**4. Concluding Remarks and Future Prospects**

Seaweeds remain largely untapped reservoirs of natural bioactive molecules [10]. In fact, more than 11,300 species of seaweeds are reported on Algabase, of which only 42 species were surveyed on category 4 (studies of extracts enriched in isolated groups or classes of complex lipids) and category 5 (studies of isolated complex lipid molecular species), most of them within the Ochrophyta phylum. This reveals that the bioprospecting potential of seaweed lipids remains largely untapped.

Complex lipids from seaweeds are emerging as bioactive molecules with hidden potential; however, their exploitation is far from being optimized and their action mechanisms are still poorly understood. This figure is likely to change as more seaweeds have their bioactive complex lipids characterized and more mechanism-oriented studies are performed.

To date, not only do most studies lack a systematic research approach, but most of the lipid bioactivities already identified refer to total lipid extracts. Indeed, only a few studies have achieved molecular isolation and characterization of bioactive lipids. Interestingly, complex lipids isolated from seaweed species with reported bioactivity have been classified mainly as GLs species. This systematic analysis pinpoints the promising results of naturally occurring GLs in seaweeds, with emphasis to their antitumor and antiinflammatory potential. The advances of emerging food/feed, nutraceutical, cosmeceutical, pharmaceutical, and complementary medicine research fields [91–93], as well as biological and experimental sciences, will contribute to boost structural characterization of complex lipids and to link lipid structure and bioactivity through different mechanisms of action.

Regardless of their polyphyletic nature, it is unquestionable that seaweeds as a whole, remain an important reservoir of lipid phytochemicals. Despite the low abundance of these biomolecules in seaweeds, they remain largely uncharacterized and unexplored. Complex lipids from seaweeds offer an unmatched chemical diversity and structural complexity when compared to terrestrial phytochemicals. It seems that seaweeds species or genera feature unique lipidomes, which likely enhances the potential number of target applications. Lipidomic characterization strategies using high-resolution apparatus, such as mass spectrometry, can be paramount to unleash the true potential of these biomolecules. The species-specific lipidome for each seaweed could be applied to the production of target bioactive lipids. Otherwise, isolated bioactive complex lipids can be used as a largescale synthesis model. While some of their natural chemotherapy diversity has already been studied, resulting in open access and proprietary compound libraries, there is still a multitude of lipids from algal origin that have hardly been characterized. The potential of these biomolecules to develop new products and processes is certainly far from being exhausted. It is expected that the bioprospecting of seaweed extracts enriched in active lipids for the formulation of high-end products can foster the added value of seaweed biomass production.

Under this scope it will be possible to put forward innovative processes for the production of farmed seaweeds biomass under controlled conditions, as these will allow to target new markets and consumers under a circular and sustainable blue bioeconomy framework.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/md19120686/s1, Table S1: Eligible studies distributed by title, published year, doi (when applicable), seaweeds species, genus, phylum, bioactivity reported, and category where they were inserted.

**Author Contributions:** Conceptualization, D.L. and M.R.D.; methodology, D.L.; validation, M.R.D., F.R., M.C.L., A.I.L., R.C. and M.R.D.; formal analysis, D.L.; data curation, D.L. and F.R.; writing original draft preparation, D.L.; writing—review and editing, F.R., M.C.L., A.I.L., R.C. and M.R.D.; supervision, A.I.L., R.C. and M.R.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors are grateful to Fundação para a Ciência e a Tecnologia (FCT, Portugal), European Union, QREN, POPH, FEDER, and COMPETE by funding CESAM (UIDP/50017/2020 + UIDB/50017/2020), and LAQV/REQUIMTE (UIDP/50006/2020 + UIDB/50006/2020). Thanks

to the project Omics 4 Algae: Lipidomic tools for chemical phenotyping, traceability, and valorization of seaweeds from aquaculture as a sustainable source of high added-value compounds (POCI-01-0145-FEDER-030962), funded by Centro2020, through FEDER and PT2020.Diana Lopes (SFRH/BD/119027/2016) is grateful to FCT, Programa Operacional do Capital Humano (POCH) and European Union through European Social Fund (FSE) for her grant. FCT is also thanked for the Scientific Employment Stimulus 2017, with a Junior Researcher contract to Felisa Rey (CEECIND/00580/2017), and an Assistant Researcher contract to Miguel Leal (CEECIND/01618/2020). This is a contribution of the Marine Lipidomics Laboratory.

**Conflicts of Interest:** The authors declare no conflict of interest.
