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Seasonal changes in phytoplankton on the north-eastern shelf of Kangaroo Island (South Australia) in 2012 and 2013

Balzano S., Ellis A. V., Le Lan C., Leterme S. C.

Oceanologia

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2015

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No. 57 (3)

251--262

EN

This work investigates for the first time the seasonal changes in phytoplankton, bacteria, and photosynthetic picoplankton as well as nutrient concentrations on the North-western shelf of Kangaroo Island, South Australia. Seawater samples were collected off Penneshaw desalination plant, where waters from the Investigator Straight, Gulf Saint Vincent and Backstairs Passage meet. Low nutrient values were measured throughout the period of study (July 2012–July 2013) suggesting the occurrence of oligotrophic conditions on the region. The phytoplankton community was dominated by Bacillariophyceae, Dinoflagellata and Cryptophyta. Prochlorococcus Cyanobacteria prevailed among picophytoplankton during most of the period of study (July 2012–July 2013). Previous studies indicate that oligotrophic environments are indeed typically dominated by Prochlorococcus. The dominant species found here seem either adapted to grow under low nutrient concentrations, possessing high surface/volume ratios, or have a mixotrophic behaviour allowing them to complement photosynthesis with predation. This study provides base knowledge on the microbial communities north of Kangaroo Island that is needed to sustain the ecosystem and associated economic activities in the future.

2

Annual phytoplankton dynamics in the Gulf Saint Vincent, South Australia, in 2011

Leterme S.C., Jendyk J. G., Ellis A. V., Brown M. H., Kildea T.

Oceanologia

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2014

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No. 56 (4)

757--778

EN

Phytoplankton communities are the basis of many marine and freshwater food webs. Their composition fluctuates depending on hydrochemical conditions, such as light, temperature, salinity, pH, nutrients and turbulence. This study investigates the effect of changing environmental conditions on the coastal phytoplankton community of the Gulf St Vincent in South Australia. This is the first study simultaneously investigating the phytoplankton communities and their environment in this area and is essential to set up the baseline of future studies. In total, 179 phytoplankton species were identified and enumerated between January and December 2011. Phytoplankton communities were numerically dominated by chlorophytes during 6 months of the survey and an intense bloom (representing 62% of the overall phytoplankton community) of the diatom Cylindrotheca closterium was observed in February. Our results suggest that in the coastal waters of the Gulf St Vincent, the variability in environmental conditions is driven by temperature, wind speed/direction and the changing levels of phosphorus. However, the variability observed during autumn and winter months seems to be driven by changing levels of nitrogen and silica. In this shallow environment, the wind speed is proportional to the stress at the ocean floor and should directly influence the resuspension of sediment and associated nutrients. Nutrient ratios were observed to investigate potential phytoplankton nutrient limitation patterns. These ratios indicated that nitrogen was usually the limiting nutrient, which is typical of marine systems. Since nutrient enrichment is generally the main factor driving the succession and composition of phytoplankton communities in coastal waters, further work is now needed to identify the sources of nutrients in this region where river runoff is limited and evaporation is high relative to precipitation.

3

The impact of turbulence and phytoplankton dynamics on foam formation, seawater viscosity and chlorophyll concentration in the eastern English Channel

Kesaulya I., Leterme S.C., Mitchell J.G., Seuront L.

Oceanologia

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2008

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No. 50 (2)

167-182

EN

The space-time dynamics of chlorophyll a concentration and seawater excess viscosity has been investigated in the hydrographically contrasting inshore and offshore water masses of the eastern English Channel. This was done during the phytoplankton spring bloom dominated by Phaeocystis globosa before and after the very large-scale formation of foam induced by an increase in wind-driven turbulence and the related wave breakings. The results suggest that the dynamics of chlorophyll a concentration and seawater excess viscosity are differentially controlled by the formation of foam through the intensity of the spring bloom and wind-generated turbulence.

4

Decadal fluctuations in North Atlantic water inflow in the North Sea between 1958-2003: impacts on temperature and phytoplankton populations

Leterme S.C., Pingree R.D., Skogen M.D., Seuront L., Reid P.C., Attrill M.J.

Oceanologia

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2008

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No. 50 (1)

59-72

EN

The circulation of Atlantic water along the European continental slope, in particular the inflow into the North Sea, influences North Sea water characteristics with consequent changes in the environment affecting plankton community dynamics. The long-term effect of fluctuating oceanographic conditions on the North Sea pelagic ecosystem is assessed. It is shown that (i) there are similar regime shifts in the inflow through the northern North Sea and in Sea Surface Temperature, (ii) long-term phytoplankton trends are influenced by the inflow only in some North Sea regions, and (iii) the spatial variability in chemicophysical and biological parameters highlight the influence of smaller scale processes.