Macroalgal forests ecology, long-term monitoring, and conservation in a mediterranean marine protected area
- Autores: Alba Medrano Cuevas
- Directores de la Tesis: Critina Linares Prats (dir. tes.), Bernat Hereu Fira (codir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2020
- Idioma: inglés
- Tribunal Calificador de la Tesis: Javier Romero Martinengo (presid.), Luisa Mangialajo (secret.), Andrés Alonso Ospina Álvarez (voc.)
- Programa de doctorado: Programa de Doctorado en Ecología, Ciencias Ambientales y Fisiología Vegetal por la Universidad de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Macroalgal beds dominate the shallow benthic Mediterranean habitats where they play a pivotal role. Among them, the canopy-forming Cystoseira sensu lato species represent the highest structural complexity level and provide unique habitats with ecological services comparable to terrestrial forests. Canopy-forming algae are in decline in many coastal areas where, among other impacts, overgrazing by herbivorous can lead to the loss of these diverse habitats shifting towards degraded sea urchin barren grounds. Conservation tools such as marine reserves or No-take zones (NTZs) have the potential to reduce some of the anthropogenic threats and to restore benthic habitats through trophic cascade effects. Besides, active ecosystem restoration strategies may speed up the recovery of impacted ecosystems. Nevertheless, there is an important lack of continuous and long-term studies providing robust ecological data of the natural dynamic and vulnerability of macroalgal assemblages while integrating the role of marine conservation.
The results of this thesis showed that the abundance and structure of the main macroalgal assemblages in the Montgrí, Illes Medes and Baix Ter Natural Park were stable at large over the last fifteen years. Overall, any effect of marine protection was observed on the most representative species of this habitat but we found a higher abundance of canopy-forming algae inside the NTZ than in unprotected areas. Contrarily, sea urchin populations were deeply affected by a severe storm in 2008 which caused the almost depletion of its populations in all the studied areas. Although similar trajectories of sea urchin abundance have been observed over the years between both protection regimes due to the large stability of the sea urchin high-density state, clear differences in the recovery of sea urchin populations were found after the storm linked to marine protection. The sea urchin populations inside the NTZ recovered slowly than the populations outside the NTZ inside due to the higher predatory fish abundance inside the NTZ. In contrast to the global widespread decline of canopy-forming macroalgal assemblages across many regions during the last decades, Treptacantha elegans has increased their distributional range and has shown an extraordinary expansion along the Catalan northern coast over the last two decades. The results of this thesis contributed to explaining this geographical and range depth extension, which could be linked to some ecological attributes such as their fast-growing dynamics, their early fertile maturity, and their high turnover rate. Besides, the molecular analyses have shown that all the populations of T. elegans in the Catalan coast constitute a single genetic group that could be originated in the MIMBT Natural Park under the marine protection benefit. Given the fast and stable population dynamics of T. elegans, this species was selected as a potential species to actively restore degraded shallow rocky ecosystems (e.g., sea urchin barren grounds) turning them into productive marine forests. In this way, the effectiveness of active restoration actions combined with passive strategies such as marine protection (e.g., NTZs) was experimentally demonstrated. This thesis addressed marine vegetation changes in the shallow rocky shores of the MIMBT Natural Park integrating the macroalgal and sea urchin dynamics in front of natural and human-related impacts, and the role and effectiveness of Marine Protected Areas and restoration actions as conservation tools at lower trophic levels. Besides, since most of this thesis is based on long-term monitoring data, a valuable baseline of the algal community’s structure and functioning was provided here which could be vital to predict and detect ecological changes that could jeopardize the preservation of marine forests.
