Abstract
Spawning periodicity and larval biology of the black coral, Antipathes fiordensis, were examined by collecting gametes in mesh nets enclosing parts of tagged colonies during the anticipated spawning season. The mode of reproduction in A. fiordensis is broadcast spawning of gametes. Spawning took place in late February and early March 1999, with one tagged colony spawning at least three times within a three-week period. Spawning appeared to be associated with peaks in sea temperature. The embryos developed into complete planula larvae with an oral pore within 3 - 4 days. Larvae ranged from 100 - 200μm in length and possessed an oral pore with long oral tufts. Most larvae became elongated by 7 days and settled on patches of biofilm on a stone.
Ultrastructural properties of planula larvae of Antipathes fiordensis were examined with a transmission electron microscope. The aboral region of the larvae was thickened and associated with high densities of sensory cells and nerve cells, indicated as a major site of substratum selection. The larvae have an oral pore and a coelenteron. The gastrodermis contained zymogen digestive cells, as in adult polyps, and collar cells with a unique cup-shaped cytoplasm held by a thin stalk. These features suggest a feeding potential for the larvae. The oral region consists of extremely long cells orientated to form a mouth and pharynx. Although the function of this region is not clear, cells seemed to be involved in active secretion.
Growth pattern and size-frequency distribution of the colonies, colony size at first reproduction, and ratio of gravid polyps at different depths were investigated for the populations of Antipathes fiordensis in Doubtful Sound. Generally increase in colony height and width is linear, but the degree of variation between these parameters increased as colony size increased, suggesting that discrete measurement of colony height or width did not represent the entire colony size. The size-frequency distribution of the colonies differed significantly between three sites. Factors controlling colony size may change greatly, even over small geographical scales. As colony size increased, proportion of mature colonies increased. Since some large colonies contained no visible gonad, it is possible that gonad development is partially controlled by environmental factors.