Response to "Comment on 'Seagrass viviparous propagules as a potential long-distance dispersal mechanism' by A. C. G. Thomson et al"

[Extract] Our original article (Thomson et al. 2015) presented data exploring Zostera nigricaulis asexually produced vegetative propagules as a potential long-distance dispersal mechanism for seagrasses. We found that the vegetative propagules of Z. nigricaulis were able to maintain buoyancy and photosynthetic health for more than 85 days, which suggested capacity for long-distance dispersal. While long-term establishment of propagules in situ was not successful due to poor seasonal conditions, highly successful establishment and growth in mesocosm-based experiments gave support for positive establishment opportunities. Resilience of seagrass meadows relies on the ability of seagrass to successfully recolonise denuded areas or disperse to new areas (Macreadie et al. 2014), and this research demonstrated that although successful establishment may be rare, vegetative propagules show re-establishment potential for declining seagrass populations. These results are consistent with results found by Stafford-Bell et al. (2015), where prolonged dispersal of Zostera muelleri vegetative fragments was predicted

Seagrass viviparous propagules as a potential long-distance dispersal mechanism

Resilience of seagrass meadows relies on the ability of seagrass to successfully recolonise denuded areas or disperse to new areas. While seed germination and rhizome extension have been explored as modes of recovery and expansion, the contribution of seagrass viviparous propagules to meadow population dynamics has received little attention. Here, we investigated the potential of seagrass viviparous propagules to act as dispersal vectors. We performed a series of density surveys, and in situ and mesocosm-based experiments in Port Phillip Bay, VIC, Australia, using Zostera nigricaulis, a species known to produce viviparous propagules. Production of viviparous propagules was higher at sites with high wind and current exposure, compared to more sheltered environments. A number of propagules remained buoyant and healthy for more than 85 days, suggesting the capacity for relatively long-distance dispersal. Transplanted propagules were found to have improved survivorship within seagrass habitats compared to bare sediment over the short term (4 weeks); however, all propagules suffered longer-term (<100 days) mortality in field experiments. Conditions outside of meadows, including sediment scouring, reduced the likelihood of successful colonisation in bare sediment. Furthermore, sediment characteristics within meadows, such as a smaller grain size and high organic content, positively influenced propagule establishment. This research provides preliminary evidence that propagules have the potential to act as an important long-distance dispersal vector, a process that has previously gone unrecognised. Even though successful establishment of propagules may be rare, viviparous propagules show great potential for seagrass populations given they are facing global decline