Littorina spp. Essays - Littorinidae, Common Periwinkle,

Littorina spp. Also known as "the Common Periwinkle" The Littorina sp p . is a small marine snail or gastropod , that is widely distributed th roughout parts of N orthern Europe and North America; where they are most commonly found along rocky shores in the intertidal zon e. Although Littorina spp. is most common in tide-pools and rocky substrate s but it can also be found in muddy or sandy substrates. (Encyclopedia Britannica "periwinkle" ). Salinity is an environmental factor that remains relatively constant in open water but at the intertidal zone it varies considerably. Salinit y levels climb due to fresh water evaporating when the intertidal zone is exposed but can also decrease when there is a n influx of fresh water that dilutes the salinity levels. Salinity levels in the ocean can vary between 30-35 ppt whereas the intertidal zone can have salinity levels between 5ppt and 40ppt depending on environmental influences. (Cohen, A 2011, Littorina littorea ) The Littorina spp. is considered a euryhali ne species, meaning it is able has developed multiple behavioral and physical adaptations that allows it to withstand a wide range of salinity. The periwinkle cannot control the salt content of their body (meaning it is an osmoconformer). This means that the salinity in their tissues fluctuates with that of the water. ( Hoyaux , J., Gilles, R. and Jeuniaux , C., 1976). When the salinity of the water is outside their range of tolerance (down to 13 ppt ) action must be taken. (Cohen, A 2011, Littorina littorea ). When the periwinkle's chemoreceptors detect an unfavorable salinity t he snail must somehow escape unfavorable conditions so that the salinity in their bodies does not exceed or deceed * 1 their range of tolerance. Since the periwinkle is a non-sessile organism it will try to reduce the effects of changing salinity by avoiding the stress and moving into a more suitable micro-habitat. Another behavioral response that the Littorina spp. possesses is their "shell closing mechanism" which allows the periwinkle to remain sealed off from the source of stress (in this case salinity) creating a hyperosmotic state *2 allowing the Littorina spp. to survive in an environment that is outside their range of tolerance; a lthough this renders them incapable of movement. ( Berger, V.J. and Kharazova , A.D., 1997 ) . Our group has decided to create an experiment to measure "How salinity affects the movement of the Littorina spp. ?" . I predict that there will be conclusive evidence that shows that when exposed to a salinity outside their range of tolerance (in this case 10 ppt ), the Littorina spp. 's movement will decrease if not cease all together compared to when they are in a salinity of tolerable levels (30ppt). I have formed this hypothesis due to the following concepts. In their natural environment the periwinkles chemoreceptors would be able to detect the gradual change in salinity which would allow them time to move out of that area of (impending) stress and into a different micro-environment. In our experiment though , t he Littorina spp. is being introduced to an environment with a salinity outside their range of tolerance abruptly, and will almost immediately initiate the "shell closing mechanism" to separate their bodies from the harmful or unfavorable external environment. (Berger, V.J. and Kharazova , A.D., 1997) . Because of this we will note that there is an overall decrease of movement because the predicted behavioral r esponse would inhibit movement resulting in a decreased amount of movement in lower salinity solution as predicted. * 1 : there is no established opposite to the word exceed in the English language, and it's quite often suggested that it is a gap in the language that needs to be filled. Deceed has come up as a possible candidate but hasn't been approved or instated. For the purposes of this paper, I have used the word deceed as an antonym to the word exceed. *2 : A cell that contains a higher number of solutes than its surroundings Citations Berger, V.J. and Kharazova , A.D., 1997. Mechanisms of salinity adaptations in marine molluscs . InInteractions and Adaptation Strategies of Marine Organisms(pp. 115-126). Springer Netherlands.