Photosynthetic microalgae are unicellular plants, many of which are rich in protein, lipids, and bioactives and form an important part of the base of the natural aquatic food chain. Population growth, demand for high-quality protein, and depletion of wild fishstocks are forecast to increase aquacultural fish demand by 37% between 2016 and 2030. This review highlights the role of microalgae and recent advances that can support a sustainable 'circular' aquaculture industry. Microalgae-based feed supplements and recombinant therapeutic production offer significant opportunities to improve animal health, disease resistance, and yields. Critically, microalgae in biofloc, 'green water', nutrient remediation, and integrated multitrophic aquaculture technologies offer innovative solutions for economic and environmentally sustainable development in line with key UN Sustainability Goals. Increasing Demand for Aquaculture Feeds Aquaculture (see Glossary) plays an increasingly important role in global food security, a critical challenge of the 21st century. The global population is forecast to increase from 7.6 to 9.8 billion by 2050 i , causing a projected food demand increase of 60-100% above 2005 levels [1,2]. In parallel, rising affluence is predicted to increase the demand for high-quality protein by 110% [2], emphasizing the need to establish sustainable ii high-protein food production networks. Currently,~57% of global protein supply is from plant sources (almost exclusively terrestrial); the remaining 43% is from animal sources (red meat, poultry, seafood, dairy, eggs, and other products) [3]. Of the 1.7 billion tonnes year −1 of animal products produced globally in 2016 iii , wild-caught and farmed fish accounted for~10% (171 million tonnes year −1 , US $143 billion) [4]. As wild-caught fish yields have plateaued over the past 20 years, fish demand has been met by an expanding aquaculture sector [4], which has increased from~20 million tonnes (1950) to~80 million tonnes (2016), at a growth rate of~2.3 million tonnes year −1 (~6%) iv. Aquaculture's contribution to meeting future food demand will require more sustainable practices that support both aquatic and terrestrial ecosystems. A key problem to date has been the high use of wild-caught pelagic fish for the production of fishmeal and fish oil for formulated aquafeeds. This has put pressure on populations of low-trophic species that are keystones in aquatic food webs (e.g., anchovies, capelin, herring, mackerel, menhaden, sardines) and which wild fisheries depend on [5,6]. It also increases the potential spread of bacterial (e.g., Vibrio cholerae [7]) and viral (e.g., iridovirus [8]) diseases via raw fish distribution. Fishmeal is a favored ingredient in fish nutrition as it is rich in protein, easily digestible, and palatable and provides a well-balanced source of essential amino acids, phospholipids, and omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Increasing use of alternative ingredients include those from animal, pla...

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A number of pharmacologically active brominated pyrrole-2-aminoimidazole (B-P-2-AI) alkaloids have been isolated from several families of marine sponges, including those belonging to the genus Stylissa. In the present study, MALDI mass spectrometry imaging (MALDI-imaging) was applied to determine the spatial distribution of B-P-2-AIs within 20 μm cross sections of S. flabellata. A number of previously characterised B-P-2-AIs were readily identified by MALDI-imaging and confirmed by MS-MS and NMR profiling. Unknown B-P-2-AIs were also observed. Discrete microchemical environments were revealed for several B-P-2-AIs including dibromophakellin which was localised within the external pinacoderm and internal network of choanoderm chambers. Additionally, dibromopalau'amine and konbu'acidin B were also found to be confined to the choanoderm, while sceptrin was found to be highly abundant within the mesohyl. Further brominated compounds of unknown structure were also observed to have distinct localisation in both choanoderm chambers and the pinacoderm. These findings provide insights into the chemical ecology of S. flabellata, as most B-P-2-AIs were found on highly exposed surfaces, where they may act to prevent pathogens, predation and/or biofouling. Moreover this study demonstrates the power of MALDI-imaging to visualise the location of a range of metabolites in situ and to characterise compounds by MS-MS directly from intact specimens without the need for extraction. These methodologies facilitate selective targeting of micro-regions of sponge to screen for symbiotic microbial candidates or genes that may be involved in the production of the correlated compounds, and may represent a change in paradigm for natural product drug development.

19Outdoor microalgae systems are a promising platform for fuels and chemicals, but are currently 20 limited by relatively low productivities. This study investigated the effects of photoacclimation 21 on the productivity of Chlamydomonas reinhardtii grown under fluctuating light regimes 22 which simulate well-mixed cultures in outdoor reactors. Simulations represented cells cycling 23 between high light and dark zones in high-density (HDFluc, light fraction (LF) = 0.5) and low-24 density (LDFluc, LF = 0.9) cultures. Each fluctuating treatment was controlled by cultures grown 25 under non-fluctuating light of the same hourly average irradiance (HDAvg and LDAvg) to 26 differentiate between light dosage and regime. The large dark fraction of HDFluc resulted in a 27 low-light acclimated phenotype displaying up-regulation of light harvesting pigments and low 28 NPQ caused by reduced levels of the dissipative protein LHCSR3. All other treatments led to 29 high-light acclimation phenotypes. HDFluc showed an estimated three-fold lower biomass yield 30 relative to light absorbed and significant reductions in the quantum yield of PSII compared to 31HDAvg. This suggests that during high light periods of fluctuating cycles, higher absorption and 32 an inability to safely dissipate excess light, resulted in greater photodamage and respiration 33 required for repair. A framework for including these findings in predictive modelling of mass 34 cultures is presented. 35 36 37 Keywords 38 Microalgae, Chlamydomonas reinhardtii, photoacclimation, non-photochemical quenching, 39 fluctuating light, mass culture, LHCSR3, photosynthesis, predictive model 40 41 3 1.0 INTRODUCTION * 42Forecasts indicate that by 2050 we will require 70% more food, [1], 50% more fuel [2], 50% 43 more fresh water [3], and ~50-80% CO2 emissions reductions [4] to sustain a population of 44 ~9.6 billion [5]. Algae biotechnologies are positioned at the nexus of these challenges as they 45 can be located on non-arable land, tap into the huge energy resource of the sun (~2600x global 46 energy demand [6]), and use CO2 to produce food, fuels and clean water. Techno-economic 47 analysis has revealed biomass productivity as a critical factor in increasing the economic 48 competitiveness of algal technologies [7]. While high-rate outdoor microalgae production 49 systems are already achieving photon conversion efficiencies (PCE) of ~2% [7, 8], which is an 50 order of magnitude higher than those of field trials for switchgrass and sugarcane (PCE ~0.2%) 51 [9][10][11], this remains far below the theoretical upper limits of ~8-10%, which could yield up to 52 77g biomass dry weight.m -2 .day -1 [12]. The focus of this study is on bridging the gap between 53 the current and theoretical PCE in outdoor mass cultures. 54 In well-mixed, high-density mass cultures, cells are subjected to dynamic light fluxes in which 55 they are repeatedly cycled between photoinhibitory high light levels at the illuminated surface 56 (up to ca. 2,000 μmol photons.m -2 .s -1 ) and light-limited d...

Microalgae biotechnologies are rapidly developing into new commercial settings. Several high value products already exist on the market, and systems development is focused on cost reduction to open up future economic opportunities for food, fuel and freshwater production. Light is a key environmental driver for photosynthesis and optimising light capture is therefore critical for low cost, high efficiency systems. Here a novel high-throughput screen that simulates fluctuating light regimes in mass cultures is presented. The data was used to model photosynthetic efficiency (PEµ, mol photon−1 m2) and chlorophyll fluorescence of two green algae, Chlamydomonas reinhardtii and Chlorella sp. Response surface methodology defined the effect of three key variables: density factor (Df, ‘culture density’), cycle time (tc, ‘mixing rate’), and maximum incident irradiance (Imax). Both species exhibited a large rise in PEµ with decreasing Imax and a minimal effect of tc (between 3–20 s). However, the optimal Df of 0.4 for Chlamydomonas and 0.8 for Chlorella suggested strong preferences for dilute and dense cultures respectively. Chlorella had a two-fold higher optimised PEµ than Chlamydomonas, despite its higher light sensitivity. These results demonstrate species-specific light preferences within the green algae clade. Our high-throughput screen enables rapid strain selection and process optimisation.