Ecosystem engineering in intertidal sand by the lugworm Arenicola marina

(1)

Mya arenaria

0 1000 2000 3000 4000

Mid Intertidal Low Intertidal

Ind. m-2

Exclusion Control Ambient

Macoma balthica

0 500 1000 1500 2000 2500

Mid Intertidal Low Intertidal

Ind. m-2

experimental setup: 2-factorial nested block design

Ecosystem engineering in intertidal sand by the lugworm Arenicola marina

Nils Volkenborn, Lubos Polerecky*, Karsten Reise

AWI, Wadden Sea Station Sylt, *MPI for Marine Microbiology, Bremen

Alfred Wegener Institute

Alfred Wegener Institute forforPolar-Polar-und Marine Research, und Marine Research, WaddenWaddenSeaSeaStation Sylt, contactStation Sylt, contact: : nvolkenborn@awinvolkenborn@awi--bremerhaven.debremerhaven.de Deposit-feeding lugworms are widespread the

dominant large burrowing macrofaunal species and consequently the major source of sediment reworking and bioirrigation of intertidal sediments in the Wadden Sea. In 2002 an ongoing large-scale, long-term lugworm exclusion experiment was started, by meshing the sediment in 10 cm depth on 6 exclusion plots, each with an area of 400m²to reveal significant effects of lugworms on ecosystem functioning.

…biogeochemical processes

Conclusions and perspectives

• Effects of ‘ecosystem engineering’ by lugworms extend beyond the vicinity of individual burrows with considerable implications for sediment properties, biogeochemical processes, and the benthic community.

• Effects are variable in space and time.

• The experiment offers ideal testing ground for further research regarding key species, biodiversity and ecosystem functioning.

• The experiment is a contribution to the European network of Marine Biodiversity and Ecosystem Functioning (MarBEF) and one part of the BMBF project NEBROC (Netherlands Bremen Oceanography).

20 meters

Exclusion plots, December 2002

500 meters Exclusion

(netted) Ambient

(undisturbed)

Control (disturbed, without net)

Low intertidal fine sand Emersion period 3-4 h grain size median ~220 µm

Mid intertidal medium sand emersion period 6-7 h grain size median ~340 µm 20 meters

BLOCK 1 BLOCK 2

BLOCK 3

BLOCK 4 BLOCK 5

BLOCK 6

Lugworms affect...

…intertidal habitat succession

…functional diversity …structural habitat complexity

0 1 2 3 4 5

Ind. in 1.000 m-2

0 2 4 6 8 10

Exclusion Control Ambient 0 1 2 3

ExclusionControl Ambient

1st year 2nd year 3rd year

carnivorous motile worms

subsurface deposit-feeding discretely motile worms surface deposit-feeding discretely motile worms mixed suspension and surface deposit feeding tube worms

M ud Fine

S a nd M ed ium S a nd C o a rse

S a nd H W L

LW L

O2(nmol cm-3)O2(nmol cm-3)

Lugworms maintain sediment permeability and facilitate oxygen penetration with increasing hydrostatic pressures

h = 20

Exclusion site

h = 0

h = 20 h = 30 h = 40 h = 50

h = 10 h = 30 h = 40

h = 0 1 cm

Lugworm site

Berkeleya rutilans spring 2003

Enteromorpha spp. Ulva specc.

summer 2004

Algae fixed to protruding polychaete tubes on lugworm exclusion plots Lugworms facilitate sulphide sensitive

species and inhibit tube building species

Enhanced recruitment of byssus drifting bivalves

-10

0

10

20

30

0 100 200 300 400

µmol L-1

depth (cm

0.0 0.5 1.0 1.5 2.0

Medium Sand Fine Sand

Fine Fraction %

Lugworms inhibit accumulation of fine particles, porewater nutrients, and sulphide

Hypothsized expansion of permeable sandflats at the cost of cohesive mudflats

2003 mid intertidal2004lowintertidal

Sediment fraction < 63 µm Porewater nutirents (NH4)

Lugworms tidal flat and lugworm burrow