ABSTRACTRecently released spores of the kelpsMacrocystis pyrifera(L.) C. Ag.,Nereocystis luetkeana(Mert.) Post. and Rupr.,Laminaria farlowiiSetch., andPterygophora californicaRupr. had different levels of net photosynthesis. Spore‐specific photosynthesis–irradiance relationships were similar in many respects forM. pyrifera, N. luetkeana, andL. farlowiispores. All three species had low rates of net light‐saturated photosynthesis. In contrast, spores ofP. californicahad higher photosynthetic potential and overall net photosynthesis than the other three species. On a cell carbon basis, however, photosynthetic rates inN. luetkeanaspores were similar to those ofP. californicaspores and higher than those ofM. pyriferaspores. Chlorophyllacontent of spores varied 10‐fold among species. The rank order of significant differences in chlorophyllacontent wasP. californica>L. farlowii>N. luetkeana>M. pyrifera.As a result, chlorophyll‐specific measurements suggestM. pyriferaandN. luetkeanaspores had much higher quantum efficiency and photosynthetic potential than eitherP. californicaorL. farlowiispores. Maternal carbon and nitrogen investment significantly differed in spores ofM. pyrifera, N. luetkeana, andP. californicawithP. californica>M. pyrifera>N. luetkeana.Carbon content in spores of each of these three species increased by about 30% during 12 h of saturating irradiance. We suggest that the photosynthetic capabilities of and maternal investment in spores may be related to the spore as a unit of dispersal, to the reproductive ecology of the parental sporophytic stages, and to the growth and physiology of the germling gametophy