Metabolism drives various biological processes, potentially influencing the ecological success and evolutionary fitness of species. Understanding diverse metabolic rates is fundamental in biology. Mechanisms underlying adaptation to factors like temperature and predation pressure remain unclear. Our study explored the role of temperature and predation pressure in shaping the metabolic scaling of an invasive mussel species (Brachidontes pharaonis). Specifically, we performed laboratory-based experiments to assess the effects of phenotypic plasticity on the metabolic scaling by exposing the mussels to water conditions with and without predator cues from another invasive species (the blue crab, Callinectes sapidus) across various temperature regimes. We found that temperature effects on metabolic scaling of the invasive mussels are mediated by the presence of chemical cues of an invasive predator, the blue crab. Investigating temperature-predator interactions underscores the importance of studying the ecological effects of global warming. Our research advances our understanding of how environmental factors jointly impact physiological processes.

Brown foundation seaweeds are key elements increasing substrate heterogeneity and shaping the biodiversity in rocky coastal ecosystems. They are, however, vulnerable species that are declining due to multiple anthropogenic and climate change stressors, leading to a shift to less structural complex habitats. We investigate the role of structural attributes of two intertidal macroalgae, Ericaria amentacea and Laurencia obtusa, in shaping the abundance and diversity of their associated epifaunal assemblages. For this aim, we measured seaweeds' biomass, thallus volume and length (used here as proxy of substrate complexity), and explored which seaweeds' substrate attribute explained better variation of epifaunal assemblages. Results showed that E. amentacea was more complex than L. obtusa and hosted a higher number of epifaunal individuals. However, unlike that expected, the epifaunal assemblage of L. obtusa was more structured with higher Shannon-Wiener diversity and Pielous' evenness. Our findings indicate that, besides seaweed's substrate attributes, other mechanisms such as wave action and chemical defense might play a role in structuring epifaunal assemblages. We suggest that a shift from E. amentacea to L. obtusa population could have effect on structure and abundance of associated epifaunal assemblages. Certainly, further investigations are needed to clear up the consequences of these changes.

Hypersaline stress is a major stressor in semi-enclosed coastal lagoons, affecting the distribution and survival of key foundation species. In this study, we investigated how Posidonia oceanica meadows responded physiologically and morphologically to different salinity concentrations both in-situ, across a natural saline gradient occurring inside the lagoon system, and in a mesocosm experiment. Leaf water relations, organic osmolytes, photosynthesis, respiration, Chlorophyll-a fluorescence, pigments content, and leaf growth were studied in P. oceanica from three different sites within the Stagnone of Marsala lagoon, as well as after exposing P. oceanica to a salinity level of 46 psu in a 30-day mesocosm experiment. Overall, we show that P. oceanica has evolved osmolar regulatory strategies and photosynthetic plasticity, allowing these meadows to cope with large salinity fluctuations (38 – 51.45 PSU). Our findings contribute to a better understanding of seagrass ecophysiological adaptation to extreme environmental conditions, as well as the importance of these populations serving as an experimental model at the Mediterranean scale for more comprehensive forecasting and management of environmental stress in these marine foundation species in an era of rapid environmental change.

Habitat complexity is one of the main influences on biodiversity in marine environments, particularly in coastal areas where foundation seaweeds provide substrate for highly diverse communities. We studied the 2D and 3D fractal dimensions of Gongolaria montagnei (Fucales) over the vegetative season and examine their relationship with the abundance, species richness and morpho-functional groups of the gastropod associated. Overall, the 3D fractal analysis method used here better describes seaweeds structural complexity compared to the traditional 2D fractal analysis, as highlighted by the higher relationship with gastropod assemblage associated to the alga in terms of abundance, number of species and morpho-functional groups. We propose this new method as a valuable tool for understanding the relationship between seaweeds and associated fauna, which is critical for gaining a better understanding of the role that algal species play in a specific habitat and the consequences of their loss.

Canopy-forming seaweeds of the genus Cystoseira (Fucales, Phaeophyceae) form diverse and productive habitats along temperate rocky coasts of the Mediterranean Sea. During the last decade, Cystoseira forests have retracted their range considerably due to many interacting environmental, biological and anthropogenic pressures. We investigated how reducing in patch-size of C. montagnei affects their associated molluscan communities at the shallow northwest rocky shores of Palermo (Sicily, Italy). Molluscs were sampled from the fronds of individual thalli, clumps of 3 and 5 thalli of C. montagnei over an annual vegetative cycle (May-September) in two sites within the Marine Protected Area "Capo Gallo-Isola delle Femmine". We measured five substrate attributes of the alga (thallus volume, canopy volume, interstitial volume, algal surface, and biomass) and explored their relationships with the diversity of the associated molluscan assemblage. A total of 3756 individuals of molluscs were collected, belonging to 30 families and 57 species, being Rissoidae the most speciose family and Barleeidae the dominant in terms of abundance. The molluscan assemblage on C. montagnei displayed significant spatial and seasonal variations, with the maximum number of individuals and species in summer, whereas evenness and diversity displayed maximum values in spring. The abundance, species richness and diversity of the molluscan assemblage decreased with decreasing in patch-size of C. montagnei, regardless of the vegetative phase of the alga or the sites considered in the study, while evenness showed an opposite trend. The substrate attributes of C. montagnei changed over the vegetative cycle of the alga and showed a similar pattern across sites with values that tended to decrease in autumn during the quiescence phase of the alga. Variation in patch-size of C. montagnei affected also the substrate attributes of the individual alga, with individual thalli becoming smaller with increasing patch-size. The algal surface of a single thallus of C. montagnei ranged on average from 956 cm(2) in spring to 289 cm(2) in autumn. Furthermore, algal surface together with thallus volume and dry weight were the substrate attributes that explained better the variation of the number of molluscan individuals and species. Overall, our results suggest that the reduction of both patch-size and algal substrate of C. montagnei forests altered the structure and composition of its associated molluscan assemblage. We argue that a reduction or loss of Cystoseira forests could probably trigger bottom-up effects in rocky shores habitats, with consequences for the whole ecosystem structure, functioning and services provided to humans.

Understanding the physiological responses of intertidal seaweeds to environmental factors is fundamental to characterize their local physiological adaptation and success in the face of climate change. We measured the photosynthetic activity and the total phenolic content of the intertidal alga Cystoseira compressa and explored their relationship with latitude or local ambient air and seawater temperatures. Our results show that, when submerged, the photosynthetic activity of C. compressa showed values typical for non-stressed thalli, and the seawater temperatures found across sites explained the variability of these values. We observed a decrease in the photosynthetic activity of C. compressa when exposed to air, compared to a submerged condition. This activity remained stationary up to 28 °C and then started to decrease with higher air temperatures. The total phenolic content of C. compressa at the end of low tide changed across the study sites from 0.12 to 0.53 % DW. Phenolic variability was explained by the long-term thermal water conditions experienced by the algae, rather than short-term variations encountered during tidal cycles. Overall, our results suggest a crucial role played by temperature in driving the physiological traits of the intertidal C. compressa .

We analyzed the occurrence and status of infralittoral fringe populations of Cystoseira spp. (Fucales) at thirteen rocky sites around the Italian coastline, and explored the relationships with relevant environmental and anthropogenic variables. We found Cystoseira populations at 11 sites: most were scattered and comprised monospecific stands of C. compressa, and only 6 sites also supported sparse specimens of either C. amentacea var. stricta or C. brachycarpa. Coastal human population density, Chlorophyll a seawater concentrations, sea surface temperature, annual range of sea surface temperature and wave fetch explained most of the variation of the status of C. compressa. We hypothesize a generally unhealthy state of the Italian Cystoseira infralittoral fringe populations and identify multiple co-occurring anthropogenic stressors as the likely drivers of these poor conditions. Extensive baseline monitoring is needed to describe how Cystoseira populations are changing, and implement a management framework for the conservation of these valuable but vulnerable habitats.