Detached effects seaweeds on soft-bottom community structure

G O A L A N D H Y P OT H E S I S

The deposition of seaweeds on the shore could modify the structure and composition of sedimentary communities due to the advantages (↑

food, ↑ complex habitat) and disadvantages (↓ oxygen and ↑ physical disturbance) of the presences of the seaweed.

Climate change has increased the frequency and strength of storms in the Arctic. This may trigger high waves and strong swell, causing the detachment of sessile organisms like seaweeds.

S T U D Y S I T E S

Presence of detached seaweeds will

Field experiment

(FACTORIAL)

SEAWEED PROCEDURAL

CONTROL CONTROL

E X P E R I M E N T A L D E S I G N AN D S A M P L I N G

Start: May 2017 End: August 2017

R E S U L T S

TAXON RICHNESS

a a

a

In Longyearbyen the composition of the benthic assemblage was also significantly affected by SEAWEED treatment.

C O N C L U S I O N

Detached effects seaweeds on soft-bottom community structure

María José Díaz

, Markus Molis

, Christian Buschbaum

and Paul Renaud

1 Section Functional Ecology, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Germany

2 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Wadden Sea Station Sylt, Germany

3 The University Centre in Svalbard, N-9071 Longyearbyen, Norway

María José Díaz Aguirre Alfred-Wegener-Institute,

Helmholtz-Center for Polar and Marine Research

Am Handelshafen 12, 27570 Bremerhaven, Germany Mail: maguirre@awi.de, Phone: +49 47148311531

- The presence of detached seaweeds increased evenness (17.6%) only in one site (Thiisbukta).

- Only In Longyearbyen, the number of individuals (14.3%) and biomass (30%) were negatively affected by detached seaweeds. No effect by manipulation.

60 km Thiisbukta

Longyearbyen

a a

a

N°

INDIVIDUALS DRY MASS [g]

a

a a

EVENNESS

a a b

SHANNON

a

a a

SEAWEED CONTROL PROCEDURAL CONTROL

a a

a a

b a

a a

a

a

a a

a a

a

Community response

- Decrease abundance - Decrease biomass

- Decrease diversity - Change the species

composition of the sedimentary community.

To determine if detached seaweeds can interfere with the

structure of the intertidal sedimentary communities in Svalbard, Arctic Norway.

I N T R O D U C T I O N

Map of Svalbard, Norway

2 sites • Thiisbukta

• Longyearbyen

Detached seaweeds effect

1 ... … 6 1 ... … 6 1 ... … 6

Seaweed treatment (Fixed factor)

Blocks

(random factor)

Seaweed

(net + seaweeds) Procedural control

(empty net) Control

(Unmanipulated area)

Sediment core with a sample

(*) Different scale by TAXON RICHNESS, N° INDIVIDUAL and DRY MASS[g]

THIISBUKTA*

LONGYEARBYEN

More abundance 39% in Thiisbukta

Absence in Longyearbyen

ABUNDANCE DETACHED SEAWEEDS EFFECT

18% (Thiisbukta)

19% (Longyearbyen)

46% (Longyearbyen)

Low presence in Thiisbukta

Detached seaweeds affect the sedimentary community.

The impact of seaweeds on sedimentary communities will be negative or positive depending on the conditions of the site.

Possibly the effects of the detached seaweeds on sedimentary communities will have repercussions on food-web.