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Atlantic Shoreline Ecology Homepage Gulf of Maine Organisms Nerita Versicolor Experiment
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Algal species in the intertidal play an important role as bioengineers. Algal canopies of Ascophyllum nodosum have been shown to greatly reduce physical stresses at high interidal zones (Bertness, et. al. 1999). These benthic algae also provide for a large primary production base within the intertidal. The light, nutrient cycling and water flow of intertidal zones exhibit the perfect characteristics for high productivity (Bertness, Mark D. 1999). Nutrient runoff from terrestrial habitats, improved gas exchange through high water flow and a large amount of light for photosynthesis explain why these algae are so profuse. Algae can be classified by whether they are ephemeral or leathery. Ephermeral types are short lived, easily eaten, and experience rapid growth. Leathery types by contrast recruit more slowly, but are difficult for animals to consume and therefore live longer (Bertness, Mark D. 1999). Ephermeral types tend to fall into the category of chlorophytes. Ulva lactuca and Enteromorpha spp. exemplify this group in New England intertidal communities (Bertness, Mark D. 1999). Leathery types divide into phaeophytes and rhodophytes, with phaeophytes being more leathery and larger and rhodophytes growing in smaller clumps in the Gulf of Maine or as crusts (Bertness, Mark D. 1999). Life history traits of algae vary from species to species, but most included alternate haploid and diploid generations (Bertness, Mark D. 1999). The diploid sporophyte releases haploid spores giving rise to gametophytes. These then fuse to form a diploid sporophyte, and the cycle begins again (Bertness, Mark D. 1999). Ascophyllum nodosum: Typically known as the knotted sea-wrack, this species is a phaeophyte. It alternates life stages between a diploid form and a haploid gametophyte. Water temperature at high tide has been associated highly with gamete release in Ascophyllum nodosum (Bacon, Linda C. & Vadas, Robert L. 1991). The onset, midpoint, and end stages of gamete release occur at 6, 10, and 15°C respectively (Bacon, Linda C. & Vadas, Robert L. 1991). The midpoint occurs at a cumulative temperature of 358°C (Bacon, Linda C. & Vadas, Robert L. 1991). A. nodosum has been shown to keep rocky substrate sheltered to the degree of 5°-10°C lower than plots without cover (Bertness, et. al. 1999). It also reduced environmental desiccation by an order of magnitude (Bertness, et. al. 1999).
Fucus spp. The rockweeds, Fucus spp. are also categorized as phaeophytes. They experience a different reproductive life history process than that of A. nodosum Fucus spp. have only one thallus form, which is diploid. The diploid thallus produces haploid gametes via meiosis, which in turn combine to form a diploid thallus structure to complete the reproductive cycle (Castro & Huber 2000). Fucus distichus has been shown to recruit based on site specific factors such as the patch size of cleared areas in which it has the ability to recruit. (Dudgeon, S. & Petraitis, Peter S. 2001). Fucus spp. also show a greater ability to recruit on a substrate covered in Balanus glandula in field tests (Farrell, Terence M. 1991). F. disticus has the ability to exhibit induced defenses in response to predation. When experimentally damaged, Van Alstyne (1988) found that Fucus increased inner concentrations of polyphenolic compounds, which disrupt animal digestion, by around 20% compared to uninjured algae. Littorina sitkana, when exposed to damaged and undamaged Fucus showed a strong preference to the damaged algae at first, and then shifted their preference over two weeks to the uninjured algae. The injured algae lost around 50% less tissue than the uninjured algae during that time (Van Alstyne, Kathryn L. 1988).
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Ascophyllum nodosum
Fucus distichus
Ascophyllum and Fucus |
