Complex sentence: They cannot be grown by vegetative means, but must go through a reproductive cycle involving an alternation of generations this makes cultivated brown seaweeds too expensive when compared to the costs of harvesting and transporting wild seaweeds.
Split into simpler sentences: They cannot be grown by vegetative means, but must go through a reproductive cycle involving an alternation of generations. This makes cultivated brown seaweeds too expensive when compared to the costs of harvesting and transporting wild seaweeds.