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PRIMARY RESEARCH PAPER
The influence of upwelling, coastal currents and watertemperature on the distribution of the red tidedinoflagellate, Noctiluca scintillans, along the east coastof Australia
Jocelyn Dela-Cruz Æ Jason H. Middleton ÆIain M. Suthers
Received: 25 February 2007 / Revised: 23 July 2007 / Accepted: 13 August 2007 / Published online: 27 September 2007
� Springer Science+Business Media B.V. 2007
Abstract Quasi-synoptic surveys along the east
coast of Australia between 28 and 34�S show that
the heterotrophic dinoflagellate, Noctiluca scintillans,
occurs along this entire stretch of the coast. Areas of
relatively high abundance of Noctiluca were observed
downstream of regions predisposed to current-
induced upwellings as a consequence of alongshore
topographic variations. High-resolution temporal and
spatial sampling of upwelling events showed that
Noctiluca was abundant (up to 28 cells l–1) within
mature upwelled waters. A high proportion ([80%) of
fed Noctiluca cells (cells with prey in their vacuoles)
was observed in the mature upwelled waters indicat-
ing that the observed increase in abundance of
Noctiluca was associated with increased feeding
activity. The absolute abundance of Noctiluca in
upwelled waters was, however, found to vary from
one upwelling location to another and between sea-
sons. In particular, highest abundances of Noctiluca
were recorded south of 31.5�S, where the East
Australian Current (EAC) characteristically separates
from the coast. The high abundances partly arise from
southward advection and retention of the Noctiluca
cells, and partly from upwelling inshore of the
separated EAC driven by cross-shelf boundary layer
fluxes. The temperature of the EAC was also found to
influence absolute abundances. Surface water temper-
atures during our summer cruise were anomalously
high due to a strong La Nina phase, and up to 4�C
warmer than during our spring cruise. We found that
the warmer surface water temperatures were associ-
ated with relatively lower average abundances of
Noctiluca in the near shore zone.
Keywords Noctiluca � Upwelling �East Australian Current � Red tides � La Nina
Introduction
The large heterotrophic dinoflagellate, Noctiluca
scintillans, is one of the most studied red tide
forming species around the world (Elbrachter & Qi,
1998). This interest partly results from the red tides
that Noctiluca forms and partly from Noctiluca’s
widespread distribution and numerical dominance in
Handling editor: J. Padisak
J. Dela-Cruz � I. M. Suthers
School of Biological, Earth and Environmental Science,
University of New South Wales, Sydney 2052, NSW,
Australia
J. Dela-Cruz (&)
New South Wales Department of Environment
and Climate Change, P.O. Box A290, Sydney South 1232,
NSW, Australia
e-mail: [email protected]
J. H. Middleton
School of Mathematics, University of New South Wales,
Sydney 2052, NSW, Australia
123
Hydrobiologia (2008) 598:59–75
DOI 10.1007/s10750-007-9140-z
these areas. Noctiluca tolerates a broad range of
environmental conditions such as water temperatures
below 0�C and up to 30�C and salinities between 10
and 37 psu (Elbrachter & Qi, 1998). Cell division and
population growth is, however, optimised over a
narrower temperature and salinity range depending
on the specific geographic region (Uhlig & Sahling,
1990; Lee & Hirayama, 1992; Uhlig & Sahling, 1995;
Huang & Qi, 1997; Fonda Umani et al., 2004;
Miyaguchi et al., 2006). For instance, the long-term
studies of Uhlig & Sahling (1995) indicate that cell
division rates of Noctiluca in the German Bight are
more than two times slower when grown in cultures
maintained at 12�C rather than at 24�C. More recent
studies suggest that optimal temperature ranges for
growth of Noctilica are lower, specifically, 15.2–
17.8�C in Japan (Miyaguchi et al., 2006) and 9–10�C
in the Northern Adriatic Sea (Fonda Umani et al.,
2004). In the latter study, the authors suggest that the
change in growth regimes is likely due to the
settlement of a ‘new cold strain’ of Noctiluca.
The east coast of Australia has been subject to
extensive red tides of Noctiluca in the last ten years
(Ajani et al., 2001). The red tides have been observed
over a wide range of the coast (30–36�S), although
greater than 90% were observed off Sydney, Austra-
lia’s largest city (Ajani et al., 2001; Dela-Cruz et al.,
2003). Previous field studies have indicated that the
abundance of Noctiluca in Sydney’s coastal waters is
highest during the spring and summer (Murray &
Suthers, 1999; Dela-Cruz et al., 2002). Specifically,
peaks in abundance were found to coincide with
periods of upwelling, which stimulate blooms of
phytoplankton that Noctiluca consumes (Dela-Cruz
et al., 2002). The incidence of upwelling events along
the coast is determined by alongshore coastal winds
and/or the strength of the poleward flowing East
Australian Current (EAC; Middleton et al., 1997).
Various regions along the coast have been shown to
be predisposed to current-induced upwelling events
as a consequence of alongshore topographic varia-
tions (Rochford, 1975; Godfrey et al., 1980;
Rochford, 1984; Hallegraeff & Jeffrey, 1993; Oke
& Middleton, 2000, 2001). Most of these upwelling
regions are located north of Sydney and thus it might
be expected that Noctiluca would be as abundant in
these northern regions as compared to off Sydney.
The many reports of red tides off Sydney could
therefore be a consequence of increased public
awareness (Hallegraeff, 1993) and/or southward
advection (Dela-Cruz et al., 2003). Certainly, the
majority of recent field studies point to the signifi-
cance of concentrating mechanisms (wind or
currents) in determining the abundance and distribu-
tion of Noctiluca (Yin, 2003; Kang et al., 2004; Liu
& Wong, 2006; Miyaguchi et al., 2006). Alterna-
tively, as described above, other autecological
aspects such as spatial or latitudinal variations in
temperature, salinity or light could account for the
relatively high numbers of Noctiluca in Sydney’s
coastal waters. Certainly, a large temperature gradi-
ent (3�C difference) exists year round along the east
coast of Australia between 31�S (north of Sydney)
and 33�S (Sydney metropolitan area; Ridgway &
Dunn, 2003).
The present study examines the responses of
Noctiluca (in terms of abundance) to various upwell-
ing events that occur in areas north of Sydney. For the
first time, a detailed account of the population
dynamics of Noctiluca during the initiation, devel-
opment and decline of an upwelling event is
provided. The study also examines whether the
hydrological gradients (e.g. temperature gradient
described above) along the east coast of Australia
between 28 and 34�S, influence the responses of
Noctiluca to the upwelling events, and consequently
influence the geographic extent of Noctiluca.
Method
Location and time of study
The main study area was located in continental shelf
waters on the far north coast of New South Wales
(NSW) between 30�050 S, 152�E and 32�050 S,
153�050 E, encompassing a region predisposed to
upwelling (Fig. 1). Upwelling events are topograph-
ically induced at Smoky Cape (SC; 30�920 S,
153�110 E) where the continental shelf narrows from
33 km at Urunga (U; 30�510 S, 153�070 E) to 16 km
at Smoky Cape (Roughan & Middleton, 2002). South
of Smoky Cape, the shelf widens to 32 km at
Diamond Head (DH; 31�730 S, 152�830 E). Currents
that flow past Smoky Cape have a dominant
longshore component, directed parallel to both the
shore and to the bottom contours on the continental
shelf (Roughan & Middleton, 2002). The mechanism
60 Hydrobiologia (2008) 598:59–75
123
for the upwelling is described by Oke & Middleton
(2000, 2001) and is similar to that of the Cape Byron
upwelling further north of Smoky Cape. Longshore
surface currents flowing past a narrowing continental
shelf accelerate, and drive a stronger cross-shelf
bottom boundary layer resulting in upwelling of colder
nutrient rich waters into shallower coastal waters.
The study was conducted in the austral spring and
summer, when the abundance of Noctiluca is rela-
tively high (Murray & Suthers, 1999; Dela-Cruz
et al., 2002), and also when the EAC has its strongest
flows (Middleton et al., 1997). Samples were col-
lected in November 1998 (austral spring) and January
1999 (austral summer), aboard two cruises on the
National Facility Research Vessel, Franklin. In
November the ship departed from Port Hacking near
Sydney in NSW and travelled north along the 50–
100 m depth contour to the main study area. In
January the ship departed from Brisbane in Queens-
land and travelled south along the 100–200 m depth
contour. Samples were collected at Urunga, Smoky
Cape and downstream at Point Plomer (PP; 31�330 S,
153�E) and Diamond Head (Fig. 1). During the
January cruise, samples were also collected from
four additional regions south of Diamond Head,
between 31.070 S, 152�E and 32�050 S, 153�050 E
(Fig. 1).
Samples were collected in across-shore and along-
shore transects, from various depths of the water
column, during the day and night, and in two seasons
(Table 1). Samples collected during the day were
152.5°E 153°E 153.5°E
32.5°S
32°S
31.5°S
31°S
30.5°S
SMOKY CAPE
URUNGA
POINT PLOMER
DIAMOND HEAD
Cape Hawke
Sth. Crowdy
Broughton Is.-Stockton Bight &
Port Stephens
Crowdy Head
100 m
0 30 km
N
night stations
day stations
152.5°E 153°E 153.5°E
32.5°S
32°S
31.5°S
31°S
30.5°S
SMOKY CAPE
URUNGA
POINT PLOMER
DIAMOND HEAD
Cape Hawke
Sth. Crowdy
Broughton Is.-Stockton Bight &
Port Stephens
Crowdy Head
NSW
100 m
0 30 km
N
0 30 km
N
night stations
day stations
night stations
day stations
Fig. 1 Map of the New South Wales coast showing the
location of the regions sampled in this study. Urunga, Smoky
Cape, Point Plomer and Diamond Head (upper case) were the
main study areas that were sampled during the November 1998
and January 1999 cruises. Regions south of Diamond Head
(lower case) were only sampled in January 1999. Plankton and
hydrographic data were collected during the day and night
along a shore-normal transect in each region
Table 1 Sampling regime and methods of collection of N. scintillans during November 1998 (austral spring) and January 1999
(austral summer) between 28 and 34�S
Regime Method—November 1998 Method—January 1999 Purpose of samples
Day sampling
(0630–1700 h)
8 stations along shore normal
transect in 4 regions, collections
via Niskin Bottles
8 stations along shore normal
transects in 8 regions,
collections via Niskin Bottles
Distribution and abundance
Night sampling
(1900–0530 h)
2 near shore stations in 4 regions,
collections via Niskin Bottles
and surface plankton net tows.
2 near shore stations in 8 regions,
collections via Niskin Bottles,
surface and subsurface plankton
net tows.
Bottle sampling to determine
distribution and abundance. Net
sampling to determine
population structure
(reproductive and nutritional
status)
Underway sampling Composite 1 h samples through
out entire time of cruise,
collections via
thermosalinograph pump at 4 m
depth.
Composite 1 h samples through
out entire time of cruise,
collections via
thermosalinograph pump at 4 m
depth.
Distribution and abundance
Hydrobiologia (2008) 598:59–75 61
123
used to provide a detailed account of the abundance
of Noctiluca during the initiation, development and
decline of the upwelling events. Samples collected
during the night were used to determine the variabil-
ity in the population structure of Noctiluca during the
upwelling events. Population structure was investi-
gated in terms of the number of cells reproducing
and feeding, activities which take place during
the evening (Uhlig & Sahling, 1982). Underway
or continual sampling was conducted to provide a
synoptic view of the spatial abundance patterns of
Noctiluca along broad sections of the east coast.
Day sampling
Day sampling was conducted between 0630 and
1700 h local time along a shore-normal transect in
each area. Each transect extended from the coast at
the 25 m isobath to the 500 m isobath (Fig. 1). Data
were typically collected at the 25, 50, 75, 100, 150,
200, 300 and 500 m isobaths, comprising an average
of eight sampling stations along each transect
(Fig. 1). Continuous depth profiles of salinity and
temperature were obtained using a Neil Brown
conductivity, temperature and depth (CTD) recorder.
Fluorescence was measured with a Seatech FLF 300
Fluorometer connected to the CTD unit. The CTD
was mounted in a General Oceanics 12-bottle Rosette
frame holding 10 l Niskin bottles with reversing
thermometers. The Niskin bottles took water samples
near the sea surface and at 25, 50, 75, 100, 150 m
depth and occasionally at 200 and 300 m depth. Two
Niskin bottles were filled at each depth to provide
enough water to calibrate the salinity and fluores-
cence readings on the CTD unit, and also to measure
the concentrations of nutrients and the abundance of
Noctiluca in the water column. On average, 18 l of
seawater were collected for each of the Noctiluca
counts. The 18 l water samples were filtered on a
90-lm mesh sieve and preserved in filtered 0.05–0.1 l
seawater containing 5% formalin. The samples were
stored in darkened containers, and after the cruise
transported to the laboratory where they were anal-
ysed. The concentrations of oxidised nitrogen
(nitrate + nitrite; NO2– + NO3
–), filterable reactive
phosphorus (FRP) and dissolved reactive silica
(SiO2) in 0.01 l of seawater were determined using
the segmented flow method, with detection limits of
0.04, 0.02, 0.12 lM for NO2– + NO3
–, FRP and SiO2,
respectively. Fluorescence readings were calibrated
against measures of chlorophyll a concentrations (Chl
a mg m–3) in the water column. Seawater (2 l) for
Chl a analysis was filtered through a 47 mm diam-
eter, 1.2 lm glass fibre filter (GC-50, Advantec)
under vacuum immediately after collection. The filter
paper was folded, blotted dry and stored in liquid
nitrogen until analysis in the laboratory. The Chl a
content of the samples was determined using the
methods outlined in Lorenzen (1967) and Jeffrey &
Humphrey (1975).
Night sampling
Night sampling took place between 1900 and 0530 h.
Samples were collected from the 50 and 100 m
isobaths in each region (Fig. 1). These near shore
stations were alternately sampled twice during the
night. A CTD cast was conducted at each station to
collect hydrographic data and water samples for
Noctiluca counts. After each CTD cast we collected
additional plankton samples using a plankton net to
determine the population structure of the Noctiluca
cells. The plankton samples were collected using a
0.2 m diameter, 100 lm mesh plankton net fitted
with a flow meter, and towed at the sea surface (2–
4 m) at a speed of 1.5 m s–1 for 10 min. Three
surface tows were conducted at each station during
both cruises. During the January cruise, subsurface
plankton net samples were collected simultaneously
with the surface tows using a multiple, opening and
closing net (EZNET) fitted with three 0.2 m diame-
ter, 100 lm mesh plankton nets, identical to the net
used in the surface tows. The EZNET was towed
obliquely at three depth intervals varying between
10–20 m, 20–30 m and 30–40 m. An operator on
board the ship electronically triggered the frames of
the EZNET to release the 100 lm mesh plankton nets
at each depth interval.
Underway sampling
Samples were collected while the ship was underway
during the entire time of each cruise. Near surface
waters (4 m) were continually pumped to a thermo-
salinograph and Wetstar Fluorometer before being
62 Hydrobiologia (2008) 598:59–75
123
pumped through a flow meter and gently onto a
100 lm mesh sieve modified to funnel the plankton
into a sample jar. The sample jar was emptied every
hour so that each water sample provided a composite
estimate of the abundance of Noctiluca (888 ± 13 l
of water filtered). Surface temperature, salinity and
fluorescence were recorded at five-minute intervals
using the thermosalinograph and fluorometer. Current
speed and direction were also determined at 5-min
intervals at various depths using an Acoustic Doppler
Current Profiler (ADCP). The ADCP data were earth-
referenced with either the bottom track velocity or
Global Positioning System (GPS) derived velocity to
provide absolute current speeds (m s–1). Wind speed
was measured with an anemometer located 19 m
above sea level, and wind direction was determined
with a Rimco wind direction unit.
Analysis of plankton samples
Preserved plankton samples were gently sieved and
rinsed with seawater through a 90-lm mesh sieve and
concentrated to 0.1 l. The abundance of Noctiluca
was determined from the entire water sample col-
lected in the Niskin bottle during the day and night
sampling. Abundance counts for the underway sam-
ples were conducted on two replicate subsamples of
the 0.1 l concentrate. The reproductive and nutri-
tional states of Noctiluca were determined from the
surface net and EZNET samples collected during the
night. The proportion of asexually dividing and
swarmer forming cells of Noctiluca (Uhlig &
Sahling, 1995) were determined from the first 250
individuals encountered in each net sample. Nutri-
tional status of Noctiluca was determined from the
first 60 cells observed in each net sample. The cells
were classed as being empty if they had no prey
particles or fed if they contained prey particles (Uhlig
& Sahling, 1995).
Analyses of data
Hydrographic data that were obtained from CTD
profiles at each station were contoured using
distance weighted least squares smoothing. Contours
for the temperature data are shown to 300 m depth,
whereas contours for the fluorescence data are
shown to 100 m depth. Fluorescence was converted
to chlorophyll a concentration (Chl a, mg m–3)
using an empirical relationship (Chl a = (0.1*fluo-
rescence) + 0.2, r2 = 0.76, n = 62). Noctiluca counts
and nutrient data were superimposed on the contour
plots. Only NO2– + NO3
– data are shown since these
were positively correlated with the other nutrients
(FRP, P \ 0.001, R = 0.91; SiO2, P = 0.007,
R = 0.69). Nutrient data for 22nd and 23rd Novem-
ber 1998 were not obtained. Hydrographic data were
supplemented with satellite images of sea surface
temperature (SST) obtained from the Common-
wealth Scientific Industrial Research Organisation
Marine Laboratories in Hobart.
Results
Incidence of upwelling and downwelling events
(determined from day sampling)
Strong upwelling favourable winds ([15 kt) from the
north-east preceded the day sampling at Urunga on
November 16 (see Roughan & Middleton, 2002).
Cold (\14�C), nutrient rich ([4 lM NO2– + NO3
–)
water was observed in the near shore zone, which was
defined as the zone extending from the coast to the
100 m isobath (E1, Fig. 2; Table 2). The upwelled
water was also observed at Smoky Cape and Point
Plomer during the following two days of sampling,
but sampling was interrupted along the Point Plomer
transect by stronger downwelling favourable winds
(up to 60 kt) from the south-west. These winds
prevailed during the next two days and presumably
caused onshore surface Ekman transport since we
found that the temperature contours in bottom water
layers of the near shore zone at Diamond Head (20th
November) were depressed downward (Fig. 2). In
addition, nutrient concentrations in the near shore
zone at Diamond Head were correspondingly low
(0.5–1 lM NO2– + NO3
–). On the 22nd November, we
repeated the day sampling at Smoky Cape and found
that this sampling coincided with the development of
a topographically induced upwelling event (E2,
Fig. 2, Table 2), which overwhelmed existing hydro-
graphic conditions (Roughan & Middleton, 2002).
During the following 2 days of sampling, we
observed cold water of\14�C in the near shore zone
at Point Plomer and Diamond Head.
Hydrobiologia (2008) 598:59–75 63
123
Day sampling on the summer cruise commenced
on the 22nd January at Urunga, where we found that
the water column in the near shore zone was highly
stratified and almost stationary (Fig. 3). At the
offshore stations the isotherms were tilted upward
to the west indicating a strong EAC flow at the shelf
break. Downstream, the isotherms were tilted more
steeply upward towards the coast at Smoky Cape,
indicative of both the stronger EAC flow in the near
shore zone, and the ensuing upwelling event (E3,
Table 2, Fig. 3). This upwelling was evident at Point
Plomer, where the 14�C isotherm was observed
inshore at the 50 m isobath. At Diamond Head,
where the continental shelf is wider, the near shore
waters were well mixed (2.8�C temperature differ-
ence between surface waters and waters at 100 m
depth), relatively cold (mean 19.5�C) and nutrient
rich (mean 2.6 lM NO2– + NO3
–), particularly in the
upper 25 m of the water column (Fig. 3). In contrast,
the upper 25 m of the water column in the offshore
waters was relatively nutrient poor (mean 0.7 lM
NO2– + NO3
–) and also up to 5.5�C warmer.
0 10 20 30 40300
200
100
0
12
16
20 22
U (16 Nov)
18
14
0 10 20 30 40300
200
100
12
1416
1822 24
DH (20 Nov)
20
10 20 30 40300
200
100
12
14
20
22
1618
24
SC (17 Nov)
0 10 20 30 40300
200
100
0
12
14
16
18
20
22
SC (22 Nov)
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100
0
12
15
18
21
24
PP (23 Nov)
0 10 20 30 40300
200
100
0
12
14 16
18 20
22
DH (24 Nov)
24
E1 E2
E5
0 10 20 30 40300
200
100
12
16
20 22
U (16 Nov)
18
14
0 10 20 30 40300
200
100
12
1416
1822 24
DH (20 Nov)
20
10 20 30 40300
200
100
12
14
20
22
1618
24
SC (17 Nov)
0 10 20 30 40300
200
100
0
12
14
16
18
20
22
SC (22 Nov)
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100
0
12
15
18
21
24
PP (23 Nov)
0 10 20 30 40300
200
100
0
12
14 16
18 20
22
DH (24 No
24
E1 E2
E5
distance along transect (km) distance along transect (km)
0 10 20 30 40300
200
100
12
16
20 22
U (16 Nov)
18
14
0 10 20 30 40300
200
100
12
16
20 22
U (16 Nov)
0 10 20 30 40300
200
100
12
16
20 22
0 10 20 30 40300
200
100
12
16
20 22
U (16 Nov)
18
14
0 10 20 30 40300
200
100
12
1416
1822 24
DH (20 Nov)
20
0 10 20 30 40300
200
100
12
1416
1822 24
DH (20 Nov)
0 10 20 30 40300
200
100
12
1416
1822 24
0 10 20 30 40300
200
100
0
12
1416
1822 2420
dept
h (m
)
10 20 30 40300
200
100
12
14
20
22
1618
24
SC (17 Nov)
10 20 30 40300
200
100
0 10 20 30 40300
200
100
10 20 30 40300
200
100
0
12
14
20
22
1618
24
SC (17 Nov)
0 10 20 30 40300
200
100
0
12
14
16
18
20
22
SC (22 Nov)
0 10 20 30 40300
200
100
0
12
14
16
18
20
22
0 10 20 30 40300
200
100
0
12
14
16
18
20
22
SC (22 Nov)
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100 14
0 10 20 30 40300
200
100
0
14
0 10 20 30 40300
200
100 14
1816
20 22 24
12
0 10 20 30 40300
200
100
0
12
15
18
21
24
PP (23 Nov)
0 10 20 30 40300
200
100
0
12
15
18
21
24
0 10 20 30 40300
200
100
0
12
15
18
21
24
0 10 20 30 40300
200
100
0
12
15
18
21
24
0 10 20 30 40300
200
100
0
12
15
18
21
24
Nov)
0 10 20 30 40300
200
100
0
12
14 16
18 20
22
DH (24 o
24
0 10 20 30 40300
200
100
0
12
14 16
18 20
22
DH (24 o
24
E1E1 E2E2
E5E5
6.32.40nitrate + nitrite (µM) 6.32.40nitrate + nitrite (µM) 6.32.40nitrate + nitrite (µM)
PP (18 Nov)
DH (20 Nov)
Fig. 2 Contoured vertical profiles of temperature (�C) along
the shore-normal transect in each region during the November
1998 cruise. The letters U (Urunga), SC (Smoky Cape), PP
(Point Plomer) and DH (Diamond Head) denote the regions
sampled during the study. Diamonds denote the location of the
day sampling stations from which the continuous (1 m depth
intervals) temperature profiles were measured. Black arrows
denote the location and timing of the six upwelling events (E1,
E2, E3, E4, E5 or E6, see Table 2) observed during the study.
Temperature data are contoured every 2�C and average
dissolved inorganic nitrogen (NO2– + NO3
– lM) plots are
superimposed on the temperature data. Nutrient data were
not available for the repeat day sampling at Smoky Cape, Point
Plomer and Diamond Head between 22nd and 23rd November
64 Hydrobiologia (2008) 598:59–75
123
South of Diamond Head, between Crowdy Head
(CR) and Cape Hawke (CH), the nutrient concentra-
tions in the water column were lower with average
concentrations of 1.5–2.0 lM for NO2– + NO3
– (Fig. 3).
The water column was highly stratified (4�C temper-
ature difference between surface waters and waters at
100 m depth) and the isotherms were relatively flat. A
temperature front was observed between the near shore
and offshore surface waters, the latter being up to 6�C
warmer (Fig. 3, 4). The temperature front was located
10 km offshore at Crowdy Head and[30 km offshore
at Cape Hawke. Upwelling was also evident south of
Cape Hawke, at Broughton Island (BI), as shown again
by the tilting of isotherms towards the coast (Fig. 3,
E4, Table 2). This upwelling process appeared to be
localised since the isotherms flattened out at Port
Stephens (PS), which was only 4.5 km downstream of
BI (Fig. 3). The concentration of nutrients appearing in
the upper 25 m of the water column at BI was also
relatively less (max. 3.7 lM NO2– + NO3
–) than that
observed in the upwelling zone at Smoky Cape (max.
5.1 lM NO2– + NO3
–).
Surface temperature and currents
SST images obtained in November and January show
the near shore presence of the EAC at Smoky Cape
where the shelf narrows, and the separation point of
the EAC from the coast occurring just south of Point
Plomer (Fig. 4). South of the EAC separation point,
the near shore surface waters were up to 5.9�C cooler
(e.g. January) than those north of the EAC separation.
Currents were generally faster offshore than near
shore, except at Smoky Cape in November and
January where currents were strong even in shallower
waters (Fig. 4). While surface currents had a net
southward flow parallel to the coast, weak northward
counter currents were measured in the near shore
zone at Urunga, Cape Hawke, BI and Port Stephens
in January, and at Diamond Head in November
(Fig. 4). Near shore currents south of the EAC
separation point were generally weaker than north
of the EAC separation point.
Phytoplankton blooms during day sampling
Phytoplankton blooms (Chl a concentrations [2 mg
m–3) were observed during the wind induced
upwelling event in November (E1; Fig. 5), the
topographically induced upwelling events at Smoky
Cape in November (E2; Fig. 5) and January (E3;
Fig. 6), and at the upwelling observed at BI and Port
Stephens in January (E4; Fig. 6). In general, phyto-
plankton were distributed in the upper 100 m of the
water column during both months of sampling. A
subsurface phytoplankton maximum was observed at
40–60 m depth at Urunga, Smoky Cape and Point
Plomer. In regions south of the EAC separation point,
the phytoplankton maximum was observed in the
upper 25 m of the water column. While the biomass
of phytoplankton was generally greater in the near
shore zone, phytoplankton were also observed at the
offshore stations. For example, the biomass of
phytoplankton (1.3 mg m–3) was relatively high at
40–60 m depth at the offshore stations at Diamond
Head subsequent to the topographically induced
upwelling in November (E2; Fig. 5). In January,
phytoplankton were also observed at subsurface
Table 2 Location and mechanism of upwellings that occurred on the east coast of New South Wales between 30�050 S, 152�E and
32�050 S, 153�050 E during November 1998 and January 1999
Upwelling Location Date Causative mechanism
E1 Urunga–Point Plomer November 16, 1998 [15 kt NE winds
E2 Smoky Cape–Diamond Head November 22–24, 1998 Topographic
E3 Smoky Cape–Diamond Head January 23–25, 1999 Topographic
E4 Broughton Is.–Port Stephens January 30–31, 1999 Unknown
E5 Diamond Head November 24, 1998 EACa separation from the coast &
cross-shelf boundary layer fluxes
E6 Diamond Head January 25, 1999 EACa separation from the coast &
cross-shelf boundary layer fluxes
a EAC = East Australian Current
Hydrobiologia (2008) 598:59–75 65
123
depths at the offshore stations at Point Plomer,
Diamond Head and Crowdy Head although the
biomass of these offshore phytoplankton populations
was relatively low (0.6–0.9 mg m–3, Fig. 6).
Abundance of Noctiluca during day sampling
Abundance of Noctiluca was relatively greater in
areas south of Smoky Cape than to north of Smoky
Cape during the topographically induced upwelling in
November (E2) and January (E3). For example in
November (E2), the average abundance of Noctiluca
determined in samples collected at Smoky Cape
(0.2 cells l–1) was up to seven times lower than those
collected at Diamond Head (1.6 cells l–1; Fig. 5).
Similarly in January (E3), the average abundance of
Noctiluca was 0.1 cells l–1 in samples collected at
Smoky Cape and 1 cell l–1 in samples collected at
Diamond Head (Fig. 6). Noctiluca was virtually
absent in samples collected from Crowdy Head in
January, but increased to 0.5 cells l–1 at Cape Hawke,
0.9 cells l–1 at BI and 1.1 cells l–1 at Port Stephens.
Abundance of Noctiluca was generally greater in the
0 10 20 30 40300
200
100
0
16
1820
2224
26
SC (23 Jan)16
18
0 10 20 30 40300
200
100
0
14
16
1820
22
2426
PP (24 Jan)
0 10 20 30 40300
200
100
0
16 18
20
22
24
26
BI (30 Jan)
0 10 20 30 40300
200
100
0
14
16 18
20
2224 26
U (22 Jan)
0 10 20 30 40300
200
100
0
2124
27
18
CR (28 Jan)
0 10 20 30 40300
200
100
020
02
22 2426 28
CH (29 Jan)
0 10 20 30 40300
200
100
0
1618
20 2224
PS (31 Jan)
distance along transect (km)400 10 20 30
300
200
100
0
16
81
2022
24
26
DH (25 Jan)
18
distance along transect (km)
edpt
h( m
)
E3
E6
E4
0 10 20 30 40300
200
100
16
1802
2224
26
SC (23 Jan)16
18
0 10 20 30 40300
200
100
0
14
16
1820
22
2426
PP (24 Jan)
0 10 20 30 40300
200
100
0
16 18
20
22
24
26
BI (30 Jan)
0 10 20 30 40300
200
100
14
16 18
20
2224 26
U (22 Jan)
0 10 20 30 40300
200
10021
24
27
18
CR (28 Jan)
0 10 20 30 40300
200
100
020
02
22 2426 28
CH (29 Jan)
0 10 20 30 40300
200
100
0
1618
20 2224
PS (31 Jan)
distance along transect (km)400 10 20 30
300
200
100
0
16
81
2022
24
26
DH (25 Jan)
18
distance along transect (km)
edpt
h( m
)
E3
E6
E4
0 10 20 30 40300
200
100
16
1802
2224
26
SC (23 Jan)16
18
0 10 20 30 40300
200
100
16
1802
2224
26
0 10 20 30 40300
200
100
16
1802
2224
26
SC (23 Jan)16
18
0 10 20 30 40300
200
100
0
14
16
1820
22
2426
PP (24 Jan)
0 10 20 30 40300
200
100
0
14
16
1820
22
2426
0 10 20 30 40300
200
100
0
14
16
1820
22
2426
PP (24 Jan)
0 10 20 30 40300
200
100
0
16 18
20
22
24
26
BI (30 Jan)
0 10 20 30 40300
200
100
0
16 18
20
22
24
26
0 10 20 30 40300
200
100
0
16 18
20
22
24
26
BI (30 Jan)
0 10 20 30 40300
200
100
14
16 18
20
2224 26
U (22 Jan)
0 10 20 30 40300
200
100
14
16 18
20
2224 26
0 10 20 30 40300
200
100
14
16 18
20
2224 26
U (22 Jan)
0 10 20 30 40300
200
10021
24
27
18
CR (28 Jan)
0 10 20 30 40300
200
10021
24
27
18
CR (28 Jan)
0 10 20 30 40300
200
100
020
02
22 2426 28
CH (29 Jan)
0 10 20 30 40300
200
100
020
02
22 2426 28
CH (29 Jan)
0 10 20 30 40300
200
100
0
1618
20 2224
PS (31 Jan)
distance along transect (km)0 10 20 30 40
300
200
100
0
1618
20 2224
0 10 20 30 40300
200
100
0
1618
20 2224
PS (31 Jan)
distance along transect (km)400 10 20 30
300
200
100
0
16
81
2022
24
26
DH an)
18
distance along transect (km)400 10 20 30
300
200
100
0
16
81
2022
24
26
DH an)
18
distance along transect (km)0 10 20 30
300
200
100
0
16
81
2022
24
26
DH an)
18
distance along transect (km)
edpt
h( m
)
E3E3
E6E6
E4E4
nnn 6.32.40itrate + nitrite (µM) 6.32.40itrate + nitrite (µM) 6.32.40itrate + nitrite (µM)
Fig. 3 Contoured vertical profiles of temperature (�C) along
the shore-normal transect in each region during the January
1999 cruise. The letters U (Urunga), SC (Smoky Cape), PP
(Point Plomer), DH (Diamond Head), CR (Crowdy Head), CH
(Cape Hawke), BI (Broughton Island) and PS (Port Stephens)
denote the regions sampled during the study. Diamonds denote
the location of the day sampling stations from which the
continuous (1 m depth intervals) temperature profiles were
measured. Black arrows denote the location and timing of the
six upwelling events (E1, E2, E3, E4, E5 or E6, see Table 2)
observed during the study. Temperature data are contoured
every 2�C and average dissolved inorganic nitrogen (NO2– +
NO3– lM) plots are superimposed on the temperature data
66 Hydrobiologia (2008) 598:59–75
123
upper 25 m of the water column, except in the
offshore waters at Diamond Head, where relatively
high numbers of Noctiluca were found at the
subsurface phytoplankton maximum (Fig. 5), subse-
quent to the topographically induced upwelling in
November (E2, Fig. 2).
The temporal variation in the abundance of
Noctiluca is summarised in Fig. 7, which arise from
data collected from day sampling of the upper 25 m
of the water column in the near shore zone of Urunga
to Diamond Head during the topographically induced
upwellings in November (E2) and January (E3). The
average abundance of Noctiluca in the upper 25 m of
the water column in areas north of the EAC
separation point was 2.7 times greater in November
than in January (Fig. 7a). In contrast, the average
abundance of Noctiluca south of the EAC separation
(i.e. Diamond Head) did not vary between the
2 months of sampling. The average abundance of
Noctiluca was significantly negatively correlated with
the average temperature of the upper 25 m of the
water column (r = –0.91, P = 0.004; Fig. 7b) and
with the average speed of surface currents (r = –0.85,
P = 0.014; Fig. 7c).
Population structure of Noctiluca during night
sampling in January
Samples collected in Niskin bottles during the night
contained a greater number of Noctiluca cells than
the samples collected during the day at the same
location (Fig. 6, 8a, b). The night sampling in January
revealed that the abundance of Noctiluca was rela-
tively greater at depth than at the surface in areas
north of the EAC separation point (Fig. 8a, b).
Generally, a greater number of Noctiluca cells per
litre was collected through the bottle sampling
(Fig. 8a, b) than the net sampling (Fig. 8c, d).
The average proportion of fed Noctiluca cells
found in subsurface (EZNET) samples was variable,
ranging from 33 ± 39% at 30–40 m depth to
65 ± 25% at 10–20 m depth (data not shown). A
relatively high proportion of fed cells was found in
the surface net samples collected south of the EAC
separation point, where Chl a concentrations were
also relatively greater (Fig. 8e, f). Despite these
relative patterns, the proportion of fed cells was not
well correlated with the Chl a concentrations
(r2 = 0.3). Asexually reproducing cells (data not
shown) were only found in the samples collected at
BI between 0330 and 0500 h. The occurrence of
reproductive cells in samples was most likely time-
dependent since BI was the only region that was
sampled just prior to sunrise.
Underway sampling of Noctiluca in surface
waters
Underway sampling of Noctiluca in surface waters
showed a longshore gradient from low abundance of
BI
PS
U
CH
PP
DH
SC
CRSCR
33°S
32°S
31°S
30°S
19 Jan 99
152°E 153°
current speed ( 2.7 m.s-1)
0 30 km
N
temp- 18°C 20°C 22°C 24°C 26°C
21 Nov 98
152°E 153°E 154°E
33°S
32°S
31°S
30°S
U
SC
PP
DH
0 30 km
N
BI
PS
U
CH
PP
DH
SC
CRSCR
33°S
32°S
31°S
30°S
19 Jan 99
152°E 153°
current speed ( 2.7 m.s-1)
0 30 km
N
BI
PS
U
CH
PP
DH
SC
CRSCR
33°S
32°S
31°S
30°S
19 Jan 99
152°E 3°E 154°E
current speed ( 2.7 m.s-1)current speed ( 2.7 m.s-1)
0 30 km
N
0 30 km0 30 km
N
temp- 18°C 20°C 22°C 24°C 26°C
21 Nov 98
152°E 153°E 154°E
33°S
32°S
31°S
30°S
U
SC
PP
DH
0 30 km
N
temp- 18°C 20°C 22°C 24°C 26°Ctemp- 18°C 20°C 22°C 24°C 26°C
21 Nov 98
152°E 153°E 154°E
33°S
32°S
31°S
30°S
U
SC
PP
DH
21 Nov 98
152°E 153°E 154°E
33°S
32°S
31°S
30°S
21 Nov 98
152°E 153°E E
33°S
32°S
31°S
30°S
U
SC
PP
DH
0 30 km
N
0 30 km0 30 km
N
Fig. 4 Representative SST
images of the New South
Wales coast taken during
the November 1998 and
January 1999 cruises. Black
arrows denote the direction
and speed (m s–1) of the
ambient surface currents
determined from Acoustic
Doppler Current Profiles.
The letters U (Urunga), SC
(Smoky Cape), PP (Point
Plomer), DH (Diamond
Head), CR (Crowdy Head),
CH (Cape Hawke), BI
(Broughton Island) and PS
(Port Stephens) denote the
regions sampled during the
study
Hydrobiologia (2008) 598:59–75 67
123
Noctiluca at Urunga to high abundance at Diamond
Head during both months of sampling (Fig. 9). A
cross-shore gradient from low to high abundance of
Noctiluca in offshore to near shore waters was also
observed during both months of sampling. The
abundance of Noctiluca was up to 1.5 times greater
in samples collected during the November cruise
(average of all samples 0.9 ± 0.2 cells l–1, n = 137;
Fig. 9a) than those collected during the January
cruise (average of all samples 0.6 ± 0.1 cells l–1,
n = 207; Fig. 9b). Areas of relatively high abundance
of Noctiluca were identified whilst the ship made its
way to the main study area (Fig. 9c). In November,
the highest abundance of Noctiluca (13.1 cells l–1)
was observed in samples collected at Port Hacking
near Sydney. Relatively high numbers of Noctiluca
were also found in samples collected near Port
Stephens (6.4 cells l–1), Cape Hawke (8.5 cells l–1)
and Laurieton (6.6 cells l–1). Very few cells
(\1 cell l–1) were found in the underway samples in
January as the ship travelled south from Brisbane,
although during this cruise relatively higher numbers
of Noctiluca were observed in samples collected at
Cape Byron (Fig. 9c).
0 10 20 30 40100
80
60
40
20
0
0.9
0.9
1.61.6
2.3
2.3
2.33.1
U (16 Nov)
distance along transect (km)
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
DH (20 Nov)
0 10 20 30 40
80
60
40
20
0
0.7
0.71.3
0.7
1 8.2.3
0.7SC (22 Nov)
distance along transect (km)
0 10 20 30 40
80
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
DH (24 Nov)
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.33.1
SC (17 Nov)
0 10 20 30 40
80
60
40
20
0
1.1
1.11.5
1.90.6
0.6
PP (23 Nov)
0 10 20 30 40100
80
60
40
20
1.3
1.32.3
2.3
PP (18 Nov)
E2
E5
E1
< 1 3.5 10.8 28.1Noctiluca (cells.L-1) < 1 3.5 10.8 28.1Noctiluca (cells.L-1) < 1 3.5 10.8 28.1Noctiluca (cells.L-1)
0 10 20 30 40100
80
60
40
20
0
0.9
0.9
1.61.6
2.3
2.3
2.33.1
U (16 Nov)
distance along transect (km)
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
DH (20 Nov)
0 10 20 30 40
80
60
40
20
0
0.7
0.71.3
0.7
1.82.3
0.7SC (22 Nov)
distance along transect (km)
0 10 20 30 40
80
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
DH (24 Nov)
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.33.1
SC (17 Nov)
0 10 20 30 40
80
60
40
20
0
1.1
1.11.5
1.90.6
0.6
PP (23 Nov)
0 10 20 30 40100
80
60
40
20
1.3
1.32.3
2.3
PP (18 Nov)
E2
E5
E1
dept
h (m
)
0 10 20 30 40100
80
60
40
20
0
0.9
0.9
1.61.6
2.3
2.3
2.33.1
U (16 Nov)
0 10 20 30 40100
80
60
40
20
0
0.9
0.9
1.61.6
2.3
2.3
2.33.1
0 10 20 30 40100
80
60
40
20
0
0.9
0.9
1.61.6
2.3
2.3
2.33.1
0 10 20 30 40100
80
60
40
20
0.9
0.9
1.61.6
2.3
2.3
2.33.1
U (16 Nov)U (16 Nov)
distance along transect (km)
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
DH (20 Nov)
distance along transect (km)
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
0 10 20 30 40100
80
60
40
20 0.8
0.8
0.8
0 10 20 30 40
80
60
40
20
0
0.7
0.71.3
0.7
1.82.3
0.7SC (22 Nov)
0 10 20 30 40
80
60
40
20
0
0.7
0.71.3
0.7
1.82.3
0 10 20 30 40
80
60
40
20
0
0.7
0.71.3
0.7
1.82.3
0 10 20 30 40
80
100
60
40
20
0.7
0.71.3
0.7
1.82.3
0.7
distance along transect (km)
0 10 20 30 40
80
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
DH (24 Nov)
distance along transect (km)
0 10 20 30 40
80
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
0 10 20 30 40
80
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
0 10 20 30 40
80
100
60
40
20
0
0.6
0.6
0.6
0.9
0.9
1.3
1.3
1.3
.1 6
2
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.33.1
SC (17 Nov)
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.33.1
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.3
0 10 20 30 40100
80
60
40
20
0.9
1.6
2.3
2.3
0
0
0
10 20 30 40100
80
60
40
20
0
0.9
1.6
2.3
2.33.1
SC (17 Nov)
0 10 20 30 40
80
60
40
20
0
1.1
1.11.5
1.90.6
0.6
PP (23 Nov)
0 10 20 30 40
80
60
40
20
0
1.1
1.11.5
1.9
0 10 20 30 40
80
60
40
20
0
1.1
1.11.5
1.9
0 10 20 30 40
80
100
60
40
20
1.1
1.11.5
1.90.6
0.6
0 10 20 30 40100
80
60
40
20
1.3
1.32.3
2.3
0 10 20 30 40100
80
60
40
20
1.3
1.32.3
2.3
E2E2
E5E5
E1E1
SC (17 Nov)
PP (18 Nov)
DH (20 Nov)
SC (22 Nov)
PP (23 Nov)
DH (24 Nov)
Fig. 5 Contoured vertical profiles of chlorophyll a (Chl a,
mg m–3; derived from fluorescence data) along the shore-
normal transect in each region during the November 1998
cruise. The letters U (Urunga), SC (Smoky Cape), PP (Point
Plomer) and DH (Diamond Head) denote the regions sampled
during the study. Diamonds denote the location of the day
sampling stations from which the data were collected. Black
arrows denote the location and timing of the six upwelling
events (E1, E2, E3, E4, E5 or E6, see Table 2) observed during
the study. The abundance of Noctiluca (cells l–1), determined
from bottle water samples collected from 0, 25, 50, 75 and
100 m depth at station, is superimposed on the Chl a data
68 Hydrobiologia (2008) 598:59–75
123
Discussion
The location of upwelling events between 30 and
33�S on the east coast of Australia appears to be
predictable. Upwelling, which was predicted to occur
at Smoky Cape due to alongshore topographic
variations, was observed during the two arbitrarily
chosen sampling times within the austral spring
(November 1998) and summer (January 1999).
Following each of the topographically induced upw-
ellings, the biomass of phytoplankton increased as
did the abundance of Noctiluca. Phytoplankton
blooms were observed at 40–60 m depth at Smoky
Cape and Point Plomer, and then in the upper surface
layers at Diamond Head, where Noctiluca was most
abundant. The high proportion of fed Noctiluca cells
observed in the upwelled waters directly implies that
the increase in abundance of Noctiluca is stimulated
by the increased availability of food (phytoplankton,
Fig 8e, f). These findings are similar to those
obtained in the upwelling regions of southern
Benguela, where Noctiluca cells were found attached
0 10 20 30 40100
80
60
40
20
0
0.7
1.3
1.8
1.8
2.3
U (22 Jan)
0 10 20 30 40100
80
60
40
20
0
1.3.2 3
SC (23 Jan)
0 10 20 30 40100
80
60
40
20
0
0.6
0.6
0.6
0.90.9
PP (24 Jan)
0 10 20 30 40100
80
60
40
20
0
0.5
0.5
0.8
0.8
0.8
.1 1
1.3 1.3
CR (28 Jan)
0 10 20 30 40100
80
60
40
20
00.61.11.5
1.9 2.32.8
CH (29 Jan)
0 10 20 30 40100
80
60
40
20
0
0.9
0.91.6
2.3
BI (30 Jan)
distance along transect (km)0 10 20 30 40
100
80
60
40
20
0
0.7
1.31.3
1.82.32.9
PS (31 Jan)
0 10 20 30 40100
80
60
40
20
0
0.6
.0 60.9
0.9
1.3
DH (25 Jan)
distance along transect (km)
htped( m
)
E3
E6
E4
0 10 20 30 40100
80
60
40
20
0
0.7
1.3
1.8
1.8
2.3
U (22 Jan)
0 10 20 30 40100
80
60
40
20
0
1.3.2 3
SC (23 Jan)
0 10 20 30 40100
80
60
40
20
0
0.6
0.6
0.6
0.90.9
PP (24 Jan)
0 10 20 30 40100
80
60
40
20
0
0.5
0.5
0.8
0.8
0.8
.1 1
1.3 1.3
CR (28 Jan)
0 10 20 30 40100
80
60
40
20
00.61.11.5
1.9 2.32.8
CH (29 Jan)
0 10 20 30 40100
80
60
40
20
0
0.9
0.91.6
2.3
BI (30 Jan)
distance along transect (km)0 10 20 30 40
100
80
60
40
20
0
0.7
1.31.3
1.82.32.9
PS (31 Jan)
0 10 20 30 40100
80
60
40
20
0
0.6
.0 60.9
0.9
1.3
DH (25 Jan)
distance along transect (km)
htped( m
)
E3
E6
E4
0 10 20 30 40100
80
60
40
20
0
0.7
1.3
1.8
1.8
2.3
U (22 Jan)
0 10 20 30 40100
80
60
40
20
0
0.7
1.3
1.8
1.8
2.3
0 10 20 30 40100
80
60
40
20
0
0.7
1.3
1.8
1.8
2.3
U (22 Jan)
0 10 20 30 40100
80
60
40
20
0
1.3.2 3
SC (23 Jan)
0 10 20 30 40100
80
60
40
20
0
1.3.2 3
0 10 20 30 40100
80
60
40
20
0
0.6
0.6
0.6
0.90.9
PP (24 Jan)
0 10 20 30 40100
80
60
40
20
0
0.6
0.6
0.6
0.90.9
n
0 10 20 30 40100
80
60
40
20
0
0.5
0.5
0.8
0.8
0.8
.1 1
1.3 1.3
CR (28 Jan)
0 10 20 30 40100
80
60
40
20
0
0.5
0.5
0.8
0.8
0.8
.1 1
1.3 1.3
8
0 10 20 30 40100
80
60
40
20
00.61.11.5
1.9 2.32.8
CH (29 Jan)
0 10 20 30 40100
80
60
40
20
00.61.11.5
1.9 2.32.8
CH (29 Jan)
0 10 20 30 40100
80
60
40
20
0
0.9
0.91.6
2.3
BI (30 Jan)
0 10 20 30 40100
80
60
40
20
0
0.9
0.91.6
2.3
0 10 20 30 40100
80
60
40
20
0
.9
0.91.6
2.31.6
distance along transect (km)0 10 20 30 40
100
80
60
40
20
0
0.7
1.31.3
1.82.32.9
(31 Jan)
distance along transect (km)0 10 20 30 40
100
80
60
40
20
0
0.7
1.31.3
1.82.32.9
(31 Jan)
0 10 20 30 40100
80
60
40
20
0
0.7
1.31.3
1.82.32.9
0 10 20 30 40100
80
60
40
20
0
0.6
.0 60.9
0.9
1.3
DH (25 Jan)
distance along transect (km)0 10 20 30 40
100
80
60
40
20
0
0.6
.0 60.9
0.9
1.3
0 10 20 30 40100
80
60
40
20
0
0.6
.0 60.9
0.9
1.3
DH (25 Jan)
distance along transect (km)
htped( m
)
E3E3
E6E6
E4E4
< 1 3.5 10.8 28.1Noctiluca (cells.L-1) < 1 3.5 10.8 28.1Noctiluca (cells.L-1) < 1 3.5 10.8 28.1Noctiluca (cells.L-1)
SC (23 Jan)
PP (24 Ja )
CR (28 Jan)
BI (30 Jan)
PS (31 Jan)
Fig. 6 Contoured vertical profiles of chlorophyll a (Chl a,
mg m–3; derived from fluorescence data) along the shore-
normal transect in region during the January 1999 cruise. The
letters U (Urunga), SC (Smoky Cape), PP (Point Plomer), DH
(Diamond Head), CR (Crowdy Head), CH (Cape Hawke), BI
(Broughton Island) and PS (Port Stephens) denote the regions
sampled during the study. Diamonds denote the location of the
day sampling stations from which the data were collected.
Black arrows denote the location and timing of the six
upwelling events (E1, E2, E3, E4, E5 or E6, see Table 2)
observed during the study. The abundance of Noctiluca(cells l–1), determined from bottle water samples collected
from 0, 25, 50, 75 and 100 m depth at station, is superimposed
on the Chl a data
Hydrobiologia (2008) 598:59–75 69
123
to diatom aggregates that were entrained within the
upwelling plumes (Painting et al., 1993; Kiorboe
et al., 1998; Tiselius & Kiorboe, 1998). High abun-
dances of Noctiluca have also recently been reported
in the upwelling regions of the southern Black Sea
(Uysal, 2002), the Ulleung Basin in Korea (Kang
et al., 2004) and southern Kerala coast in India
(Sahayak et al., 2005). Thus it would appear that
areas of relatively high abundance of Noctiluca (‘hot
spots’) might be predicted based on the location of
upwellings. Certainly in the present study, a number
of Noctiluca ‘hot spots’ were observed downstream
or near areas known to induce upwelling (Fig. 9). It is
of particular significance however, that the absolute
abundance of Noctiluca in upwelled waters varied
from one upwelling location to another and between
seasons. As discussed below, it is likely that the
combined effects of the current speed and flow, and
the temperature of the surface water layers (defined
here as the upper 25 m of the water column)
determined the absolute abundance of Noctiluca in
the upwelled waters.
Influence of EAC speed and flow
on the abundance of Noctiluca in upwelled waters
In a previous study we found that the EAC has the
potential to advect Noctiluca cells away from the
original area that might have stimulated population
growth (Dela-Cruz et al., 2003). Here we also suggest
that the southward flow of the EAC may partly
explain the gradual increase in the abundance of
Noctiluca from Smoky Cape to Diamond Head. For
example, in November the EAC travelled at an
average speed of 0.7 m s–1 in the near shore zone
between Smoky Cape and Point Plomer. At these
speeds, a cell will be advected a distance of 60.5 km
per day and therefore take only 1 day to reach
Diamond Head. With an average growth rate of 0.5
doublings per day (Elbrachter & Qi, 1998), we would
expect the abundance of Noctiluca at Diamond Head
to be double the abundance of Noctiluca at Smoky
Cape. The predicted estimates are consistent with the
sampling data which showed that the average abun-
dance of Noctiluca in the near shore zone at Smoky
Cape and Point Plomer was 1.0 cell l–1, and the
average abundance of Noctiluca in offshore waters at
Diamond Head was 2.8 cells l–1. We used data
collected from offshore waters at Diamond Head
for comparison as our results showed that when the
EAC separated from the coast just south of Point
Plomer, the surface water layers and the plankton
oN
ulitcac
c(.slleL
1-)
0
1
2
3
4
5
Nov-98
Jan-99
U SC PP DH
lhC
am(
g.m
3-)
0
0.4
0.8
1.2
1.6
nd
nd
etm
pre
utar
C°(e
)
20
21
22
23
24
25
26
27
nd
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ucrren
stp
(dee
m.s
1-)
nd
oN
ulitcac
c(.slleL
1-)
0
1
2
3
4
5
Nov-98
Jan-99
U SC PP DH
lhC
am(
g.m
3-)
0
0.4
0.8
1.2
1.6
nd
lhC
am(
g.m
3-)
0
0.4
0.8
1.2
1.6
am(
g.m
3-)
0
0.4
0.8
1.2
1.6
nd
nd
A)
D)
etm
pre
utar
C°(e
)
20
21
22
23
24
25
26
27
nd
etm
pre
utar
)
20
21
22
23
24
25
26
27
nd
B)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ucrren
stp
(dee
m.s
1-)
nd0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
ucrren
stp
(dee
m.s
1-)
nd
C)
Fig. 7 Average abundance of Noctiluca (cells l–1), tempera-
ture (�C), surface current speed (m s–1) and chlorophyll a (Chl
a, mg m–3) at Urunga (U), Smoky Cape (SC), Point Plomer
(PP) and Diamond Head (DH) during the topographically
induced upwelling events in November 1998 and January
1999. Averages were determined using data collected in the
upper 25 m of the near shore zone, which was defined as the
zone extending from the coast to the 100 m isobath
70 Hydrobiologia (2008) 598:59–75
123
communities within them, including Noctiluca, were
entrained offshore (Fig. 5).
The physical separation of the EAC from the coast
has long been known to drive cold nutrient rich slope
water from the continental slope towards the near
shore zone (Rochford, 1975; Godfrey et al., 1980) and
stimulate blooms of diatoms (Hallegraeff & Jeffrey,
1993). Recent studies have further concluded that
upwelling is often observed inshore of the separated
EAC due to cross-shelf boundary layer fluxes (Rou-
ghan & Middleton, 2002). Both of these mechanisms
may explain the origin of the near shore phytoplank-
ton blooms and Noctiluca population at Diamond
Head, where during both cruises, we observed colder
water and further nutrient enrichment (E5, E6,
Table 2). The cross-shelf boundary layer fluxes
inshore of the separated EAC upwelled the subsurface
plankton communities (including Noctiluca) that were
advected southward from Smoky Cape (Roughan &
Middleton, 2002), and the further nutrient enrich-
ments from the EAC separation stimulated growth of
phytoplankton (and subsequently Noctiluca).
U SC PP DH CR CH BI PS
30-40 m
U SC PP DH CR CH BI PS
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2fed cells
Chl a
0
0.05
0.1
0.15
U SC PP DH CR CH BI PS
30-40 m
0
10
20
30
40
50
60
70
80
90
100
U SC PP DH CR CH BI PS
fed cells
Chl a
U SC PP DH CR CH BI PS
30-40 m
U SC PP DH CR CH BI PS
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2fed cells
Chl a
U SC PP DH CR CH BI PS
30-40 m
U SC PP DH CR CH BI PS
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2fed cells
Chl aE)
0
0.05
0.1
0.15
U SC PP DH CR CH BI PS
30-40 m
0
10
20
30
40
50
60
70
80
90
100
U SC PP DH CR CH BI PS
fed cells
Chl a
0
0.05
0.1
0.15
U SC PP DH CR CH BI PS
30-40 m
0
10
20
30
40
50
60
70
80
90
100
U SC PP DH CR CH BI PS
fed cells
Chl a
0
0.05
0.1
0.15
U SC PP DH CR CH BI PS
30-40 m
0
10
20
30
40
50
60
70
80
90
100
U SC PP DH CR CH BI PS
fed cells
Chl a
F)
0.2
0.25surface
10-20 m
20-30 m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
U SC DH PP CR CH BI PS
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
25 m
50 m
75 m
90 m
surface
100 m STATION
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
lhC
am (
g .m3-)
0.2
0.25surface
10-20 m
20-30 m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
U SC DH PP CR CH BI PS
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
25 m
50 m
75 m
90 m
surface
100 m STATION
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
lhC
am(
g .m3-)
0.2
0.25surface
10-20 m
20-30 m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
U SC DH PP CR CH BI PS
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
25 m
50 m
75 m
90 m
surface
100 m STATION
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0.2
0.25surface
10-20 m
20-30 m
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
U SC DH PP CR CH BI PS
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
25 m
50 m
75 m
90 m
surface
100 m STATION
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
B)
D)
lhC
am(
g.m3-)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9surface
10-20 m
20-30 m
0
0.5
1
1.5
2
2.5
3
3.5
U SC PP DH CR CH BI PS
surface
10 m
20 m
30 m
40 m
sllec def(%
)o
Nulitc
ca(
.sllecL
1-)
oN
ulitcc a
(c.sl leL
1-)
50 m STATION
0
10
20
30
40
50
60
70
80
90
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9surface
10-20 m
20-30 m
0
0.5
1
1.5
2
2.5
3
3.5
U SC PP DH CR CH BI PS
surface
10 m
20 m
30 m
40 m
sllec def(%
)o
Nulitc
ca(
.sllecL
1-)
oN
ulitcca
(c.slleL
1-)
50 m STATION
0
10
20
30
40
50
60
70
80
90
100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9surface
10-20 m
20-30 m
0
0.5
1
1.5
2
2.5
3
3.5
U SC PP DH CR CH BI PS
surface
10 m
20 m
30 m
40 m
sllec def(%
)o
Nulitc
ca(
.sllecL
1-)
oN
ulitcca
(c.slleL
1-)
50 m STATION
A)
C)
0
10
20
30
40
50
60
70
80
90
100
Fig. 8 Abundance (A–D) and nutritional status (E, F) of
Noctiluca at the 50 and 100 m night sampling stations in each
region during the January 1999 cruise. The figure shows a
comparison between two sampling methods, bottle sampling
(A, B) and net sampling with a neuston net and an EZNET (C,
D). Bottle samples were collected 0, 10, 20, 30 and 40 m depth,
whereas samples collected by the EZNET tows were collected
at three depth intervals, 10–20 m, 20–30 m and 30–40 m
depth. Abundance of Noctiluca at 0 m depth in plot B is shown
on the secondary y-axis. Chlorophyll a concentrations in
surface waters are shown in plots E and F. The letters U
(Urunga), SC (Smoky Cape), PP (Point Plomer), DH (Diamond
Head), CR (Crowdy Head), CH (Cape Hawke), BI (Broughton
Island) and PS (Port Stephens) denote the regions sampled
during the study
Hydrobiologia (2008) 598:59–75 71
123
Another physical mechanism that might explain
the relatively high abundance of Noctiluca at Dia-
mond Head could be related to the slowing and
reversal of near shore currents after the EAC
separation point (Fig. 4). The change in current
speed is known to modify the surface wave pattern
and cause an accumulation of surface debris (Church
& Cresswell, 1986), which in the present study might
well have included Noctiluca as it is ordinarily
positively buoyant due to its large cell vacuole
(Kesseler, 1966). Indeed, high abundances of Noctil-
uca in coastal embayments and fringes have also
been attributed to concentrating or accumulating
mechanisms such as prevailing winds and strong
currents (Yin, 2003; Kang et al., 2004; Liu & Wong,
2006; Miyaguchi et al., 2006).
Influence of water temperature on the abundance
of Noctiluca in upwelled waters
The difference in the temperature of surface waters
and difference in the absolute abundance of Noctiluca
between the spring and summer cruises were the most
notable trends found in this study. Surface water
temperatures during the summer were anomalously
high due to a strong La Nina phase (Berkelmans &
Oliver, 1999) and up to 4�C warmer than during the
spring. These warmer surface water temperatures
were negatively correlated with relatively lower
average abundances of Noctiluca in the near shore
zone. These results give rise to the hypothesis that the
temperature of the water directly influences the
absolute abundance of Noctiluca. Previous studies
conducted in the North Sea (Uhlig & Sahling, 1995),
South China Sea (Huang & Qi, 1997) and Japan (Lee
& Hirayama, 1992) have shown that Noctiluca is
unable to survive above water temperatures of 25�C.
In the present study, we found that Noctiluca was
absent from the surface water layers of the near shore
zone at Urunga, Smoky Cape and Point Plomer
during the summer cruise, when day time tempera-
tures were as high as 27�C. Chlorophyll a
concentrations in the surface water layers were not
observed to be lower during the summer cruise
compared to the spring suggesting that the
Fig. 9 Maps of the New South Wales coast showing the
overall spatial abundance patterns of Noctiluca (cells l–1),
determined from the underway sampling (A) between Urunga
and Diamond Head in November 1998, (B) between Urunga
and Port Stephens in January 1999 and (C) during the transit to
the main study area during both cruises. The letters U
(Urunga), SC (Smoky Cape), PP (Point Plomer), DH (Diamond
Head), CR (Crowdy Head), SCR (South Crowdy), CH (Cape
Hawke), BI (Broughton Island) and PS (Port Stephens) denote
the regions sampled during the study. The size of the symbols
corresponds with the magnitude of abundance of Noctiluca.
Black arrows denote the greatest number of Noctiluca cells
determined by the underway sampling. The thick black line
denotes the position of the East Current (EAC) front
72 Hydrobiologia (2008) 598:59–75
123
phytoplankton prey of Noctiluca was sufficiently
abundant, yet a lower average abundance of Noctil-
uca was still observed in the summer (Fig. 7a, d).
The alongshore and vertical distribution patterns
of Noctiluca observed during the summer also appear
to provide support for the temperature hypothesis.
For example, we observed a marked (6�C) decrease
in the temperature of the surface water layers south of
the EAC separation point. This large temperature
difference was not observed in the corresponding
scenario during the spring cruise (E2), when water
temperatures in areas north of the EAC separation
point were below 25�C, and also only 0.7�C warmer
than that south of the EAC separation. During the
night sampling on the summer cruise we found a
relatively high abundance of Noctiluca in the cooler
deeper waters of the near shore zone at Urunga,
Smoky Cape and Point Plomer, unlike during the
spring, when Noctiluca was most abundant in the
upper 25 m of the water column (data not shown).
Also of note was the relatively greater abundance of
Noctiluca at night compared to the day. This
difference may be related to the nocturnal feeding
and reproductive strategies of Noctiluca (review
Elbrachter & Qi, 1998). When Noctiluca feeds at
night it tends to sink as its cell vacuoles fill with food
(Omori & Hamner, 1982; Uhlig & Sahling, 1990;
Buskey, 1995). Thus, the cell division rates of
Noctiluca might have been optimal at depth at
Urunga, Smoky Cape and Point Plomer as the cells
would not have only been in cooler waters (\25�C)
but would have also had access to the subsurface
phytoplankton blooms (Chl a up to 2.5 mg m–3).
There have been very few reports of Noctiluca red
tides north of the EAC separation point (Ajani et al.,
2001) where average summertime SSTs are above
25�C. One study on Noctiluca in the higher latitudes
of the east coast of Australia (27.5�S, 153�, Moreton
Bay, Queensland) showed that Noctiluca was a
dominant component of the plankton (Heil et al.,
1998). However, the authors suggested that the
plankton communities that were sampled during their
study may not have been typical because the samples
were collected during a one-in-twenty year flood
event (Heil et al., 1998). In addition, the study was
conducted during the austral winter when water
temperatures in Moreton Bay are known to be as low
as 15�C (pers. com. S. Albert, University of Queens-
land). The lowest temperature at which local
populations of Noctiluca exist is presently unknown
but recent reports describe a growing number of
blooms of Noctiluca in the cooler waters of the
Tasman Sea as far south as 42�S (e.g. Albinsson,
2005). Growth of Noctiluca at the lower temperature
ranges may be indeed be optimal as suggested by
recent studies conducted in Japan and the North
Adriatic Sea (Fonda-Umani et al., 2004; Miyaguchi
et al., 2006). These recent studies as well as our
observations of Noctiluca along the east coast of
Australia point to the likelihood that temperatures
below 25�C are optimal for growth of Noctiluca but
also highlight a need for culturing studies to deter-
mine the temperatures that promote optimal cell
division of local populations.
In summary, we sampled during six upwellings
and found that during each upwelling Noctiluca was
relatively abundant within the upwelled waters. We
find that areas of relatively high abundance of
Noctiluca along the NSW coast may be predicted
based on the location of topographically induced
upwellings. We also find that the absolute abun-
dance of Noctiluca in these upwelled waters is likely
to vary over time as well as vary among upwelling
locations depending on the speed, direction and
temperature of the EAC. It is likely that the
abundance of Noctiluca in upwelled waters north
of the EAC separation point will be lower than south
of the EAC separation point, especially during the
austral summer. This is because the relatively faster
currents north of the EAC separation point may
advect the cells southward and/or offshore, and the
warmer surface water temperatures may limit growth
or survival of Noctiluca. These observations high-
light the dynamic physical–biological interactions
that make it difficult to resolve the spatial and
temporal variability in the abundance of Noctiluca
within coastal ecosystems. If our sampling was not
at the scale of these oceanographic processes, we
may not have resolved the variability in the
abundance of Noctiluca between 30 and 33�S.
Acknowledgements The authors thank the crew and captain
of the RV Franklin, and the scientific crew from the
Commonwealth Scientific and Industrial Research
Organisation, for providing us with their relentless and
enthusiastic support in the collection of this data. We also
thank the scientific crew members from the University of New
South Wales and the New South Wales Environment
Protection Authority, especially Moninya Roughan, Augy
Hydrobiologia (2008) 598:59–75 73
123
Syahailatua, Richard Piola, Greg Nippard, David Ghisolfi,
Anne-Marie Wong and Penny Ajani. We thank Steve Rutten
and Matthew Taylor for their assistance in the analyses of field
samples. This project was funded by the Australian Research
Council through grants to Iain Suthers and Jason Middleton,
and by an Australian Postgraduate Award (Industry) to Jocelyn
Dela-Cruz.
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