reduced precipitation effects in T. junceum and C. arenaria by retaining most available water. Thus, maintaining P. oceanicawrack on beaches could be a valuable, eco-sustainable strategy for supporting the resilience of dunes under ongoing climate change.

Dissolved oxygen in water represents an essential substrate for most marine ecosystems. Its concentration is steadily decreasing in response to global warming. Alhough short-term impacts are well understood, the spatiotemporal paucity of instrumental records, coupled with numerical simulations with conflicting predictions about the future of oxygen deficient zones (ODZs) in the tropical Pacific, makes it difficult to make long-term predictions about the future of oxygen in the oceans and the resulting impact on marine ecosystems.

An alternative and complementary approach is given by the study of global warming events in the history of our planet that have left a tangible and measurable trace in the geological record. The use of geochemical and morphometric analyses on fossil organisms can provide important information on the long-term response of ocean habitability to temperature rise. We show here new evidence in favor of tropical subsurface oxygenation during the Paleocene-Eocene Thermal Maximum (PETM), a rapid global warming event that serves as a “geologic analogue” to ongoing warming.

The isotopes of organic nitrogen on fossil planktonic foraminifera shells indicate that the tropical Pacific ODZ contracted during the PETM, implying an increase in oxygen in the vicinity. The plication of the metabolic theory of aquatic ectotherms in the fossil record, shows that the increase in size of tropical planktonic foraminifera, despite warming, implies that oxygen availability increased in the tropical Pacific.

These changes are consistent with biogeochemical models for the SSP5-8.5 scenario for 2300, in which a decline in biological productivity and subsequent respiration rates allow tropical oxygen to increase, even as global ocean oxygen decreases. The upping tropical oxygen may have alleviated the physiological stress on planktonic organisms in areas of higher biodiversity, helping to avoid a mass extinction of planktonic organisms during the PETM, despite the largest benthic extinction in the Cenozoic.

Crustose coralline algae (CCA) are among the major calcifying organisms in the Mediterranean Sea and are important foundation taxa in the photic zone. They enhance the structural complexity of marine ecosystems, promoting settlement and metamorphosis of various invertebrates. Due to multiple local factors and climate change effects, coralligenous reefs are in decline. Investigations on CCA, the foundation species, are therefore necessary to know their adaptability to different conditions and thus to evaluate the possibility of possible restoration actions based on CCA transplantation. To this end, a manipulative field experiment was conducted in Costa Paradiso (North Sardinia, Italy) where CCA recruited at 35 m of depth on artificial substrates (terracotta and ceramics 10x10 cm tiles) with varying initial coverage (high and low): to disentangle the effects of irradiance from those of the temperature, three treatments were used by fixing the tiles at 1) 15 m of depth where they were placed in a natural cavity so that the algae could experience the 35 m light irradiance but water temperature above the thermocline (LLHT), at 2) 15 m of depth outside the cavity (HLHT), and at 3) the same origin depth, 35 m, where irradiance was low and temperature below the thermocline (LLLT). The recruits exhibited greater growth when exposed to higher temperature compared to those in combined low light and low temperature conditions. A posteriori, molecular and morphological analyses were conducted to identify the CCA species which allowed estimating the species-specific growth rate at the studied conditions.

Managing marine aquatic resources is a complex challenge due to the intricated processes unfolding at sea. This challenge is amplified in the Mediterranean Sea, where pronounced seascape, climatic, and social variability critically affect the biodiversity of the basin across sub-regions. The traditional approach to fisheries management in this area has long relied on stock assessment with classical stock-recruitment models to reconstruct historical population dynamics and predict their response to different effort regulation measures. However, these methods lack robust predictive power due to their limited ability to incorporate changing environmental conditions and anthropogenic pressure. Our work proposes a spatially explicit metapopulation model of the European hake (Merluccius merluccius) within the area of the Adriatic and Ionian Seas. The model integrates the effect of environmental variables on life-history traits and larval connectivity. This approach, therefore, allows us to predict the response of the hake stock to different scenarios of climate change (RCPs) and fishing pressure, generating a realistic representation of the stock dynamics in the medium to long term and predicting the potential future spatial distribution of the stock. This tool enables the mapping of different performance indicators in space and time, informing the development of area- and effort-based management strategies that optimize resource conservation while identifying areas particularly sensitive to management interventions. This modelling framework provides a flexible and valuable tool for designing effective marine protected area networks and facilitating sustainable fisheries management practices.

In the Mediterranean Sea the temperature increase has accelerated over recent years, affecting at different levels key species like the endemic seagrass Posidonia oceanica. Recently, in warm-edged locations of Mediterranean basin, P. oceanica bleaching (i.e. discoloration of leaves still attached to the shoots) has been observed in late summer, but the factors that trigger the phenomenon remain unknown. This study aimed at i) estimating the spatio-temporal variability of P. oceanica leaf condition in Konnos Bay, Cyprus (mensurative experiment) and ii) investigating the role of light irradiation and temperature on leaf bleaching by a reciprocal transplant of plant cuttings from different depths under a light gradient obtained by using shading nets (manipulative experiment). To pursue our goals, morphological (i.e. leaf area, leaf necrosis, leaf bleaching) and eco-physiological (i.e. chlorophyll, carotenoids, anthocyanins) responses were considered. The hypothesis supported by the mensurative experiment is that interactive effects of irradiance and temperature (both continuously recorded by loggers) are responsible for the extent of bleaching and, as consequence, during summertime, shallow untouched P. oceanica plants are expected to bleach before the deep ones due to the exposure to higher temperature and irradiance conditions. The manipulative experiment could shed light on the effects of the variability of conditions influencing the seagrass leaf status of transplanted plants. More specifically, the occurrence of bleaching on deep cuttings transplanted at shallow depth without shading net, would support the hypothesis of the join temperature and light sudden variation in bleaching induction. Both approaches will allow to identify a potential modulation of light harvesting pigments found in the shoots at different depths as a plant defense strategy. Analyses are ongoing and both experiments will last until August 2024.