New insights into the ecology and conservation of bryozoansfrom global diversity patterns to the resopnses to antrhopogenic stressors in the Mediterranean Sea

Resumen

Marine ecosystems are directly threatened by multiple and interactive human stressors at global and local scales. Hence, it is vital to study biodiversity and ecological patterns through a multi-disciplinary approach. In this thesis, we focused on bryozoans, an abundant group of sessile marine invertebrates distributed worldwide, but generally understudied. Accordingly, in this thesis we provide different approaches to understand discovery and macroecological patterns at global scales, and the response of species to different stressors at local scales, combining the use of open databases, the in situ monitoring of natural populations, experiments in aquaria and the development of restoration techniques. At global scale, in Chapter I we unraveled discovery patterns of fossil and extant bryozoans and showed the highest number of fossil species described, highlighting that the current biodiversity represents only a small proportion of Earth’s past biodiversity. Beyond these differences, both groups showed an increase in the taxonomic effort during the past century. Despite this progress, future projections of discovery patterns of both groups showed a large proportion of species remaining to be discovered by the final of this century. In Chapter II, most of the global diversity patterns of marine sessile groups, including bryozoans, showed a non-unimodal latitudinal pattern with a dip in the number of species at the equator and a higher diversity in the Southern ocean. Moreover, this region will be less affected by global warming at the final of this century. In contrast, our analyses showed that the most sampled region was North Temperate Atlantic, highlighting the importance to quantify environmental drivers considering sampling effort biases. For this reason, we tested the effect of using the popular method of rarefaction (ES50) vs the incorporation of a frequency index of sampling effort as co-variate in quantitative models. Despite we obtained the same best predictors for both approaches (depth, nitrate, and SST), the models using the correction of sampling biases through frequency index showed better fitting. Focusing on the Mediterranean Sea, in Chapter 3 we studied the responses of bryozoans to different stressors. First, we showed that two abundant and common bryozoans, Pentapora fascialis and Myriapora truncata, displayed different tolerances to warming through the combination of in situ monitoring and experiments in aquaria. Moreover, in Chapter 4 the in situ monitoring of P. fascialis populations revealed its fast population dynamics, with high recruitment and growth rates, and a high capacity of recovery. Accordingly, we observed an increase in the density of its populations in the Medes Island Marine Reserve since the 1990s. However, we evidenced that diving can impact on the density, recruitment, survival, and size of the colonies, registering lower values in frequented localities. For this reason, in Chapter 5, we tested and developed different restoration techniques for P. fascialis, focusing on the recruitment enhancement through the installation of recruitment surfaces and the transplantation of adult colonies. The successful results and the affordable and economic cost of tested techniques aim to encourage the managers of Marine Protected Areas to apply similar methodologies. The results presented in this thesis show the importance to combine different approaches to understand the global and local ecological patterns of understudied but abundant groups. Our findings enlarge the current ecological knowledge of bryozoans at different scales, and highlight that more effort is needed to protect vulnerable populations.