Reproductive phenology of the kelp Ecklonia radiata at its Australian warm-range edge and the influence of environmental factors

Context: Range-edge populations persist closer to their physiological thresholds, often limiting reproductive output. Kelps are foundation species on temperate reefs, but their reproductive phenology at range edges remains poorly understood.

Aims: We assess the reproductive phenology of Ecklonia radiata at its eastern Australian warm range edge in relation to local environmental conditions and make comparisons with populations throughout Australia.

Methods: E. radiata fertility was monitored over multiple years and environmental predictors of fertility were assessed using generalised additive models. Fertility responses were compared with data from centre and cold range-edge populations.

Key results: The proportion of fertile E. radiata plants increased as daylength declined and the length of fertile tissue was positively correlated with temperature. The magnitude of spore release was variable and responded to episodic swell and rainfall events. This is contrary to spore-release data from centre and cold range-edge populations, which demonstrated seasonal patterns correlated with temperature.

Conclusion: Spore release was lower at the warm range edge, yet year-round spore release demonstrated flexibility in response to local environmental conditions.

Implications: Flexible reproductive phenology of E. radiata at its warm range edge may be advantageous for sustaining populations at low latitudes under climate change.