Urbanisation is considered as one of the most critical and widespread threats to coastal marine ecosystems. The aim of this study was to compare the density, percentage cover, thickness of clumps, condition index and size-frequency distribution of Mytilus galloprovincialis between urban and non-urban shores, at nested spatial scales, in the Northern Portuguese coast. M. galloprovincialis was selected as model because it is economically and ecologically relevant. Moreover, the relationship between mussel size and the other variables (i.e. density, percentage cover, thickness and condition index) were investigated. Mussels on urban shores showed a smaller density and a greater frequency of larger individuals. A significant negative correlation between mussel length with density and with thickness of clumps was also found. Our results seem to indicate that recruitment has declined on urban shores and, as a result, intraspecific competition is also smaller, leading to more resources being available for a fewer individuals which can reach larger sizes. As mussel beds support a great biodiversity of invertebrates and provide many ecosystem services, urbanisation may have indirect effects on communities associated with mussels. Understanding the vulnerability of mussel beds to urbanisation could inform management.

Macroalgae have low nutrient bioavailability, often requiring pretreatments—physical, chemical, or biological—typically using low-solid loading hydrolysis, which produces separate liquid and solid phases. In contrast, high-solid loading hydrolysis offers a single-phase alternative, though it remains underexplored for macroalgae. This study evaluated the effectiveness of high-solid loading hydrolysis for breaking polysaccharides and increasing the availability of nutrients and antioxidant compounds in Codium tomentosum. Treatments using mixtures containing 25% dry biomass and 75% water or 0.5N and 1N NaOH, autoclaved for 30 or 60 min, were performed. Among the tested treatments, high-solid loading alkaline autoclaved treatment (1N NaOH, 60 min) was most effective in reducing neutral detergent fiber and enhancing the availability of bioactive compounds, particularly soluble proteins and phenols. Based on these results, a sequential enzymatic hydrolysis with Natugrain^® at 0.2 and 0.4% was also applied to pre-treated C. tomentosum with water or 1N NaOH. Enzymatic hydrolysis after autoclaving had no major effect on fiber, soluble protein, or ash, but increased phenol levels. In conclusion, high-solid loading alkaline treatment (1N NaOH) followed by enzymatic hydrolysis with Natugrain^® enzyme reduced fiber content and enhanced soluble protein and phenolic compounds, thereby improving the nutritional and functional potential of C. tomentosum for inclusion in animal feeds.

Macroalgae are increasingly recognized as a valuable source of nutrients and bioactive compounds for animal nutrition, including for aquatic species. However, the complex structure of the macroalgal cell wall limits the accessibility of intracellular components, restricting their use in feeds. To overcome this limitation, macroalgal hydrolysis using various technological treatments has been tested, often employing a low solid-to-water ratio, which complicates downstream processing due to phase separation. In contrast, high-solids loading hydrolysis has the advantage of producing a single and consolidated fraction, simplifying subsequent processing and application. The present study assessed the effectiveness of high-solids loading water or alkaline (0.5 and 1N NaOH) autoclaving for 30 or 60 min, applied alone or followed by sequential enzymatic hydrolysis, using a xylanase-rich enzymatic complex aimed at promoting cell wall disruption and increasing the extractability of intracellular components in the red macroalga Palmaria palmata with minimal free water. The 1N NaOH treatment for 30 min decreased neutral and acid detergent fiber while increasing Folin–Ciocalteu total phenolic content (GAE) (expressed as gallic acid equivalent) and the water-soluble protein fraction and decreased crude protein, indicating enhanced extractability of these components. Microscopic examination showed relatively mild structural changes on the surface of P. palmata after high-solids loading alkaline (1N NaOH) autoclaving for 30 min. Following alkaline or water treatment, the enzymatic complex hydrolysis further increased the Folin–Ciocalteu total phenolic content (GAE), with minimal effects on NDF, ADF, or crude protein. Overall, these results showed that high-solids loading alkaline autoclaving, with or without subsequent enzymatic hydrolysis, effectively disrupts P. palmata cell walls and induces substantial modifications while simplifying processing by avoiding phase separation.

The effects of dietary inclusion of the macroalgae Codium tomentosum, either untreated or pre-treated with high-solid-loading alkaline hydrolysis, on the oxidative status, intestinal immune responses, and gut microbiota was evaluated in European seabass juveniles. Four diets, a control diet (CTR) and three diets containing 7.5% C. tomentosum, either untreated (COD) or pre-treated for 30 min (COD30) or 60 min (COD60), were formulated and fed for 11 weeks. Fish fed the COD30 diet showed increased intestinal lipid peroxidation, higher plasma lysozyme activity, and reduced total glutathione, compared with CTR and COD. In parallel, distal intestine inflammatory (TNF-α, IL-10, IL-1β) and apoptotic (CASP3, CASP9) gene expression was downregulated relative to COD diet, suggesting a dissociation between oxidative damage and inflammatory activation. In fish fed COD60, intestinal lipid peroxidation plasma lysozyme activity were reduced and distal intestine inflammatory and apoptotic gene expression was lower than in COD diet. Hepatic oxidative stress markers were not affected by dietary treatment. DGGE analysis revealed no significant changes in microbial richness or diversity, although COD30 increased digesta community similarity. Overall, high-solid-loading alkaline pre-treatment of C. tomentosum for 60 min mitigated the oxidative and inflammatory/apoptotic impacts associated with dietary inclusion of the untreated macroalga, supporting ingredient processing as a strategy to improve the functional value of macroalgal aquafeeds.

The red macroalgae Palmaria palmata is rich in protein and bioactive compounds and has been identified as a promising dietary ingredient for aquafeeds, with the potential to partially replace selected plant-based feed components. A digestibility trial and a growth trial were conducted to evaluate the potential of untreated and pretreated P. palmata as feed ingredients for juvenile European seabass ( Dicentrarchus labrax ), with initial body weights of 63.2 g and 38.0 g, respectively. Five diets were formulated: a control diet without macroalgae, and four diets including either 7.5% or 15% of untreated and pretreated P. palmata , replacing plant ingredients. The apparent digestibility coefficients of dry matter, crude protein, lipids, and gross energy did not differ among diets. The dietary inclusion of up to 15% P. palmata significantly increased the growth performance and feed efficiency compared to the control diet, without affecting nutrient digestibility, digestive enzyme activities, plasma metabolites, or whole-body composition of the fish. The pretreatment applied to P. palmata significantly increased soluble protein content and decreased neutral detergent fiber, but did not further improve growth or feed efficiency. Overall, these results indicate that up to 15% P. palmata can be successfully incorporated into the diets of juvenile European seabass, improving growth performance without adverse effects on nutrient digestibility. Further work is required to evaluate the functional properties and implications for fish health of P. palmata as well as to assess its economic viability within commercial aquafeed formulations.

The mussel, Mytilus galloprovincialis Lamarck, 1819 is an ecologically and economically relevant species on European coasts. It is very abundant in the Atlantic intertidal fringe of the Iberian Peninsula where is harvested in natural systems and/or cultured intensively on rafts. Aquaculture production is dependent on their abundance in natural environments because juveniles are collected in rocky shores and then attached to ropes on rafts. Moreover, it provides habitat for many species, enhancing local biodiversity. The aim of this study was to explore effects of harvesting on the annelid assemblage associated with mussels. To achieve this, two rocky shores, where mussels are intensively harvested, were selected in Galicia (NW Iberian Peninsula). At each shore, two different sites were considered; at each site, 4 replicates (10x10cm) of harvested mussel clumps and 4 replicates of non-harvested clumps (control) were collected. Size and number of mussels at each replicate were compared between treatments (harvested-control). Moreover, annelids at each replicate were identified to species level. A total of 1351 individuals and 27 species were found. Abundance, taxon richness, Margalef index and assemblage composition were compared between treatments by means of univariate and multivariate techniques. Results pointed out that harvested clumps showed a lower and more homogenous mussel size than control clumps, as expected. Regarding annelids, the interaction between treatment and site was significant for the multivariate assemblage structure and for the total abundance. Therefore, the effect of harvesting is dependent on the spatial scale considered.