Forecasting impacts of changing detrital biodiversity on Australia's estuarine ecosystems

A project undertaken at the University of Technology Sydney and supervised by B Kelaher

Annually, the world’s estuarine and coastal areas contribute more than US$12.6 trillion worth of ecosystem goods and services, more than twice that provided by the world’s forests. Much of this value is derived from the rich microbial and faunal communities of soft sediments, which play an important role in global carbon and geochemical cycling and support food webs that include commercially-important fisheries, threatened shore birds and marine mammals. Our recent work has identified substantial changes to the detrital inputs (non living organic material) into soft-sediment systems in Australian estuaries since 1950 from predominantly seagrass dominated towards more labile micro- and macroalgal sources. These long term changes to detrital composition may cause sediment anoxia, decreased biodiversity, productivity and ecosystem function. This raises previously unaddressed but important questions about (i) whether soft sediment habitats in urbanised Australian estuaries are heading towards the severe anoxia, reduced biodiversity and decreased fish production of heavily populated coasts in other parts of the world and (ii) whether intervention by coastal managers is necessary to prevent degradation of our ecologically and economically important soft sediment systems.

Our project will address these key questions, by experimentally manipulating detrital diversity, type and loading, as well as nutrient levels in estuarine soft-sediment systems. This work is significant because it focuses on soft sediment eutrophication caused by excessive detritus, which is one of the most severe widespread impacts of coastal ecosystems, and the cause of loss of fisheries resources and ecosystem function. Our experiments will determine whether observed changes in detritus based food webs from seagrass dominated towards more labile micro- and macroalgal sources will make soft sediment communities more susceptible to anoxic conditions, threatening vital estuarine productivity. As coastal populations increase, this knowledge will be invaluable for maintaining water quality criteria that ensure the sustainability of estuarine soft-sediment communities and the food webs and ecosystem functions that they support.
Figure 1. Botany Bay is highly developed estuary showing symptoms of excessive nutrient enrichment

Figure 2. Experiments in Botany Bay investigating the links between detrital impacts and food availability for fish and wading birds

Figure 3. Tidally-driven field work in Botany Bay often requires very early starts