Estudi de la dinàmica poblacional i de l’efecte d’un impacte puntual produït a una població de Cystoseira crinita al Port de la Selva

Some of the most characteristic communities of well-lit backgrounds of temperate oceans are macroalgae forests. In the Mediterranean these forests are formed by algae of the genus Cystoseira. These are the main habitat-forming species in Mediterranean deep-sea rocky beds. Currently, Cystoseira forests are experiencing a significant decline that is affecting the services offered by these ecosystems, due to various impacts, such as habitat destruction, eutrophication or the rise in temperatures due to climate change. This study has focused on a specific species of the genus Cystoseira: Cystoseira crinita, a relict species on the Catalan coast that inhabits in shallow waters of environments with small wave action and high intensity of light. The first objective of the project was to study the dynamics and reproduction of a population of Cystoseira crinita during the year 2017, which lives in a coastal basin of half a meter deep in Port de la Selva. A monthly sampling of this population was carried out during the years 2017 and 2018, where a seasonal variation marked by the intensity of light and temperature was observed, with peaks in spring and falls in winter. The second objective was to study, on the one hand, the effect of a punctual impact produced in July of 2018 in this population, where the basin was in a state of anoxia and caused the mortality of a Much of the population, and on the other hand, the possible causes of this disturbance. In general, there was a significant decrease in the density of individuals in the months after the impact, but no variation in the size structure of the population, as a result of the surviving individuals located at the ends of the cuvette. Thanks to a record of the temperatures inside and outside the cuvette that was carried out during the year 2017 and 2018 it was observed that the mortality detected coincided with an increase in extreme temperatures due to climate change, coinciding with the increase in the concentration of nutrients and the little renovation of the water were the causes of the impact. Finally, in order to see how the population will evolve in the future, there has been a forecast of how it could harm a climate change scenario in which we find the species studied, and the whole of marine biodiversity