We investigated the potential of seaweeds as feedstock for oil-based products, and our results support macroalgae (seaweeds) as a biomass source for oil-based bioproducts including biodiesel. Not only do several seaweeds have high total lipid content above 10% dry weight, but in the brown alga Spatoglossum macrodontum 50% of these lipids are in the form of extractable fatty acids. S. macrodontum had the highest fatty acid content (57.40 mg g À1 dw) and a fatty acid profile rich in saturated fatty acids with a high content of C18:1, which is suitable as a biofuel feedstock. Similarly, the green seaweed Derbesia tenuissima has high levels of fatty acids (39.58 mg g À1 dw), however, with a high proportion of PUFA (n-3) (31% of total lipid) which are suitable as nutraceuticals or fish oil replacements. Across all species of algae the critical parameter of fatty acid content (measured as fatty acid methyl esters, FAME) was positively correlated (R 2 = 0.67) with total lipid content. However, the proportion of fatty acids to total lipid decreased markedly with total lipid content, generally between 30% and 50%, making it an inaccurate measure of the potential to identify seaweeds suitable for oil-based bioproducts. Finally, we quantified within species variation of fatty acids across locations and sampling periods supporting either environmental effects on quantitative fatty acid profiles, or genotypes with specific quantitative fatty acid profiles, thereby opening the possibility to optimize the fatty acid content and quality for oil production through specific culture conditions and selective breeding.

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We investigated the spatial, seasonal, and withinplant variation in total fatty acids (TFA) and fatty acid (FA) composition in the brown seaweeds Dictyota bartayresii sampled from Nelly Bay, Orpheus Island, and Kissing Point (Northern Queensland, Australia) and Dictyopteris australis sampled from Nelly Bay. Both species were present year round, but with no consistent seasonal pattern in plant size, and had an annualized mean content of TFA of 5 % dry weight (dw) that is among the highest recorded for seaweeds. For Dictyota, larger plants had a higher content of TFA and a higher proportion of polyunsaturated omega-3 FA (PUFA(n-3)) than smaller plants, while for Dictyopteris, the TFA content and the proportion of PUFA(n-3) were unrelated to plant size. TFA in Dictyota varied considerably between locations (~40 %) (3.5-5.5 % dw) and to a lesser degree between seasons (~10 %) with a lower content of TFA and higher proportion of PUFA(n-3) in winter. Dictyopteris had añ 10 % higher content of TFA in winter but with no seasonal pattern in the composition of FA. There was also within-plant variation in FA, as TFA decreased from the tips toward the base in both species, and in Dictyopteris, the tips had a higher proportion of saturated FA (SFA) and PUFA(n-3) than the base. The presence of site-and species-specific variation in the content and composition of fatty acids reinforces the need for detailed analyses of the biochemical profile of seaweed biomass, including their extracts or purified compounds, if the focus is nutritional applications based on lipids.

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