Acoustic investigation of the primary production of an Australian temperate macroalgal (Ecklonia radiata) system
Randall, J and Johnson, CR and Ross, J and Hermand, J-P, Acoustic investigation of the primary production of an Australian temperate macroalgal (Ecklonia radiata) system, Journal of Experimental Marine Biology and Ecology, 524 Article 151309. ISSN 0022-0981 (2020) [Refereed Article]
Temperate marine systems are dominated by rocky reef macroalgal habitats, and there is now evidence that some seaweed communities are retreating in a manner consistent with climate change. Obtaining measurements of primary production across entire assemblages of algae over ecologically meaningful spatial scales is difficult, and acoustic techniques emerge as a method to consider. Acoustics has the potential to detect oxygen in gaseous form, hence it can measure primary production that is unseen by methods that use dissolved oxygen to estimate productivity. With levels of dissolved oxygen in kelp environments regularly reaching supersaturation, it is possible – even likely – that ecologically significant proportions of production have been neglected by traditional methods. To investigate the potential use of underwater acoustics in monitoring productivity of macroalgal habitats an experiment was run over two weeks during the Austral summer in February 2012 in Canoe Bay, Tasmania. This paper details the results of ray-based acoustic predictive models for two periods during the experiment chosen to compare contrasting diurnal productivity periods, together with inverted acoustic propagation waveguide features from the empirical experiment itself for these periods. Results of the Bellhop modelling suggest that acoustic transmissions can detect ecologically significant proportions of oxygen in gaseous form in seaweed environments (>5% of total predicted production). However, changes in diurnal cycles of oxygen production were not seen in the empirical acoustic data during the experimental period, indicating that it is unlikely that there was a significant level of oxygen in gaseous form in the canopy layer. This work details the first research into the use of acoustics to measure productivity in macroalgal systems. It is possible that further research, particularly in highly productive environments or when conditions are more favourable, may prove acoustics to be a useful tool for assisting in monitoring primary productivity in seaweed communities.