AARHUS

UNIVERSITET

VERSITET

KARSTEN DAHL SENIOR ADVISOR

AARHUS

UNIVERSITY

UNI

FLORA AND FAUNA ON RE-ESTABLISHED REEFS

- EXPERIENCE FROM THE BLUE

REEF PROJECT

By: Karsten Dahl, Steffen Lundsteen, Ole

Gorm Norden Andersen, Cordula Göke

and Berit Langkilde Møller

Setting the scene (1)

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pecie

s

0

50

100

150

200

250

300

350

Salin

ity

(psu)

0

5

10

15

20Red algal

Brown algal

Green algal

Salinity Effect of salinity

Example

Macrophyte data

from:

Nielsen et al, 1995

Setting the scene (2)

Substrat

Human impact:

• Boulder extraction

• Gravel extraction

• Fishery with

dredging gear

Depth

Light Human Impact:

• Phytoplankton produc-

tion (eutrophication)

• Re-suspension

• Changes in foodwebs

(Riemann et al, 2015 Estuaries and Coast vol 39 issue 1)

Læsø Trindel • Monitored the reef since 1991 as part of the

National monitoring program.

Conclusion: a reef in a poor condition

Investigations of benthic communities

at Læsø Trindel

• 2007 and 2012: Intensive quantitative

investigations of:

– species specific biomass of fauna and

macroalgae

– solitary fauna species numbers

Blu

e R

eef

pro

ject

New reef structures

Imported boulders cover:

27600 m2

Cover in depth intervals

1½-4½m: 7175 m2

4½-7½m: 11725 m2

7½-10m: 8500 m2

Quantitative investigations of

biodiversity

• Suction sampler (“underwater vacuum cleaner”):

– Gentle, not harming even fragile species

– Able to sample swimming

organism like crustaceans

living among the

macroalgae

– Quick

Pump

"Waterflow"

Suction aggregate

Suctionpipe

Samplingframe

Filterboxor

filternet

Rope

Benthic sampling • Frame sampling at the gravely/sandy seabed

Size: 1/6m2 – suction to 10cm

depth.

All samples in 2007 and a

few in 2012

• Frame sampling on large boulders

Size: (1/10m2)

Most samples in 2012

• Total sample area:

• 2007: 4,7m2

• 2012: 7,2m2

•

Assumptions: Estimations of biomass and

species number per m2 on the new reef

• Only algal and fauna on the top layer of boulders.

• Boulders are round and lay side by side with holes

in between.

• 1/6 of the boulder surface is in contact with other

boulders or the seabed.

• The top frame sample represent 1/6 and the side

frame sample 4/6 of the boulder surface.

Average biomass of taxonomic groups

2012

3m

2007

5-6

m

2012

5-6

m

2007

8-1

0m

2012

8-1

0m

Ash

fre

e d

ry w

eig

ht

in g

/m2

0

100

200

300

400

500

RHODOPHYTA

PHAEOPHYTA

CHLOROPHYTA

POLYCHAETA

GASTROPODA

ECHINODERMATA

CRUSTACEA

BRYOZOA

BIVALVIA

ANTHOZOA

Others

Av. biomasses of dominant species

2012 3m

2007 5-6m

2012 5-6m

2007 8-10m

2012 8-10m

As

h f

ree

dry

we

igh

t in

g/m

2

0

100

200

300

400Metridium senile

Electra pilosa

Asterias rubens

Desmarestia viridis

Desmarestia aculeata

Laminaria juvinil

Saccharina latissima

Laminaria dig/hyp

Chorda filum

Ectocarpus siliqulosus

Delesseria sanguinea

Polysiphonia stricta

Phyllophora pseudoc.

Others

Average number of solitary fauna

individuals/tax. group/m2

2012 3m

2007 5-6m

2012 5-6m

2007 8-10m

2012 8-10m

nu

mb

er

of

ind

ivid

ua

ls

0

5000

10000

15000

20000

25000

30000

35000

CRUSTACEA

GASTROPODA

BIVALVIA

ANTHOZOA

NEMATODA

POLYCHAETA

ECHINODERMATA

Others

Average number of most frequent

solitary fauna species/m2

2012 3m

2007 5-6m

2012 5-6m

2007 8-10m

2012 8-10m

No

of

ind

ivid

ua

ls

0

5000

10000

15000

20000

25000

30000

35000 Jassa falcata

Ischyrocerus anguipes

Parajassa pelagica

Caprella linearis/septentrionalis

Gammarellus homari

Monocorophium insidiosum

Metridium senile

Nematoda

Hiatella arctica

Mytilus edulis

Pusillina sarsii

Asterias rubens

Others

Summing up: what was achieved in 3 years

• What was lost in ash free dry weight?

– Fauna 220 kg

– Algal vegetation 1280 kg

– Total 1480 kg (< 3% infauna)

• What was gained – so far?

– Fauna 3075 kg

– Algal vegetation 7400 kg

– Total 10475 kg

Surplus of app: 6100 kg ash free algal biomass

and 2850 kg fauna biomass

State of the colonization process - year 2016

• Very scattered distribution of normally

community structuring species in northern

Kattegat:

– Chondrus crispus

– Phyllophora pseudoceranoides

– Coccotylus truncatus

– (Coralina officinalis)

– (Ahnfeltia plicata)

• Newcomer in 2016

– Dilsea carnosa

Observed development and expectation and

development for the years to come (1)

• More species

• A full developed

understory of

red algal species

• Increase in algal

biomass

(more and fully

grown kelp species

2009

20102011

20122013

20142015

2016

Co

ve

r (%

)

0

10

20

30

40

50Saccharina latissima

Laminaria dig/hyp

Observed development and expectation and

development for the years to come (1)

• Less fauna biomass?

– Likely some sea anemones will

loose the battle of space to

algal species

– The presence of bryozoans on

the algal vegetation has

increase with the increased

biomass of perannual algal

biomasses

2006 (before)

2008 2009 2011 2012 2015 2016

Thanks to

”The vacuum cleaner gang”:

Michael Bo Rasmussen, Jens Larsen,

Peter Stæhr og Jan Dangaard Nielsen

- Daniel K. Johansson for lab-assistance

- Statens Naturhistoriske Museum

- And to you for the attention

Dahl, K., Støttrup, J.G., Stenberg, C., Berggreen, U.C, Jensen, J.H.

2016. Best practice for restoration of stone reefs in Denmark (codes of

conduct). Aarhus University, DCE – Danish Centre for Environment and

Energy, 33 pp. Technical Report from DCE – Danish Centre for

Environment and Energy No. 91.

http://dce2.au.dk/pub/TR91.pdf