Notes on growth and behaviour of the American razor clamEnsis directus in the Wadden Sea and the predation on it by birds

Swennen, C.; Leopold, M.F.; Stöck, Martin

doi:10.1007/bf01992773

Cited by 40 publications

(28 citation statements)

References 8 publications

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“…Dörjes (1992) assumed a maximum length up to 100 mm (2 years) for the Vogelsand. Mühlenhardt-Siegel et al (1983), Swennen et al (1985) and Palmer (2004) found also different maximum lengths at different study sites (Table 3). However, at both study sites, most individuals did not reach the maximum size.…”

Section: Discussionmentioning

confidence: 74%

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The fate of an immigrant: Ensis directus in the eastern German Bight

Dannheim

Rumohr

2011

Helgol Mar Res

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We studied Ensis directus in the subtidal (7-16 m depth) of the eastern German Bight. The jackknife clam that invaded in the German Bight in 1978 has all characteristics of a successful immigrant: Ensis directus has a high reproductive capacity (juveniles, July 2001: Amrumbank 1,914 m -2 , Eiderstedt/Vogelsand: 11,638 m -2 ), short generation times and growths rapidly: maximum growth rates were higher than in former studies (mean: 3 mm month -1 , 2nd year: up to 14 mm month -1 ). Ensis directus uses natural mechanisms for rapid dispersal, occurs gregariously and exhibits a wide environmental tolerance. However, optimal growth and population-structure annual gaps might be influenced by reduced salinity: at Vogelsand (transition area of Elbe river), maximum growth was lower (164 mm) than at the Eiderstedt site (outer range of Elbe river, L ? = 174 mm). Mass mortalities of the clams are probably caused by washout (video inspections), low winter temperature and strong storms. Ensis directus immigrated into the community finding its own habitat on mobile sands with strong tidal currents. Recent studies on E. directus found that the species neither suppresses native species nor takes over the position of an established one which backs up our study findings over rather short time scales. On the contrary, E. directus seems to favour the settlement of some deposit feeders. Dense clam mats might stabilise the sediment and function as a sediment-trap for organic matter. Ensis directus has neither become a nuisance to other species nor developed according to the 'boom-and-bust' theory. The fate of the immigrant E. directus rather is a story of a successful trans-ocean invasion which still holds on 23 years after the first findings in the outer elbe estuary off Vogelsand.

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Section: Discussionmentioning

confidence: 74%

“…However, at both study sites, most individuals did not reach the maximum size. Optimal growth for the European E. directus is assumed generally in the deeper eulittoral respectively shallow sublittoral between 0 and 20 m depth (Swennen et al 1985;Beukema and Dekker 1995;Armonies and Reise 1999).…”

Section: Discussionmentioning

confidence: 99%

The fate of an immigrant: Ensis directus in the eastern German Bight

Dannheim

Rumohr

2011

Helgol Mar Res

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“…Razor clams were accidently introduced to the Wadden Sea with ballast water in 1978 (Dannheim & Rumohr, 2012; Freudendahl, Nielsen, Jensen, & Jensen, 2010; von Cosel, Dörjes, & Mühlenhardt‐Siegel, 1982), and the species has since extended its range substantially over the last three decades (Dekker & Beukema, 2012). Common eiders, common scoters, and various shorebird and gull species regularly use this new source of food (Swennen, Leopold, & Stock, 1985; Tulp et al, 2010). Compared with other bivalve species, razor clams represent an energy‐rich prey organism with a good shell–flesh‐ratio (own unpublished data).…”

Section: Discussionmentioning

confidence: 99%

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

Enners¹,

Schwemmer²,

Corman³

et al. 2018

Ecology and Evolution

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Herring gulls (Larus argentatus) are opportunistic predators that prefer to forage in the intertidal zone, but an increasing degree of terrestrial foraging has recently been observed. We therefore aimed to analyze the factors influencing foraging behavior and diet composition in the German Wadden Sea. Gulls from three breeding colonies on islands at different distances from the mainland were equipped with GPS data loggers during the incubation seasons in 2012–2015. Logger data were analyzed for 37 individuals, including 1,115 foraging trips. Herring gulls breeding on the island furthest from the mainland had shorter trips (mean total distance = 12.3 km; mean maximum distance = 4.2 km) and preferred to feed on the tidal flats close to the colony, mainly feeding on common cockles (Cerastoderma edule) and shore crabs (Carcinus maenas). In contrast, herring gulls breeding close to the mainland carried out trips with a mean total distance of 26.7 km (mean maximum distance = 9.2 km). These gulls fed on the neobiotic razor clams (Ensis leei) in the intertidal zone, and a larger proportion of time was spent in distant terrestrial habitats on the mainland, feeding on earthworms. δ 13C and δ 15N values were higher at the colony furthest from the mainland and confirmed a geographical gradient in foraging strategy. Analyses of logger data, pellets, and stable isotopes revealed that herring gulls preferred to forage in intertidal habitats close to the breeding colony, but shifted to terrestrial habitats on the mainland as the tide rose and during the daytime. Reduced prey availability in the vicinity of the breeding colony might force herring gulls to switch to feed on razor clams in the intertidal zone or to use distant terrestrial habitats. Herring gulls may thus act as an indicator for the state of the intertidal system close to their breeding colony.

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“…In the Wadden Sea, oystercatchers have been observed foraging on E. americanus at low tide (Swennen et al 1985;Dernedde 1994). Faecal and stomach studies of Common Eider from Norway and from the Danish and Dutch Wadden Sea have revealed E. americanus in its diet (Leopold 2002;Freudendahl and Nielsen 2003;Cadee 2006).…”

Section: Mortalitymentioning

confidence: 99%

“…They reach a refuge given the size-dependent burrow depth and their fast withdrawal response when approached by an enemy. Oystercatcher (Haematopus ostralegus) (Swennen et al 1985), gulls (Larus sp.) (Schneider 1982;Dernedde 1994;Knudsen 2001), Common Eider (Somateria mollissima) (Freudendahl and Nielsen 2003) and Common Scoter (Melanitta nigra) (B. Jacobsen, personal communication) are known as consumers of E. americanus, but to what extent their consumption inXuence the standing stock of clams is unknown.…”

Section: Introductionmentioning

confidence: 99%

The introduced clam Ensis americanus in the Wadden Sea: field experiment on impact of bird predation and tidal level on survival and growth

Freudendahl

Nielsen

Jensen³

et al. 2009

Helgol Mar Res

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In the Danish Wadden Sea the intertidal distribution of the introduced bivalve Ensis americanus (syn. E. directus) is restricted to a narrow zone around the mean low water level. To test the possible impact of birds and submersion time on dynamics and distribution of the clams, adult specimens of E. americanus collected near the low water line were transplanted to two intertidal sites and established in open and net-covered experimental plots for 9 weeks (autumn 2001). The lowest survival of clams was registered at the low-shore-site (LSS) in plots open to bird predators, suggesting that birds such as Common Eider (Somateria mollissima) or Oystercatcher (Haematopus ostralegus) may control the abundance of E. americanus at the lower tidal levels. For clams showing increment in shell length during the study period, the shell growth rates were highest at the LSS and lowest in the open plots at the highshore-site (HSS). DiVerences in immersion time and thus food supply may explain this pattern. Body mass index (BMI) of the clams showed basically the same pattern as the survivorship: lowest BMI in open plots at the LSS and highest in the covered plots at this site. Clams from the HSS were intermediate in their BMI. Disturbance by birds in the open plots at the LSS may explain the low BMI. In conclusion birds may be an important factor controlling abundance of E. americanus in the lower intertidal zone.

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Notes on growth and behaviour of the American razor clamEnsis directus in the Wadden Sea and the predation on it by birds

Cited by 40 publications

References 8 publications

The fate of an immigrant: Ensis directus in the eastern German Bight

The fate of an immigrant: Ensis directus in the eastern German Bight

Intercolony variations in movement patterns and foraging behaviors among herring gulls (Larus argentatus) breeding in the eastern Wadden Sea

The introduced clam Ensis americanus in the Wadden Sea: field experiment on impact of bird predation and tidal level on survival and growth

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