Macroalgae sampling focused on abundant specimens, yielding a total of 10 red macroalgae samples collected in 2021 and 2023 from various locations across the Archipelago of San Andrés, Providencia, and Santa Catalina. A summary of the sampling data is presented in Table SM1. Of these, eight samples were collected from San Andrés Island, while two samples were obtained from Providencia Island.

Red macroalgae are recognized as sources of photoprotective compounds, including chlorophylls, phycobiliproteins, polyphenols, sulfated polysaccharides, carotenoids, and MAAs (Pangestuti et al. 2018). Aqueous extracts were obtained from each algal sample, and their photoprotective parameters were evaluated. Sun protection factor (SPF) was measured at extract concentrations of 5, 10, and 20 mg ml−1, while UVA radiation protection (UVAr) and critical wavelength (λc) were assessed at a concentration of 5 mg ml−1. Benzophenone-3 (BP-3) as a positive control was tested at a concentration of 5 mg ml−1 in all experiments.

At the highest concentration evaluated (20 mg ml−1), SPF values ranged from 3.56 for the extract of Gracilaria sp. Greville, 1830 to 23.14 for the extract of Laurencia obtusa (Hudson) J.V.Lamouroux, 1813 to 20 mg ml−1. The extract of L. obtusa showed the highest photoprotective activity and was classified as a medium photoprotector in the UVB range, according to the EC classification (European Commission 2009). In contrast, the extract of Gracilaria sp. displayed the lowest SPF value and was considered inactive (Fig. 1).

Photoprotection parameters (SPF, UVAr, λc) of aqueous extracts of red algae from San Andrés and Providencia Islands. a SPF measured at extract concentrations of 20 mg ml−1 (red circles), 10 mg ml−1 (yellow triangles) and 5 mg ml−1 (blue diamonds), joined by dashed lines for visual support. UVB protection scale: high (white), medium (blue), low (pink); none (gray). b UVAr protection (orange columns) evaluated at extract concentrations of 5 mg ml−1 and λc critical wavelength (black columns) evaluated at extract concentrations of 5 mg ml−1

When tested at lower concentrations (5 mg ml−1), only the extract of L. obtusa exhibited UVB protection based on the EC classification (European Commission 2009). Species of this genus are well known for producing MAAs, compounds with high photoprotective potential (Stein et al. 2013).

Tested at extract concentrations of 5 mg ml−1, UVAr values ranged from 0.49 (Gracilaria sp.) to 1.15 (Ceramium sp. 1 Gaertner ex Stackhouse, 1797), with 9 out of 10 samples meeting the criteria for maximum protection labelling. Similarly, λc critical wavelength values ranged from 360.9 nm (Gracilaria sp.) to 373.3 nm (Ceramium sp. 1), with 8 out of 10 extracts fulfilling the broad-spectrum photoprotection criteria established by EC standards (European Commission 2009; Padera 2015). The UVAr showed that 9 out of 10 samples had values above 0.8, indicating optimal UVA protection, which could be promising for cosmetic formulations offering both UVB and UVA protection.

De la Coba et al. (2019) demonstrated that topical formulations containing MAAs enhance UVA and UVB protection through different biological effective protection factors (BEPFs). Their findings highlight the role of MAAs in mitigating UV-induced damage, reinforcing the hypothesis that these compounds contribute significantly to photoprotection in marine organisms. In this context, the MAA content of each extract was characterized to correlate the photoprotective activity parameters (SPF, UVAr, λc) of algal aqueous extracts.

The MAA content in the 10 algal extracts evaluated revealed the presence of six known MAAs, shinorine (1), palythine (2), asterine-330 (3), porphyra-334 (4), palythine-threonine (5) and palythinol (6). Additionally, a minor signal corresponding to an unidentified MAA (unID1) was detected. The retention time, maximum absorbance wavelength, protonated molecular ion mass ([M + H] ⁺), MS/MS fragmentation patterns, and identification details of these compounds are summarized in Table SM2.

From extracts of red algae collected at San Andrés Island, four common MAAs (shinorine (1), palythine (2), asterine-330 (3), and porphyra-334 (4)) were identified in Gracilariopsis cf. tenuifrons (C.J.Bird & E.C.Oliveira) Fredericq & Hommersand, 1989, Dasya sp. C. Agardh, 1824 and Ceramium sp. 2. Additionally, palythine-threonine (5) was detected in Acanthophora spicifera (Vahl) Børgesen, 1910, collected in April of 2023 (A. spicifera sample 1) and October of 2023 (A. spicifera sample 2). Palythinol (6) was identified in L. obtusa, while an unidentified MAA (unID1) was detected in Ceramium cf. nitens (C.Agardh) J.Agardh, 1851 and Ceramium sp.1. Extracts from Gracilaria from Providencia Island contained shinorine (1), palythine (2), asterine-330 (3), and porphyra-334 (4), and palythinol (6). In contrast, no MAAs were detected in Spyridia filamentosa.

The quantitative data obtained in this study (Fig. 2) indicate that total MAA content in the analyzed samples ranged from 0.18 to 1.54 mg g−1 DW. These values align with the expected concentrations for species within the orders Ceramiales and Gracilariales, which typically exhibit MAA levels ranging from 1 to 2 mg g−1 DW, while some members of the Gracilariales may exceed 2 mg g−1 DW of MAAs. However, several species of macroalgae have been contain significantly lower MAA concentrations, even below 0.1 mg g−1 DW (Sun et al. 2020).

Quantification of mycosporine-like amino acids in extracts of red algae from San Andrés and Providencia Islands

Life habits of algae as well as their location in the intertidal zone may explain differences in MAA profile, with lower concentrations in algae thriving in the infralittoral and greater concentrations in algae from the supralittoral zone as these are more exposed to intense sunlight. These differences suggest that specific habitat conditions may influence MAA production, although it remains unclear how local environmental conditions impact the biosynthesis of these compounds.

The highest MAA concentrations were detected in L. obtusa (1.54 mg g−1 DW) and A. spicifera both collected in October 2023 (1.20 mg g−1 DW). These values are higher than those reported for the same species in Brazil, where L. dendroidea exhibited MAA concentrations ranging from 0.06 to 1.36 mg g−1 DW and A. spicifera from 0.04 to 0.44 mg g−1 DW (Briani et al. 2018). However, these values are lower than concentrations reported for other samples collected in the Colombian Caribbean in 2022, where A. spicifera reached 2.50 mg g−1 DW and L. obtusa exhibited values as high as 6.49 mg g−1 DW of MAAs (Urrea-Victoria et al. 2025). This variation in MAA concentrations may be attributed to environmental differences, genetic variability within populations, or physiological responses to local stressors. Future studies should further evaluate these factors to better understand the underlying causes of these fluctuations.

Similarly, samples of Gracilariopsis cf. tenuifrons from San Andrés Island exhibited a high MAA content (1.45 mg g−1 DW), comparable to G. longissimi (0.80–1.62 mg g−1 DW) reported in other regions (Álvarez-Gómez et al. 2019). Gracilariopsis cf. tenuifrons, as reported by Torres et al. (2015), demonstrated significant variation in MAA content when cultured under different levels of photosynthetically active radiation (PAR). Under higher PAR conditions (600 and 1000 μmol m−2 s−1), total MAA content increased by approximately 20%, with a notable rise in palythinol (6) concentration, which showed a strong correlation with increased irradiance. These findings suggest that G. tenuifrons under laboratory conditions exhibits a remarkable capacity to accumulate MAAs, similar to other Gracilariopsis species. This further supports the role of MAAs in photoprotection against high irradiance and can explain high values of MAA concentration in Gracilariopsis cf. tenuifrons.

In relation to the concentrations of individual MAAs (Fig. 2), shinorine (1) concentrations ranged from 0.01 to 0.75 mg g−1 DW, with the highest values found in Gracilariopsis cf. tenuifrons and Ceramium cf. nitens, while Gracilaria sp. and Dasya sp. exhibited the lowest levels of this compound. Palythine (2) concentrations ranged from 0.05 to 0.54 mg g−1 DW, with the highest value detected in L. obtusa, and the lowest in the Ceramium sp. 2. Asterine-330 (3) levels ranged from 0.04 to 0.10 mg g−1 DW, with the highest concentration in G. tenuifrons, while L. obtusa had the lowest concentration (Fig. 2). Porphyra-334 (4) concentrations ranged from 0.01 to 0.92 mg g−1 DW, with the highest values observed in A. spicifera, L. obtusa, and G. tenuifrons, while Gracilaria sp. and Ceramium cf. nitens had the lowest concentrations of this MAA. The sample of A. spicifera collected in October 2023 had 0.02 mg g−1 DW of palythine-threonine. Additionally, palythinol was identified in the L. obtusa sample (0.04 mg g−1 DW).

A heatmap (Fig. 3) was created to compare the results of SPF, UVAr, λc, porphyra-334 (4) concentration, and total MAAs at a concentration of 5 mg ml−1. Red colors indicate values above average, while blue colors reflect values below average, allowing a visual interpretation of the relationship between MAA concentration and photoprotective activity. The heatmap grouped into four clusters: Cluster 1, which included only Gracilaria sp., exhibited the lowest values for SPF, UVAr, and λc, with a low content of MAAs. Cluster 2 featured L. obtusa, which showed the highest UVB photoprotection values and the highest MAA concentrations, highlighting its potential for cosmetic applications. Cluster 3, the largest group, displayed average photoprotection values and low MAA concentrations. Finally, Cluster 4, including G. tenuifrons and A. spicifera, also exhibited high MAAs concentrations and important photoprotection parameters, suggesting this species as promising for its photoprotective properties.

Heatmap of photoprotective properties of aqueous extracts from red algae tested at a concentration of 5 mg ml−1. Variables shown include SPF, UVAr, λc, porphyra-334 concentration, and total mycosporine-like amino acids content. Highlighted bold numbers correspond to each cluster

In the heatmap, species of L. obtusa and A. spicifera collected in October 2023 as well as G. tenuifrons showed high photoprotection and significant MAA concentrations among the evaluated samples due to their high exposure to sunlight. The Archipelago of San Andrés, Providencia, and Santa Catalina receives high levels of UV radiation annually (5313.1 Wh m−2 per day); according to official data (IDEAM et al. 2017), algae from the intertidal zone are expected to produce high concentrations of MAAs as means of protection against solar radiation.

Species such as Gracilaria sp., Ceramium cf. nitens, Ceramium sp. 1, and Ceramium sp. 2 showed lower MAAs concentration. Concentrations of MAAs are highly dependent on algal species, as it has been reported in various studies (Korbee et al. 2006; Pliego-Cortés et al. 2019; Geraldes et al. 2020). Other opportunities to obtain MAAs from red algae would be through cultures since optimized cultivation methods for obtaining MAAs have shown that increasing nitrogen availability and UV radiation can yield MAA concentrations as high as 8.9 mg g−1 DW (Peinado et al. 2020). This suggests that cultivating macroalgae under controlled conditions could enhance MAA content, increasing their potential for commercial applications.

UVAr values above 0.8 indicate that the extract is ranged as maximum UVA protection, which is particularly advantageous for cosmetic formulations designed to provide both UVB and UVA protection. When correlating MAA content with UVAr and λc parameters, it was observed that despite high Porphyra-334 (4) levels in L. obtusa and G. tenuifrons, extracts from these species did not meet the broad-spectrum protection criteria based on λc. This suggests that other compounds may contribute to UVAr and λc. Furthermore, photoprotective formulations containing MAAs such as shinorine (1), asterine-330 (3), and porphyra-334 (4), which strongly absorb in the UVA region, have not been classified as UVA sunscreen filters (Médice et al. 2023). These findings indicate that the mere presence of MAAs does not necessarily ensure UVA protection, as exemplified by the extract of Laurencia obtusa sample, which exhibited high UVB protection but relatively low UVA protection.

Commercial products such as Helionori™, Algamarine™, and Helioguard™ 365 sunscreens already use marine-derived MAAs like porphyra-334 (4) as active ingredients. The use of polymeric gels with Pluronic F-127® in formulations with MAAs has also demonstrated photoprotection in vivo tests (Tosato et al. 2015). In response to the growing demand for natural and environmentally friendly products, MAAs obtained from red macroalgae are potentially valuable as promising ingredients for the cosmetic industry.

In conclusion, this study allowed the identification and quantification of six known MAAs from Caribbean algae. Aqueous extracts from L. obtusa showed the highest concentration of MAAs (1.54 mg g−1 DW), with porphyra-334 (4) being the predominant compound. Heatmap analysis revealed a significant correlation between MAA concentration and photoprotective capacity, with L. obtusa showing a direct association between high MAA levels and UVB protection, achieving a SPF of 23.14. Additionally, A. spicifera, characterized by a high porphyra-334 (4) content, exhibited broad-spectrum photoprotection. These findings align with previous reports from algae belonging to the Gracilariales and Ceramiales orders. However, due to their low local abundance and biomass, the studied macroalgae cannot be considered optimal candidates as sustainable sources of bioactive metabolites for photoprotective cosmetic applications.