Environmental variability influences seagrass resilience, but the strength and relative importance of factors are rarely assessed over the complete lifecycle. This study examined the effects of abiotic (salinity, temperature, water depth) and biotic (grazing by black swans) factors on Ruppia spp. over the complete lifecycle. Structures were set up in two estuaries that prevented and allowed natural swan grazing of the seagrasses, before the start of the growing season. The density of life stage(s) were measured from germination to senescence. Our results showed that swans impacted some but not all life stages. Seedling densities were significantly higher in the plots that allowed natural grazing compared to the exclusion plots (e.g. 697 versus 311 seedlings per m^-2). Swans removed ≤10% of seagrass vegetation but a dormant seedbank was present and new propagules were also observed. We conclude that grazing by swans provides some benefit to seagrass resilience by enhancing seedling recruitment. We further investigated the drivers of the different lifecycle stages using general additive mixed models. Higher and more variable salinity led to increased seed germination whilst temperature explained variation in seedling density and adult plant abundance. Bet-hedging strategies of R. polycarpa were identified including a dormant seedbank, continuous germination and seedling emergence over variable conditions (salinity 2-42 ppt; temperatures 11-28°C). These strategies may be key determinants of resilience to emerging salinity and temperature regimes from a changing climate.

Primary Presenter: Chanelle Webster, Edith Cowan University (chanelle.webster@ecu.edu.au)

Authors:

Kathryn McMahon, Edith Cowan University  (k.mcmahon@ecu.edu.au)

Paul Lavery, Edith Cowan University  (p.lavery@ecu.edu.au)

Caitlyn O'Dea, Edith Cowan University  (caitlyn.odea@ecu.edu.au)

Marta Sánchez Alarcón, Uluu  (marta.alarcon@uluu.com.au)