Memoria de tesis doctoral presentada por Uxue Tilves Matheu para obtener el título de Doctora en Ciencias del Mar por la Universitat Politècnica de Catalunya (UPC), realizada bajo la dirección de la Dra. Ana María Sabatés Freijó y de la Dra. Verónica Lorena Fuentes del Institut de Ciències del Mar (ICM-CSIC).-- 149 pages, appendices, [EN] Jellyfish are important components of marine ecosystems, being a key link between lower and higher trophic levels. Jellyfish blooms occur sporadically and unpredictably in coastal areas and often have important socio-economic consequences for fisheries and tourism. This PhD thesis addresses some questions regarding the potential impact, positive and/or negative, that jellyfish have on fish populations in the Catalan coast (NW Mediterranean). [...], [ES] Las medusas son componentes importantes de los ecosistemas marinos ya que son un vínculo clave entre el zooplancton más pequeño y los niveles tróficos superiores. Las proliferaciones de medusas ocurren esporádica e impredeciblemente en áreas costeras y con frecuencia tienen importantes consecuencias socioeconómicas para la pesca y el turismo. Esta tesis doctoral aborda algunas cuestiones relacionadas con el potencial impacto de las medusas, tanto positivo como negativo, sobre las poblaciones de peces en la costa catalana (NO Mediterráneo). [...], This student has been supported by a pre-doctoral fellowship of the
FPI program (Spanish Ministry of Economy and Competitiveness). The research carried out in the present study has been developed in
the frame of the FISHJELLY project, CTM2010-18874 and CTM2015-68543-R, Peer Reviewed

Memoria de tesis doctoral presentada por Joan Mir Arguimbau para obtener el título de Doctor en Ciències del Mar por la Universitat de Barcelona (UB), realizada bajo la dirección de la Dra. Ana María Sabatés Freijo del Institut de Ciències del Mar (ICM-CSIC).-- 255 pages, 48 figures, 18 tables, 2 annexes, [EN] Blue whiting, Micromesistius poutassou (Risso, 1827), is a mesopelagic gadoid widely distributed in the North Atlantic and the Mediterranean Sea, inhabiting waters over the shelf edge and continental slope. The species plays an important role in the marine food web feeding on pelagic crustaceans and mesopelagic fish and being consumed by a wide range of predators from pelagic and benthic habitats. It is a species of commercial interest, exploited in the northern colder areas of the Mediterranean. Despite its ecological and commercial significance, information on its biology and behaviour is mostly restricted to the Atlantic waters, and the information for this species in the Mediterranean is very scarce. In the last decade, blue whiting population has displayed a decreasing trend in the NW Mediterranean, and now it remains at very low levels. In this context, this Ph.D. thesis aims to unveil the main drivers (physical, biological and anthropogenic) of the population dynamics of blue whiting in the NW Mediterranean Sea.
The blue whiting population parameters have been updated and the growth of the species and its relationship among reproduction and energy reserves have been described. Blue whiting reaches the first maturity at around 18 cm TL for both sexes that is achieved the spawning season following its birth. Females and males show different growth curves, with females reaching higher sizes than males. Spatial segregation by age and size has been observed. While smaller individuals (age 0 and 1) remain in the shelf break (130-250 m depth), the large ones (age >2) are more abundant in the upper slope (250-550 m). The largest individuals (>26 cm TL, age >3) display movements along the year and approach the coast in winter for reproduction, disappearing in summer and autumn. The study of the feeding ecology highlight the relevance of the Myctophidae fish as the main prey for blue whiting. This energetic prey is mainly consumed in spring and summer, which might allow the species to recover energy reserves after the reproductive period and supply the energetic demands of the fast growth season. The dominance of fish in the blue whiting diet evidences that the trophic position of the species in the Mediterranean is higher than in the Atlantic, where it mainly prey on Euphausiacea and zooplanktonic crustaceans. [...], [CAT] La maire, Micromesistius poutassou (Risso, 1827), és un gàdid mesopelàgic que es troba àmpliament distribuït a la zona oriental de l’oceà Atlàntic i al mar Mediterrani. Juga un paper important en les xarxes tròfiques marines ja que s’alimenta de crustacis i peixos mesopelàgics alhora que és presa d’una gran varietat de depredadors tant de l’hàbitat pelàgic com bentònic. Tot i la seva importància ecològica i comercial, la informació sobre l’espècie està centrada principalment en les poblacions de l’Atlàntic, i la informació de les poblacions del Mediterrani és molt escassa. Durant l’última dècada, la població de maire al Mediterrani nord-occidental ha anat disminuint i actualment es manté a nivells molt baixos d’abundància. En aquest context, aquesta tesis doctoral pretén dilucidar els principals impulsors (físics, biològics i antropogènics) de la dinàmica poblacional de la maire al Mediterrani nord-occidental.
En aquesta tesi, s’actualitzen els paràmetres poblacionals de la maire i es descriu el creixement de l’espècie i la relació amb la reproducció i les reserves energètiques. La maire assoleix la primera maduresa als 18 cm en ambdós sexes, a la qual arriba en la primera època de posta després del naixement. El creixement de l’espècie mostra diferències segons el sexe, les femelles assoleixen talles majors que els mascles. S’ha observat una segregació espacial per talles i edats: mentre els individus més petits (edats de 0 i 1) tendeixen a ser en el trencant de la plataforma (130-250 m de profunditat), els individus grans (edat >2) són més abundants al talús superior (250-550 m de profunditat). Els individus més grans (>26 cm, edat > 3 anys) realitzen moviments al llarg de l’any, apropant-se a la costa per a reproduir-se a l’hivern, i desapareixent a l’estiu i la tardor. L’estudi de l’ecologia tròfica destaca la importància dels peixos mictòfids com a presa principal de la maire al Mediterrani. Aquestes preses són molt energètiques i consumides principalment durant la primavera i l’estiu, la qual cosa permet que la maire recuperi les reserves energètiques després del període reproductor i alhora pugui satisfer l’alta demanda energètica de l’època de creixement ràpid. La dominància de peixos en la dieta de la maire al Mediterrani evidencia una posició tròfica major respecte a la maire de l’Atlàntic, on l’espècie depreda principalment eufausiacis i crustacis zooplanctònics. [...], The present thesis was conducted in the Institut de Ciències del Mar (ICM-CSIC; Barcelona, Spain) within the framework of the WINFISH Project (Role of vertical mixing processes and dense water formation in the spawning strategy and recruitment of winter breeding fishes in the NW Mediterranean; CTM2015-68543-R- Funded by the Spanish Ministry of Economy and Competitiveness, Spanish Government). J. Mir-Arguimbau was supported by a predoctoral fellowship of the FI program of the Secretaria d’Universitats i Recerca de la Generalitat de Catalunya, Spain, and Fons Social Europeu (FSE) (2019FI_B2 00183). This thesis acknowledges the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S), Peer reviewed

Memoria de tesis doctoral presentada por Vanesa María Raya Rodrigálvarez para obtener el título de Doctora en Ciències Marines por la Universitat Politècnica de Catalunya (UPC), realizada bajo la dirección de la Dra. Ana María Sabatés Freijo del Institut de Ciències del Mar (ICM-CSIC).-- 207 pages, The early developmental stages of fish, eggs and larvae, found in the planktonic environment are subject to a high mortality. Thus, the study of larval survival has been a key issue in fisheries science since the early 20th century. Spatial patterns in the larval fish communities are influenced by a complex array of environmental processes that interacts with fish biology at different temporal and spatial scales. These processes include those of large scale, such as climate patterns and seasonal and interannual environmental variability, which determine adults’ distribution and their spawning strategies. At local and short time scale, larval fish communities are shaped by the hydrodynamics that influence fish larval dispersal and retention, and by biologic factors, such as food concentration and predation, that ultimately determine their survival. This thesis characterises the structure of the larval fish community in summer and winter in the Catalan coast (NW Mediterranean), an area with a wide array of environmental conditions and high hydrodynamic activity. The aim is to understand its spatial and interannual variability in response to changes in environmental conditions, including oceanographic variables and hydrodynamic processes. Within the context of climate change, the thesis describes long-term changes in the structure of the summer larval fish communities and aims to understand the interactions between larvae of established species and species that are expanding northwards in the area., To investigate the influence of winter environmental conditions on the structure of fish larval communities, two winters, 2017 and 2018, with contrasting environmental conditions were compared. 2017 was mild, while 2018 was more severe, with intense vertical mixing and deep-water formation and cascading events that enhanced shelf-slope water exchanges. Differences in the structure of larval fish community were found in relation to shelf-slope water exchange processes. A high spatial heterogeneity in larval fish communities was detected in the summers of 2003, 2004 and 2012, related to environmental factors, such as the continental shelf structure, latitudinal difference in surface temperature, primary productivity, and stratification level. Hydrodynamic structures such as instabilities of the Northern Current and anticyclonic eddies, also played an important role in the configuration of these communities. In summer, over three decades, 1980s, 2000s and 2010s, an increase in sea water temperature and a decrease in chlorophyll were detected. Changes in the composition and abundance of the larval fish community were also detected. These were mainly due to the presence of warm water species in the area for the first time, or to their increase in abundance, in the 2000s in relation to the northward expansion of the adults' range. Other species showed a decline in abundance over time, probably due to the decrease in chlorophyll. This work quantitatively compared the survival chances for larvae of E. encrasicolus (a established species) and S. aurita (a species expanding northwards). To this aim, a new method, the Box-Balance Model, was developed to evaluate the role of hydrodynamic structures in their mortality. The model revealed that despite the warming trend would contribute to the expansion of S. aurita, it has not yet developed an adaptation strategy as successful as that of E. encrasicolus, a well-established species in the area, This thesis was conducted in the Institut de Ciències del Mar (ICM – CSIC) and was made possible thanks to the projects CACO (REN 2002-01339/MAR), FISHJELLY (MAR-CTM2010-18874) and WINFISH (CTM2015-68543-R). This work acknowledges the Severo Ochoa Centre of Excellence accreditation (CEX2019- 000928-S), Peer reviewed