when conditions are unfavourable due to prolonged dryness or exposure to low salinity waters, "dunaliella" cells undergo sexual reproduction. two haploid vegetative motile cells will touch flagella and then fuse their equal-sized gametes with one another in a very similar way to "chlamydomonas" by the formation of a cytoplasmic bridge.  after this isogamous fertilization, the diploid zygote, which is red and/or green in colour, develops a thick and smooth wall and takes on a circular shape very similar to the cyst form of "dunaliella". in fact, after observing zygotes, there was discussion on whether the cysts seen after and algal bloom at the dead sea in 1992 were in fact, zygotes. the wall of the zygote will serve to protect the cell during a resting period in the harsh conditions until finally, the zygote will undergo meiosis and release up to 32 haploid daughter cells via a tear in the cellular envelope. asexual resting cysts may be a possibility, though has not been studied enough to confirm.