| Epiphytes | ||
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Costs: The presence of epiphytes on Ascophyllum may damage the seaweed by removing tissue, and weighing down the plant thereby reducing its access to light needed for photosynthesis. It may also increase the amount of drag on the plant stipes and increase the rate of breakage or detachment of branches (Williams and Seed; John et al 1992). The presence of epiphytes can slow the growth of the Ascophyllum and may decrease its reproductive success, but researchers have found that the presence of L. obtusada does not significantly affect the success of individual Ascophyllum plants (John et al 1992). Benefits: Grazing can sometimes be beneficial to the plant by decreasing the surface area of the plant, thereby reducing drag and the frequency of breakage at sites exposed to moderate and high amounts of wave action. Grazers may also benefit the plant by consuming and dispersing seeds, as well as excreting nitrogen in the form of Ammonium into the water near the plant increasing the nitrogen available for uptake by the seaweed (Taylor & Rees 1998). Algal Epiphytes There is evidence that nutrient exchange occurs between the host and Polysiphonia lanosa, an obligate epiphyte of Ascophyllum nodosum. P. lanosa depends on Ascophyllum for some amount of minerals and amino acids which it obtains directly from Ascophyllum (Penot 1993; Ciciotte & Thomas 1997). It has also been shown that there is a reciprocal exchange of carbon between Ascophyllum and P. Lanosa (Ciciotte & Thomas 1997). |
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