Cultures of Chlamydomonas are disclosed comprising greater than 340 mg/l triacylglycerols (TAG). The cultures can include buoyant Chlamydomonas. Methods of forming the cultures are also disclosed. In some embodiments, these methods comprise providing Chlamydomonas growing in log phase in a first culture medium comprising a nitrogen source and acetate, replacing the first culture medium with a second medium comprising acetate but no nitrogen source, and subsequently supplementing the second medium with additional acetate. In some embodiments, a culture can comprise at least 1,300 mg/l triacyglycerols. In some embodiments, cultures can be used to produce a biofuel such as biodiesel.