Introduced Marine Species of the North Sea Coasts

Abstract

About 80 non-indigenous species are assumed to have been introduced into the North Sea by transoceanic shipping and aquaculture. The number is certainly underestimated as most small organisms received insufficient attention at the species level. Also, the seafaring tradition of the North Sea countries is much longer than our biological surveys are. Most exotic invertebrates originate from the western Atlantic and were introduced by shipping, while most algae stem from the Pacific and came with the introduced oysters. A peak of newcomers was observed in the 1970s. Most of the arrivals became established in brackish environments, at harbor sites and in the vicinity of oyster farms, fouling on hard substrates or living as epibionts. A few live in sediments, are holoplanktonic or are parasites. At the open coast, approximately 6% of the macrobenthic species are exotics, while in estuaries their share is up to 20%. Most exotics have been encountered in the southern North Sea first, and many did not spread further north. About 25% of the established non-natives are widespread and attain locally high abundances. As a consequence, some inshore habitats are entirely dominated by exotics. The overall effect on the ecosystem seems to be more additive than one of displacement. This suggests that the coastal biota of the North Sea are quite capable of accommodating newcomers. However, this is no guarantee that the next introduced species may not cause severe ecological change or economic harm. There is a need to minimize the risk of unintentional introductions by ballast water treatment and by adhering to quarantine procedures in aquaculture. Current research on exotics in the North Sea is regarded as inadequate for proper evaluation and management requirements. I N T R O D U C T I O NM a r i t i m e traffic across the o c e a n s a n d c u l t u r i n g of n o n m a t i v e o r g a n i s m s at the e d g e of the s e a c o n t r i b u t e d to the s p r e a d a n d e s t a b l i s h m e n t of a n e v e r i n c r e a s i n g n u m b e r of exotic s p e c i e s in coastal a n d b r a c k i s h w a t e r e n v i r o n m e n t s . Exotic species of the N o r t h Sea are h e r e o p e r a t i o n a l l y d e f i n e d as s p e c i e s o c c u r r i n g only o u t s i d e the r e g i o n of t h e A t l a ntic c o a s t of E u r o p e (Gibraltar to N o r t h C a p e ) ; h e n c e M e d i t e r r a n e a n a n d P o n t o -C a s p i a n s p e c i e s are c o n s i d e r e d as exotics. We f u r t h e r restrict this o v e r v i e w to s p e c i e s w h i c h h a v e p r e s u m a b l y a r r i v e d by m e a n s of h u m a n t r a n s p o r t , b o t h i n t e n t i o n a l as w e l l as u n i n t e ntional i n t r o d u c t i o n s . B o u n d a r i e s of the N o r t h Sea are d e f i n e d a c c o r d i n g to t h e N o r t h S e a T a s k Force (1993), w h i c h i n c l u d e s t h e C h a n n e l r e g i o n in t h e south, t h e S k a g e r r a k a n d K a t t e g a t in t h e east, a n d t h e S h e t l a n d I s ...

Long-term changes in the macrozoobenthos around the rocky island of Helgoland (German Bight, North Sea)

“…As to exotic species, it is particularly coastal environments (Wadden Sea, river estuaries) which have been extensively invaded by those species over the last few decades (Nehring and Leuchs 1999;Reise et al 1999;Wolff 1999;Lenz et al 2000) while the offshore hard-bottom macrofauna around Helgoland has so far been relatively unaffected. This situation, however, might change rapidly with the arrival of another exotic species, e.g.…”

Nonnative macrobenthos in the Wadden Sea ecosystem

“…In addition, the North Sea coastal waters flowing through the Wadden Sea contain about 14 phytoplankton and two zooplankton nonnative taxa (Gollasch et al, 2009;Reise et al, 1999) while permanent populations of alien fish are not yet known. The number of alien species in the Wadden Sea is close to average when compared to similar assessments in other coastal regions (Table 4).…”

“…We confine this study to macrobenthos because nonnative micro-and meiobenthos is not known for the Wadden Sea. For phyto-and zooplankton, coastal waters flowing through the Wadden Sea are not a meaningful subregion and lists for the entire North Sea should be consulted (i.e., Reise et al, 1999;Gollasch et al, 2009), and permanent resident and seasonally visiting fish of nonnative origin have not yet been recorded in the waters of the Wadden Sea.…”

Associations between macrobenthos and invasive cordgrass, Spartina anglica, in the Danish Wadden Sea

“…Provided the signiWcant roles and feasibility for experimental analysis, macrofauna assemblages are generally regarded as important indicators of system resilience to disturbances, such as biological invasions, pollution and eutrophication (Snelgrove 1998;Levin and Talley 2000). The accelerating concerns on bioinvasions in coastal soft-sediments have inspired much recent research (Reise et al 1999Thieltges et al 2006;Cottet et al 2007;Nehring and Hesse 2008).…”