1 DTU Aqua, Technical University of Denmark

BlueReef

Rebuilding of Marine Cavernous Boulder Reefs in Kattegat

Claus Stenberg1, Karsten Dahl2, Else Marie Stamphøj3, Josianne

Støttrup1, Per Dolmer1

and Anni Dalgas3

1National Institute of Aquatic Resources2The National Environmental Research Institute3The Danish Forest and Nature Agency


What

is a Cavernous

Boulder Reef?


Background

•

On a national level cavernous boulder reefs in shallow waters have been an extensively exploited habitat targeted for their high concentration of easy to excavate large boulders suitable for construction of harbour jetties and sea defences.

•

A cautious estimate indicates a reduction

from more than

34 km2

to only 5 ha left untouched.

•

Læsø

Trindel

in Kattegat is an example of a destroyed boulder reef


Why

are

boulder

reefs

important? •

Offshore cavernous boulder reefs in shallow waters have a high biodiversity and is now a rare and yet biological important subtype of the natural habitat 1170 Reef at a national and European level.

•

The conservation status at Læsø

Trindel

is unfavourable. –

Unstable conditions:–

Physical changes–

Changes in algae community


Læsø

Trindel -

a unstable

boulder

reef


Læsø

Trindel Before

-

After

Year

1831 Year

1978

Depth

4 feet

~1.2 mDepth

3.8 m


•

Objectives–

The project objective

is to restore and maintain a favourable

conservation status of the offshore reef habitat at Læsø Trindel.

–

Fulfilment

of DK’s obligations according

to the Habitats directive.

•

Project frame–

The project budget is Euro 4.8 million (DKK 35 million).

–

Started1/8 2006 and will finish in the spring of 2012. –

Partners:

•

Danish Forest

and Nature Agency, •

National Environmental

Research Institute

•

National Institute

for Aquatic

Resources


Project Project activitiesactivities

Geological survey

Hydrograpical

survey

Biological surveyReconstruction

Public awareness


MapMap of the of the projectproject areaareaLæsø

Trindel, existing

reef


BlueReefBlueReef Design Design


BiologicalBiological MonotoringMonotoringTo document

the effects

of restoring

the offshore

”1170 reef

habitat”, physical

and biological structure

and function:

•

Detailed

flora and fauna surveilliance; suction

sampling, gillnet, traps

(estimate

species diversity, abundance, biomass, length

distribution, etc.).

•

Trophic

links and ecosystem

dynamics

The individual

elements in the monitoring programme

are

linked

and important

for

assessing

conservation

status of the restored reef.


Pump

"Waterflow"

Suction aggregate

Suctionpipe

Samplingframe

Filterboxor

filternet

Rope


ResultsResults of of BiologicalBiological MonitoringMonitoring

B V-M All areas

No

of ta

xono

mic

aly

dist

inct

spe

cies

ore

spe

cies

gro

ups

0

50

100

150

200

250 Sessile faunaMotile faunaMacrophytes Fish Total number of

macroalgae, fish, sessile and motile fauna species identified


Macroalgae


Fauna organism as function of macroalgal

biomasses

Algal biomasses (g ash free dry weight/m2)

0 20 40 60 80 100 120 140 160 180

Tota

l fau

na b

iom

ass

(g a

sh fr

ee d

ryw

eigh

t/m2 )

0

5

10

15

20

25

30

35B


Fish fauna

Multi-meshed gillnet

Area

A 6-10 m B 2-6 m C 6-10 m

CP

UE

N (n

umbe

rs/s

tatio

n)

0

100

200

300

400

500

600

Area

A 6-10 m B 2-6 m C 6-10 m

CP

UE

bio

mas

s (k

g/st

atio

n)

0

1

2

3

4

5

6

7Cancer_pagurus Carcinus_maenas Centrolabrus_exoletus Ctenolabris_rupestris Cyclopterus_lumpus Gadus_morhua Icelus_bicoris Labrus_bergylta Labrus_bimaculatus Limanda_limanda Microstomus_kitt Myoxocephalus_scorpius Pleuronectes_platessa Psetta_maxima Solea_solea Spinachia_spinachia Symphodus_melops Trachinus_draco Zoaces_viviparus Hyperoplus_lanceolatus Mullus_surmuletus Pollachius_virens Scophthalmus_rhombus Zeugopterus_punctatus Lycodes_vahli Merlangius_merlangus Pholis_gunnellus Pollachius_pollachius

Numbers Biomass

Most fish in numbers and biomass in the shallow

corkwing

wrasse

rock cook

ballan

wrasse


Fish

fauna -

acoustic

telemetry tracking


The ”new”

reefJuly

2008


The ”new”

reef

ScanningHoffmann AS

August 2008


The ”new”

reefAugust 2008


The ”new”

reef

•

Video file

August 2009


Direct and indirect spinoffs from Blue Reef


Direct and indirect spinoffs from Blue Reef

•

Restoration and stabilisation

of the reef

at Læsø

Trindel. •

Knowledges

on

how

to restore

the rare cavernous

boulder

reefs

in shallow

waters.•

Knowledge

on

the effects

on

nature and the interaction

between

the”

new nature”

and fish

populations.•

A stepping

stone

within

the

marine Natura 2000 network•

Sanctuary

for donor populations.

•

Focus

on

marine nature, marine restoration and management.

•

New opportunities

for tourismand outdoor

life.

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