Coral Reefs (1988) 6:207-218
Studies on Halimeda
II. Reproduction, particularly the seasonality of gametangia formation,
in a number of species from the Great Barrier Reef Province*
Edward A Drew and Kay M Abel
Australian Institute of Marine Science, PMB No 3, MSO, Townsville,
Queensland 4810, Australia
*Contribution No 368 from the Australian Institute of Marine Science
Abstract
Seventeen species of Halimeda have been grown in the laboratory in an
open-circuit seawater cascade during a 6-year period. All but one grew
vegetatively (generated new segments) to some extent and several
species grew luxuriantly. A few species also reproduced vegetatively
by developing new plants at the ends of fine runners. However, most
significant was the production of gametangia by all the species in the
cascade whilst several of those species, plus one not grown in the
cascade, were also observed fertile in the field. Different material
from a single collection sometimes became fertile in the cascade in
successive years and then often at very similar times of year,
suggesting a distinct seasonality and response to environmental
stimuli. Some lunar periodicity was also detected in the fertility of
three species. Species-specific differences in the structure of
gametangial clusters, particularly the size of the gametangia, were
observed. In all species examined, gametophore branches ended in
unexpanded tips which often had a distinct, thickened cap. Upon
maturity, the contents of all the gametangia were explosively released
through these discharge papillae. This release usually commenced only
5 to 15 minutes after the plants were re-illuminated the day following
appearance of gametangia although two species, H incrassata and H melanesica, often released their gametes in the late afternoon.