Identifying critical recruitment bottlenecks limiting seedling establishment in a degraded seagrass ecosystem /631/158/854 /704/158/1745 article

© 2017 The Author(s). Identifying early life-stage transitions limiting seagrass recruitment could improve our ability to target demographic processes most responsive to management. Here we determine the magnitude of life-stage transitions along gradients in physical disturbance limiting seedling establishment for the marine angiosperm, Posidonia australis. Transition matrix models and sensitivity analyses were used to identify which transitions were critical for successful seedling establishment during the first year of seed recruitment and projection models were used to predict the most appropriate environments and seeding densities. Total survival probability of seedlings was low (0.001), however, transition probabilities between life-stages differed across the environmental gradients; seedling recruitment was affected by grazing and bioturbation prevailing during the first life-stage transition (1 month), and 4-6 months later during the third life-stage transition when establishing seedlings are physically removed by winter storms. Models projecting population growth from different starting seed densities showed that seeds could replace other more labour intensive and costly methods, such as transplanting adult shoots, if disturbances are moderated sufficiently and if large numbers of seed can be collected in sufficient quantity and delivered to restoration sites efficiently. These outcomes suggest that by improving management of early demographic processes, we could increase recruitment in restoration programs

Australian seagrass seascapes: present understanding and future research directions

Seagrass seascapes are 100s m to 1000s of km coastal regions in nearshore, sandy to muddy benthic environments that are characterized by the presence of seagrasses. Here we explore the development of seagrass seascape research in Australia. Determining the distribution of seagrasses started with mapping their extent, but improvements in remote sensing and statistical modelling has allowed us assess the large scale spatial distribution and temporal dynamics of seagrass seascapes. We use a case study from Moreton Bay, near Brisbane, Queensland to demonstrate changes in seagrass meadows over time. Terrestrial landscape indices and their use in seagrass studies is reviewed. Some indices perform better to summarize patch to meadow scale changes in the distribution and structure of seagrasses. A case-study is then presented, comparing landscape indices calculated from observed changes in seagrass patches and meadows to a spatially-explicit model simulation, to explore the drivers for changes in the seagrass seascape's demographic processes, clonal growth and recruitment from seeds. The role of landscape structure in the movement and abundance of associated fauna in seagrass seascapes using landscape approaches is then reviewed. This is followed by a summary outlining directions for future research that combine landscape ecology and remote sensing techniques with population and community biology

Reproductive, dispersal and recruitment strategies in Australian seagrasses

Seagrasses are a relatively small group of marine angiosperms that have successfully colonised the oceans and includes monecious, dioecious and hermaphroditic species. They display a range of mating systems, dispersal mechanisms and recruitment strategies that have allowed them to adapt and survive within the marine environment. This includes a general reduction in the size and complexity of floral structures, and subsurface pollination (hydrophily) in the majority of species. Fertilisation occurs through water-dispersed pollen that is typically filamentous and sticky, however, recent work has also suggested that marine invertebrates may play a role in pollen movement and fertilisation. Seed size and morphology varies widely among species, from fleshy floating fruit (e.g. Posidonia) to small negatively buoyant seeds less than 0.5 mm (e.g. Halophila). Nearly all species retain some capacity of asexual reproduction through rhizome elongation or the production of asexual fragment or propagules that can be more widely dispersed. These differences in reproductive strategies have important effects on recruitment and dispersal potential and subsequent population dynamics. Direct estimates of dispersal and recruitment are inherently difficult to assess in seagrasses, but the use of novel genetic and predictive modelling approaches are providing new insights into these important processes. This chapter highlights the main reproductive strategies and adaptations seagrass have undergone in response to reproducing in a marine environment, with an emphasis on Australian seagrass species. We highlight the current state of knowledge in Australian seagrass reproductive biology and future directions in seagrass reproductive biology research