Littorines and their relatives feed on various plant matter, including diatoms, algal sporlings, microalgae and macroalgae, lichens, and detritus. Littoriina spp. are considered here, while other species BATILLARIA spp., EPITONIUM spp. & LACUNA spp. are dealt with in another section

Winkles feed mainly on diatoms and unicellular algae, and to a lesser extent on macroalgae and lichens.  Because much of the food is scraped directly from the substratum, especially when feeding on sandstone, erosive activities may be high.  Based on average content of sand in the gut of Littorina planaxis on the rocky shores of La Jolla, California it is estimated that 100 average-sized individuals will excavate about 860cc of sandstone substratum every decade.  North 1954 Biol Bull 106: 185. Photograph courtesy James Watanabe, Hopkins Marine Station, Pacific Grove, California SeaNet.

NOTE  this species is now keenae

NOTE  the calculation is based on 1.6mg sand for an average-sized 8mm length individual for a gut-passage time of 2-6h (at 17-30^oC field temperature)

Littorina keenae with arrows showing
notable shell identification features 2X

Studies at the Bodega Marine Laboratory, California show that littorines in Bodega Bay, California eat red and green microalgae, blue-green algae (Cyanophyta), diatoms, and sporelings of macroalgae.  The graph shows estimated rates of growth of Littorina scutulata, L. plena, and L. keenae assessed over a 29-mo study period.  Chow 1987 J Exp Mar Biol Ecol 110: 69. Photograph courtesy James Watanabe, Hopkins Marine Station, Pacific Grove, California SeaNet.

Littorina plena with arrow
showing identification
feature on aperture2X

West-coast winkles feed on diatom films, lichen, and algae. Diets vary with location and species and, in particular, with radular morphology.  For example, chisel-shaped radular cusps of Littorina scutulata enable them to scrape black lichen from rocks in the upper-shore spray zone (see photo on Right).  In contrast, the coarser shaped cusps of L. sitkana permit better exploitation of drift algae stranded in tidepools. Behrens Yamada 1989 Mar Biol 103: 403. Photograph on Left courtesy James Watanabe, Hopkins Marine Station, Pacific Grove, California SeaNet.

NOTE the author does not include photos of radulae in her presentation; however, for interest's sake, on the Right is a radula of an Alaskan species Littorina naticoides, viewed lengthwise, but at an angle of 45^o to show the shape of the scraping cusps.  Reid & Golikov 1991 The Nautilus 105: 7.

Littorina scutulata showing
opercular morphology 3X

In areas of Barkley Sound, British Columbia the upper intertidal region is primarily populated with red algae Mazzaella (cornucopiae) parksii, along with fucoids Fucus distichus and Pelvetiopsis limitata.  The chief non-limpet grazers in this zone are littorines Littorina scutulata.  Counts show that densities of littorines may reach 70 ^. 100cm^-2 in growths of M. cornucopiae and 15 ^. 100cm^-2 in fucoids, suggesting a preference for the red-algae habitat.  Results of substratum-preference tests and feeding assays show that Mazzaella is preferred over the fucoids (see histogram). The authors propose that on a broader scale L. scutulata may indirectly affect competitive interactions between Mazzaella and the 2 fucoids in this high-level area.  Possible follow-up research to thisstudy would be to re-examine preferences of the littorine in relation to presence of potentially defensive secondary metabolites in the algae, most notably, tannins in the brown algae. Kim & DeWreede 1996 Bot Mar 39: 561. Photograph on Left courtesy Mike Hawkes, Botany Department, UBC.

NOTE  the authors note that some of the smaller, similar-appearing species, L. plena may have gotten mixed in with L. scutulata

NOTE  these tests involve placing a number of snails in a container with equal amounts of the 3 algae and counting their disposition on the algal fronds 15min later. Note that this experiment does not assess whether the winkles are feeding on the test algae; however, other tests show that feeding does occur

Littorina scutulata amongst red
alga Gloiopeltis furcata. The
snails may be feeding on this
alga or on microalgae 1X

Gut analyses of Littorina scutulata and L. sitkana collected from a variety of habitats on rocky shores around the southern end of Vancouver Island, British Columbia reveal that both species are opportunistc omnivores.  In locations where the species co-occur the diets are similar. However, L. scutulata differs in that it can subsist on sparse growths of microflora in the supralittoral area, whereas L. sitkana is restricted to microenvironments with abundant growths of microalgae and macroalgae. Protists and animal matter such as nematodes, copepods, annelids) are eaten by both species.  Seagrasses Phyllospadix and Zostera are also consumed, but only when present in decomposing litter.  These results differ from those of other investigators mainly in the extents to which macroalgae, animal matter, and decaying plant matter are present in the diets.  Voltolina & Sacchi 1990 Hydrobiologia 193: 147. Photograph below courtesy Dave Cowles, Walla Walla University, Washington wallawalla.edu.

Not much algae is present with this large aggregation of winkles
Littoriina sitkana in a small cove in San Juan Island, Washington

In Barkley Sound, British Columbia Littorina spp. snails are important grazers of high-level red algae Mazzaella parksii. During prolonged exposure to sunlight, especially during spring and summer spring tides, the distal parts of the fronds of the alga become bleached. These bleached parts stay on the plants for some time and are eaten by littorines. Interestingly, in paired-choice experiments conducted at the Bamfield Marine Sciences Centre, British Columbia using Littorina spp., these bleached portions are preferentially consumed over normal photosynthetic tissues. The authors suggest that the preferential consumption of the bleached portions, which are located distal to the more basally sited photosynthetic tissues, may actually be of advantage to Mazzaella in diverting grazing pressure away from its vital photosynthetic tissues. The authors suggest that softer texture of the bleached portions, perhaps combined with improved nutritional content, may be contributing factors to their greater palatability to the snails. Heaven & Scrosati 2004 Hydrobiologia 513: 239.