Ecology of Atlantic Shores
Snail Life Histories
Comparing Distribution Changes of Four Snail Species in Response to a
Seasonal Reduction in Temperature
Snail Life Histories
Since my project focused primarily on snails, I have provided some information on the four species I observed in the rocky intertidal. This is a general summary of their life history and importance within the intertidal community.
Generalized Prosobranch (anteriorly-gilled snails)
The Periwinkles (Littorines)
Periwinkles are a fairly common snail genus seen along the Atlantic shoreline. Three of these species are dominant grazers in the New England rocky intertidal. They are all herbivorous snails that use a tongue-like radula while grazing. A radula is a flat belt with replaceable chitonous or calcium carbonate teeth. Littorines typically feed on diatoms or algae, but exhibit a strong preference for fleshy algae, such as Ulva lactuca, and less of a preference for Ascophyllum nodosum, Fucus vesiculosis, and Chondrus crispus (Lubchenco 1978). The tissue is scraped into their mouths where the food is mixed with mucus and pulled into the digestive system. Their main predators include crabs such as C. maenas, H. sanguineaus, and C. borealis and sea stars such as the Asterias species.
*Littorina littorea- Common periwinkle
The species Littorina littorea was introduced to New England from Europe in the 1860s and has become the most dominant herbivore within the rocky intertidal in that area. It is typically a medium to dark gray color with very little variation from this. It has planktonic development and can reach about 2-3cm in length. It is a habitat generalist and can therefore play a significant role in the structure and organization of communities along shoreline habitats. Two examples of this are that it can severely limit distribution of green algae and its sporelings because of high grazing activity (Bertness, 1999: Lubchenco 1978, 1983) as well as displace a native mud snail in a separate salt marsh population (Bertness 1999: Brenchley & Carlton 1983). The other two littorines are smaller, native species that are typically never found in very high densities (Bertness 1999), mostly likely due to the success of L. littorea.
*Littorina obtusata- Smooth
L. obtusata is, on average, smaller than L. littorea but larger than L. saxatilis. It has a compressed shell with a smooth point but shell morphology and thickness can be highly variable, as is color. It is known for plastic responses of shell thickening to avoid predation by crabs, particularly in protected areas (Bertness 1999). A common feature of this organism is that it is often associated with huge canopies of A. nodosum and the yellow and green morphs, in particular, can resembles gas bladders of A. nodosum which can help in avoiding predation.
*Littorina saxatilis- Rough periwinkle
Taxonomy (same as L. littorea except for species name)
L. saxatilis, sometimes referred to as L. rudis, is found very high in the intertidal on rocky substrates such as cliffs and boulders. It is a very small animal, that is found up to 8mm in length. This is thought to be an adaptation for living in a splash zone, because it prevents dessication and dislodgement by wind and waves (Atkinson & Newbury 1984). It also possesses a rough, curved shell which holds large amounts of water to avoid dessication on the high cliffs that are not often submerged. Typically, L. saxatilis is exposed to air for 70-95% of a day. It was found to have the ability to survive for forty two days without water (Bertness 1999: Newell 1979) and is thus very highly adapted to survival in the upper intertidal.
Nucella lapillus- Dog whelk
N. lapillus is a predatory snail of a different family than the littorines. It preys upon mussels and barnacles by using its file-like radula to bore a hole into the prey's shell and consuming their insides. It resides in low to mid intertidal zones. They have a direct development meaning the young hatch fully developed from the egg cases. They vary in morphology and color but are generally white to cope with heat stress in protected habitats where there are less of its predators. Their main predators are crabs, birds and sea stars (Bertness 1999).