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.