The reproductive phenology of Delesseria sanguinea and Odonthalia dentata off the Isle of Man

Samples of individual plants of Delesseria sanguinea and Odonthalia dentata were collected from shallow subtidal populations off the south end of the Isle of Man during the reproductive season. Reproductive bladelets were measured and their state of fertility noted. In Delesseria, male bladelets appeared in early September and achieved maximum size in mid October when bladelets of all sizes became fertile; the largest of these dehisced first and all were spent by mid December. Females appeared 3 weeks later; carpogonia were fertilized during October but carpospores were not released until about February when maximum bladelet length was reached. In about half the bladelets carpogonia remained unfertilized and did not grow further and only 40% of successful fertilizations resulted in carpospore release. Tetrasporangial bladelets did not appear until November and tetraspores were released in January and February while bladelets were still growing. Gametophytes and tetrasporophytes existed in about equal numbers. In Odonthalia, all three types of bladelet appeared in early November and fertilization took place in December, but later-developing carpogonia seemed to remain unfertilized in spite of a second wave of production of spermatangia, resulting in a low fertilization success of about 7%. Both carpospores and tetraspores dehisced from January to April. In this species the gametophytes formed about 58% of the population, a proportion expected from equal survival of number of spores per parent.