Response of the coastal plankton community of south-eastern Tasmania through the 2015/16 MHW event and beyond

Miss Rhian Evans1, Assoc / Prof. Mary-Anne Lea1, Prof. Mark Hindell1, Dr Kerrie Swadling1

1Institute Of Marine And Antarctic Studies, University of Tasmania, Hobart, Australia

Abstract

During the summer of 2015/16, the continental shelf ecosystem off south-east Tasmania experienced the longest and most extreme marine heatwave on local record. This event has been attributed to anomalous convergence of heat linked to the increase in both the duration and the southwards penetration of East Australian Current (EAC) eddies. As a result of this movement of sub-tropical water south, zooplankton communities have responded through species range shifting, and a tendency towards warm-water signature communities dominated by smaller size classes.

Zooplankton were collected over the summer season both during the marine heatwave in 2015/16 and the subsequent, cooler 2016/17 summer (~3 °C cooler). Nineteen stations east of Bruny Island were sampled between November and May to catch the productive summer periods. Cluster analysis revealed a significant difference in community structure between the two years, while principal components analysis highlighted seawater temperature and chlorophyll-a concentration as the main biophysical drivers of the variation.

Work is currently underway to explore the nature of the differences in community structure: (1) species identification, (2) tracking presence and abundance of warm water indicator species common to the EAC, and (3) detailed analyses of the size spectra of the communities. A change in both the species composition and the size distribution of local zooplankton will have cascading effects up the food web. In a region supporting a diverse array of resident and migratory marine predators, this knowledge will inform local models to predict the effects of climate change on these populations.

Biography

Rhian is currently a PhD student at the Institute of Marine and Antarctic studies and has lived in Tasmania for the last 4 years. Previous to this, she completed a Master of Research in Marine Biology at the University of Southampton, UK, the results of which were published in Deep Sea Research II in 2013.

Since then, she has worked for a range of NGO and university based research projects all over the world, mostly concerned with the movement ecology, abundance and distribution, and genetic diversity of marine predators including marine mammals and seabirds, sharks and turtles.

Currently, Rhian’s research is investigating the biophysical drivers of a productive, biologically diverse ecosystem on the continental shelf off SE Tasmania. More specifically, this region is part of a rapidly warming “hotspot” and this research will describe the effects that this rise in temperature might have on the planktonic community structure, fish biomass and the resulting effects on the range of resident and migratory marine mammals and birds which inhabit the region.

About the Association

The Australian Coastal Society (ACS) was initiated at the Coast to Coast Conference in Tasmania in 2004. The idea was floated as a means for those interested in coastal matters to communicate between conferences and where possible take resolutions of the conference to appropriate levels of government.

The idea was discussed further at the Coast to Coast Conference in Melbourne in 2006 and it was agreed that Bruce Thom develop a constitution of a company limited by guarantee that would operate on a national basis.

This plan was accomplished and in 2008 at the Coast to Coast Conference in Darwin the constitution was ratified and an Executive appointed. The company received charitable status in 2011.

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