Introduced macroalgae in Denmark
When, where, how and
which effects?
Peter A. Stæhr
Freshwaterbiological Laboratory
Biological Institute, Univ. Copenhagen
Some ”basic” questions:
 What is a macroalgae?
 What characterizes an invasive macroalgae?
 Which steps are involved in macroalgal
invasions?
 What are the likely impacts of an invasion?
Macroalgae?
Macroalgae?
Steneck & Dethier 1994
Invasive macroalgae?
Williams & Smith 2006
Number of introductions
Invasive macroalgae?
Williams & Smith 2006
Macroalgae in Danish waters
Ns = North Sea
Sk = Skagerrak
K = Kattegat
Lf = Limfjorden
Sa = Northern beltsea
Sb+Sm = Great belt
Lb = Little belt
Su = Oresound
Bm+Bb = Baltic sea
Map of diving locations in the Danish marine monitoring program.
From 19892003: 9738 observations with 290 taxa, including 9 invasive
Which macroalgal NIS?
Red
(159)
Bonnemaisonia hamifera Dasya baillouviana
Gracilaria vermiculophylla
Polysiphonia elongella new!
Heterosiphonia japonica
= Dasysiphonia sp.
Neosiphonia harveyi
Which macroalgal NIS?
Red
(159)
Bonnemaisonia hamifera Dasya baillouviana
Gracilaria vermiculophylla
Heterosiphonia japonica
= Dasysiphonia sp.
Neosiphonia harveyi
Brown
(126)
Colpomenia peregrina
Sargassum muticum
Fucus evanescens
Dictyota dichotoma
Which macroalgal NIS?
Red
(159)
Bonnemaisonia hamifera Dasya baillouviana
Gracilaria vermiculophylla
Heterosiphonia japonica
= Dasysiphonia sp.
Neosiphonia harveyi
Brown
(126)
Colpomenia peregrina
Sargassum muticum
Green
(91)
Codium fragile ssp. tomentosiodes / scandiavicum
Fucus evanescens
Dictyota dichotoma
Where from, how and when?
Class
Species
Origin
Transport
Year Europe
Year DK
Red
Bonnemaisonia
hamifera
Pacifics
(Japan)
Ship?
1890
(England)
1900
Red
Dasya
baillouviana
Mediterranean
Ship?/oysters?
Natural
1961
Red
Heterosiphonia
japonica
Pacifics
Ship?/oysters?
1994
(Holland)
2005
Red
Neosiphonia
harveyi
Epiphytes?
1908
(England?)
1986
Red
Gracilaria
vermiculophylla
Ship?/oysters?
1935
(Norway?)
2003
Brown
Colpomenia
peregrina
Pacifics
Oysters?
1905
(France)
1939
Brown
Fucus
evanescens
North Atlantics
Ship / natural
Natural
1948
Brown
Sargassum
muticum
Pacifics
(Japan)
Oysters?
1960s
(France?)
1984
Atlantic
Brown
Dictyota
dichotoma
Oysters /
natural?
Natural
1939
Green
Codium fragile
ssp.
tomentosoides
Atlantics
(Japan)
Ship/oysters?
1900 ca
(Holland)
Green
Codium fragile
ssp.
scandinavicum
Atlantics
(Sibiria, Japan)
Ship/oysters?
1919
(Denmark)
Pacifics /
NW Atlantics
Pacifics
1919
Where and how much?
Relativ dækning
af samfund)
of community)
cover (% (%
Relative
Regional distribution
10
Bonnemaisonia hamifera
Codium fragile
Colpomenia peregrina
Dasya baillouviana
Dictyota dichotoma
Fucus evanescens
Gracilaria vermiculophylla
Neosiphonia harveyi
Sargassum muticum
1
0.1
0.01
0.001
Ns
K+Lf
Salty (34 ppm)
Sa
Lb
Sb+Sm
Regions
Regioner
Su
Bw
Bm+Bb
Fresh (5-10ppm)
Where and how much?
10
Bonnemaisonia hamifera
Codium fragile
Colpomenia peregrina
Dasya baillouviana
Dictyota dichotoma
Fucus evanescens
Gracilaria vermiculophylla
Neosiphonia harveyi
Sargassum muticum
1
0.1
0.01
Depth
interval
Dybdeinterval
(m) (m)
26-28
24-26
22-24
20-22
18-20
16-18
14-16
12-14
10-12
8-10
6-8
4-6
2-4
0.001
0-2
cover (%(%ofafcommunity)
Relativedækning
Relativ
samfund)
Depth distribution
Where and how much?
Relativ cover
dækning
af samfund)
of community)
(% (%
Relative
Development in time
10
Bonnemaisonia hamifera
Codium fragile
Colpomenia peregrina
Dasya baillouviana
Dictyota dichotoma
Fucus evanescens
Gracilaria vermiculophylla
Neosiphonia harveyi
Sargassum muticum
1
0.1
0.01
Year
Årstal
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
0.001
Summary on Danish NIS
• 10-12 ”new” species out of 376 total
• NIS species amount to 3.75% of total
cover
• Most NIS in salty regions
• Most at 2-4m (7%) and 20-22m (6%)
• No obvious increase during recent years
• Gracilaria is expected to spread fast
• Lack of knowledge about NIS ecological
impact in Dk more research
Invasion phases:
Donor population
(1) Uptake, transport
(2) Release and establisment
(3) Spread (natural/associated)
Effect
(4) Impacts (large)
1
2
3
Time
4
Invasion of new populations
Barriers of invasion:
Donor region
Geographical
Physiological
Life-history
Biotic resistance
Recipient region
Sargassum muticum in Denmark
– invasion and ecological effects
Sargassum muticum - phenology
• Large (>2m) brown macroalgae (order Fucales)
• Related to Fucus vesiculosus and Halidrys siliquosa
• Floating vesicles
• Broad temperature (10-30 oC) and
salinity (18-34 o/oo) tolerance
• Monoecious ~self fertilizing
• High regeneration ability
• Pseudo-perenial life-cycle
Invasion
history
• Origin – Asia (Japan)
• 60’ies – North America
-> Oysters
• 70’ies – Europe
(English Channel)
-> oysters
??
• 1984 - Denmark
-> oysters?
-> sekundary spread
(drifting)?
2000?
Rang no.
% of total macroalgal cover
Temporal development in community structure
Relative change 1990– 97
Sargassum muticum
Halidrys siliquosa
Epibionts on Sargassum (S) and Halidrys (H)
No clustering
Species richness
Individual density
Biomass
ol
lu
sc
a
Cn
i
da
ria
ha
et
a
Sargassum muticum
Po
lyc
Po
rif
er
a
M
Cr
us
ta
ce
a
Ec
hi
no
de
rm
at
a
Ur
oc
ho
rd
at
a
mgAFDW / 100g FW algae ± SE
Same epifauna but more on Sargassum
2500
Halidrys siliquosa
2000
1500
1000
500
0
Seasonal variation in standing biomass
Sargassum
Large fluctuation in
growth, production and
loss
Loss to grazers = 1-2%
 99% of production is
accumulates as detritus
Halidrys
Even growht, production and loss
Fast decomposition

fast release
Impacts of S. muticum in Denmark
• Since the introduction in 1984, Sargassum muticum has become
the most common macroalgae in Limfjorden
• The invasion has changed the macroalgal community structure
with significant reductions in the cover of other large perennial
browalgae
• The invasionen has not changed the epifaunal species
composition, but has increased epifaunal abundance and
seasonal variation
• The invasionen has resulted in a more unstabil and fluctuating
biomass, with faster growth, turnover and nutrient release, similar
to systems experiencing eutrophication
Litterature:
• Wernberg-Møller, Thomsen & Stæhr (1998). Master thesis, RUC.
• Wernberg-Møller, Thomsen & Stæhr (1998). Urt 22:128-132.
• Stæhr, Pedersen, Thomsen, Wernberg & Krause-Jensen (2000). Mar Ecol-Prog Ser 207:79-88.
• Wernberg, Thomsen, Stæhr & Pedersen (2001). Botanica Marina 44:31-39.
• Wernberg, Thomsen, Stæhr & Pedersen (2004). Helgoland Marine Research 58:154-161.
• Pedersen, Stæhr, Wernberg & Thomsen (2005). Aquatic Botany 83:31-47.
•Thomsen M., Krause-Jensen D., Wernberg T., Stæhr P.A. og Nils Risgaard-Petersen. (2005) Fremmede
tangarter i Danmark: Hvilke? Hvor udbredte? Hvornår? Urt 29: 110-115
• Thomsen, Wernberg, Stæhr & Pedersen (2006). Helgoland Marine Research 60:50-58.
•Thomsen MS, Wernberg T, Stæhr PA, Krause-Jensen D, Risgaard-Petersen N, Silliman BR. 2007. Alien
macroalgae in Denmark - a national perspective. Marine Biology Research 3: 61-72
Further information (Mads Thomsen website on NIS):
http://cem.ecu.edu.au/coastal-marine/themes/reefecology/marine_invaders_bibliography.php