Transcript Wednesday_1_REISS_ICESOCC_ZOOPLNKTON.pptx

Chlorophyll – a (mg m-3)
Acoustic krill Biomass (g m-2)
How and when are meso-plankton important in
the carbon cycle of the Southern Ocean
Most studies have shown that micro zooplankton consume about 6070% of PP in Southern Ocean (Calbet and Landry 2004)
Both Krill and Salps can be important, Salps more so than Krill
(Dubischar and Bathmann 1997, Pakhomov et al. 1997, Perissinotto et
al. 1997; Bernard et al. 2013)
Recent studies have argued that krill were important in both DOC and
Iron recycling
Iron 0.2 to 4 ng L-1 Day-1 krill (Tovar-Sanchez et al. 2007)
krill excretion (not just NH4) influences bacterial production
(Arestigu et al. 2014 PLOS; Ruiz-Halpern et al. 2014)
Questions
What does variability in the main species look like in time and in space
What are the impacts of principal taxa on productivity in US AMLR
area
How do these impacts vary when using acoustic estimates instead of
nets
How does winter summer differences impact our thoughts about
system
Krill/Ice/Salp Interactions
Krill
600
(no. m^-2
Salp density
0.6
400
0.4
200
0.2
Krill density
(no 100m^-3)
Salp
Krill proportional
recruitment
0.8
0
0
875
1750
2625
3500
12
11
Year
10
9
8
Month
Ice
7
6
5
4
3
Sea ice extent
10^6 km^2
2
1
79
81
83
85
87
89
91
Year
93
95
97
99
01
03
Loeb et al. 1997
Krill decline means a potential change in
grazing and cycling of carbon and iron
12
11
Year
10
Krill density has declined 80% since mid
70’s
8
7
6
5
4
3
Sea ice extent
10^6 km^2
2
1
79
81
83
85
87
89
91
93
95
97
99
01
Year
Correlated with ice decline
03
Ice dynamics are important but what will
dynamics be if ice is no longer
important?
1000
Krill Density (no. m^2)
Month
9
100
Phytoplankton community is changing
10
Atkinson et al. (2004)
2004
2000
1996
1992
1988
1984
1980
1976
1
US AMLR Survey Grid
Program examines the dynamics of
krill, zooplankton and higher
predators in relation to krill fishery
Scotia
Sea
Drake
Passage
From 1990 to 2011 mostly two
surveys per summer.
Latitude
ACC
Net tows (1.8m IKMT, 500 um net)
To 170m, at ~100 stations leg
Bransfield
Strait
Full CTD to 750m. Bottles at 11
standard depths
Weddell Sea
3 frequency acoustic models for
estimation of krill and myctophids
Longitude
Since 2012 Switched to winter
(August – September)
How does productivity vary
spatially and interannually?
10 yr SeaWiFs mean
•Production in the SSI exhibits distinct
(low-high-low) spatial structure
•AMLR sampling recovers spatial
structure
•Pattern typical of High nutrient low
chlorophyll areas (Drake)
Ecosystem productivity
80
A
60
2
Iron, nM
Silicate, µM
Pattern of macronutrients is
rather conservative and
increase with salinity
B
40
1
Dissolved iron exhibits
similar relationship with
20
0
0
33.4
33.8
34.2
33.4
33.8
34.2
0
8
Light (UML depth) limits
production
-3
25
50
log Chl-a, mg m
Depth of UML, m
D
X 1000
C
75
6
100
33.4
33.8
34.2
Salinity
salinity (Weddell shelf
source)
4
33.4
33.8
34.2
Salinity
Hewes et al. 2008
Production maximal at
intermediate salinity
Ecosystem productivity
Peak in chl-a biomass may be
competition between UML depth
and iron concentration
0
B
25
2
Iron, nM
Depth of UML, m
C
50
Explains intermediate peak
1
75
100
33.4
33.8
0
33.4
34.2
33.8
Salinity
7.0
34.2
Explains low biomass in
Bransfield
Explains low biomass in ACC
6.0
Does UML depth explain
temporal variability
5.5
Observed
Predicted
5.0
Mean salinity
34.3
34.2
34.1
34
33.9
33.8
33.7
4.5
33.6
Log chla
6.5
Moving on to krill and mesozooplankton
Joinville Island Area - 18000 km2 – influenced by Weddell
Bransfield Strait – 24, 000 km2. Has distinct oceanographic features
West Area – 38 000 km2. Most influenced by ACC
Elephant Island – 48000 km2, sampled since 1977. Longest time series
Temporal variability in primary production
37.5
75.0
112.5
AREA
EI
JI
SA
WA
Winter
0.0
Integrated chl-a_100m
150.0
Significant interannual
variability
Year
Integrated and UML
chl-a highly correlated
Correlated across areas
Copepods (no. m-2)
1000
0.0664x
y = 4.5586e
R² = 0.53
100
10
1
0
10
20
30
40
50
60
Krill (no. m-2)
100
1000
100
0.0551x
y = 1.1436e
R² = 0.27
10
1
0
10
20
30
40
50
60
Integrated Chlorophyll-a (mg m-2)
10
1
Krill Larvae (no. m-2)
Temporal variability in production drives
spinup of planktonic system
What is impact of krill on chlorophyll-a?
0
10
20
30
40
50
60
Integrated Chlorophyll-a (mg m-2)
Grazing rates in LTER area
(Bernard et al. 2013)
Temporal variability in Grazing rates
Percent of Standing Stock Chl-a in AMLR area
30
0.25
Salps
Krill
0.2
20
0.15
15
0.1
10
0.05
5
0
1985
0
1990
1995
2000
2005
2010
2015
Percent SS by Krill
Percent SS by Salpsl
25
Tons of Krill
Time series of acoustic biomass in AMLR Region
1E+07
Order of magnitude
differences within
areas between years
1E+06
Biomass uncorrelated
with chl-a reflects
different time and
space scales of
production
1. E+05
1E+04
1994 1996 1998 2000 2002 2004 2006 2008 2010 2012
Year
Differences in acoustic and net based estimates
Suggest bias in ecological role of krill
Krill (number m-2)
1000
Acoustics
Nets
100
10
1
0.1
1995
Order of magnitude
differences in
abundance between nets
and acoustic estimates
of density
Substantial
underestimation of
abundance by nets
2000
2005
Year
2010
2015
Estimates of Grazing rates as a Percent of Standing Stock
For acoustic estimate of krill density
18
Percent SS chla day-1
18
16
Acoustic based
16
14
Net-based
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
1990
1995
2000
Year
2005
2010
2015
A more realistic role for krill in remineralization?
30
30
Salps
Percent SS by Salps
25
Acoustics
20
20
15
15
10
10
5
5
0
1985
1990
1995
2000
2005
2010
0
2015
Percent SS by Acoustics
25
Questions
How badly are we underestimating production?
How do we cover space and time?
Winter Cruises (2012 -2016)
(August – September)
2012
2013
2014
Winter Cruises (2012 -2016)
(August – September)
E. superba
3500
2625
AREA
EI
JI
SA
WA
1750
875
0
T. macrura
250
200
150
100
50
Summer Winter
Season
Winter Cruises (2012 -2016)
(August – September)
Tons of Krill
1E+07
1E+06
1. E+05
1E+041994199619982000200220042006200820102012
Year
520 Kt
Concentration of Krill biomass
BIOMASS (M tons)
Area
EI
WA
SA
Summer
3.1
2.1
0.5
Winter
0.065
0.14
2.9
Krill biomass was
concentrated 50% of mean
summer biomass in 20%
of sampling area.
Condition of Krill (how do they get food)
Summer
Winter
Thoughts
Decoupling of primary production and krill and salp dynamics
Suggests that simple response krill / salp ratios are probably
incorrect – this matters to thoughts of when where contribution is
high
Current estimates of grazing pressure by krill are most likely low by
an order of magnitude - does this matter to Bio-geo-chemical
models
Winter conditions could serve as a baseline metabolism for the
mesozooplankton not contaminated by chl-a or by krill
Super concentration of krill in areas during winter has implications
for local regional ideas of bacterial and micro-zooplanktonic roles
in upper water column
Is the future of the Antarctic one of krill decline
And increased food chain length
Alternate pathways in
part of the Scotia Sea
food web, showing
shifts between (a)
years when krill are
abundant across the
Scotia Sea and (b)
years when krill are
scarce.
Murphy E et al. Phil. Trans. R. Soc. B 2007;362:113-148
Chlorophyll – a (mg m-3)
Acoustic krill Biomass (g m-2)
Variability in time and in space
1000
1000
100
100
10
10
Series2
Series1
Series2
Series1
1
1985
1990
1995
2000
2005
2010
2015
1
1985
0.1
0.1
1000
1000
100
100
10
10
1990
1995
2000
2005
2010
2015
Series2
Series1
1
1985
1990
1995
2000
2005
2010
2015
1
1995
2000
2005
2010
2015
Series2
Series1
0.1
0.1