Green macroalgae (Chlorophyta) currently represent a residual fraction (<1%) of global seaweed biomass production landings. In turn, red (Rhodophyta) and brown (Ochrophyta) macroalgae dominate the remaining percentage of aquaculture production, exceeding 32 million tonnes per annum. However, the industry relies on a relatively low number of species, in which as few as seven macroalgal genera collectively represent the bulk of global production metrics. At present, innovation and increased sustainability of the industry calls for diversification of macroalgal species/strains in aquaculture to counteract potential adverse effects ensuing from genetic impoverishment, decreased resilience to disease and climate change. Despite the dominance of red and brown seaweed regarding production figures, aquaculture of green macroalgae has witnessed an increasing trend in productivity and diversification over the last decades, particularly in Asia, where green seaweed taxa often occupy specific market niches in the food sector. Furthermore, growing interest in green seaweeds in aquaculture has been highlighted for different applications in emerging western markets (eg IMTA, biorefineries, food delicacies), owing to a unique diversity of cytomorphologies, ecophysiological traits, propagation capacities and bioactive compounds featured by this group of macroalgae. Cultivation technologies are relatively well developed, but sustainability assessments are scarce and required to unlock the potential of green seaweeds. Although it is likely that green macroalgae will remain occupying specialised market niches, in which high‐value products are favoured, we argue that aquaculture of chlorophytan taxa presents itself as a compelling option under the current quest for commercial diversification of products and expansion of the sector.

Bryopsidales (Chlorophyta) are cultured and consumed in several regions of the planet and are known for their high nutritional value and bioprospection potential, due to a high content of relevant polar lipids and polysaccharides. Among other characteristic features, these marine algae are known for possessing unique photosynthetic pigment-protein complexes and for the absence (in nearly all species investigated) of a functional xanthophyll cycle, a ubiquitous photoprotection mechanism present in most algae and plants. With the aim of characterizing the photophysiology of this atypical group of algae, we investigated the changes in pigment content and polar lipidome of two Bryopsidales species (Codium tomentosum and Bryopsis plumosa) exposed for 7 days to low or high irradiance (20 vs. 1,000 μmol photons m–2 s–1). Our results show that high light has a strong effect on the pigment composition, triggering the time-dependent accumulation of all-trans-neoxanthin (t-Neo) and violaxanthin (Viola). High light-acclimated macroalgae also displayed a shift in the characteristic polar lipidome, including a trend of accumulation of lyso-glycolipids, and highly unsaturated phospholipids and betaine lipids. We hypothesize that the observed shifts on the lipid composition could promote the interaction between t-Neo and Viola with the siphonaxanthin–chlorophyll–protein complexes (SCP) of photosystem II (PSII) within the thylakoid membranes of the chloroplasts. Light induced changes in pigment and lipid composition could contribute to the fitness of Bryopsidales algae by reducing damages to the photosynthetic apparatus under increased irradiance.

Codium tomentosum is a marine green macroalga with multiple value-added applications that is being successfully used as an extractive species in sustainable integrated multi-trophic aquaculture systems. Nonetheless, growth conditions of this species at an early development phase still require optimization. The present study addresses, under controlled laboratory conditions, the effects of photoperiod (long vs. short-day) and light spectra (white, blue, and red light) on growth and pigment composition of C. tomentosum. Relative growth rate was approximately 2× higher under long-day photoperiod (average of 39.2 and 20.1% week−1 for long and short-day, respectively). Concentrations per dry weight of major pigments such as chlorophyll a (Chla) and siphonoxanthin (Siph) were significantly higher under long-day photoperiod. Relative growth rates were higher under red light, intermediate under white light, and lower under blue light. These last results were rather surprising, as Siph-Chla/Chlb light harvesting complexes of Codium have increased absorption in the blue-green region of the light spectra. Changes in carbon allocation patterns caused by the spectral composition of light and overgrowth of green microalgae in blue light cultures could explain the differences recorded for relative growth rate. Long-day photoperiod and light sources with preferential emission at the red region of the light spectra were identified as optimal for growth of C. tomentosum at early development stages. These lighting conditions can reduce the time required to reach the necessary biomass before transfer to grow-out systems. Overall, these findings can shorten production time, increase macroalgal productivity, and enhance aquaculture revenues.

Codium tomentosum is a recently domesticated green macroalga, being currently cultured as an extractive species in integrated multi-trophic aquaculture (IMTA). Optimization of light requirements in outdoor systems must be achieved to increase the market value of cultivated algal biomass. The present study addresses the seasonal effects of light intensity and wavelength on productivity, pigment composition and epiphyte overgrowth in C. tomentosum cultured in a land-based IMTA system. Exposure to high light (non-filtered sun light) lead to higher net productivities in spring. However, non-filtered sun light caused significantly reduced productivities during summer when compared to filtered sun light (~ 4x lower irradiance levels). Furthermore, lower photosynthetic capacity (Fv/Fm) was observed in macroalgae cultured under high light during summer, indicating photoinhibition. Treatments with filtered sun light (low and red light) showed intermediate and more stable productivities. Epiphyte biomass was higher under high light and the lowest epiphyte overgrowth was recorded under red light. Concentrations of light-harvesting pigments were lower in summer than in spring, indicating a seasonal photoacclimation of macroalgae. An opposite seasonal trend was observed for accessory xanthophylls, as the main role of these pigments is photoprotection. Higher all-trans-neoxanthin and violaxanthin concentrations were found in high light than in low or red light treatments, confirming the important role of these biomolecules in the photoprotection of C. tomentosum. This study underlines the importance of controlling light to optimize algal growth outdoors and enhance the production of high-value compounds (i.e., pigments). Additionally, this practice can also reduce epiphyte overgrowth, thus enhancing the valorization of macroalgal biomass derived from C. tomentosum aquaculture.