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Atlantic Shoreline Ecology Homepage Gulf of Maine Organisms Nerita Versicolor Experiment Abstract
Introduction
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The distribution of intertidal organisms is a complex function of both biological and physical interactions. These factors contribute to intertidal zonation, a phenomenon in which upper distribution limits of organisms are due to physical factors and lower limits due to biological interactions (Castro, P. & Huber, M.E. 2000). Light exposure, salinity, temperature, air exposure, and wave action are all factors that can limit distribution of intertidal organisms quite readily (Knox, G.A. 2001). Adaptation to salinity changes include a myriad of responses comprised of escape, reduction of contact, regulation and acclimation (Kinne 1967). Mobile animals tend to employ the escape behavior when exposed to an unfavorably saline environment (Knox, G.A. 2001). Field and laboratory experiments have shown that Nerita versicolor's distribution is highly dependent on exposure to physical environmental factors (Bovbjerg, R.V. 1984). Nerita versicolor is a banded, amber colored gastropod with four "teeth" jutting from the shell near its operculum that spends much of its time in the upper intertidal (Bovbjerg, R.V. 1984). Nertia spp. are cryptic in their native rocky intertidal habitats. They experience little predation, seen only to be preyed upon by Octopus vulgaris (Bovbjerg, R.V. 1984). Nerita spp. spawn continuously, with no seasonal degeneration of the gonads (Hughes, R.N. 1971). Occurring in an approximate 1:1 ratio, no sexual reversal has been detected (Hughes, R.N. 1971). Males transfer large amounts of spermatophores to the females via a gelatinous tube (Hughes, R.N. 1971). Spawning always occurs at night, and females carry a store of spermatophores in their spermatophore sac at all times (Hughes, R.N.). Sexually mature at 16-19 mm, Nerita versicolor deposit a mean number of 143 egg capsules per year on the substrate, which then hatch into a fairly long pelagic veliger state (Hughes, R.N. 1971). Dispersal by the pelagic veliger form implies a large distribution that involves minimal active selection by the organisms themselves. Distribution due to food preference has not been correlated with food availability in Nerita versicolor due to nonspecified foraging habits. Bovbjerg (1984) scraped the surface film from areas in which Nerita spp. were feeding to determine what food was present for nerites to scrape with their radulas. Along with sand particles and detritus, algal cells both filamentous and sheet-like, flagellates, diatoms, and nematodes were observed (Bovbjerg, R.V. 1984). On examining fecal pellets of the gastropods, their consumption content reflected very closely those materials found on the hard substrate (Bovbjerg, R.V. 1984). Response to tidal fluctuation and light exposure were found to be highly correlated with nerite movement in the intertidal by Bovbjerg (1984). He found no correlation between nerite movement and salinity or temperature in tide pools however. The purpose of this study was to examine physical factors that have not been found to influence the distribution of Nerita versicolor in a more direct fashion. A focus on salinity asked questions left only on the periphery of other studies. It was expected that nerite movement and retention rates would be, at least in part, affected by changes in salinity due to evaporation in intertidal pools.
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Nerita versicolor Phylum: Mollusca Class: Gastropoda Order: Arachaeogastropoda Genus: Nerita Species versicolor: |
