Climate variability drives plankton community composition changes: the 2010–2011 El Nin˜o to La Nin˜a transition around Australia

basir barthos;

The strong La Nin˜a of 2010–2011 provided an opportunity to investigate the ecological impacts of El Nin˜o-Southern Oscillation on coastal plankton communities using the nine national reference stations around Australia. Based on remote sensing and across the entire Australian region 2011 (La Nin˜ a) was only modestly different from 2010 (El Nin˜ o) with the average temperature declining 0.2%, surface chlorophyll a up 3% and modelled primary production down 14%. Other changes included a poleward shift in Prochlorococcus and Synechococcus. Along the east coast, there was a reduction in salinity, increase in nutrients, Chlorophytes and Prasinophytes (taxa with chlorophyll b, neoxanthin and prasinoxanthin). The southwest region had a rise in the proportion of 19-hexoyloxyfucoxanthin; possibly coccolithophorids in eddies of the Leeuwin Current and along the sub-tropical front. Pennate diatoms increased, Ceratium spp. decreased and Scrippsiella spp. increased in 2011. Zooplankton biomass declined significantly in 2011. There was a reduction in the abundance of Calocalanus pavo and Temora turbinata and increases in Clausocalanus farrani, Oncaea scottodicarloi and Macrosetella gracilis in 2011. The changes in the plankton community during the strong La Nin˜a of 2011 suggest that this climatic oscillation exacerbates the tropicalization of Australia.