Biannual Spawning and Temporal Reproductive Isolation in Acropora Corals

Area of Science:

• Marine Biology
• Coral Reef Ecology
• Reproductive Biology

Background:

• Coral spawning events in Western Australia's oceanic reefs occur in autumn and spring.
• The extent of species and colony participation in these dual spawning seasons was previously unknown.

Purpose of the Study:

• To investigate colony participation in two distinct spawning events over three years.
• To determine if reproductive seasonality in Acropora corals is influenced by habitat or Symbiodinium partners.
• To analyze the genetic basis of spawning seasonality in Acropora tenuis.

Main Methods:

• Tracking and tagging of 1,855 Acropora colonies across 13 species over three years.
• Bayesian clustering analysis of microsatellite markers to assess genetic divergence.
• Investigating the influence of habitat conditions and Symbiodinium partners on reproductive seasonality.

Main Results:

• Seven of 13 Acropora species spawned in both autumn and spring; five spawned only in autumn, and one only in spring.
• Most tagged colonies spawned once annually, but five colonies spawned in both seasons within a single year.
• Colonies of Acropora tenuis spawning in different seasons showed significant genetic divergence, indicating temporal reproductive isolation.

Conclusions:

• Temporal reproductive isolation is common in Acropora populations at Scott Reef.
• Spawning season appears to be a genetically determined trait in Acropora tenuis.
• Interbreeding between genetically distinct groups can occur occasionally, particularly when environmental conditions favor a second gametogenic cycle.