Camille A. White1, D. Jeffrey Ross1, Neville Barrett1, Megan Hartog1 and Catriona K. Macleod1
1Institute for Marine & Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
As coastal urbanisation and industry intensify, nutrient enrichment from human activity has been identified as a key local impact on the function of macroalgal communities in inshore reef ecosystems. As macroalgae communities are often fundamental for the delivery of ecosystem services, understanding the local-scale sensitivity or resilience of these systems is critical. In south-east Tasmania, open cage finfish aquaculture is well established, however, to be sustainable it must operate without adversely impacting ecosystem services. Developing monitoring methods which are sensitive to a loss of resilience, yet simple and cost-effective enough to be used in ongoing monitoring is a challenge. In this study we designed and tested a method based on a suite of relatively easy-to-observe functional parameters and nutrient enrichment indicators in macroalgae communities. Parameters were designed to characterise ecosystem structure (canopy, brown/green/red algae understorey, substrate), along with typical responses to nutrient enrichment, such as the cover of epiphytic, filamentous and nuisance algae. The method was tested through diver-based surveys across a localised enrichment gradient. While it was successful in detecting a farm gradient of enrichment, the confounding influence of wave exposure made interpretation of data difficult. Multiple lines of evidence and robust baseline data are key to resolving effects, particularly in the diffuse enrichment zone. While this technique shows promise for detecting impacts of enrichment from human activity on reef communities, it also highlights the susceptibility of algae communities in low wave exposure sites to impacts of enrichment, regardless of the source of nutrients.