Coral reefs are among the most productive and biodiverse marine ecosystems on Earth, often referred to as the “tropical rainforests” of the sea. They provide essential ecosystem goods and services that support the livelihoods of nearly 1 billion people worldwide through fisheries, tourism, and coastal protection. While most research has traditionally focused on reefs existing in optimal environmental conditions—clear, shallow, and nutrient-poor waters—this book expands the scope by addressing a less explored but increasingly important topic: coral reefs and communities that persist at the edge of their environmental limits.

This novel volume offers a comprehensive synthesis of current knowledge (e.g., geology, ecology, ecosystem services) on reefs found in environments once considered unsuitable for coral growth, including - but not limited to - turbid waters, high-nutrient systems, mesophotic depths, and areas with fluctuating temperature, pH, and oxygen levels. Drawing on examples stretching the world’s coral reefs such as the Indo-Pacific, Caribbean, South Atlantic, Red Sea, and Persian/Arabian Gulf, this book examines how these unique systems function, how they differ from traditional reefs, and what their potential is as natural laboratories for understanding reef resilience in a changing ocean. It highlights emerging evidence that some extreme reefs may act as refugia or resilience hotspots in the face of global climate change, while also acknowledging ongoing scientific debates and knowledge gaps that require further investigation.

Targeted at researchers, graduate students, environmental managers, and policymakers, this first book about this important topic provides a critical resource for advancing both scientific understanding and evidence-based decision-making. By systematically compiling and analyzing dispersed research, it offers a foundation for developing more effective science-based conservation and climate adaptation strategies.

Marcelo O. Soares is a marine scientist based in Fortaleza, Brazil, whose research focuses on marginal and extreme reef systems, particularly along the Southwestern Atlantic. His work integrates benthic ecology, ecosystem functioning, and human impacts in turbid, sediment-influenced environments. He has led and contributed to multiple national and international projects examining reef responses to climate change, coastal development, and pollution. A strong advocate for interdisciplinary and applied science, Marcelo also works at the science–policy interface in Brazil. His expertise directly supports the book’s focus on extreme marginal reefs (and communities) as potential resilience hotspots and their role in future conservation strategies. Marcelo Soares has been an associate professor at the Federal University of Ceará (UFC) (Brazil) since 2010 and also served as a visiting professor at the Leibniz Center for Tropical Marine Research (ZMT) (Bremen, Germany) during the book’s development.

Tyler B. Smith is a marine ecologist based in the U.S. Virgin Islands, specializing in coral reef resilience, ecosystem dynamics, and climate change impacts. His research spans the Caribbean and other tropical regions, with emphasis on how disturbance and environmental variability shape shallow and mesophotic reef communities. He has contributed extensively to long-term monitoring and interdisciplinary initiatives aimed at forecasting reef futures. Tyler’s work bridges ecological theory and applied conservation, making him a key contributor to understanding how reefs persist under stress. His expertise is central to the book’s exploration of resilience in marginal and changing environments. Tyler Smith is a professor at the University of the Virgin Islands and directs the Coral Reef Resilience Laboratory based in St. Thomas, which conducts research worldwide.

Emma Camp is a coral reef scientist based in Sydney, Australia, recognized for her pioneering research on corals living in extreme environments, including highly variable temperature, low pH, and low oxygen conditions. Her work investigates the physiological and ecological mechanisms that enable coral survival under stress, with important implications for climate change adaptation. She has conducted research across diverse regions, including the Great Barrier Reef, Coral Triangle and the Caribbean Sea, and is also active in coral restoration innovation. Her research provides critical insights into the potential of extreme reefs to function as climate refugia. As Team Leader of the Future Reefs Program within the Climate Change Cluster at the University of Technology Sydney, Prof. Camp leads interdisciplinary research focused on the physiology, ecology, and biogeochemistry of coral reef systems.

Verena Schoepf is a coral reef scientist based in Amsterdam, The Netherlands. Her research focuses on a central question in climate change biology: how do multiple, interacting climate change stressors shape the future of coral reefs? Specifically, her work examines how environmental heterogeneity across spatial and temporal scales modulates coral health and resilience under ocean warming, acidification, and deoxygenation. Her research approach combines controlled aquarium experiments that simulate future ocean conditions with field studies of extreme reef environments that function as natural laboratories, including the macrotidal Kimberley region of NW Australia or semi-enclosed bays in the Caribbean. By integrating eco-physiological and biogeochemical tools, her work provides insights into the traits and processes that underpin resistance to multifaceted climate stress and promote adaptive capacity in a rapidly changing ocean. She is an Associate Professor at the Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, and an Adjunct Research Fellow at the Oceans Institute, University of Western Australia.