Overcoming critical recruitment bottlenecks limiting seedling establishment in degraded seagrass ecosystems

Seagrass ecosystems are global providers of critical ecological processes in coastal ecosystems. Restoration of degraded systems is central to recovering these processes, but success has been elusive. Seagrass literature shows few programs successfully incorporate seeds to restore areas despite seeds representing a sustainable alternative to vegetative transplants. The high rates of failure have hindered the use of seeds in seagrass restoration. Paradoxically, failures are common because the science of seed-based restoration is grossly underdeveloped. This project focuses on reasons behind high failure rates of seeds, and developing strategies based on a quantitative understanding of processes influencing recruitment.

Life-cycle population models have been valuable in the development of restoration theory and practice of terrestrial species. In particular models allow the quantification of early life-stage transitions, from seed, to germinant, to emerged seedling, identifying which of these transitions are the most limiting in plant recruitment. Armed with this knowledge restoration practitioners can target those life-stage transitions most responsive to management. However, only recently have seagrass ecologists accepted the importance of early life-history components in seagrasses. Consequently, early life-history demography is remarkably sparse across seagrass species and the ability to manage seagrass populations effectively is limited by our understanding of the demography of early life-history components. To tackle this challenging problem and to move seagrass restoration to a level observed in terrestrial systems, Dr Statton and Professor Kendrick use a demographic approach adopted from terrestrial models.

Another major hurdle in restoring functional seagrass communities is the lack of an integrated framework to identify and overcome the ecological processes and conditions that inhibit seedling establishment.  Unlike seagrass restoration in its current state which is an ad hoc, location-specific activity, the team aims to develop principles of seedling establishment through an integrated framework referred to as ‘a systems approach’. Seagrass life-cycle models are the basis of our systems framework, describing and quantifying the important demographic stages and transitions. Key ecological processes they believe to influence the probability of a successful transition to the next life-stage will be identified and potential management strategies to modify the processes and conditions controlling life-stage transitions will be developed.

They develop this approach for two seagrass species with contrasting life-histories, Posidonia australis and Halophila ovalis, where knowledge gained will be applicable to a wider range of species with similar life-history components. P. australis is listed as a near threatened species on the IUCN Red List of Threatened Species, losing 1.8% of its distribution annually.  Recently, there is greater interest in restoring species that produce dormant seeds with a shift towards tropical Australia due to mining and port development (Port Curtis, Dampier, Onslow, Browse Basin, Wheatstone). Halophila ovalis is in abundance in these sub-tidal habitats and is a major source of food for endangered macro-grazers; dugongs and turtles. H. ovalis is also the focus of applied research on impacts of dredging on its survival and persistence (Chevron Wheatstone ERMP, Woodside Browse Basin, WAMSI Dredging Node). Their study will complement this applied research focus by exploring seed restoration for this common seagrass species.

Collaborator/s

  • Professor Robert J. Orth, Virginia Institute of Marine Science