Although benthic filamentous algae are interesting targets for wastewater treatment and biotechnology, relatively little is known about their biochemical composition and variation in response to growth conditions. Fatty acid composition of four benthic filamentous green algae was determined in different culture conditions. Although the response was partly species-dependent, increasing culture age, nitrogen deprivation and dark exposure of stationary phase greatly increased both total fatty acid content (TFA) from 12-35 to 40-173 mg g(-1) dry weight (DW) and the relative proportion of polyunsaturated fatty acids (PUFAs) from 21-58% to 55-87% of TFA, with dark exposure having the greatest effect. However, the main variation in fatty acid composition was between species, with Uronema being rich in C16:0 (2.3% of DW), Klebsormidium in C18:2 omega 6 (5.4% of DW) and Stigeoclonium in C18:3 omega 3 (11.1% of DW). This indicates the potential of the latter two species as potential sources of these PUFAs. (C) 2015 Elsevier Ltd. All rights reserved.