Alice Mirasole

We investigated the seasonal and interannual variability of ichthyoplankton assemblages across 2 submarine canyons (Dohrn and Cuma) and a nearby coastal site, represented by the Long-Term Ecological Research station MareChiara (LTER-MC), in the south-central Tyrrhenian Sea. Based on seasonal surveys conducted in 2022 and time-series data collected between 2023 and 2024, our findings show that seasonality is the primary driver of community composition, with clear and recurrent shifts in assemblage structure across seasons. Interannual variability was also evident, and co-occurred with changes in hydrographic conditions. Spatial differences between the 2 submarine canyons were limited, suggesting similar ecological functioning. However, comparison with the coastal site revealed pronounced contrasts in species composition and diversity, highlighting cross-shelf connectivity and the possible influence of canyon-driven hydrodynamics on larval dispersal and retention. Overall, the study highlights consistent seasonal and interannual patterns in ichthyoplankton assemblages across the investigated sites. While spatial differences between the 2 canyons were limited, comparison with the coastal site revealed distinct community structures, suggesting a cross-shelf gradient in species composition. These results provide baseline information on the spatial and temporal variability of larval fish assemblages in the south-central Tyrrhenian Sea and contribute to a better understanding of ichthyoplankton distribution in data-limited Mediterranean regions.

Following the unprecedented marine heatwaves of summer 2022, extensive flowering of the endemic seagrass Posidonia oceanica was witnessed across the western Mediterranean. To unravel the causes of this event, we conducted a pan-Mediterranean analysis across 442 sites spanning all Mediterranean ecoregions, with 76% exhibiting flowering. Flowering differed regionally, with both highest flowering prevalence (over 90%) and flowering intensity (up to 0.75) recorded in the Liguro-Provençal and Balearic Seas. We demonstrate that regions experiencing large summer sea surface temperature anomaly with high marine heatwave cumulative intensity displayed the highest flowering intensity. The probability of flowering was very likely when marine heatwave cumulative intensity exceeded ⁓120°C days. These findings suggest that marine heatwaves trigger flowering in P. oceanica and, given the high energetic cost of sexual reproduction, continued ocean warming may shift energy allocation toward flowering. This shift could profoundly affect the species’ reproductive strategies, posing major challenges and uncertainties for its long-term evolution.

Ocean acidification (OA) driven by increasing atmospheric CO ₂ is altering marine biodiversity. However, impacts of OA on ecosystem functioning at the community level, including calcification, primary production and nutrient uptake, remain largely unknown. Here, we conducted community transplant experiments at natural CO ₂ vents to assess how declining pH affects marine community species composition, biomass, and key ecosystem processes over time. Our results indicate that community shifts caused by declining pH lead to decreased biomass and calcification rates, while photosynthesis and nutrient uptake rates increased. By leveraging OA field model systems and in situ measurements of ecosystem functioning, this study provides critical insights into how OA‐induced biodiversity loss reshapes the structure and functioning of temperate marine coastal ecosystems.

Seagrass meadows are natural carbon sinks, yet the effect of ocean acidification on their carbon burial capacity remains poorly understood. Here we investigated natural carbon dioxide vents in Ischia, Italy to assess how seawater pH influences carbon burial in an area dominated by the seagrass Posidonia oceanica . Organic carbon burial rates (mean ± standard error) between 1954 – 2021 were low under ambient conditions (1.5 ± 0.5 g m ^-2 yr ^-1 ) but increased sharply under acidified conditions (7 ± 1 g m ^-2 yr ^-1 ), reaching sevenfold higher values under extreme acidification (10 ± 3 g m ^-2 yr ^-1 ). Stable isotopes suggest that these patterns reflect changes in the relative contribution of seagrass, macroalgae, and epiphytes to buried carbon. These findings reveal that ocean acidification can substantially alter coastal carbon cycling, potentially through shifts in community composition, with important implications for understanding past and future feedbacks between seagrass ecosystems and the marine carbon cycle.

Global climate change exacerbates the incidence of marine heatwaves (MHWs), which have increased in intensity and frequency over the past years, causing se

Marine habitat-forming species provide crucial ecosystem functions and services worldwide. Still, the individual and combined long-term effects of ocean acidification and warming on bryozoan populations, structures, and microbiomes remain unexplored. Here, we investigate the skeletal properties, microbiome shifts, and population trends of two bryozoan species living inside and outside a volcanic CO₂ vent, a natural analog to future ocean acidification conditions. We show that bryozoans can acclimatize to acidification by adjusting skeletal properties and maintaining stable microbiomes. However, we document a decrease in microbial genera playing essential functions under acidified conditions. Moreover, we show that ocean acidification exacerbates bryozoan cover loss and mortality caused by ocean warming. The observed shifts in the microbiome and cover suggest that, despite their morphological plasticity, bryozoan species will be heavily impacted by future ocean conditions, posing a threat to many benthic ecosystems in which they play a pivotal role.

Global ocean warming and acidification are two of the major threats to many marine calcifying habitat-forming species, potentially affecting entire ecosystems. Consequently, the need for a better understanding and predicting the response of marine calcifiers has never been more pressing. Paradoxically, the individual and combined long-term effects of these stressors on bryozoans have remained largely unexplored, despite their great abundance and diversity globally. Here, we first evaluate the changes in skeletal structure and mineralogy, and the associated microbiome composition on the populations of Pentapora ottomuelleriana (encrusting) and Myriapora truncata (erect) bryozoan species living inside and outside a volcanic CO2 vent in Ischia Island. We then examine the effects of a long-term exposure to elevated pCO2 and its combined effects of ocean warming on the proportion of cover of populations of the encrusting species through time after summer. Both bryozoan species show indicators of acclimatization by adjusting skeletal properties and having stable microbial communities under acidification conditions. However, we document novel patterns about microbiome shifts in response to future ocean acidification in bryozoans for the first time. Microbial genera known to have essential functions to the host such as biosynthesis of defense compounds or thermal protection were depleted at the acidified site, which suggest early warnings of potential deterioration of bryozoan health under near future ocean conditions. The proportion of cover of the encrusting species also decreased from 2016 to 2020 in both studied sites, with faster declines at the acidified ones. Our model suggests that the increasing seawater temperature drove a decline in the bryozoan cover although the combined effects with acidification accelerated its mortality rates in the CO2 vent. More multidisciplinary research combining both environmental stressors on a wider range of calcifying species is needed to better understand the adaptive capacity of the holobiont to a changing environment.