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

Abstract

Shell size distribution patterns of marine gastropod populations may vary considerably across diVerent environments. We investigated the size and density structure of genetically continuous periwinkle populations (Littorina littorea) on an exposed rocky and a sheltered sedimentary environment on two nearby islands in the south-eastern North Sea (German Bight). On the sedimentary shore, periwinkle density (917 § 722 individuals m ¡2 ) was about three times higher than on the rocky shore (296 § 168 individuals m ¡2 ). Mean (9.8 § 3.9 mm) and maximum (22 mm) shell size of L. littorea on the sedimentary shore were smaller than on the rocky shore (21.5 § 4.2 and 32 mm, respectively), where only few small snails were found. Additionally, periwinkle shells were thicker and stronger on the rocky than on the sedimentary shore. To ascertain mechanisms responsible for diVerences in population structures, we examined periwinkles in both environments for growth rate, predation pressure, infection with a shell boring polychaete (Polydora ciliata) and parasitic infestation by trematodes. A crosswise transplantation experiment revealed better growth conditions on the sedimentary than on the rocky shore. However, crab abundance and prevalence of parasites and P. ciliata in adult snails were higher on the sedimentary shore. Previous investigations showed that crabs prefer large periwinkles infested with P. ciliata. Thus, we suggest that parasites and shell boring P. ciliata in conjunction with an increased crab predation pressure are responsible for low abundances of large periwinkles on the sedimentary shore while high wave exposure may explain low densities of juvenile L. littorea on the rocky shore. We conclude that biotic factors may strongly contribute to observed diVerences in size structure of the L. littorea populations studied on rocky and sedimentary shores.

An environmental stress model correctly predicts unimodal trends in overall species richness and diversity along intertidal elevation gradients

“…At Nord-Ost Hafen, periwinkle abundance remained similar across elevations and was lower than at Kringel, which suggests a weaker grazing role at Nord-Ost Hafen. Dogwhelks (Nucella lapillus) and green crabs (Carcinus maenas) are important predators on North Atlantic rocky shores (Ropes 1968;Menge 1976;Eschweiler et al 2009;Wong et al 2012). At Kringel, both species increased in abundance toward low elevations, which also agrees with the ESM expectation of an increasing consumer pressure with decreasing stress (Menge and Sutherland 1987).…”

Species richness and diversity across rocky intertidal elevation gradients in Helgoland: testing predictions from an environmental stress model

“…On Helgoland rocky shores, periwinkles (Littorina spp.) and green crabs (Carcinus maenas) are important consumers (Janke 1990;Eschweiler et al 2009). The most abundant periwinkles, Littorina littorea and L. obtusata, feed readily on the green algae Ulva spp.…”

Comparing the ability of a non-indigenous and a native seaweed to induce anti-herbivory defenses

“…Both were selected for this study because they are (1) very abundant on Helgoland (e.g. Eschweiler et al 2009), (2) consume considerable amounts of M. stellatus (unpublished data HY Yun), and (3) diVer in their geographical distribution. L. littorea is absent from the donor region for the Helgoland population of M. stellatus, whereas I. granulosa inhabits both the donor and recipient region (Ingolfsson 2006;Reichert and Buchholz 2006).…”