Gongolaria barbata (Sargassaceae, Fucales) is a widespread species for which several infraspecific taxa have been described, indicating its polymorphism. This study contributes to the understanding of the molecular, nomenclatural, morphological and ecological aspects of G. barbata in the Mediterranean and sheds light on the infraspecific diversity and its implications for the taxonomy of this species. Molecular analyses were performed using sequencing of the mitochondrial cox1 gene on both haptophytic and pleustophytic forms from different sites in the Adriatic and Tyrrhenian Seas. Vegetative and reproductive morphology was studied on thalli samples from the Adriatic. Our results showed that there are different morphotypes within G. barbata populations related to specific environmental conditions, suggesting infraspecific variation. In contrast, molecular analyses showed no differences between samples, regardless of whether individuals are growing “attached” to a substrate or “unattached”. We also discussed the taxonomic status and nomenclatural issues related to certain infraspecific taxa previously proposed for G. barbata. In particular, the confusion surrounding Cystoseira aurantia is clarified.

Ericaria amentacea, a key habitat-forming brown macroalga on Mediterranean rocky coasts, faces severe decline due to anthropogenic stressors and climate change. Natural recovery is hindered by its limited dispersal and connectivity potential, and active restoration is therefore critical to restocking lost populations. This study evaluates a two-phase restoration approach combining laboratory culture and suspended aquaculture to optimize E. amentacea restoration, enabling multiple culture cycles within a single fertility window. Three experimental conditions were tested: (A) 5 days in the laboratory followed by 12 days in suspended aquaculture, (B) 12 days in the laboratory followed by 5 days in suspended aquaculture, and (C) 17 days in the laboratory without suspended aquaculture. Culture performance was assessed in terms of coverage, length of individuals, and photosynthetic efficiency. Results outlined that condition C achieved the best performance at the final time point. Condition B showed intermediate outcomes, with length and photosynthetic efficiency comparable to condition C, but lower coverage, with significant recovery post-outplanting. Condition A exhibited poor resilience, with declining coverage and reduced photosynthetic efficiency. These findings suggest that a moderate reduction in laboratory culture (12 days) may represent an effective trade-off between resource efficiency and germling development. This approach is particularly relevant in the context of climate change, where shorter fertility periods and extreme events challenge restoration efforts. This study highlights the potential of integrated laboratory-aquaculture protocols to enhance the scalability and success of E. amentacea restoration, offering a promising strategy for marine habitat recovery.

Ericaria amentacea is a brown alga endemic to the Mediterranean Sea and is highly threatened by human activities. A growing concern in coastal water is the increasing detection of titanium dioxide nanoparticles (nano-TiO₂), a widespread component in commercial sunscreens, whose effect are still largely unexplored. Here, we combined photophysiological, metabolic, biochemical, and ultrastructural analyses to assess the responses of both germlings and adult thalli of E. amentacea after 10 and 20 days of exposure to four nano-TiO₂ concentrations (0, 5, 50, and 500 μg L^-1) under controlled laboratory conditions. In adult thalli, nano-TiO₂ exposure induced moderate but detectable alterations in photosynthetic performance and primary productivity, characterized by transient stimulation at low concentrations followed by efficiency decline under higher doses and prolonged exposure. These shifts were accompanied by chlorophyll a depletion and activation of antioxidant defences, indicative of oxidative stress. In contrast, germlings displayed pronounced sensitivity across all exposure levels, with significant reductions in PSII efficiency, pigment loss, and enhanced oxidative stress even at the lowest tested concentration. SEM-EDS analyses confirmed the penetration and accumulation of TiO₂ particles inside algal tissues, particularly in germlings, underscoring their limited capacity to prevent nanoparticle adhesion and uptake. Collectively, our results provide the first mechanistic evidence that sunscreen-derived nanoparticles impair key physiological processes in a Mediterranean foundation species, with early life stages being highly vulnerable. This sensitivity is of particular concern because germling recruitment coincides with the peak tourist season, when nanoparticle release from sunscreen use is maximal, creating a seasonal bottleneck for population renewal. Our findings highlight the negative effect of nano-TiO₂ on this endemic Mediterranean fucalean species, underscoring the urgent need to investigate these emerging pollutants and their impacts on key ecosystem-services providers.

Cystoseira sensu lato (s.l.) (Fucales, Phaeophyceae) form structurally complex marine forests along the warm-temperate coasts of the Mediterranean Sea and the eastern Atlantic Ocean. They are experiencing widespread decline, yet their conservation and restoration are hindered by taxonomic uncertainty. Within Cystoseira sensu stricto (s.s.), species boundaries among taxa traditionally referred to as C. compressa, C. foeniculacea, C. humilis (including the C. canariensis morphotype), and C. pustulata have long been debated due to the high plasticity and partial overlap of diagnostic morphological traits. Here we reassess species boundaries within the Cystoseira s.s. complex using an integrative approach combining morphology, ecology, and multilocus genetic data. We collected specimens from 20 sites spanning the Mediterranean–Atlantic distribution. Genomic DNA was extracted from 220 specimens and Sanger sequencing generated 243 new sequences (ITS2: n = 99; cox1: n = 88; rbcL–rbcS: n = 56). We inferred single-locus and concatenated phylogenies, reconstructed haplotype networks, and applied multiple single-locus species delimitation approaches to test the robustness of inferred boundaries. We consistently recovered two primary lineages corresponding to C. foeniculacea and a C. compressa complex, the latter including specimens historically identified as C. pustulata and the C. humilis with the C. canariensis morphotype. Within an integrative framework that prioritises cross-locus concordance and diagnosability, we recognise two species-level lineages in Cystoseira s.s. and treat the morpho-ecologically coherent entities within C. compressa at the variety rank. Accordingly, we propose the new status and combination Cystoseira compressa var. pustulata (Ercegović) D’Ambros Burchio & Falace, comb. et stat. nov.