The Role of the seagrass Posidonia oceanica onthe sea urchin Paracentrotus lividus
2008
Pinna, Stefania
In this research several aspects of the interaction between the seagrass Posidonia oceanica andthe sea urchin Paracentrotus lividus were investigated. The 1st experiment was a descriptive studythat had the aim to investigate whether protection has the same effect on the population structure ofP. lividus occurring on rocky reef habitat and in P. oceanica. The 2nd is also a descriptive study thathad the aim to estimate herbivory pressure of P. lividus on P. oceanica through indirect measures.Specifically, it was asked what portion of the seagrass leaf is attacked by the sea urchins, whetherthe abundance of grazing marks depend on the number of sea urchins and whether herbivory of P.lividus depends on shoot density of the seagrass. The 3rd experiment was done to estimate the dailymigrations of P. lividus from a rocky habitat to P. oceanica patches and particularly if they dependon the size of sea urchins and the distance from the patch edge. It was postulated that P. lividusmoves randomly to the seagrass patch and that the probability of reaching it could decrease with thedistance. The 4th experiment had the purpose to investigate the role of P. oceanica structure on P.lividus distribution manipulating the seagrass structure and modifying the shoot density and leafhigh. Also, in this experiment artificial (plastic) seagrass units mimicking natural seagrass havebeen used so that different combinations of shelter and food were provided.
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