New insights into the ecology and conservation of bryozoans: from global diversity patterns to the responses to anthropogenic stressors in the Mediterranean Sea = Noves aproximacions a l’ecologia i conservació dels briozous: des dels patrons globals de diversitat fins les respostes als impactes humans al Mar Mediterrani

Abstract

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, from understanding global diversity patterns to evaluating the ecological responses of species to different impacts in order to protect marine ecosystems. 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 for both marine sessile species and bryozoans 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, encouraging to incorporate this methodology in future studies.

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 Pentapora 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. Our results highlight that the over frequentation of divers compromises the future viability of populations, highlighting the need to explore other active management strategies. 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, such as bryozoans. Our findings enlarge the current ecological knowledge of bryozoans at different scales, and highlight that more effort is needed to protect vulnerable populations.

Els ecosistemes marins estan sotmesos a múltiples impactes a escales locals i globals i que a més interaccionen entre ells. Per aquesta raó, és important estudiar els patrons de biodiversitat i ecològics a través d’una aproximació multi-disciplinària, que pot anar des d’entendre els patrons de diversitat global fins a avaluar les respostes ecològiques de les espècies enfront diferents impactes, per així conservar i gestionar adequadament les comunitats marines. Fins aquest moment, la majoria d’estudis relacionat s’han centrat en grups carismàtics i populars, com ara les gorgònies, els coralls, les macroalgues o les fanerògames marines. En canvi, aquesta tesis es centra en l’estudi dels briozous, un grup abundant de invertebrats sèssils marins distribuïts per tot el món, però generalment poc estudiats. Per aquesta raó, el principal objectiu d’aquesta tesis és utilitzar diferents aproximacions per entendre els patrons de descobriment i macro-ecològics a escala global, i la resposta a diferents impactes a escala local, combinant el ús de bases de dades globals, el seguiment in situ de les poblacions, experiments en aquaris i el desenvolupament de tècniques de restauració. A més, la present tesis vol proporcionar un marc de treball per identificar, gestionar i conservar les poblacions vulnerables en el context de l’augment de les activitats humanes que afecten els ecosistemes marins. Els resultats presentats en aquesta tesis mostren la importància d’aplicar diferents aproximacions per entendre els patrons ecològics globals i locals de grups abundants però poc estudiats, com són els briozous. Els resultats obtinguts contribueixen a augmentar el coneixement dels patrons ecològics dels briozous a diferents escales, i mostren que cal més esforç per protegir les poblacions vulnerables. Així, mesures de gestió adaptativa i de restauració i són necessàries per promoure la conservació dels ecosistemes marins en un context de impactes creixents derivats de l’activitat humana tant a escales locals com globals.