RED TIDE AND ANOXIA IN A COASTAL EMBAYMENT OF THE...

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GRANT PITCHER TREVOR PROBYN MAYA PFAFF ED RYBICKI DECLAN SCHROEDER RED TIDE AND ANOXIA IN A COASTAL EMBAYMENT OF THE SOUTHERN BENGUELA UPWELLING SYSTEM

Transcript of RED TIDE AND ANOXIA IN A COASTAL EMBAYMENT OF THE...

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GRANT PITCHER TREVOR PROBYN MAYA PFAFF ED RYBICKI DECLAN SCHROEDER

RED TIDE AND ANOXIA IN A COASTAL EMBAYMENT OF THE SOUTHERN BENGUELA UPWELLING SYSTEM

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EMBAYMENT: ST HELENA BAY Located at the southern end of the Benguela Current Large Marine Ecosystem.

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St Helena Bay is formed by a cape – Cape Columbine – that modulates the upwelling process by influencing across-shelf structure in alongshore flow thereby creating a zone of retention.

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SST – NOAA AVHRR 5-year composite July 98-Jun03

Chl – SeaWiFS 5-year composite July 98-Jun03

The retention zone formed by this embayment also functions to enhance productivity.

Upwelling is intensified within the vicinity of the cape [and also occurs in a narrow band along the northern shores of the bay], but the increased residence time within the bay tends to lead to warming and increased stratification.

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St Helena Bay is plagued by events of mortality – as depicted here by a stranding of 2000 tons of the rock lobster [Jasus lalandii] in April 1997.

During the late 80s and 90s an increase in such events is considered to have led to major changes in the living resources within the bay [including the lobster resource which declined from contributing about 60% to <10% of total lobster landings on the South African coast].

Despite their importance, these events of mortality remained poorly described.

Although it was assumed that they were a consequence of low oxygen linked to red tides there were few observations or measurements to support these assumptions.

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APPARENT CONTRADICTION: typical measures of DO in St Helena Bay show low concentrations to be confined to cold bottom waters, while red tides developed under conditions of downwelling and were associated with warm water and high DO concentrations.

17.5°E 18.0°E 18.5°E

-33.0°S

-32.5°S

-32.0°S

L

N

M

O

34

56

W

Eland's Bay

Cape Columbine

Lamberts BayNortier Station

WW

Bergriver mouth

Dwarskersbos

In recent years we have attempted to answer a number of questions relating to low oxygen in St Helena Bay through initiation of several sampling programmes [to better understand these mortality events].

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Q1: To what extent is oxygen depletion in bottom waters confined to the bay [driven by local biological consumption triggered by high productivity]?

Examined the temperature-oxygen regime of St Helena Bay by sampling stations W, 3,4,5,6 at approximately monthly intervals from November 2008 to November 2011.

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W

3

4

5

6

Temperature [oC]

Temperature: individual profiles in grey and mean profiles in black.

Variability is highest inshore, in association with a narrow band of upwelling. There is a marginal warming of surface waters, and a more notable cooling of bottom waters, moving offshore, in association with increased stratification.

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Moving offshore, mean surface oxygen concentrations remained similar, but bottom oxygen concentrations show a clear minimum at station 3 [within the bay] – here the mean oxygen concentration was ~1 ml l-1, with many profiles depicting notably lower concentrations. In deeper waters outside of the Bay, bottom oxygen concentrations in colder, mid-shelf waters were shown to increase. These observations pointed to a deep pool of oxygen depleted water confined to the bay.

W

3

4

5

6

Temperature [oC] DO [ml l-1]

Dissolved Oxygen: similarly showed high variability inshore, in both surface and bottom waters.

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d)

4

3.5

3

2.5

2

1.5

DO

(m

l l-1

) W

3

4

5 6

2008-11

A three-dimensional plot of bottom DO along the transect over time showed seasonal expansion/contraction of the deep-water pool of low-oxygen water [the lowest concentrations occurring at station 3 in autumn]. Considered these data to indicate that low oxygen waters in St Helena Bay were a consequence of local depletion driven by high bay productivity.

St Helena Bay deep-water low-oxygen pool

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Q2: Is there any evidence of long-term change in the bottom pool of low oxygen water in St Helena Bay? [as the cause of recent declines in the lobster resource]

To assess long-term change in St Helena Bay: compared our recent measures of bottom temperature and DO at stations W, 3, 4, 5 and 6, to monthly data collected at stations M, N, L and O between 1957 and 1962 [50 years ago].

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Mean bottom temperatures were shown to follow a coherent across-shelf trend [declining with increasing depth, with minimum values outside of the bay].

W M ST3 N ST4 L St5 O St6

6

8

10

12

14

16

18

Te

mp

era

ture

(oC

)

a)

In combining the data sets [for the comparison] stations were ordered [on the x-axis] according to water depth.

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W M ST3 N ST4 L St5 O St6

6

8

10

12

14

16

18

Te

mp

era

ture

(oC

)

a)

W M St3 N St4 L St5 O St60

1

2

3

4

5

6

7

8

Dis

so

lve

d O

xyg

en

(m

l l-1

)

b) However DO concentrations were lowest toward the center of the bay (at St3, 70m), where they exhibited low variance. Outside of the bay DO concentrations increased with increasing depth toward the mid-shelf. The coherence of the recent and historic data in demonstrating these cross-shelf trends suggests the absence of any long-term trend in either temperature or DO.

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c)

4

3.5

3

2.5

2

1.5

O

DO

(m

l l-1

)

L

N

M

1957-62

d)

4

3.5

3

2.5

2

1.5

DO

(m

l l-1

)

W

3

4 5

6

2008-11

Three-dimensional plots of the data [1957-62 and 2008-11] showed remarkable similarity [both spatially and seasonally]. Any differences are likely to be attributed to the comparison of data from different station positions and depths [e.g., the greater seasonality evident in the recent data is a likely result of the inclusion of data from a shallower depth].

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Q3: How does this bottom pool of low oxygen water impact the nearshore (<20m)? [the habitat of the lobster resource]

To address this question we maintained a bottom mooring including a WET Labs Water Quality Monitor at 19 m depth. The mooring was located off Eland’s Bay [the site of many mortalities] and maintained for a period of 3 years [Nov 2008 – Nov 2011].

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Nearshore time series of bottom DO concentrations [station W] was shown to exhibit significant temporal variability closely linked to the physical environment as represented by bottom temperature.

D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N0

2

4

6

8

10

12

14

16

18

D

O (

ml l-1

)

Te

mp

(oC

)

2009 2010 2011

The close correlation of bottom oxygen with temperature is driven by advection, with oxygen minima clearly linked to upwelling events, while episodes of bottom oxygenation occurred in association with downwelling events or winter mixing.

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D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N0

2

4

6

8

10

12

14

16

18

D

O (

ml l-1

)

Te

mp

(oC

)

2009 2010 2011

General tendency for DO concentrations to decrease during the course of the upwelling season; minima in autumn [concentrations declined to <0.2 ml l-1].

The threat posed by increasingly low DO concentrations during the upwelling season was terminated by wind reversals associated with winter – the consequent mixing as is evident from the temperature records lead to abrupt ventilation of bottom waters.

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9 10 11 12 13 14 15 16 17 18 19

Temperature (oC)

0

1

2

3

4

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8

Dis

so

lve

d o

xyg

en

(m

l l-1

)

All data y = -8.83 + 1.00x; r2 = 0.71

The close relationship between bottom temperature and DO concentration [at station W] is depicted by this positive correlation.

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Isolation of November and December data, when upwelling was most intense, showed temperatures to be lower, and the DO concentrations to be higher than predicted by the linear fit;

while isolation of March and April data, toward the end of the upwelling season, showed temperatures to be warmer, and the DO concentrations to be lower than predicted by the linear fit.

However this relationship varies seasonally:

9 10 11 12 13 14 15 16 17 18 19

Temperature (oC)

0

1

2

3

4

5

6

7

8

Dis

so

lve

d o

xyg

en

(m

l l-1

)

All data y = -8.83 + 1.00x; r2 = 0.71

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As an example, the predicted DO concentration for 10 oC water for November and December is 1.58 ml l-1, while for March and April it is 0.34 ml l-1. These findings tend therefore to indicate a seasonal decline in the bottom oxygen content of St Helena Bay of 1̴.2 ml l-1 during the course of the upwelling season.

9 10 11 12 13 14 15 16 17 18 19

Temperature (oC)

0

1

2

3

4

5

6

7

8

Dis

so

lve

d o

xyg

en

(m

l l-1

)

All data y = -8.83 + 1.00x; r2 = 0.71

Nov-Dec data y = -6.52 + 0.81x; r2 = 0.81

Mar-Apr data y = -9.66 + 1.00x; r2 = 0.90

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The habitable nearshore zone is influenced by:

1] the seasonal decline in DO concentrations in the deep water pool, 2] the seasonal expansion of the pool, and 3] by incursions of this water into the nearshore environment as dictated by the upwelling-downwelling cycle.

Habitat compression is therefore likely during late summer and autumn as determined by the depth of the thermocline and corresponding oxycline, and their intersection with the nearshore zone.

However, this seasonally persistent hypoxia in bottom waters did not appear to be the cause of significant mortalities.

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Q4: Are red tides the cause of the large mortalities in St Helena Bay?

In recent years made use of satellite derived ocean colour radiometry to track the development and impact of red tides.

European space agency’s Envisat-1 Medium Resolution Imaging Spectrometer [MERIS].

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16 Feb 09 14 Mar 09 11 Apr 09 1 May 09

17.56 oE 18.36 oE 17.56 oE 18.36 oE 17.56 oE 18.36 oE 17.56 oE 18.36 oE

31.44 oS

32.32 oS

Initial build-up of the bloom was observed in February in the northern reaches of the bay.

By March the bloom was shown to extend in a narrow band over a distance of >100 km.

Diminished upwelling and the development of inshore counter currents result in the southward progression of the bloom.

In early May the bloom was shown to accumulate in the shallow, southern reaches of the bay and on the 5th May large fish and lobster mortalities were observed.

Example: 2009 tracked a bloom dominated by the dinoflagellate Ceratium balechii.

2009

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The mortality confined to a 16 km stretch of shoreline between the Berg River mouth and Dwarskersbos – 14 stations sampled on 5 May 2009.

Bottom oxygen concentrations on 5th May 2009.

The bottom oxygen regime within the Bay was shown to exhibit extreme alongshore variability with oxygen concentrations in the vicinity of the mortality severely depleted [as depicted by the size of the bubble]. At both the shallow stations 3 and 4 [<5m depth] DO concentrations through the entire water column were <0.1 ml l-1.

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Surface concentrations Ceratium balechii

Bottom oxygen concentrations

Those stations in the vicinity of the mortality [were oxygen concentrations were lowest] contained few distinguishable Ceratium cells, but large quantities of phytodetrital matter, providing evidence of a large oxygen demand created though heterotrophic degradation of an exceptionally high carbon load.

Surface phytoplankton concentrations revealed similar variability with high concentrations of Ceratium balechii at those stations where oxygen concentrations were elevated.

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Decay tends to follow accumulation of the bloom in shallow nearshore environments under conditions of strong downwelling.

An intense front is established by inshore oxygen demand which indicates limited lateral exchange with oxygenated surface waters further offshore [this biologically-driven front is established independent of any density gradient].

The exceptional phytodetrital production associated with red tides, and the reduced volume of water within the confines of this shallow environment, result in the depletion of oxygen through the entire water column.

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Of importance in the prediction of these events of anoxia is determination of the transition to bloom decay.

Consider the inaccessibility of sub-thermocline nutrients to be a primary contributor to bloom decay in these warm nearshore waters. Determination of uptake rates for nitrate [NO3] and ammonium [NH4] measured using 15N incorporation indicate the exhaustion of the nutrients in these waters in <3 hours [although conclusion ignores probable recycling of NH4 and possible diffusion of NO3 ].

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Also of possible relevance in the decay of the bloom were the presence of active viruses of the family Phycodnaviridae [those that specifically infect eukaryotic algae].

Bp

V1

78

LdMNPV

80

Poxviridae

Baculoviridae

Asfarviridae

Iridoviridae

Herpesviridae

Coccolithovirus Prymnesiovirus

Phaeovirus

Prasinovirus

Chlorovirus

These large dsDNA viruses [labelled EB] were analysed in bloom events and classified by analysis of the DNA polymerase gene.

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Estimates of microzooplankton grazing rates [determined by the dilution method, d-1] provided evidence of a further contributor to heterotrophic degradation of the blooms.

Polykrikos schwartzii

Gyrodinium spirale

Particularly high estimates of microzooplankton grazing were attributed to the presence of high concentrations of large heterotrophic dinoflagellates .

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To conclude:

Mass mortalities in St Helena Bay, appear to result from episodic events of anoxia linked to the inshore decay of exceptional phytoplankton blooms [red tides]; events that appear unrelated to the seasonal development of hypoxia in cold bottom waters.

The transient and localized scale of episodic events of anoxia within the Bay contribute to the challenge of monitoring and predicting these events.

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In addition to seasonally persistent hypoxia in the bottom waters of St Helena Bay, episodic anoxia may occur throughout the water column of shallow, non-stratified, nearshore environments following the decay of red tides accumulated under conditions of strong downwelling.

Bloom decay is driven by the inaccessibility of sub-thermocline nutrients and low oxygen concentrations are observed in warm water.

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The exceptional phytodetrital production associated with the decay of red tides, and the reduced volume of water within the confines of the shallow nearshore environment, result in the depletion of oxygen through the entire water column.

These events of shallow water anoxia are likely to be maintained only under benign weather conditions [as wind-induced mixing or wave action will lead to their termination]. The transient and localized scale of episodic events of anoxia within the Bay contribute to the challenge of monitoring and predicting these events.

An intense front is established by inshore oxygen demand which indicates limited lateral exchange with oxygenated surface waters further offshore. This biologically-driven front is established independent of any density gradient.

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Bp

V1

78

LdMNPV 80

Poxviridae

Baculoviridae

Iridoviridae

Asfarviridae

Herpesviridae

Coccolithovirus Prymnesiovirus

Phaeovirus

Chlorovirus

Prasinovirus

Key: EB – Elands Bay (bracketed number) – Number of clones with similar DNA sequences UPV – Unknown Phycodnavirus (followed by accession number)

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Result Summary Kathryn Morrissey MSc Thesis

Large dsDNA viruses were analysed in a bloom event that occurred in Elands Bay in 2013. Viruses identified were classified to reside within the Phycodnaviridae family by analysis of the DNA polymerase gene. Majority of sequences were found to be within the Prymnesiovirus genera, represented by EB 1.1, EB 1.2 and EB 1.3 in fig. 1. Viruses related to the Coccolithovirus and Prasinovirus genera were also present, EB 3 and, EB 4 and EB 5 respectively (Fig.1 ). Another group was identified with closest genetic resemblance to the Herpesviridae family, represented by EB 2 (Fig. 1). Viruses EB 1.1, EB 1.2 and EB 2 show significant separation from relative groups with bootstrapping values >90%. This indicates new virus clades of Phycodnaviridae identified.

Figure 1. Phylogenetic tree produced using Mega 5 software. Phylogeny was determined using Nearest Neighbour Interchange heuristic method, with 500 bootstrapping replications. Branch length cut off for bootstrapping was set at <50%

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In addition to the 24-hour incubation of BOD bottles….

….which provide only initial and end point measurements of O2….

….we also incubated 10 L light and dark polycarbonate carboys….

….into which we inserted these RINKO‐I fast‐response, high‐resolution oxygen sensors [based on an optical phosphorescence principle] able to provide continuous measures of O2 fluxes within the carboys.

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9h 12h 15h 18h 21h 24h 3h 6h 9h 12h 15h 18h 21h 24h 3h 6h 9h-80

-40

0

40

80

120

160

200

240

O2 P

rod

uctio

n (

µm

ol l-1

)

m = NP

13.7 µmol l -1 h-1

(a)

LB 127 µmol l-1

DB -21 µmol l-1

m = dark R

0.9 µmol l -1 h-1

m = night R

2.9 µmol l -1 h-1

Comparison of the results as obtained from the 1] BOD bottles and Winkler titrations, and 2] the polycarbonate carboys and Rinko sensors [incubated 21 January 2013].

+ represents the increase in O2 in the light BOD bottle

+ represents the decrease in O2 in the dark BOD bottle [after 24 hours] ….these data compare favourably with the continuous measures of O2 as provided by the Rinko sensors in the

light ------- and dark ------- carboys.

The slopes of the lines fitted to the Rinko data provide direct estimates of: 1] net production during the day, 2] respiration during the night, and 3] respiration in the dark bottle.

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To further conceptualize these episodic events of anoxia we reviewed data we have collected following a similar mortality in April 1998 [also in the region of Dwarskersbos].

At the time of this mortality 3 transects were sampled in the St Helena Bay region.

Ceratium balechii

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Lambert’s Bay Elands Bay Dwarskersbos

Conditions were strongly stratified; notable downwelling off Dwarskersbos.

Inshore pH levels were also exceptionally low (6.6) confirming high rates of heterotrophic respiration and the oxidation of organic material.

Off LB and EB good correspondence of inshore fluorescence and oxygen maxima indicated the presence of a healthy bloom; here low oxygen was confined to cold bottom waters. Off Dwarskersbos high inshore fluorescence coincided with a zone of severe oxygen depletion [extending to only 10m] providing evidence of bloom decay.

High inshore fluorescence demarcated a narrow band of red tide.

0102030

DISTANCE (km)

0

50

100

0102030

DISTANCE (km)

0

50

100

051015

DISTANCE (km)

0

10

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30T T T 0

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30

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30

0

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30F F F 0

50

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0

50

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30O O O 0

50

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0

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30pH pH pH

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Knowledge of bloom dynamics in bays has also contributed to understanding the mechanisms impact [Pitcher and Probyn 2011]. In St Helena Bay able to distinguish two categories of oxygen-deficient waters are evident in the nearshore environment of St Helena Bay: 1] Seasonally persistent hypoxia 2] Episodic anoxia .

F: How does coastal morphology and bathymetry affect HAB dynamics in upwelling systems?

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Satellite observations provide a useful tool in tracking bloom development in association with various coastline configurations. Bernard et al. [submitted] track the development of a Ceratium balechii bloom and consequent anoxia. Bloom was initially observed to the north of St Helena Bay, but under diminished upwelling activity inshore counter currents resulted in its southward progression. Entrainment into the shallow, southern reaches of the Bay, where subthermocline nutrients, necessary for bloom maintenance are inaccessible, resulted in bloom degradation and anoxia with consequent mortalities. Surveillance as depicted here enables continual assessment of the risk posed by these blooms to marine resources and the coastal environment.

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Approach This study will seek to establish the nature of mass, episodic phytoplankton mortality within HABs leading to the transfer of organic matter to the heterotrophic microbial community. Specifically we will attempt to quantify micro-zooplankton grazing, virus-mediated cell lysis and programmed cell death, as plankton mortality processes.

Dr Pierre Durand Molecular Medicine and Haematology, University of the Witwatersrand

“Ecology and evolution of programmed cell death in the microbial world”

CONCEPT PAPER: LINKAGES BETWEEN HARMFUL ALGAL BLOOMS AND ANOXIA

Problem • In contrast to the efforts to establish the conditions, mechanisms and strategies that control

phytoplankton cell growth and bloom development, considerably less effort has focused explicitly on phytoplankton mortality.

• To date our studies have focused on the role of nutrient input and limitation in bloom development and demise rather than the role of microbial activity in carbon transformation and oxygen consumption.

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D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S ON

0

2

4

6

8

10

12

14

16

18

20

S

I (o

C)

T (

oC

)

(a)

(b)

D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N

2009 2010 2011

0

20

40

60

80

100

120

140

160

Ch

l a

(m

g m

-3)

(c)

Estimates of phytoplankton biomass followed the general seasonal trend of the stratification index: following winter minima, Chl a concentrations increased after the transition to spring and peaked in summer/autumn. The exceptional dinoflagellate blooms [red tides; Chl a >100 mg m-3] present in 2008-09 were absent during the years of reduced upwelling [2009-10 and 2010-11] and strong downwelling.

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Seasonality is clearly evident, upon which a strong temperature signal at the event scale is superimposed.

Physical characterization of the nearshore environment is provided by sea temperature at 5 and 20 m off Elands Bay, and a stratification index derived from the difference between these measurements.

D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S ON

0

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6

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18

20

S

I (o

C)

T (

oC

)

(a)

(b)

2009 2010 2011

Amplitudes in temperature following winter mixing are weakest and the stratification index is lowest.

Transition to the upwelling season is associated with the cooling of bottom waters and warming of surface waters causing the stratification index to peak in late summer/autumn.

S W W S S S W

Seasons of reduced upwelling are characterized by high stratification owing to extended periods of mid-season relaxation or reversal of upwelling winds and the introduction of warm [>18 oC] nutrient depleted water into the bay.

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Bottom temperatures and DO concentrations at station 3, obtained from a bottom mooring deployed from 7 February - 8 November 2012, depict the relative stability of the bottom waters of St Helena Bay.

During late summer and autumn temperatures varied by only 0.60 oC at which time DO concentrations were maintained at < 1.56 ml l-1 with a minimum of 0.12 ml l-1 in April. With the onset of winter, deep mixing caused a notable increase in both temperature and DO reaching maxima of 11.96 oC and 5.43 ml l-1 in late August.

With the transition to spring temperatures declined with the onset of upwelling and DO concentrations showed a similar trend. During mid-October following three weeks of intense upwelling, particularly cold waters were introduced into the Bay with temperatures declining to 7.91 oC. These waters were characterised by notably higher DO concentrations and are considered to originate from the mid-shelf region.

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Assessment of long-term change through comparison with dissolved oxygen data collected from June 1957 – December 1962. de Decker [1970]

St Helena Bay monitoring line: Stations 3 – 6 sampled at monthly intervals from Nov 2008 – Nov 2011.

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J A S O N D J F M A M J-8E6

-6E6

-4E6

-2E6

0

2E6

4E6

6E6

8E6

1E7

1.2E7

1.4E7

1.6E7

1.8E7

2E7

2.2E7

N d

isp

lace

me

nt (k

m)

08-09

09-10

10-11

11-12

Provide within season indices of the spring transition, the intensity and evolution of upwelling, and the duration of upwelling.

Wind Regime: Annual wind variability depicted by cumulative upwelling winds represented by a summation of the north component of winds from 1 July to 30 June each year [have an accumulative effect on ecosystem productivity and structure] .

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2008-09 initially characterised by strong downwelling prior to the spring transition to upwelling winds in mid-September, intense upwelling winds were observed for the following 7 months (cumulative N displacement 1.9x107 km), except for 2 week reversal during December-January 2009-10 defined by a longer upwelling season of less intense upwelling (cumulative N displacement 1.6x107 km), notable reversal/relaxation of winds in November-December and during March 2010-11 was noted by a further decline in upwelling winds (cumulative N displacement 1.1x107 km), particularly for the period December-March 2011-12 characterised by initial period of very moderate downwelling followed by an extended upwelling season of intense upwelling (cumulative N displacement 2.2x107 km).

J A S O N D J F M A M J-8E6

-6E6

-4E6

-2E6

0

2E6

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N d

isp

lace

me

nt (k

m)

08-09

09-10

10-11

11-12

The phasing of seasonal wind forcing contributed to a 2-fold inter-annual variance in the cumulative wind stress over the 4-year period of interest.

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Satellite derived ocean colour radiometry was used to assess influence of wind variability on bay-scale productivity.

The development of high biomass, particularly during late summer and early autumn, typified seasons of higher cumulative upwelling winds (2008-09 and 2011-12). The dominance of dinoflagellates at this time led to the development of extensive red tides in early 2009 and 2012.

The absence of red tides in 2010 and 2011 followed seasons of reduced cumulative wind stress (2009-10 and 2010-11). Extended periods of mid-season relaxation appear to retard the development of high biomass blooms.

MERIS images captured between November 2008 and April 2012 were used to establish a time series of spatially averaged Chl a concentrations obtained within a 10km radius of station W.

D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M

2009 2010 2011

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atia

lly A

ve

rag

ed

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l a

(m

g m

-3)

-08 2009 2010 2011 -12

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April 1998 May 2009

Sampling of anoxia linked to events of red tides: profiles of temperature, dissolved oxygen, fluorescence and pH.

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Anoxia and associated events of mortality in 2012 occurred intermittently over several weeks. Initially mortalities were recorded in late March north of Lambert’s Bay and spread southward to the Berg River region by mid-May.

24 Feb 12 5 Mar 12 19 Mar 12 2 Apr 12

17.56 oE 18.36 oE 17.56 oE 18.36 oE 17.56 oE 18.36 oE 17.56 oE 18.36 oE

31.44 oS

32.32 oS 2012

In 2012 the bloom was dominated by Ceratium furca.

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6 8 10 12 14 16 18

Temperature [oC]

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]

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a)

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2008-11

Three-dimensional plots of monthly temperature for the periods 1957-62 and 2008-11 are also similar, except for the warmer inshore waters in the 2008-11 plot owing to the inclusion of data from the shallow inshore station W.