Biodiversity is undergoing rapid and worrying changes, partially driven by anthropogenic activities. Human impacts and climate change (e.g., increasing temperature and ocean acidification), which act at different spatial scales, represent the most serious threats to biodiversity and ecosystem structure and function. In the Mediterranean Sea, complex systems such as fucoid algae and seagrasses, characterized by a high associated biodiversity, are regularly exposed to natural and anthropogenic pressures. These systems, particularly sensitive to a variety of stressors, evolved several physiological and biochemical traits as a response to the different pressures which they are subjected to. For instance, they produce a huge quantity of secondary metabolites such as phenolic compounds, to adapt to different environmental stressors and to defend themselves from biological pressures. These natural products are receiving increasing attention due to their possible applications in a wide range of industrial sectors. In this paper we provide an overview on the ecological role of phenolic compounds from the genus Cystoseira sensu lato and Posidonia oceanica (L.) Delile, also highlighting their potential use as ecological biomarkers.

The chief purpose of Marine Protected Areas (MPAs) is biodiversity conservation. The effects that invasive alien species (IAS) have on MPAs, and vice versa, are not yet fully known, even though assessing them is crucial for MPA planning. Management plans require sound knowledge of the pathways of introduction, the impact and current distribution of IAS. Monitoring plans are essential for preventing and reducing the risk of IAS introduction. In this respect, the involvement of citizen scientists in gathering data (validated by taxonomic experts) on the occurrence of IAS, that would otherwise be impossible to collect, may be crucial. We report on our experience of citizen science in the Egadi Islands MPA with the project ‘Caulerpa cylindracea – Egadi Islands’, aimed at monitoring the spread dynamics of the ‘sea grape’ C. cylindracea. The project registered 156 sightings and also allowed collection of records and information concerning other non-indigenous and cryptogenic species, e.g. the spotted sea hare (Aplysia dactylomela), the harpoon weed (Asparagopsis armata), the red sea plume (Asparagopsis taxiformis), the tube-building sabellid (Branchiomma bairdi), the blue spotted cornet fish (Fistularia commersoni) and the nomad jellyfish (Rhopilema nomadica).

The Mediterranean Sea, one of the most complex marine ecosystems, is inhabited by a rich and diverse biota which is disproportionate to its dimensions. It is currently affected by different pressures, mainly driven by human activities such as climate change and bioinvasions. This Sea, also due to its geographic position (wedged between the temperate climate of central Europe and the arid climate of northern Africa), seems to be one of the regions most susceptible to global climate change. The increased rates of introduction and spread of marine alien species may represent a supplementary stress factor to Mediterranean marine native biota already challenged by climatic abnormalities. The Suez Canal is considered to be the main vector of introduction of non‐indigenous marine species into the Mediterranean Sea. Due to the dramatically accelerating rate of such introductions and due to the sheer magnitude of shipping traffic, the Mediterranean Sea may be considered as a true hotspot of marine bioinvasions. The complexity of interactions between native and invasive species and the associated resulting impacts make environmental management of such an issue particularly difficult. A collaboration between researchers, resource management agencies and policy makers is called for to bolster the effectiveness of invasive species management procedures.

The aim of this study was to test the effects of temperature on phenolic content of the brown seaweed Cystoseira amentacea. Phenolic compounds are secondary metabolites involved in different protection mechanisms as, for example, against grazers, epiphytes and UV radiation. Seasonal variations of phenolic content in C. amentacea were analysed and laboratory experiments, in which C. amentacea was exposed to an increase of temperature (25°C and 30°C), were performed. Total phenolic content (TPC) was determined colorimetrically with the Folin–Ciocalteu reagent. In C. amentacea, a seasonal pattern in TPC was observed, with a maximum value in winter-spring. C. amentacea responded significantly to the temperature treatments with a consistent decrease in TPC after 48 h.