measuring the vulnerability of a community of species to a given pressure: benthos and bottom trawl...

Measuring the vulnerability of a community of species to a given pressure:

Benthos and bottom trawl in the Barents Sea.

Jørgensen, LL, Certain G, Thangstad T, Planque B   

Spatial workshop outputs: Annual meeting Paris 3-7 Dec 2012

How environmental disturbance affects a community of species

Benthic community delivering ecosystem goods and services

Benthic end member community with opportunistic species

Mixture where S, A and B increase

Disturbance

Pearson & Rosenberg 1978

Classical, experimental approach to measure disturbance effect on biodiversity:

Benthic community

Environmental noise Directed disturbance (”Pressure a, b or c”)

Natural fluctuations difficult to separate from pressure induced

Need to make the link between pattern and pressure more explicit

Pointing toward the species showing the ”effect”

qS

i

qi

q pD

1/1

1

qS

i

qiiz

q ZpD

11

1

1

Hill Leinster & Cobbold (2012)

Zi = the ”average” similarity of species i with

the remaining species

All species differs in the same way

Coding species in accordance to the effect from a defined pressure

Sp

ecie

s

Traitssize growth

Sp. 1

Sp. 2

Sp. 3

3 1 11 3 3

3 2 1

mobility

Theoretical indicator species:3 3 3

4

2

3

A similarity measure is convenient if the theoretical species has some meaning ex:

”the most vulnerable species”

0

Trawling impact 2

93 B

aren

ts S

ea S

pec

ies

6 TraitsMobility Speed Strata Body shape Body Texture Mean weight

A theoretically super-vulnerable species

From an given community sample, we can measure the

community vulnerability

V = community vulnerabilityv= species vulnerabilityP = frequencyi=1...S speciesj=1...L locations

S

i i

ijj v

pV

1 1

Application to Benthic communities in the Barents Sea (1)

Trawled area (VMS)

Benthos station

Norwegian coast Bear Island Hopen deep Front Svalbard

Co

mm

un

ity

Vu

lner

abili

ty

2

4

6

Application to Benthic communities in the Barents Sea (2)

T nT T nT T nT T nT T nT

Statistical distribution of community vulnerability in Hopen Deep area:

Expected vulnerability

Fre

qu

ency

Benthos communities in trawled area

Benthos communities in untrawled area

HighLow

Conclusion

This general method estimate the community vulnerability if a species vulnerability to a given

pressure can be assessed.

•The geographical borders of the used polygons needs more evaluation

•Other covariates potentially affecting a community vulnerability ?

•New more exhaustive datasets will be included

Way forward