Indicadores moleculares de calidad ecológica y conectividad entre sistemas lacustres. Implicaciones para la aplicación de la Directiva Marco del Agua

Abstract

Diatoms are a diverse and ubiquitous group of microalgae that play a fundamental role in aquatic ecosystems as primary producers and key components of trophic networks. They are essential to the photosynthetic process, significantly contributing to global primary production and nutrient cycles such as carbon, nitrogen, and silicon. Their unique silica-based cell walls allow them to adapt to a variety of aquatic environments, from open oceans to freshwater systems. Additionally, their morphological and genetic diversity enables them to respond rapidly to changes in environmental conditions, making them reliable bioindicators for water quality assessment in both marine and freshwater ecosystems. Diatoms are used in biomonitoring due to their sensitivity to variations in physical and chemical water parameters, such as nutrients, pH, salinity, and temperature. This makes them useful in monitoring programs, such as the European Union's Water Framework Directive, to assess the ecological status of aquatic ecosystems. Furthermore, their application extends beyond ecological studies to fields like biotechnology, nanotechnology, forensic science, and biofuels, thanks to the optical and mechanical properties of their frustules. On the other hand, Mediterranean ponds, although small ecosystems often overlooked in conservation strategies, play a crucial role in regional biodiversity, providing essential habitats for rare or endangered species. These water bodies are highly dynamic and represent ideal environments to study ecological processes and species' responses to environmental changes. Regarding biomonitoring methodologies, molecular techniques such as DNA barcoding and high-throughput sequencing (HTS) have significantly improved the accuracy and speed of diatom species identification, overcoming the limitations of traditional morphological identification methods. These advancements enable a more efficient assessment of biodiversity and ecosystem health. In particular, the rbcL genetic marker has been highlighted in diatom community monitoring, as it provides taxonomic resolution at the species level and can reveal diversity patterns and community composition more accurately than conventional methods. Despite their ecological importance, the population dynamics and distribution of diatoms still present unresolved questions. Studying spatial variation patterns, such as distance decay, is key to understanding how geographic factors affect the genetic structure and diversity of diatom populations in aquatic habitats. This approach may provide insights into local adaptation mechanisms and resilience to environmental changes, which has direct implications for freshwater ecosystem conservation. In summary, diatoms are fundamental organisms both for ecology and technological applications. Their use in environmental biomonitoring is essential for the protection and management of aquatic ecosystems, especially in the context of climate change and environmental degradation. The integration of molecular techniques offers new opportunities to improve the efficiency and accuracy of biodiversity studies and conservation strategies. The main objective of this thesis is to explore the use of diatoms as bioindicators of the ecological status of aquatic ecosystems, with a particular focus on Mediterranean ponds. To achieve this, a comprehensive analysis of diatom biodiversity and community composition was conducted, applying advanced morphological and molecular techniques. The study also aimed to assess the relationship between spatial variations and the genetic structure of diatom populations, as well as to develop tools based on these microalgae for water quality monitoring in line with the European Union's Water Framework Directive requirements. In Article I of the thesis, the application of diatoms as bioindicators in Mediterranean ponds is studied. A sampling of diatoms was conducted in different ponds to analyze the diversity and composition of the communities in relation to environmental parameters such as nutrients, temperature, and pH. The results showed that diatom diversity is high, and diatom communities respond sensitively to changes in water quality, highlighting their potential as tools in environmental monitoring programs. Article II focuses on the application of advanced molecular technologies, such as high-throughput sequencing (HTS) and the use of the rbcL genetic marker, for the precise identification of diatom species in environmental samples. Through this methodology, a more efficient and accurate identification of diatom communities was achieved compared to traditional morphological methods. This article demonstrates the advantage of molecular tools in detecting cryptic species and improving the monitoring of aquatic biodiversity. In Article III, the population dynamics of diatoms are studied, exploring the concept of distance decay and how the genetic structure of populations varies based on the geographic distance between ponds. It was found that diatom populations exhibit patterns of isolation by distance, implying low genetic connectivity between isolated habitats, which may influence local adaptation and resilience to environmental changes. Overall, the thesis demonstrates that diatoms are highly effective bioindicators for water quality monitoring in aquatic ecosystems, especially in Mediterranean ponds. Advances in molecular techniques have improved the precision of diatom community identification and monitoring, overcoming the limitations of traditional methods. The research reveals that diatom communities respond sensitively to environmental variations, making them key tools in water resource management. Furthermore, the observed patterns of isolation by distance in diatom populations suggest that habitat connectivity is an important factor for preserving genetic diversity, which has implications for conservation strategies. In conclusion, this thesis contributes to the understanding of the use of diatoms in biomonitoring and highlights the importance of new molecular methodologies in the study of aquatic biodiversity and environmental management.