Posidonia oceanica meadows are Mediterranean coastal habitats of great conservation importance. This study is focused on a meadow located at Tremiti Islands Marine Protected Area (Adriatic Sea, Italy), which was monitored in 2003, 2015, and 2020 to evaluate its health state over time in relation to coastal human activities, which have been highly affecting this MPA for the last 20 years. To assess any change in the physiognomy of the meadow, rhizome density, percentage coverage, and lower limit progressions and/or regression over time were evaluated by scuba diving, while the distribution and extension of the meadow were assessed through habitat mapping using a side-scan sonar. Moreover, phenological and lepidochronological analyses were performed on the collected rhizomes to assess the leaf area index (LAI, m²m⁻²) and the rhizome age (lepidochronological years). Our study showed a general deterioration of P. oceanica meadow from 2003 to 2020, with a significant reduction of its absolute and relative rhizome density and LAI at almost all sampling stations, absence of renovation of the meadow, and lower limit regression and overall worsening of the main conservation status indicators. However, appropriate management actions, such as the establishment of mooring buoy fields, supported the improvement of the P. oceanica status at the local scale with a significant increase in density and LAI and the presence of active stolonization processes, suggesting that mitigation actions can play a crucial role in the conservation of this habitat. On the contrary, local anthropogenic impacts, especially anchoring and coastal development, markedly affect the resilience of P. oceanica meadows to global stressors, such as climate change.

The brown seaweed Rugulopteryx okamurae is currently included in the list of invasive alien species of European Union concern due to its rapid expansion that is causing both ecological and economic impacts. In this study, we report the first record of R. okamurae in the Southern Adriatic Sea, off the coast of Bari, Italy, currently representing the easternmost limit of its distribution in the Mediterranean Sea. Morphological observations combined with rbcL and psbA sequence analyses confirmed the taxonomic identification. Field surveys carried out between April 2023 and January 2024 highlighted the conspicuous occurrence of R. okamurae over a total surface of approximately 6.5 ha. Two main human-mediated pathways occurring near the sites of the first observation of the alien species may have been responsible for its introduction: the trade in living organisms for human consumption and maritime transport related to the proximity of the port of Bari to the invaded area. Future studies will aim to identify and implement practical, cost-effective management strategies to mitigate this alarming bioinvasion.

Coastal lagoons are dynamic transitional water ecosystems hosting valuable biological communities, including rich and diverse macrophyte assemblages. Aquatic macrophytes must cope with large fluctuations of environmental conditions on a spatial and seasonal scale. Salinity is one of the most variable parameters, changing from nearly freshwater to hypersalinity, and it is known to have a strong influence on the composition and structure of macrophyte assemblages. This study is focused on the effect of salinity on macrophyte communities of the eight most important coastal lagoons of Apulia (south-eastern Mediterranean Sea). A set of eleven transitional water body types (sensu Water Framework Directive) were allocated in a range of meso- to hyperhaline lagoons. Macrophyte sampling was carried out between 2011 and 2019, and a total of 324 samples (18 sampling stations × 2 seasons × 9 years) was analyzed. Then, macrophyte occurrence in each transitional water body (T-WB) was expressed as frequency values (%) and assemblages were compared to assess any similarity in relation to four salinity classes (mesohaline, polyhaline, euhaline and hyperhaline). Species richness varied according to the salinity class, being much higher in polyhaline and euhaline T-WBs and strongly decreasing at the extremes of the salinity range (mesohaline and hyperhaline T-WBs). Moreover, the statistical analysis showed a high resemblance of macrophyte assemblages of T-WBs within the same salinity class, which shared a great number of species. Four distinct macrophyte communities were distinguished, reflecting the salinity conditions of different T-WB types and confirming the effectiveness of a lagoon typology based on this descriptor.

Native macroalgal proliferations are emerging as an additional pathway of ecosystem disruption in the Mediterranean Sea, alongside classic invasions by non-indigenous species. Here, we report an unprecedented, large-scale proliferation of the native red alga Dudresnaya verticillata at the Tremiti Islands Marine Protected Area (southern Adriatic Sea), where the species formed extensive filamentous mats across shallow rocks, seagrass meadows, rhodolith and corallith beds, and incoherent bottoms. Underwater surveys documented the widespread occurrence of D. verticillata across the archipelago, and a quantitative photographic analysis was carried out at a representative site characterized by multiple habitat types across the observed depth range of proliferation (10–25 m). Stratified photographic transects were used to estimate percent cover, quantify substrate associations, and evaluate co-occurring benthic components. Taxonomic identification was supported by ad hoc sampling and morphological characters. Overall, D. verticillata covered a mean of 48.7 ± 19.3% of the investigated area, with total cover differing significantly with depth. The highest mean cover occurred at 10–15 m on infralittoral rocky bottoms (60.8 ± 17.4%; 0–90%), intermediate values were recorded at 20–25 m on biogenic/incoherent substrates (49.0 ± 21.3%; 0–100%), and the lowest cover was observed at 15–20 m within a Posidonia oceanica meadow (38.7 ± 15.0%; 0–81%). Degradation forms were detected at all depths, but their relative contribution increased at 20–25 m. These results document a sustained native proliferation with elevated spatial dominance, characterized by rapid expansion and high local cover, highlighting the need to incorporate native “outbreak” dynamics into monitoring and management initiatives in the Mediterranean Sea.

Mediterranean seagrass meadows formed by Posidonia oceanica underpin coastal ecosystem functioning but are rapidly declining under cumulative anthropogenic pressures. In the Adriatic Sea, where meadows are sparse and fragmented, effective restoration strategies are urgently needed to enhance resilience without further degrading donor habitats. We developed and tested a non-invasive transplantation method based exclusively on organic and natural materials, and on the recovery of naturally uprooted P. oceanica bundles. The approach was implemented in the Tremiti Islands Marine Protected Area (Italy, Adriatic Sea) using shoots displaced by human activities and natural processes during summer 2022 and thus avoiding extraction from wild meadows. Transplants were monitored over 3 yr to assess persistence, density, and cover. Natural P. oceanica meadows in the study area were investigated to compare patterns observed in transplanted meadow areas. Persistence and consolidation of transplanted shoots showed 86% of initial shoot density and 74% of seagrass cover retained after 3 yr. Density proved to be the most reliable metric for monitoring, while cover offered a rapid seasonal assessment at the end of the vegetative period. The method may be applied to any other P. oceanica meadows, as well as to other seagrass species under similar conditions. This study represents the first transplantation of P. oceanica in the western Adriatic Sea. The method used avoids the extraction of cuttings from healthy donor meadows and the use of artificial inorganic materials, representing a nature-based solution. When combined with measures aiming to reduce ongoing mechanical stress, such an approach may contribute to the conservation and recovery of seagrass meadows.