Until recently, the prevailing view of marine life at high latitudes has been that organisms enter a general resting state during the dark Polar Night and that the system only awakens with the return of the sun. Recent research, however, with coordinated, multidisciplinary field campaigns based on the high Arctic Archipelago of Svalbard, have provided a radical new perspective. Instead of a system in dormancy, a new perspective of a system in full operation and with high levels of activity across all major phyla is emerging. Examples of such activities and processes include: Active marine organisms at sea surface, water column and the sea-floor. At surface we find active foraging in seabirds and fish, in the water column we find a high biodiversity and activity of zooplankton and larvae such as active light induced synchronized diurnal vertical migration, and at seafloor there is a high biodiversity in benthic animals and macroalgae. The Polar Night is a period for reproduction in many benthic and pelagic taxa, mass occurrence of ghost shrimps (Caprellides), high abundance of Ctenophores, physiological evidence of micro- and macroalgal cells that are ready to utilize the first rays of light when they appear, deep water fishes found at water surface in the Polar night, and continuous growth of bivalves throughout the winter. These findings not only begin to shape a new paradigm for marine winter ecology in the high Arctic, but also provide conclusive evidence for a top-down controlled system in which primary production levels are close to zero. In an era of environmental change that is accelerated at high latitudes, we believe that this new insight is likely to strongly impact how the scientific community views the high latitude marine ecosystem. Despite the overwhelming darkness, the main environmental variable affecting marine organisms in the Polar Night is in fact light. The light regime during the Polar Night is unique with respect to light intensity, spectral composition of light and photoperiod.

The Polar and Subpolar region comprise one of the seven regions in the world, from the Arctic to the Antarctic, the Atlantic, Pacific, and Indian Oceans. Marine biodiversity in the polar and subpolar regions is one of the richest on earth, hosting important populations of crustaceans, pelagic and benthic species that provide resources for the many seabirds and marine mammals that congregate there. However, these ecosystems, as well as their biodiversity, are vulnerable and already affected by the impacts of climate change and other threats. The high climatic dynamics in those areas have already generated strong modifications to the environment, with irreversible losses in biodiversity and diminished ecosystem services that are essential for the whole planet. The current need to study and understand the biodiversity of the world's oceans makes polar and sub-polar areas key regions for taxonomic and ecological studies.

The Arctic is often portrayed as being isolated, but the reality is that the connectivity with the rest of the planet is huge, be it through weather patterns, global ocean circulation, and large-scale migration patterns to name but a few. There is a huge amount of public interest in the ‘changing Arctic’, especially in terms of the rapid changes taking place in ecosystems and exploitation of resources. There can be no doubt that the Arctic is at the forefront of the international environmental science agenda, both from a scientific aspect, and also from a policy/environmental management perspective. This book aims to stimulate a wide audience to think about the Arctic by highlighting the remarkable breadth of what it means to study its ecology. Arctic Ecology seeks to systematically introduce the diverse array of ecologies within the Arctic region. As the Arctic rapidly changes, understanding the fundamental ecology underpinning the Arctic is paramount to understanding the consequences of what such change will inevitably bring about. Arctic Ecology is designed to provide graduate students of environmental science, ecology and climate change with a source where Arctic ecology is addressed specifically, with issues due to climate change clearly discussed. It will also be of use to policy-makers, researchers and international agencies who are focusing on ecological issues and effects of global climate change in the Arctic. About the Editor David N. Thomas is Professor of Arctic Ecosystem Research in the Faculty of Biological and Environmental Sciences, University of Helsinki. Previously he spent 24 years in the School of Ocean Sciences, Bangor University, Wales. He studies marine systems, with a particular emphasis on sea ice and land-coast interactions in the Arctic and Southern Oceans as well as the Baltic Sea. He also edited a related book: Sea Ice, 3rd Edition (2017), which is also published by Wiley-Blackwell.

This open access book summarizes peer-reviewed articles and the abstracts of oral and poster presentations given during the YOUMARES 9 conference which took place in Oldenburg, Germany, in September 2018. The aims of this book are to summarize state-of-the-art knowledge in marine sciences and to inspire scientists of all career stages in the development of further research. These conferences are organized by and for young marine researchers. Qualified early-career researchers, who moderated topical sessions during the conference, contributed literature reviews on specific topics within their research field. .

Marine Ecology: Processes, Systems, and Impacts offers a carefully balanced and stimulating survey of marine ecology, introducing the key processes and systems from which the marine environment is formed, and the issues and challenges which surround its future conservation.

Scientific research on cold-adapted microorganisms (specifically polar microbes) is of great interest, since Arctic and Antarctic regions harbor diverse and active populations of microorganisms. However, these microorganisms are subject to impacts of environmental perturbations. For example, climate change will modulate the distribution and activity of many cyanobacteria and algal species in polar environments that contribute significantly to global carbon fixation and oxygen production. Moreover, many microorganisms that have remained frozen for thousands of years can revive their metabolic activity and re-join the modern microbial community. For survival in freezing environments, polar microorganisms have established specific regulatory mechanisms which are now being challenged by new, rapidly changing environmental conditions. Remarkable progress has been made to uncover microbial adaptation to anthropogenic activities such as high irradiance, nutritional deprivation, UV-B radiation, heat, cold, desiccation, and heavy metals. Studies have enabled a basic understanding of gene regulatory pathways for morphological, physiological, metabolic, and genetic adaptations to various environmental stresses. To further elucidate physiological adaptation mechanisms and molecular diversity in polar regions, this Research Topic is focused on microbes in polar regions, looking at their biodiversity, ecological adaptations, the impact of climate change on their lifestyles, and biotechnological application of microbes for a sustainable future.

The book presents the most relevant research of the participants of the VII International Conference of Young Scientists "Complex Investigation of the World Ocean" (CIWO-2023). This conference was held at Saint Petersburg State University in May 15-19, 2023 (Saint Petersburg, Russia). It covers a wide range of fundamental and applied marine and limnology studies combined in eight sections: Ocean Physics, Ocean Biology, Ocean Chemistry, Marine Geology, Marine Geophysics, Marine Ecology and Environmental Management, Physical and Biological interactions (interdisciplinary section), Oceanological Technology and Instrumentation. The aim of this book is to show the relevance of the marine research due to the crucial role of the World Ocean in determining climate change on Earth, huge resources (fish resources, oil, gas and ore deposits, etc.) and intensive development of infrastructure in coastal and offshore zones. All these topics were marked within the framework of realization of the United Nations Decade of Ocean Science for Sustainable Development (2021-2030). The studies presented in the book covers the wide spectrum of different the most important marine and limnology issues: thermohaline structure of water body and interactions between ocean and atmosphere, dynamic of the ocean, marine ice in polar regions, biodiversity of the marine ecosystems, adaptation of marine life to climate changes, geological and geophysical investigations in oil and gas regions, sedimentation, paleooceanology and biostratigraphy, hydrochemistry of estuary regions and carbon fluxes, microplastic pollution of the ocean, eutrophication and etc.