Annual dynamics of a macroalgal rocky community in the Gulf of Pozzuoli (Naples, Italy): exploring variations across ecological, structural and functional traits of dominant populations

This study investigated the annual dynamics of a macroalgal community inhabiting the rocky shores of Bacoli coast (Gulf of Pozzuoli, Italy) to assess differences in resource use and allocation among three dominant species sharing the same habitat: Dictyota spiralis Montagne, 1846, Cladophora prolifera (Roth) Kützing, 1843, and Jania pedunculata var. adhaerens (J.V.Lamouroux). The community was monitored over one year, considering species composition and key ecological attributes, including photosynthetic efficiency, pigment and carbohydrate concentration, specific thallus area and dry matter content, and antioxidant production. Algal coverage varied, with D. spiralis dominating in spring and C. prolifera and J. pedunculata in summer and autumn. The highest photosynthetic activity was measured in C. prolifera. None of the three species showed signs of stress across sampling dates. C. prolifera and J. pedunculata, characterized by higher thallus dry matter content and lower specific area, exhibited a resource-conserving strategy, allocating more carbon to structural biomass. Conversely, the greater thallus area and tannin concentration in D. spiralis indicated preferential investment in photosynthetic tissues and chemical defenses, consistent with a growth-oriented strategy. Elevated summer temperatures and irradiance were associated with reduced antioxidant activity in all species, suggesting physiological adjustments to changing environmental conditions. Overall, these findings demonstrate species-specific optimization of the trade-off between the photosynthetic performance and allocation of resources to defense. The rapid responses to seasonal fluctuations highlight local adaptation processes affecting macroalgal ecological dynamics in this coastal habitat and provide a valuable baseline for assessing species-specific sensitivity and resilience to environmental change, supporting future investigations and practical applications.