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Introduction: Partners in Slime |
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Why move? “Mobility is a key determinant of the survival and reproductive success of animals” (Cain, 1985). Every day intertidal communities are teaming with creatures that move in and around in their distinct zones, searching for food, or mates. Some avoid predators or shift position due to competition for space. Some of these creatures movements are so slow that they can hardly be observed even when peering closely at the sessile creatures on the rocks. Sometimes they are not moving at all in an attempt to avoid drying out in the air. All do eventually move however and in specific ways, even if only at a snails pace, as I will show in my study. One of, if not the main problem, of intertidal organisms is keeping their position on shore, and their position in the intertidal. It must be able to orient itself upshore or downshore depending on its preferred habitat (Erlandsson et al, 1998). Some species may have particular food they like found only in that specific habitat which keeps them shuffling through this area. Some species, i.e. limpets will return to their home or ‘scar’ by cues such as trail following (Gendron, 1977). Due to this positioning of species in their specific habitats and also due to competition for space, patterns of zonation are noticed in intertidal areas. Movement and maintenance of a specific altitude in the intertidal could also be attributed to avoidance of predators. We know that rocky intertidal snails exhibit dramatic morphological variation across environmental gradients. Studies have linked this as a response to predation. Numerous shells attributes can deter predation, thickness and spines included (Vermeij,1982). Thicker shells, for example, could suggest that natural selection events may be facilitated by Green crab invasive from the Gulf of Maine. In a study by Trussell (2000) regression analysis revealed both shell mass and thickness deceased with increase latitude (colder temperatures). Transplantation experiments conducted between northern and southern sites along the coast of Maine show that water temperature can also influence the distribution of types of snails. Deposition and maintenance of shells should be more difficult in cold water regions because calcium carbonate becomes less saturated and more soluble in colder temperatures (Trussell, 2000). The upper reaches of snail populations on the coasts may be a result of the difficulty of actually forming shells. Local migration is crucial to gene flow between marine gastropods that do not broadcast larvae. In some populations of L.saxatilis throughout the Atlantic Coasts, contrasting morphologies occupy different tidal levels of the same shore. There are two distinct morphs one at the upper and one at the lower shore, overlapping in distribution at a small mid shore region. Hybrids can be found here. (Erlandsson et al, 1998) Information about how animals move through complex and patchy habitats is crucial to understanding how animals use their habitat. Spatial and temporal patterns of distribution and population dynamics might be revealed. Dispersal could be influenced by many factors including the species own mobility and specificity for different resources and food, or its ability to perceive different aspects of its habitat perhaps in the form of cues (Chapman, 2000) L.saxatilis's limited dispersal is influenced by its direct-development (Sokolov, 2002). Its young hatch from eggs, and join the adults as juveniles. T.muricatus movement and mating is influenced by moisture and rainfall (Hamilton & Winter 1984). The ability to move makes it possible for small intertidal organisms, such as gastropods L.saxatilis and T.muricatus to forage and mate. Both of these species prefer to do most of their movement in the higher intertidal, meaning that they are subject to harsher conditions and often may not even move much in an attempt to escape desiccation. In order to see and observe movement by these snails I conducted this study. The specific purpose of this study was to determine any movement patterns of Littorina saxatilis after being transplanted to a new location, and to determine the movement patterns of Tectarius muricatus overnight. ON to: or... All information found on this site is for educational purposes only. Unless otherwise specified, all images are property of Kathryn Brown. For permission to use contact: Kathryn Brown (site creator) or Clark University Worcester, MA © 2004
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