Ecosystem exploitation and trophodynamic indicators: a comparison between the Northern Adriatic Sea and

Southern New England

Fabio Pranovi* & Jason S. Link**

*Dipartimento di Scienze Ambientali, Università di Venezia -Italy

**NOAA, National Marine Fisheries Service Northeast Fisheries Science Center -USA

Semi-enclosed basin

surface area 14178 km2

average depth <35 m

strong riverine outflows

recurrent eutrophication

high fishing pressure

Peculiarity:

‘Atlantic lacuna’

Northern Adriatic Sea

Open system

surface area 64060 km2

average depth 60 m

water flows northeast to southwest

high fishing pressure

Southern New England

Very high primary production

Model descriptions

years of reference 1997-200020 nodes Phytoplankton - Piscivorous fish

years of reference 1996-200033 nodes Phytoplankton – Whales/highly migratory sp.

NAS SNEOriginal structure

Differences due to geographical and oceanographic features, data availability, and different degree of food web aggregation

Aggregation according to the main ecological compartments

NAS SNE (number of original nodes)

Plankton 4 9Benthos 8 7Nekton 5 11Mammals/birds - 4Detritus 3 2Fishery 5 1

Ecosystem structure comparison

Biomass

Production

NAS SNEB/P 4.48 1.37B/N 2.97 2.94N/P 1.51 0.47

NAS SNEB/P 0.09 0.03

B/N 5.76 14.38 N/P 0.02 0.002

0

0.2

0.4

0.6

0.8

Plankton Benthos Nekton Mam./Birds

NASSNE

0

0.2

0.4

0.6

0.8

1

Plankton Benthos Nekton Mam./Birds

NASSNE

%

%

Total biomass vs Trophic Level

Ecosystem structure comparison

0

0.2

0.4

0.6

0.8

1

1.2

0 1 2 3 4 5 6

Trophic Level (TL)

Tota

l Bio

mas

s (%

)

NASSNE

{

Biomass accumulation

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Sum of allconsumption

Sum of allexports

Sum of allrespiratory

flows

Sum of allflows intodetritus

Total systemthroughput

Sum of allproduction

NASSNE

Ecosystem comparison in terms of flows

In absolute terms,SNE 3-4 times higher than NAS

tC/TST 43% NAS 47% SNE

tPP/tR 1.23 for both

TST and TE

NASTE=8.4%

SNETE=15.5%

IIIIIIIVV

57% 55%

38% 36%

7%4%

1%0.4%

0.1%0.02%

TE 10.7

TE 10.7

TE 5.1

TE 4.5

TE 20

TE 13.5TE 13.7

TE 11.5

overall effect

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

KS

Keystoneness index

overall effect-2.2

-2

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

KS

Libralato et al., Ecol. Mod., 2006

NAS

SNE

∑≠

=n

ijiji m2ε

Overall effects (estimated by MTI matrix)

Keystoneness index (overall effect weighted for biomass)

KSi=[log(εi(1-pi)]

Large copepods

Gelatinous zooplankton

Phytoplankton

B. detritus feeders

B. omnivores

Phytoplankton

Nekton Fisheries Benthos Plankton Detritus Mam./Birds

Nekton Plankton Fisheries Benthos Detritus Mam./Birds

MTI NAS

SNE

Mixed Trophic Impactweighted by the inverse of the impacted group biomass (1/Bj)

Estimates the absoluteeffect of the variationof a unit of the impacting group

Both the systemsshow the presence of ‘top down’ effects

Nekton (demersal) Nekton (pelagic) Benthos

Nekton (pelagic) Benthos Nekton (demersal)

Ecosystem comparison in terms of fisheries

NASotter trawls, "rapido" trawlsmid-water trawls hydraulic dredges

SNEbottom-tending otter trawls scallop dredges mid-water trawls

0

20

40

60

80

Zooplan

kton

Macrob

enthos

Pelagic

fish

Benthi

c fish

Sharks

Marine m

ammals

NASSNE

0

25

50

75

100Zo

oplan

kton

Macrob

entho

s

Pelagic

fish

Benthi

c fish

Sharks

Marine

mam

mals

Sea bi

rds

NASSNE

Ecosystem comparison in terms of fisheries

Target species

NAS 1.76 t km-2 y-1

SNE 3.05 t km-2 y-1

Discarded species

NAS 0.61 t km-2 y-1 (34%)

SNE 0.97 t km-2 y-1 (32%)

Total catch/P Total catch/Q

NAS SNE NAS SNEBenthos 0.69 0.03 0.14 0.01Nekton (pelagic) 0.02 0.06 0.01 0.01Nekton (demersal) 0.11 0.14 0.03 0.07

TE PP TLc PPR % gCm-2y-1 %

NAS 8.4 142 2.57 13.0

SNE 15.5 539 2.90 7.6

Fisheries and ecosystem functioning

Total catchNAS 2.36 t km-2 y-1

SNE 4.03 t km-2 y-1

TEPTEPPRL

TLc

ln1

1

⋅⋅−=

−

Libralato et al., MEPS (in press)

NAS 0.1081

SNE 0.11650

500

1000

1500

2000

2500

1 2 3 4 5

TL

Prod

uctio

n

Loss of production

Y2

Y3

Y4

L index

To use the loss in production as a proxy for quantifying the

disruption of the ecosystem due to

fishing harvesting

Overfished!

Conclusions The comparison of these two ecosystems highlights some

interesting similarities – despite their differences – in terms of structure & functioning, such as:

– the dominant role played by the benthos;

– the presence of ‘top down’ effects- namely fishing;

– catch composition (both target and discarded groups);

As we move towards implementation of Ecosystem Based Management in these areas, these systemic observations will continue to become increasingly important

both systems were overexploited