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?

Steneck & Dethier 1994

Invasive macroalgae? Williams & Smith 2006

Invasive macroalgae? Williams & Smith 2006 Number of introductions

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 hamiferaDasya baillouvianaGracilaria vermiculophylla Heterosiphonia japonica = Dasysiphonia sp. Neosiphonia harveyi Polysiphonia elongella new!

Red (159) Brown (126) Bonnemaisonia hamiferaDasya baillouvianaGracilaria vermiculophylla Heterosiphonia japonica = Dasysiphonia sp. Neosiphonia harveyi Colpomenia peregrinaSargassum muticumFucus evanescens Dictyota dichotoma Which macroalgal NIS?

Red (159) Brown (126) Green (91) Bonnemaisonia hamiferaDasya baillouvianaGracilaria vermiculophylla Heterosiphonia japonica = Dasysiphonia sp. Neosiphonia harveyi Colpomenia peregrinaSargassum muticumFucus evanescens Codium fragile ssp. tomentosiodes / scandiavicum Dictyota dichotoma Which macroalgal NIS?

ClassSpeciesOriginTransportYear EuropeYear DK Red Bonnemaisonia hamifera Pacifics (Japan)Ship? 1890 (England)1900 Red Dasya baillouvianaMediterraneanShip?/oysters?Natural1961 Red Heterosiphonia japonicaPacificsShip?/oysters? 1994 (Holland)2005 Red Neosiphonia harveyi Pacifics / NW Atlantics Epiphytes? 1908 (England?)1986 Red Gracilaria vermiculophyllaPacificsShip?/oysters? 1935 (Norway?)2003 Brown Colpomenia peregrinaPacificsOysters? 1905 (France)1939 Brown Fucus evanescensNorth AtlanticsShip / naturalNatural1948 Brown Sargassum muticum Pacifics (Japan)Oysters? 1960s (France?)1984 Brown Dictyota dichotoma AtlanticOysters / natural?Natural1939 Green Codium fragile ssp. tomentosoides Atlantics (Japan)Ship/oysters? 1900 ca (Holland) 1919 Green Codium fragile ssp. scandinavicum Atlantics (Sibiria, Japan)Ship/oysters? 1919 (Denmark) Where from, how and when?

Where and how much? Regional distribution Regions Relative cover (% of community) Salty (34 ppm) Fresh (5-10ppm)

Relative cover (% of community) Depth interval (m) Where and how much? Depth distribution

Where and how much? Development in time Year Relative cover (% of community)

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 Summary on Danish NIS

Donor population Invasion of new populations (2) Release and establisment (1) Uptake, transport (3) Spread (natural/associated) (4) Impacts (large) Invasion phases: Time Effect

Donor region Recipient region Physiological Geographical Life-history Biotic resistance Barriers of invasion:

Sargassum muticum in Denmark – invasion and ecological effects

Large (>2m) brown macroalgae (order Fucales) Related to Fucus vesiculosus and Halidrys siliquosa Floating vesicles Broad temperature (10-30 o C) and salinity (18-34 o / oo ) tolerance Monoecious ~self fertilizing High regeneration ability Pseudo-perenial life-cycle Sargassum muticum - phenology

2000? Invasion history 60’ies – North America -> Oysters Origin – Asia (Japan) 70’ies – Europe (English Channel) -> oysters Denmark -> oysters? -> sekundary spread (drifting)? ? ?

Rang no. % of total macroalgal cover

Temporal development in community structure Relative change 1990– 97

Sargassum muticum Halidrys siliquosa

No clustering Epibionts on Sargassum (S) and Halidrys (H)

Species richness Individual density Biomass

Same epifauna but more on Sargassum

Large fluctuation in growth, production and loss Loss to grazers = 1-2%  99% of production is accumulates as detritus Even growht, production and loss Sargassum Halidrys Seasonal variation in standing biomass

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: Stæhr, Pedersen, Thomsen, Wernberg & Krause-Jensen (2000). Mar Ecol-Prog Ser 207: Wernberg, Thomsen, Stæhr & Pedersen (2001). Botanica Marina 44: Wernberg, Thomsen, Stæhr & Pedersen (2004). Helgoland Marine Research 58: Pedersen, Stæhr, Wernberg & Thomsen (2005). Aquatic Botany 83: 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: Thomsen, Wernberg, Stæhr & Pedersen (2006). Helgoland Marine Research 60: Thomsen MS, Wernberg T, Stæhr PA, Krause-Jensen D, Risgaard-Petersen N, Silliman BR Alien macroalgae in Denmark - a national perspective. Marine Biology Research 3: Further information (Mads Thomsen website on NIS): ecology/marine_invaders_bibliography.php