Pattern, synchrony and predictability of spawning of the tropical abalone Haliotis asinina from Heron Reef, Australia

The spawning biology of the tropical abalone Haliotis asinina on Heron Reef , Australia, was investigated to identify putative environmental and endoge nous factors controlling spawning. Spawnings by II. asinina were highly reg ular and, in comparison to most other haliotids and marine invertebrates, f requent and extremely synchronous. These events appeared to be regulated by more than 1 environmental cue. The spawning season of H. asinina extends f rom October to April and is associated with an increase in water temperatur e. During the spawning season, recently captured abalone, housed in flow-th rough aquaria, released gametes for 2 nights every 2 wk during the new and full moons. However, the exact date of spawning did not correlate precisely with the lunar cycle. Occasionally the spawning events between 2 populatio ns of H. asinina on Heron Reef that were 1.5 km apart differed by 1 d, sugg esting that differential tidal regimes might influence the date of spawning . The population that was exposed to slightly longer spring low tides occas ionally spawned 1 d earlier. In the aquaria, the onset of male spawnings wa s earlier than the onset of female spawnings by an average of 31 min. The t ime of spawning of either sex was highly correlated with the evening high t ide; males spawned an average of 19 min prior to the high tide, and females spawned 11 min after the high tide. Spawnings were highly synchronous amon gst individuals, with 90% commencing spawning within 89 min of the first in dividual that spawned. A greater percentage of individuals spawned when in the presence of the opposite sex and the frequency of male ejaculation was greater when in the presence of females. Synchronous spawning patterns pers isted for 6 wk in H. asinina maintained in aquaria; after this period, spaw nings continued but were irregular and asynchronous. We propose that low ti de exposure and time of high tide indirectly regulate the date and time of spawning respectively, and that these tidal elements influence the spawning biology of H. asinina by maintaining endogenous rhythms that persist in no n-tidal environments for at least 6 wk.