MEPS 589:13-31 (2018)  -  DOI:

Seasonal succession of phytoplankton community structure from autonomous sampling at the Australian Southern Ocean Time Series (SOTS) observatory

Ruth Eriksen1,2,*, Thomas W. Trull1, 2, Diana Davies1, Peter Jansen1, Andrew T. Davidson3, Karen Westwood3, Rick van den Enden3

1Antarctic Climate and Ecosystems Cooperative Research Centre, Private Bag 80, Hobart, Tasmania 7001, Australia
2CSIRO Oceans and Atmosphere, Castray Esplanade, Battery Point, Tasmania 7004, Australia
3Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050, Australia
*Corresponding author:

ABSTRACT: Limited knowledge of phytoplankton community structure in the Southern Ocean hampers our understanding of ecosystem function and its response to changes expected this century from anthropogenic CO2 emissions and associated climate warming. To address this gap, we obtained records of phytoplankton community composition and nutrient concentrations, collected at 9-d intervals over the austral production season from September 2010 to April 2011 at the Southern Ocean Time Series observatory (46°56’S, 142°15’E) using an autonomous sampler, accompanied by hourly sensor-based estimates of water column structure and light levels. Satellite ocean colour and in situ fluorescence showed a moderate increase in phytoplankton biomass, 4-5 fold, from winter to mid-summer. Total cell number and biovolume increases were larger (up to 80-fold and 40-fold, respectively), reflecting the importance of heterotrophs and smaller organisms. The haptophyte Phaeocystis antarctica dominated abundances (up to 75%), but only constituted a few percent of total biovolume, which was dominated by diatoms and dinoflagellates. Ciliates contributed less than 5% of abundance, while tintinnids were rarer still. Community analysis of species similarities identified 3 distinct clusters, tracking seasonal shallowing of the mixed layer (from 500 to 50 m) and decreased silicate availability (from ~4 to <1 µM). The diatom:dinoflagellate biovolume ratio decreased more strongly than their abundance ratio, consistent with progression towards small weakly silicified diatoms in summer. Silicoflagellates were associated with elevated winter and spring silicate levels. The overall nitrate/silicate depletion ratio was ~2, indicating significant export by the non-diatom community. Exploratory correlative analysis of the biological diversity with environmental conditions suggests mixed layer depth and silicate levels as more likely drivers than inputs from subtropical waters or biomass accumulation.

KEY WORDS: Southern Ocean Time Series · Phytoplankton · Autonomous sampler · Community structure · Phaeocystis

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Cite this article as: Eriksen R, Trull TW, Davies D, Jansen P, Davidson AT, Westwood K, van den Enden R (2018) Seasonal succession of phytoplankton community structure from autonomous sampling at the Australian Southern Ocean Time Series (SOTS) observatory. Mar Ecol Prog Ser 589:13-31.

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