This study examined phytoplankton communities in Algoa Bay, South Africa at different temporal scales. A time-series from 2010-2012 showed strong seasonal variability in sea surface temperature, with cooler temperatures and higher chlorophyll-a in 2010/2011 and warmer temperatures and lower chlorophyll-a in 2011/2012. This corresponded to dominance of south-easterly winds in 2010/2011 which cooled waters and increased phytoplankton biomass. Sampling trips found dinoflagellates dominant in early summer 2011 and pennate diatoms dominant in early autumn 2012, corresponding to nutrient levels and water column mixing at the time.

1. 1. Introduction
Algoa Bay is an open, shallow bay of <70m in depth on the
south-east coast of South Africa (Schumann et al., 2005). This
bay is located on the western boundary, current of the
Agulhas warm subtropical waters (Fig. 1).
This study was motivated by the culturing of the Pacific
oyster (Crassostrea gigas) in this region and because of
limited phytoplankton research beyond the neritic zone in
Algoa Bay.
3. Study Area and Methods
The study was located in the western sector of Algoa Bay on
the south-eastern coast of South Africa. Sampling was centred
at a station located on an oyster farm (33°56’48.65S;
25°36’40.70E) about ±1km from the Port Elizabeth harbour
(Fig. 2). Sampling was undertaken through a deployment of a
mooring (15 September 2010 to 4 June 2012) on the oyster
farm and two field studies (29 Nov to 1 Dec 2011- early
summer and 27 to 29 March 2012- early autumn) providing
further spatial details.
7. Acknowledgments
National Research Foundation (NRF), University of Cape Town (UCT) & Marine Research Institute (Ma-Re), UCTNational Research Foundation (NRF), University of Cape Town (UCT) & Marine Research Institute (Ma-Re), UCT
Postgraduate Funding Office .Postgraduate Funding Office .
Thanks to Mariculture Research team at the Department of Agriculture, Forestry & Fisheries (DAFF) for all resourcesThanks to Mariculture Research team at the Department of Agriculture, Forestry & Fisheries (DAFF) for all resources
and expertise.and expertise.
To the department of Biological Sciences and Oceanography (UCT) staff and postgraduate studentsTo the department of Biological Sciences and Oceanography (UCT) staff and postgraduate students..
Department of Environmental Affairs (DEA), Oceans & Coasts for the funding my WIOMSA symposium attendance.Department of Environmental Affairs (DEA), Oceans & Coasts for the funding my WIOMSA symposium attendance.
5. Discussion and conclusion
Temporal and spatial variability in environmental conditions such as dominance of south-easterly winds and periodic wind relaxation, stratification, nutrient depleted
waters, and increased surface warming in early summer enhanced Gonyaulax polygramma and other species to be the more abundant. In early autumn; mixed water
column and less solar radiation created favorable conditions for pennate diatoms of Pseudo-nitzschia species to be the most numerous .
This study shown that phytoplankton production in Algoa Bay is highly variable on a seasonal scale. These are not restricted by nutrient supply but mainly driven by the
hydrography and circulation dynamics on the bay, and the dominating Agulhas Current system governed by prevailing winds and SST resulting in high variability in
phytoplankton communities and biomass at spatial and temporal scales.
S.W. Mbambo, C.L. Moloney, G.C. Pitcher and S. Jackson
sfisowalter@gmail.com
6. Literature cited
DAWES, C. J. (1998) Phytoplankton. Marine Botany. 2nd edition. John Wiley and Sons Inc., New York, NY.
SCHUMANN, E.H., CHURCHILL, J.R.S. and H. J. ZAAYMAN. (2005) Oceanic variability in the western sector of Algoa
Bay, South Africa. African Journal of Marine Science, 27, 65-80.
2. Aim
This project is aimed at understanding the role of the physics
(seawater temperature and winds), and chemistry (nutrients)
in driving phytoplankton communities and assemblages.
These were examined at three different scales: event
(upwelling/algal bloom), seasonal and inter-annual scales.
1
2
3
a b
a b
Fig. 3: Time-series plot of chlorophyll-a concentrations (blue dots) and SST (red dots)
from 15 Sept 2010 to 4 June 2012. A 48-hourly running mean is shown for SST
values.
Fig. 4: (a) Progressive wind vectors from 1 October 2010 to 01 May 2011. (b) 1
October 2011 to 1 May 2012. Grey circles denote field trips and the green
star indicates the period with the highest chlorophyll-a concentration in
the time-series.
Fig. 5: SST (°C) profiles for each of the three transects measured in early summer
(left panel) and early autumn (right panel). NB: 3 transects are
represented by red numbers on the right(1, 2 and 3).
Fig. 6: MDS plots for samples in Algoa Bay in early summer. (a) Nitrate concentrations (µM.L-1
) in each
sample. (b) Sample grouping of 30% level of similarity, showing patterns of sample assemblages
within each nitrate concentration range.
Fig. 7: MDS plots for samples in early autumn. (a) Nitrate concentrations ( µM.L-1
) in each sample.
(b) Sample grouping of 50% level of similarity and to show patterns in sample grouping to
nitrate concentration ranges .
Fig. 8: Phytoplankton species and mean cells concentrations (cells.ml-3
) for fifteen
most numerous species found in Algoa Bay in both 2011 (early summer) (a)
and 2012 (early autumn) b) fieldtrips.
Dinoflagellates of Gonyaulax polygramma and other
Gonyaulax spp. that were dominant in the early
summer of 2011 in Algoa Bay.
Pennate diatoms of Pseudo-nitszchia spp. that were
dominant in the early autumn of 2012 in Algoa Bay.
Typical ski-boat used for the 2011/2012 field trips with a portable CTD (SeaCat
SBE-19) “Sea bird’’ anchored.
4. Results
Time-series showed (Fig.3) a strong seasonal variability in sea-surface temperature (SST). The summer of 2010/11 was cooler, with higher chl-a
concentration. The summer of 2011/12 was warmer compared to the previous summer with lower chlorophyll-a concentration.
Dominance of south-easterly winds in summer of 2010/11, were responsible for notable cooling and elevated phytoplankton biomass. However;
absence of south-easterly winds in summer of 2011/12 was associated with warming and low phytoplankton biomass (Fig. 4).
Sampling trips: A Sampling trip in early summer found a strong thermocline at a depth of approximately 15m, and SST ranged between 13.5 and 21°C.
In early autumn, deep water mixing was evident where the thermocline dropped to about 30m, with a SST range of 16.5 - 21°C.
In early summer samples showed a 30% similarity level and higher NO3 concentrations in transect 1. Early autumn had 50% similarity level in the
samples, and higher NO3 were noted for stations 1-3, while the rest was depleted.
In the early summer dinoflagellates of Gonyaulax polygramma and other species were the most abundant, whereas in early autumn pennate diatoms
of Pseudo-nitzschia species.
a b
Centric diatoms of Thalassiosira sp. were one of the
most abundant species in the early autumn of 2011 in
Algoa Bay.
Pennate diatoms of Thalassionema sp. were also
abundant in the early autumn of 2012 in Algoa Bay.
Sifiso Mbambo