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Skin cancer is one of the most common types of cancer worldwide, with exposure to UVB radiation being a significant risk factor for its development. To prevent skin cancer, continuous research efforts have focused on finding suitable photoprotective ingredients from natural sources that are also environmentally friendly. This study aimed to develop oil-in-water photoprotective nanoemulsions containing marine macroalgae extract. A Box–Behnken experimental design was used to identify the most promising formulation composition, resulting in optimal physical properties. These properties, including droplet size, polydispersity index (PDI), and zeta potential, were evaluated using dynamic light scattering (DLS). To assess the photoprotection capacity of the formulations, electrical impedance spectroscopy (EIS) was employed to evaluate alterations in the electrical characteristics of excised pig skin membranes placed in Franz cells equipped with a 4-electrode set-up. The final composition of the nanoemulsion was caprylic/capric triglycerides 4%, Macrogolglycerol ricinoleate 30%, and algae extract 1%. The nanoemulsions had an average droplet size of 128.5 ± 8.6 nm, a PDI of 0.25 ± 0.06, and a zeta potential of 45.14 ± 0.02 mV. Compared to the control group, the photoprotective capacity of the oil-in-water nanoemulsions was statistically significant. Specifically, only a 15% reduction in the skin membrane electrical resistance following UVB exposure was observed when the formulation containing algae extract was used, whereas a 50% reduction was observed for the vehicle. In conclusion, this work demonstrates that the developed nanoemulsions based on natural ingredients show promising protective capacity against UVB exposure of the skin.

The growing demand for safe and effective natural ingredients in cosmetic formulations has prompted research into marine-derived compounds, particularly phlorotannins from brown algae. These compounds exhibit diverse bioactivities, including tyrosinase inhibition, which is relevant for the treatment of skin hyperpigmentation disorders. This study aimed to optimize the ultrasound-assisted extraction (UAE) of phlorotannins from the brown macroalga Dictyopteris justii and to evaluate the in vitro tyrosinase inhibitory activity of the resulting extract. A Box–Behnken design was employed to optimize the extraction parameters: ethanol concentration, solid-to-liquid ratio, temperature, and time. Total phlorotannin content (TPhC) was quantified using the DMBA colorimetric method, and the optimized extract was evaluated for tyrosinase inhibitory activity using a commercial colorimetric assay. The IC₅₀ of the extract was determined and compared with kojic acid. The optimal extraction conditions were identified as 70% ethanol, a 1:10 solid-to-liquid ratio, 25 °C, and 20 min. Under these conditions, the TPhC reached 2.874 ± 0.069 mg phloroglucinol equivalents per gram of dry extract, with a 9% extraction yield. Chromatographic analysis suggests the presence of hydroxypentafuhalol-B in the extract.The optimized extract showed significant tyrosinase inhibitory activity with an IC₅₀ of 0.51 mg/mL, compared to 46.61 µg/mL for kojic acid. This study demonstrates the successful optimization of UAE for obtaining a phlorotannin-rich extract from D. justii with reproducible extraction efficiency and potent tyrosinase inhibition. These findings support the potential application of D. justii extracts in the development of cosmetic products targeting hyperpigmentation.

Rhodoliths are free-living calcareous nodules composed of non-geniculate coralline Rhodophyta algae. One potential rhodolith bioturbator is the sand tilefish Malacanthus plumieri, which builds mounds with these nodules over sand bottoms. Here, we tested (1) whether mounds act as a different habitat within a rhodolith bed, supporting specific associated assemblages, and (2) the potential role of M. plumieri as a bioturbation agent on rhodolith beds. We used multiple techniques (benthic and fish assemblage assessments, and videos with marked rhodoliths to assess fish behavior) to compare fish-built mounds with non-mounded control areas. M. plumieri was not observed removing rhodoliths from mounds; however, it spent 15% of its time rearranging mounds or adding new rhodoliths to the mound. A higher fish richness was recorded on mounds (mean = 9.4 + or - SE 1.7) compared with the non-mounded control areas (5.5 + or - SE 2.7) (t = -2.2; p < 0.05). The benthic assemblages also differed between the mounds and the control areas (PERMANOVA, Pseudo-F = 11.8 and p < 0.01). The categories that contributed most to dissimilarity between mounds and non-mounded control areas (SIMPER) were crustose coralline algae free of epiphytes and sand (15.5%), Dictyota jamaicensis (9.8%), Dictyota pulchella (9.4%), sand (9.3%) and Dictyopteris justii (8.2%). Because of their contribution to seascape heterogeneity, we suggest that the presence of M. plumieri mounds is an important variable in predicting diversity in rhodolith beds.

Polyphenolic chemical defenses of plants have traditionally been classified as immobile or quantitative and as such are believed to have low to negligible rates of turnover. This assumption is an important element in many ecological theories of chemical defense that invoke cost versus benefit relationships, because (1) turnover increases the metabolic cost of maintaining an effective level of defense, and (2) changes in the rate of turnover could affect the conclusions of studies that rely upon static concentration (standing crop) measurements, since changes in compound synthesis may not emerge as corresponding changes in compound concentration. By using a stable-isotope labeling technique, we measured rates of synthesis and turnover for the polyphenolic compounds of marine brown algae in laboratory and field experiments. During the laboratory experiment, we observed the relatively rapid turnover of phlorotannins in a population of the tropical brown alga Lobophora variegata. In order to determine if such metabolic turnover in brown algae occurred under natural conditions, we then measured in situ rates of synthesis, polymerization, and turnover for extractable phlorotannins in two species of tropical marine brown algae, Sargassum hystrix var. buxifolium (Fucales) and Dictyopteris justii (Dictyotales), over a 17-day period in the field. We found that phlorotannins in L. variegata and S. hystrix var. buxifolium demonstrated rapid rates of turnover in laboratory culture and in situ field experiments, respectively. The trends for D. justii also support the presence of turnover. Results indicate that (1) the assumption that algal polyphenolics can be grouped with the tannins of vascular plants as \"immobile\" defenses needs to be reevaluated, (2) estimates of the metabolic cost of algal polyphenolics that presume negligible rates of turnover may significantly underestimate the total cost of defense, and (3) studies designed to test the predictions of ecological theories for the phlorotannin concentrations of tropical brown algae may be affected by changes in the rates of metabolic turnover.[PUBLICATION ABSTRACT]