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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/217738
Unravelling causes and consequences of marine biodiversity changes in East Atlantic and Mediterranean ecosystems
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[eng] Marine communities have been affected by multiple stressors increasing over the last decades, such as overfishing and climate change, resulting in negative effects throughout ecosystems. However, these impacts do not have homogeneous effects globally. Instead, systems across regions experience different impacts and rates of change shaped both by regional and global drivers. Furthermore, organisms within the same community can suffer from different impacts or respond to the same impact in distinct ways due to different ecological traits or life history strategies. These responses can include reductions or increments in the abundance of the populations of affected species, with the term "winners" often used to refer to organisms that may benefit from global change. Another common response, especially to warming, is shifts in distribution ranges. These shifts can be latitudinal, migrating northwards, or vertical, moving towards deeper waters. Previous studies have addressed these processes mainly focusing on abundance and biomass displacements, but a holistic approach that considers several aspects of the ecosystem, such as production, biodiversity and trophic characteristics across different taxonomic groups is still missing.
The main goal of this P.hD.was establishing a comparison of areas within the Atlantic and Mediterranean by using an integrative analysis of indicators, calculated from data collected from scientific bottom trawl surveys, and species groups in order to achieve a better understanding of ongoing spatiotemporal changes. Several types of indicators were considered to analyse different aspects of ecosystem functioning and dynamics. To reflect the variety of responses and calculate these indicators, three taxonomic groups were considered (fishes, cephalopods, and crustaceans), in which several traits were analysed. Spatial variability was accounted both at the regional scale by comparing different subregions of the Western Mediterranean and at the oceanic scale with a study comparing the Barents Sea, North Sea, Western Mediterranean, and South African coast.
To do that, complementary methods were applied for addressing several specific questions regarding the distribution and ecosystem dynamic. Analyses of subregional differences and temporal trends in the Western Mediterranean were performed using ANOVA and linear regressions, respectively. Then, the relationship between ecological indicators and environmental variables and fishing were studied using Generalised Additive Models (GAMs) to assess the status of alleged taxa winners in the Western Mediterranean and test for bathymetric changes in the indicators in the East Atlantic areas and the Mediterranean Sea.
Several regional patterns were detected in the Western Mediterranean, often following the latitudinal gradient of temperature within the area. However, in many cases, interrupted or even discontinuous gradients were reported, due to localised variability in the environment and/or human impacts, especially on the North Catalan coast. In terms of taxa, fishes showed negative trends in most indicators, while cephalopods and crustaceans experienced more favourable results. Despite this, a detailed examination of cephalopods signalled the possibility of negative effects of increasing temperatures beyond certain thresholds. In the East Atlantic and Mediterranean Sea comparison, temporal changes in depth range were reported in several indicators in accordance with the Depth Refuge hypothesis, although they did not follow large-scale gradients but were influenced by the conditions and characteristics of individual regions.
Overall, this Ph.D. reveals the existence of numerous spatial patterns and temporal trends regarding marine biodiversity and emphasises the unequal responses to both
environmental drivers and anthropogenic pressures among the considered ecological groups. These differences were further signalled by the variation and interrelationship of several indicators, often related to recorded shifts in the community, such as the functional changes in the North Sea and Barents Sea, the eastward migrations occurring in South Africa, or the complex sub-regional combination of fishing and environmental impacts observed over the Western Mediterranean. Overall, these results highlight that environmental change impacts may have notable consequences for ecosystem composition at several scales. The use of ecological indicators and taxonomic groups was proven to be a useful tool to further my understanding on the ongoing marine changes as well as their extent and implications.
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VELOY DOMINGUEZ, Carlos. Unravelling causes and consequences of marine biodiversity changes in East Atlantic and Mediterranean ecosystems. [consulta: 3 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/217738]