Restoration of the seagrass Amphibolis antarctica - temporal variability and long-term success

The loss of seagrass meadows is an increasing problem worldwide. The important role that these meadows play in coastal ecosystems has resulted in substantial attention to the development of seagrass restoration techniques. Here, I present long-term (up to 5 years) results of seagrass restoration off the coast of Adelaide, South Australia, where >5,000 ha of seagrass has been lost and where trials of traditional restoration techniques using seeds and transplants have failed due to high levels of sand and water movement. Hessian (burlap) sandbags were deployed bimonthly (with some interruptions) from November 2007 to November 2012 (a total of 24 deployments), with a mix of single- and double-layered bags, to provide a stable substrate for naturally occurring Amphibolis seedlings to recruit to. At the end of the study (January 2013), bags deployed in August 2009 had similar stem densities to those found in adjacent natural meadows (15.2 ± 1.4 (SE) vs 18.6 ± 2.5). Bags deployed in May 2008 and August 2011 had 12.8 ± 2.3 and 13.2 ± 2.2 stems, respectively. Furthermore, stem lengths on older bags were greater than those on natural meadows (42.1 ± 4.2 after 62 months vs 30.2 ± 1.5 cm). While there was some interannual variation in recruitment success, the strongest predictor of success was deployment month. Bags deployed outside the austral winter recruitment season did not retain the ability to catch a large number of recruits, indicating that any restoration using this technique will have to be undertaken between approximately May and August to maximize chances of success.Jason E. Tanne

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