Increased sea ice cover disrupts food web structure in Antarctic … · 2017-07-05 · 12th SCAR...

Increased sea ice cover disrupts food web structure in Antarctic coastal benthic ecosystem

Loïc N. MICHEL, Bruno DANIS, Philippe DUBOIS, Marc ELEAUME, Jérôme FOURNIER, Cyril GALLUT, Philip JANE & Gilles LEPOINT

Contact: [email protected]

12th SCAR Biology Symposium – 10-14/07/2017 – Leuven, Belgium

Sea ice in Antarctica

Image: NASA

Sea ice is a major environmental driver of ecological processes in Antarctica

▪ Water column mixing▪ Benthic-pelagic coupling▪ Niche partitioning▪ Benthic community

structure▪ …

Sea ice in Antarctica

Image: NASA

Sea ice is a major environmental driver of ecological processes in Antarctica

▪ Water column mixing▪ Benthic-pelagic coupling▪ Niche partitioning▪ Benthic community

structure▪ …

Sea ice is a highly dynamic system

Seasonal patterns of sea ice cover

Normal cycle:

Source: NOAA

Austral summerThinning and breakup of sea ice

Austral winterThick sea ice cover

Changes in Antarctic sea ice cover

From King (2014), Nature 505: 491-492.(Data 1979-2012)

Spatial extentChanges in sea ice concentration

Climate change causes contrasted changes in sea ice cover in Antarctica

Changes in Antarctic sea ice cover

From King (2014), Nature 505: 491-492.(Data 1979-2012)

West Antarctic Peninsula

From Massom & Stammerjohn (2010), Pol . Sci. 4: 149-186(Data 1979 -2004)

Spatial extentChanges in sea ice concentration

Temporal extentChanges in sea ice season duration

Climate change causes contrasted changes in sea ice cover in Antarctica

Study site: Dumont d’Urville station

East Antarctica, Adélie LandPetrels Island

Austral summer 2007-08

Study site: Dumont d’Urville station

East Antarctica, Adélie LandPetrels Island

2013-2015: Event of high spatial and temporal sea ice coverage

No seasonal breakup during austral summers 2013-14 and 2014-15



Study site: Dumont d’Urville stationTime of sampling : Austral summer 2014-15

This is the sea(Please trust me)

Study site: Dumont d’Urville stationTime of sampling : Austral summer 2014-15

This is the sea(Please trust me)

How will benthic communities respond to sudden changes in sea ice cover?

How could increased sea ice cover impact structure of benthic food webs?

Food web structure in marine ecosystems

Phytoplankton Benthic biofilm + detritus Sea ice algae

Food web structure in marine ecosystems

Resources supporting the consumers

Phytoplankton Benthic biofilm + detritus

Horizontal dimension

Sea ice algae

Food web structure in marine ecosystemsTr

op

hic

po

siti

on

of

the

con

sum

ers




Vertical dimension

Sea ice algae

Food web structure in marine ecosystemsTr

op

hic

po

siti

on

of

the

con

sum

ers




Vertical dimension

Here: models based on trophic markers (stable isotope ratios) were used to as proxies of both food webs dimensions

Sea ice algae

Horizontal dimension: use of a mixing model (SIAR) to identify main food items of consumers

Vertical dimension: use of a trophic position model (tRophicPosition)

Sampling: under ice SCUBA diving

Sampling: food items

1. Sympagic algae

2. Suspended particulate organic matter (SPOM)


3. Benthic brown algae Himantothallusgrandifolius


4. Benthic biofilm (heterogeneous mix of microalgae, bacteria, amorphous material and detrital items)

Some sampled consumersPerkinsiana sp. Flabelligera mundata

Harmothoe sp.

Adamussium colbecki

Marseniopsis sp.

Heterocucumis sp. Sterechinus neumayeri

27

seastar Odontaster validus

Odontaster validus is found throughout Antarctica and the

Antarctic Peninsula, South Shetland Islands, South Orkney

Islands, South Sandwich Islands , South Georgia Island, Shag

Rocks, Marion and Prince Edward Islands, and Bouvet Island at

depths from 0 to 914 meters [7,10,11,12,14]. O. validus is the most

abundant seastar in the shallow shelf waters of Antarctica and is

most abundant from 15 to 200 meters [9]. O. validus has a broad

disc and short arms tapering to blunt tips [7]. O. validus has been

collected at sizes up to seven centimeters in radius from its center

to the tip of an arm [7,11]. O. validus varies in color including dark

brown, purple, purple-red, orange, red-orange, red, brick red, dark

carmine, and pink; it may have light colored arm tips [7,11,14]. O.

validus has a characteristic position with its arm tips slightly raised

[7].

O. validus is usually bright to dull red on the dorsal (abactinal)

surface and yellowish white to pale pink on the ventral (actinal)

surface [16]. O. meridionalis is generally pale brown or yellowish white on the dorsal : surface and lighter on the

ventral surface [16]. Color in both species can be highly variable and is not always reliable as a field character; the

only sure way is to check the number of spines on the actinal plates [16].

Here's a juvenile and adult of Odontaster

validus. Size-frequency distribution of O.

validus can vary with location and is a

reflection of the general level of

productivity of a habitat: at McMurdo

Station, their size and number decrease

with depth; at Cape Evans, they are more

numerous and generally smaller; and, at

East Cape Armitage, they are less

numerous and very small [3]. O. validus is

slow growing; well-fed individuals need

about nine years to reach thirty grams wet

weight which is near the mean size of

shallow-water individuals at McMurdo

Station [3]. Based on its growth rate,

collected sizes, and knowledge from other

seastars, O. validus may live beyond one

hundred years of age, with very low

turnover in a population [17].

Odontaster validus

Ammothea carolinensis

Trophon longstaffi

Hemigellius sp.

Some sampled consumersPerkinsiana sp. Flabelligera mundata

Harmothoe sp.

Adamussium colbecki

Marseniopsis sp.

Heterocucumis sp. Sterechinus neumayeri

27

seastar Odontaster validus

Odontaster validus is found throughout Antarctica and the

Antarctic Peninsula, South Shetland Islands, South Orkney

Islands, South Sandwich Islands , South Georgia Island, Shag

Rocks, Marion and Prince Edward Islands, and Bouvet Island at

depths from 0 to 914 meters [7,10,11,12,14]. O. validus is the most

abundant seastar in the shallow shelf waters of Antarctica and is

most abundant from 15 to 200 meters [9]. O. validus has a broad

disc and short arms tapering to blunt tips [7]. O. validus has been

collected at sizes up to seven centimeters in radius from its center

to the tip of an arm [7,11]. O. validus varies in color including dark

brown, purple, purple-red, orange, red-orange, red, brick red, dark

carmine, and pink; it may have light colored arm tips [7,11,14]. O.

validus has a characteristic position with its arm tips slightly raised

[7].

O. validus is usually bright to dull red on the dorsal (abactinal)

surface and yellowish white to pale pink on the ventral (actinal)

surface [16]. O. meridionalis is generally pale brown or yellowish white on the dorsal : surface and lighter on the

ventral surface [16]. Color in both species can be highly variable and is not always reliable as a field character; the

only sure way is to check the number of spines on the actinal plates [16].

Here's a juvenile and adult of Odontaster

validus. Size-frequency distribution of O.

validus can vary with location and is a

reflection of the general level of

productivity of a habitat: at McMurdo

Station, their size and number decrease

with depth; at Cape Evans, they are more

numerous and generally smaller; and, at

East Cape Armitage, they are less

numerous and very small [3]. O. validus is

slow growing; well-fed individuals need

about nine years to reach thirty grams wet

weight which is near the mean size of

shallow-water individuals at McMurdo

Station [3]. Based on its growth rate,

collected sizes, and knowledge from other

seastars, O. validus may live beyond one

hundred years of age, with very low

turnover in a population [17].

Odontaster validus

Ammothea carolinensis

Trophon longstaffi

In total: 28 taxa (9 phyla, all present functional guilds)

Hemigellius sp.

Material & methods: analysisUniversity of Liège’s setup:

Vario MICRO cube EA coupled to an Isoprime 100 IRMS

Horizontal dimension – mixing model

S y m p . a lg a e B io fi lm

4

5

6

7

8

9

C/N

ra

tio

High reliance of many benthic invertebrates on sympagic material exported to the seafloor

Main food item of 8 out of 14 primary consumers / omnivores (up to 80% of diet)

Why is it preferred by many consumers over more abundant food items such as biofilm?

Better nutritional value? Unlikely…

Better palatability? Pure aggregates of microalgae…

Horizontal dimension – mixing modelPreliminary microscopic examination: Benthic biofilm = heterogeneous mix of microalgae, bacteria, amorphous material and detrital items


Yannick LARA – Poster nr. 28Session 1.2 (Tuesday)


Here: importance of benthic biofilm in food web comparatively limited despite high abundance

Role of benthic biofilm in the food webPreliminary microscopic examination: Benthic biofilm = heterogeneous mix of microalgae, bacteria, amorphous material and detrital items


Ross Sea: Benthic invertebrates consume more detritic matter in sea-ice influenced locations (Norkko et al. (2007), Ecology 88: 2810-2820)



Ross Sea: Benthic invertebrates consume more detritic matter in sea-ice influenced locations (Norkko et al. (2007), Ecology 88: 2810-2820)

Important variation in benthic ecosystem response to sea ice: sudden changes vs. stable conditions?

However: no data about dynamics of biofilm accumulation!

Here: long-lived benthic invertebrates with low metabolic rates lowisotopic turnover? Is isotopic equilibrium reached?

Our model could underestimate actual biofilm importance for invertebrate feeding

Vertical dimension – Trophic position modellingTr

op

hic

po

siti

on

Tro

ph

on

lon

gst

aff

i

Am

mo

thea

caro

linen

sis

Ster

ech

inu

sn

eum

aye

ri

Op

hiu

rasp.

Dip

last

eria

sb

ruce

i

Od

ont

ast

er v

alid

us

Dec

olo

po

da

au

stra

lis

Parb

orl

asi

a c

orr

ug

atu

s

Salia

ster

ias

bra

chia

ta

Aco

do

nta

ster

sp.

Iso

tea

liaa

nta

rcti

ca

Overall: low trophic positions compared

to literature

Vertical dimension – Trophic position modellingTr

op

hic

po

siti

on

Tro

ph

on

lon

gst

aff

i

Am

mo

thea

caro

linen

sis

Ster

ech

inu

sn

eum

aye

ri

Op

hiu

rasp.

Dip

last

eria

sb

ruce

i

Od

ont

ast

er v

alid

us

Dec

olo

po

da

au

stra

lis

Parb

orl

asi

a c

orr

ug

atu

s

Salia

ster

ias

bra

chia

ta

Aco

do

nta

ster

sp.

Iso

tea

liaa

nta

rcti

ca

Overall: low trophic positions compared

to literature

Dominant omnivore taxa:

very low trophic levels, mostly

feeding directly on primary producers

The food web we expectedTr

op

hic

po

siti

on

of

the

con

sum

ers



Shift in resources supporting consumersTr

op

hic

po

siti

on

of

the

con

sum

ers



High dependency of benthic invertebrates on sea ice-derived organic matter

Shift in resources supporting consumersTr

op

hic

po

siti

on

of

the

con

sum

ers



High dependency of benthic invertebrates on sea ice-derived organic matter

Influence on interspecific ecological interactions (e.g. competition) and community structure?

Shift in trophic position of consumersTr

op

hic

po

siti

on

of

the

con

sum

ers



Trophic positions of many consumers lower than in other studies

Shift in trophic position of consumersTr

op

hic

po

siti

on

of

the

con

sum

ers



Trophic positions of many consumers lower than in other studies

Influence on energy flow and secondary production by key omnivore taxa?

Sea ice & food web structure

Increase of sea ice cover strongly influences the benthic food web by modifying both its horizontal and its vertical structure

Expected food web Increased sea ice conditions

Take home message

▪ Important sea ice cover is linked with high reliance of coastal benthic invertebrates on sympagic algae

Take home message


▪ Resource use and trophic levels of Adélie Land consumers markedly differed from results obtained in other locations. High trophic plasticity of Antarctic invertebrates? Sudden changes vs. stable conditions?

Take home message



▪ Interpretation of results is complicated by lack of background data ("normal" conditions) and by physiological features of studied organisms

Take home message



▪ Interpretation of results is complicated by lack of background data ("normal" conditions) and by physiological features of studied organisms

Despite being interpreted as a positive signal by mainstream media, local or large-scale trends of sea ice increase in Antarctica could actually

have strong impacts on benthic ecosystems

Funding

Image: NASA

Belgian Federal Science Policy Office (BELSPO)

vERSO (Ecosystem Resilience in Southern Ocean) and RECTO (Refugia and Ecosystem Tolerance in the Southern Ocean) projects

French Polar Institute (IPEV)

Image: NASA

Thanks for your attention

Download this presentation: http://hdl.handle.net/2268/212612

Mixing law: "You are what you eat"

An animal’s stable isotope composition is a proportional mix of its food items’ stable isotope compositions

Tom Davis

Horizontal dimension: mixing model

Mixing law: "You are what you eat"

An animal’s stable isotope composition is a proportional mix of its food items’ stable isotope compositions

Tom Davis

Horizontal dimension: mixing model

Analysis of stable isotope composition of consumers and potential fooditems

Use of SIAR (Stable Isotope Analysis in R) mixing model

Quantitative estimates of contributions of each food item to eachconsumer diet

Identifications of resources supporting each consumer’s populations

Stable isotopes: you are what you eatMixing law: an animal’s stable isotope composition is a proportional mix of its food

items’ stable isotope compositions

U

Stable isotopes: you are what you eatMixing law: an animal’s stable isotope composition is a proportional mix of its food

items’ stable isotope compositions

U

Analysis of stable isotope composition of a consumer and those of its potential fooditems through mass spectrometry

Estimation of contributions of each item to consumer diet

Stable isotopes: you are what you eatReal-life ecosystems : many potential food items + natural variability of isotopic

compositions

S1

S2S3

S5

S4S6

C

Necessity of complex mathematical tools: mixing models (SIAR – Stable Isotope Analysisin R)

SIAR parameters

Image: NASA

SIAR 4.2 in R 3.2.2

No concentration dependencies

TEFs: Δ13C = 0.40 ± 1.20 ‰; Δ15N = 2.30 ± 1.61 ‰ (mean ± SD; TEFs for aquatic consumers from McCutchan et al. 2003 Oikos 102: 378-390)

106 iterations

Burn-in size: 105

Results - SIAR modelling

Sympagic algae

SuspendedParticulateOrganic Matter(SPOM)

Benthic algae+ Biofilm

OV: O. validus; SN: S. neumayeri; DB: D. brucei; HA: Harmothoe sp.; FM: F. mundata; PO: Polycirrus sp.; OP: Ophiura sp.; PE: Perkinsiana sp.; TL: T. longstaffi; MA: Marsienopsis sp.; HE: Heterocucumis sp.; LE: Laternula elliptica; AC: Adamussium colbecki; ST: Staurocucumis sp.

Co

ntr

ibu

tio

n t

o c

on

sum

er d

iet

Vertical dimension: trophic position model1

5N

/14N Primary consumers

TL = 2

Primary producersTL = 1

Secondary consumersTL = 3

The heavy nitrogen stable isotope(15N) follows a predictable stepwise enrichment pattern with increasing

trophic level

Vertical dimension: trophic position model

https://github.com/clquezada/tRophicPosition

15N

/14N Primary consumers

TL = 2

Primary producersTL = 1

Secondary consumersTL = 3

The heavy nitrogen stable isotope(15N) follows a predictable stepwise enrichment pattern with increasing

trophic level

Measurement of stable isotope composition of consumers and

baseline items (primary producers)

Use of tRophicPosition model to infer trophic level of animals

Low trophic positions of consumers

Image: NASA

Results: food sources and primary consumers

-2 5 -2 0 -1 5 -1 0

2

4

6

8

1 0

1 3

C (‰ )

1

5N

(‰

)

H a rm o th o e s p .

F la b e ll ig e ra m u n d a ta

P o ly c irru s s p .

P e rk in s ia n a s p .

T ro p h o n lo n g s ta f f i

M a rs e n io p s is s p .

L a te rn u la e llip t ic a

A d a m u s s iu m c o lb e c k i

O p h iu ra s p .

S te re c h in u s n e u m a y e r i

D ip la s te r ia s b ru c e i

O d o n ta s te r v a lid u s

H e te ro c u c u m is s p .

S ta u ro c u c u m is s p .

S P O M

B io film

H im a n to th a llu s b la d e s

S y m p a g ic a lg a e

F o o d ite m s

P o ly c h a e te s

M o llu sc s

E c h in o d e rm s

Results: secondary consumers

Image: NASA

-2 5 -2 0 -1 5 -1 0

2

4

6

8

1 0

1 2

1 3

C (‰ )

1

5N

(‰

)

S a lia s te r ia s b ra c h ia ta

A c o d o n ta s te r s p .

Is o te a lia a n ta rc t ic a

D e c o lo p o d a a u s t ra lis

A m m o th e a c a ro lin e n s is

P a rb o r la s ia c o rru g a tu s

Inter-annual change in isotopic compositions

Image: NASA

Increased sea ice cover disrupts food web structure in Antarctic … · 2017-07-05 · 12th SCAR...

Documents

Transcript of Increased sea ice cover disrupts food web structure in Antarctic … · 2017-07-05 · 12th SCAR...