What environmental factor primarily influences coral spawning timing?

The primary environmental factor that influences coral spawning timing is sea surface temperature (SST). Corals typically spawn in response to specific temperature cues, which are often linked to seasonal changes. When the water temperature rises to a certain threshold, it triggers the reproductive processes within the corals, leading to synchronized spawning events. This synchronization is essential for successful fertilization and recruitment of larvae, as it increases the likelihood of gamete encounter.

Salinity levels, while they can affect coral health and survivability, do not have the same clear connection to the timing of spawning events. Water clarity impacts light penetration and the ability of corals to photosynthesize but is not a direct trigger for spawning. Current strength might influence the dispersal of larvae once spawned, but it does not play a role in the timing of when corals choose to spawn. Thus, sea surface temperature stands out as the key factor influencing the timing of coral spawning.