Grazing on green algae by the periwinkleLittorina littorea in the Wadden Sea

Abstract

On sedimentary tidal flats in the Wadden Sea near the Island of Sylt, the periwinkle Littorina littorea occurred preferentially on clusters and beds of mussels and on shell beds (100 to 350 m-2), achieved moderate densities on green algal patches or mats (20 to 50 m-2), and remained rare on bare sediments (<5 m-2). Green algae covering > 10 % of sediment surface appeared in summer on approximately one third of the tidal zone, mainly in the upper and sheltered parts and almost never on mussel and shell beds. In feeding experiments, L. fittorea ingested more of the dominant alga, Enteromorpha, than of U/va, irrespective of whether or not algae were fresh or decaying. The tough thalli of Chaetomorpha were hardly consumed. Snails feeding on Enteromorpha produced fecal pellets from which new growth of Enteromorpha started. In the absence of periwinkles, Enteromorpha developed on mussels and the attached fucoids. Experimentally increased snail densities on sediments prevented green algal development, but the snails were unable to graze down established algal mats. It is concluded that natural densities of L. httorea hardly affect the ephemeral mass development of green algae on sediments. However, where the snails occur at high densities, i.e. on mussel beds, green algal development may be prevented.

Habitat-specific size structure variations in periwinkle populations (Littorina littorea) caused by biotic factors

“…benthic diatoms and green algae such as Ulva spp.) and/or a limited time available for feeding due to strong wave action on the exposed rocky shore (Brown and Quinn 1988;Wilhelmsen and Reise 1994;Reid 1996;Fenske 1997). Thus, faster growth may be responsible for thinner and weaker periwinkle shells in L. littorea living on bivalve aggregations in the Wadden Sea.…”

“…Hawkins and Hartnoll 1983;Anderson and Underwood 1997). SpeciWcally, periwinkles aVect benthic community structure and recruitment success of structurally important seaweeds (Lubchenco 1978;Janke 1990;Wilhelmsen and Reise 1994;Albrecht 1998;Buschbaum 2000;Trussell et al 2002Trussell et al , 2003. The ecological eVect of periwinkles may vary with body size.…”

“…We chose the exposed rocky shore of the island of Helgoland and a sheltered soft sediment environment near the island of Sylt as study areas. At both sites, genetically identical populations of the periwinkle L. littorea (Wilhelmsen 1998) reach high densities of hundreds of individuals per square metre (Janke 1990;Wilhelmsen and Reise 1994;Buschbaum 2002;Reichert and Buchholz 2006). Our Wrst step was to establish the shell morphology and the size and density distribution of L. littorea on the exposed rocky and sheltered sedimentary shores.…”

Age-dependent zonation of the periwinkle Littorina littorea (L.) in the Wadden Sea

“…Densities of up to 2,000 m -2 were reported from intertidal mussel beds (Albrecht and Reise 1994) and Fenske (1997) supposed that the available resources on the mussel beds were sufficient to maintain a high population density of L. littorea and rejected the possibility of intraspecific competition. The snails feed on the microalgal films (diatoms) covering the mussel shell surfaces including young sporelings of ephemeral algae or young stages of barnacles, and thus play an important role in structuring the mussel bed community (Wilhelmsen and Reise 1994;Albrecht 1998). Near the island of Sylt these mussel beds gradually extend from mid-intertidal to adjacent shallow subtidal zones and, therefore, present an excellent site for studying zonation patterns of L. littorea in the Wadden Sea.…”

Effects of barnacle epibionts on the periwinkle Littorina littorea (L.)

“…However, in the rather unstable sediments of the Wadden Sea, sessile algae and invertebrates depend on biogenic hard substrates, such as epibenthic molluscs. Periwinkles Littorina littorea (L.) are common epibenthic organisms in the Wadden Sea (Wilhelmsen and Reise 1994), providing suitable attachment sites for sessile organisms.…”