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Volume 17, 2025
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The Serendipity of Discovery: Life of a Geochemist
Vol. 17 (2025), pp. 1–22More LessMy strategy for writing this autobiography is to use examples of how working on seemingly different projects can often lead to outcomes more important than originally envisioned. Serendipity is a happy accident—specifically, the accident of discovering something useful without directly looking for it. This often occurs when two research projects converge unexpectedly. The main text contains examples of how serendipity has led me to important discoveries, including (a) finding surprisingly high 228Ra activities in the ocean; (b) developing a means of rapidly and quantitatively extracting radium from seawater; (c) devising a rapid, sensitive method of measuring 224Ra and 223Ra; (d) realizing the scale and biogeochemical importance of submarine groundwater discharge; and (e) conceiving a method to estimate the total flux of submarine groundwater discharge to the Atlantic Ocean. The Supplemental Material fleshes out details of these discoveries and places them in the context of my other investigations.
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Climate and Human Evolution: Insights from Marine Records
Vol. 17 (2025), pp. 23–53More LessThe relationship between climate and human evolution is complex, and the causal mechanisms remain unknown. Here, we review and synthesize what is currently known about climate forcings on African landscapes, focusing mainly on the last 4 million years. We use information derived from marine sediment archives and data-numerical climate model comparisons and integration. There exists a heterogeneity in pan-African hydroclimate changes, forced by a combination of orbitally paced, low-latitude fluctuations in insolation; polar ice volume changes; tropical sea surface temperature gradients linked to the Walker circulation; and possibly greenhouse gases. Pan-African vegetation changes do not follow the same pattern, which is suggestive of additional influences, such as CO2 and temperature. We caution against reliance on temporal correlations between global or regional climate, environmental changes, and human evolution and briefly proffer some ideas on how pan-African climate trends could help create novel conceptual frameworks to determine the causal mechanisms of associations between climate/habitat change and hominin evolution.
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The Science, Engineering, and Validation of Marine Carbon Dioxide Removal and Storage
Vol. 17 (2025), pp. 55–81More LessScenarios to stabilize global climate and meet international climate agreements require rapid reductions in human carbon dioxide (CO2) emissions, often augmented by substantial carbon dioxide removal (CDR) from the atmosphere. While some ocean-based removal techniques show potential promise as part of a broader CDR and decarbonization portfolio, no marine approach is ready yet for deployment at scale because of gaps in both scientific and engineering knowledge. Marine CDR spans a wide range of biotic and abiotic methods, with both common and technique-specific limitations. Further targeted research is needed on CDR efficacy, permanence, and additionality as well as on robust validation methods—measurement, monitoring, reporting, and verification—that are essential to demonstrate the safe removal and long-term storage of CO2. Engineering studies are needed on constraints including scalability, costs, resource inputs, energy demands, and technical readiness. Research on possible co-benefits, ocean acidification effects, environmental and social impacts, and governance is also required.
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Oyster Restoration to Recover Ecosystem Services
Vol. 17 (2025), pp. 83–113More LessOyster reef loss represents one of the most dramatic declines of a foundation species worldwide. Oysters provide valuable ecosystem services (ES), including habitat provisioning, water filtration, and shoreline protection. Since the 1990s, a global community of science and practice has organized around oyster restoration with the goal of restoring these valuable services. We highlight ES-based approaches throughout the restoration process, consider applications of emerging technologies, and review knowledge gaps about the life histories and ES provisioning of underrepresented species. Climate change will increasingly affect oyster populations, and we assess how restoration practices can adapt to these changes. Considering ES throughout the restoration process supports adaptive management. For a rapidly growing restoration practice, we highlight the importance of early community engagement, long-term monitoring, and adapting actions to local conditions to achieve desired outcomes.
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Revered and Reviled: The Plight of the Vanishing Sea Cucumbers
Vol. 17 (2025), pp. 115–142More LessSea cucumbers paradoxically suffer from being both highly prized and commonly disregarded. As an Asian medicine and delicacy, they command fabulous prices and are thus overfished, poached, and trafficked. As noncharismatic animals, many are understudied and inadequately protected. Despite presenting a rich diversity of life histories, members of this broad taxonomic group (class Holothuroidea) are often managed simply as “sea cucumbers” in fisheries worldwide. One cannot imagine fishes (class Pisces) being given the same universal treatment. Yet this may happen for species of sea cucumber that differ on the same fundamental level as tilapia and tuna. As more sea cucumbers reach an endangered status and wild populations become depleted to the point of collapse, critical questions arise about the relevance of established conservation and governance strategies. This article reviews the main threats faced by exploited sea cucumbers, outlines conservation and governance effectiveness, identifies gaps in knowledge, and explores management and research perspectives in the context of climate change and booming fisheries crime. We stress the perilous state of harvested sea cucumbers globally and the urgent need for action.
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The State of Marine Social Science: Yesterday, Today, and into the Future
Vol. 17 (2025), pp. 143–165More LessRapidly changing ocean conditions are resulting in changes in marine species and across entire ecosystems that, in turn, affect communities and individuals who rely on these resources for their livelihoods, culture, and sustenance. Marine social science, an emerging field that embraces diverse methods to understand human–ocean relationships, is increasingly called on to contribute to transdisciplinary ocean science that can inform the evidence-based policy and management needed to address these changes. Here, we review the state of marine social science as a growing field of study. First, we outline the history of marine social science, including the emergence of the field and the social science disciplines and community it encompasses. We then discuss current marine social science research themes as a framework to understand key ocean issues, which is followed by a commentary on the future of marine social science research.
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Insights Gained from Including People in Our Models of Nature and Modes of Science
Vol. 17 (2025), pp. 167–191More LessAcross the natural sciences, humans are typically conceptualized as external disruptors of nature rather than adaptable components of it. Historical evidence, however, challenges this dominant schema. Here, we describe the broad repertoire of ecological functions performed by people in place-based societies across the Pacific Ocean over millennia, illustrating their roles as ecosystem engineers, dispersers, bioturbators, nutrient cyclers, predators, and herbivores. By considering the reciprocal relationships between people and the ecosystems within which they are embedded, evidence of humanity's ability to experiment, learn, adapt, innovate, and sustain diverse and resilient social–ecological relationships emerges. Therefore, recognizing people as inseparable components of marine ecosystems and their millennia of engagement with coastal ocean spaces is critical to both understanding marine ecosystems and devising resilient and equitable ocean policies.
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Standardized Methods to Assess the Impacts of Thermal Stress on Coral Reef Marine Life
Vol. 17 (2025), pp. 193–226More LessThe Earth's oceans have absorbed more than 90% of the excess, climate change–induced atmospheric heat. The resulting rise in oceanic temperatures affects all species and can lead to the collapse of marine ecosystems, including coral reefs. Here, we review the range of methods used to measure thermal stress impacts on reef-building corals, highlighting current standardization practices and necessary refinements to fast-track discoveries and improve interstudy comparisons. We also present technological developments that will undoubtedly enhance our ability to record and analyze standardized data. Although we use corals as an example, the methods described are widely employed in marine sciences, and our recommendations therefore apply to all species and ecosystems. Enhancing collaborative data collection efforts, implementing field-wide standardized protocols, and ensuring data availability through dedicated, openly accessible databases will enable large-scale analysis and monitoring of ecosystem changes, improving our predictive capacities and informing active intervention to mitigate climate change effects on marine life.
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Coral Disease: Direct and Indirect Agents, Mechanisms of Disease, and Innovations for Increasing Resistance and Resilience
Vol. 17 (2025), pp. 227–255More LessAs climate change drives health declines of tropical reef species, diseases are further eroding ecosystem function and habitat resilience. Coral disease impacts many areas around the world, removing some foundation species to recorded low levels and thwarting worldwide efforts to restore reefs. What we know about coral disease processes remains insufficient to overcome many current challenges in reef conservation, yet cumulative research and management practices are revealing new disease agents (including bacteria, viruses, and eukaryotes), genetic host disease resistance factors, and innovative methods to prevent and mitigate epizootic events (probiotics, antibiotics, and disease resistance breeding programs). The recent outbreak of stony coral tissue loss disease across the Caribbean has reenergized and mobilized the research community to think bigger and do more. This review therefore focuses largely on novel emerging insights into the causes and mechanisms of coral disease and their applications to coral restoration and conservation.
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Lessons Learned from the Sea Star Wasting Disease Investigation
Vol. 17 (2025), pp. 257–279More LessMarine invertebrate mass mortality events (MMEs) threaten biodiversity and have the potential to catastrophically alter ecosystem structure. A proximal question around acute MMEs is their etiologies and/or environmental drivers. Establishing a robust cause of mortality is challenging in marine habitats due to the complexity of the interactions among species and the free dispersal of microorganisms from surrounding waters to metazoan microbiomes. The 2013–2014 sea star wasting disease (SSWD) MME in the northeast Pacific Ocean highlights the difficulty in establishing responsible agents. In less than a year of scientific investigation, investigators identified a candidate agent and provided at the time convincing data of pathogenic and transmissible disease. However, later investigation failed to support the initial results, and critical retrospective analyses of experimental procedures and reinterpretation of early findings disbanded any candidate agent. Despite the circuitous path that the investigation and understanding of SSWD have taken, lessons learned from the initial investigation—improving on approaches that led to misinterpretation—have been successfully applied to the 2022 Diadema antillarum investigation. In this review, we outline the history of the initial SSWD investigation, examine how early exploration led to spurious interpretations, summarize the lessons learned, provide recommendations for future work in other systems, and examine potential links between the SSWD event and the Diadema antillarum MME.
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Land Bridges and Rafting Theories to Explain Terrestrial-Vertebrate Biodiversity on Madagascar
Vol. 17 (2025), pp. 281–299More LessMadagascar's celebrated land-vertebrate assemblage has long been studied and discussed. How the ancestors of the 30 different lineages arrived on the island, which has existed since 85 Mya and is separated from neighboring Africa by 430 km of water, is a deeply important question. Did the colonizations take place when the landmass formed part of Gondwana, or did they occur later and involve either now-drowned causeways or overwater dispersal (on vegetation rafts or by floating/swimming)? Following a historical review, we appraise the geological–geophysical evidence and the faunal-suite colonization record. Twenty-six of the clades are explained by temporally stochastic overwater dispersals, spanning 69–0 Mya, while two others are considered Gondwanan vicariant relicts. Due to a lack of information, the remaining two groups cannot be evaluated. The findings thus appear to resolve a debate that has rumbled along, with sporadic eruptions, since the mid-1800s.
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Effects of Environmental and Climatic Changes on Coral Reef Islands
Vol. 17 (2025), pp. 301–324More LessCoral reef islands are low-lying, wave-deposited sedimentary landforms. Using an eco-morphodynamic framework, this review examines the sensitivity of islands to climatic and environmental change. Reef island formation and morphological dynamics are directly controlled by nearshore wave processes and ecologically mediated sediment supply. The review highlights that reef islands are intrinsically dynamic landforms, able to adjust their morphology (size, shape, and location) on reef surfaces in response to changes in these processes. A suite of ecological and oceanographic processes also indirectly impact hydrodynamic and sediment processes and thereby regulate morphological change, though the temporal scales and magnitudes of impacts on islands vary, leading to divergent morphodynamic outcomes. Climatic change will modify the direct and indirect processes, causing complex positive and negative outcomes on islands. Understanding this complexity is critical to improve predictive capabilities for island physical change and resolve the timescales of change and lag times for impacts to be expressed in island systems.
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How Does the Ocean Melt Antarctic Ice Shelves?
Vol. 17 (2025), pp. 325–353More LessThe present-day state and future of the Antarctic Ice Sheet depend on the rate at which the ocean melts its fringing ice shelves. Ocean heat must cross many physical and dynamical barriers to melt ice shelves, with the last of these being the ice–ocean boundary layer. This review summarizes the current understanding of ice–ocean boundary-layer dynamics, focusing on recent progress from laboratory experiments, turbulence-resolving numerical simulations, novel observations, and the application to large-scale simulations. The complex interplay between buoyant meltwater and external processes such as current shear leads to the emergence of several melting regimes that we describe, as well as freezing processes. The remaining challenges include developing new parameterizations for large-scale ice–ocean models based on recent advances and understanding the coevolution of melt and basal topography.
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Physics of the Seasonal Sea Ice Zone
Vol. 17 (2025), pp. 355–379More LessThe seasonal sea ice zone encompasses the region between the winter maximum and summer minimum sea ice extent. In both the Arctic and Antarctic, the majority of the ice cover can now be classified as seasonal. Here, we review the sea ice physics that governs the evolution of seasonal sea ice in the Arctic and Antarctic, spanning sea ice growth, melt, and dynamics and including interactions with ocean surface waves as well as other coupled processes. The advent of coupled wave–ice modeling and discrete-element modeling, together with improved and expanded satellite observations and field campaigns, has yielded advances in process understanding. Many topics remain in need of further investigation, including rheologies appropriate for seasonal sea ice, wave-induced sea ice fracture, welding for sea ice freeze-up, and the distribution of snow on seasonal sea ice. Future research should aim to redress biases (such as disparities in focus between the Arctic and Antarctic and between summer and winter processes) and connect observations to modeling across spatial scales.
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Improving Ocean Management Using Insights from Space
Vol. 17 (2025), pp. 381–408More LessAdvancements in space-based ocean observation and computational data processing techniques have demonstrated transformative value for managing living resources, biodiversity, and ecosystems of the ocean. We synthesize advancements in leveraging satellite-derived insights to better understand and manage fishing, an emerging revolution of marine industrialization, ocean hazards, sea surface dynamics, benthic ecosystems, wildlife via electronic tracking, and direct observations of ocean megafauna. We consider how diverse space-based data sources can be better coupled to modernize and improve ocean management. We also highlight examples of how data from space can be developed into tools that can aid marine decision-makers managing subjects from whales to algae. Thoughtful and prospective engagement with such technologies from those inside and outside the marine remote sensing community is, however, essential to ensure that these tools meet their full potential to strengthen the effectiveness of ocean management.
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New Technologies for Monitoring Coastal Ecosystem Dynamics
Vol. 17 (2025), pp. 409–433More LessIn recent years, our view of coastal ecosystems has expanded and come into greater focus. We are currently making more types of observations over larger areas and at higher frequencies than ever before. These advances are timely, as coastal ecosystems are facing increasing pressures from climate change and anthropogenic stressors. This article synthesizes recent literature on emerging technologies for coastal ecosystem monitoring, including satellite monitoring, aerial and underwater drones, in situ sensor networks, fiber optic systems, and community science observatories. We also describe how advances in artificial intelligence and deep learning underpin all these technologies by enabling insights to be drawn from increasingly large data volumes. Even with these recent advances, there are still major gaps in coastal ecosystem monitoring that must be addressed to manage coastal ecosystems during a period of accelerating global change.
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Arctic Continental-Shelf Sediment Dynamics
Vol. 17 (2025), pp. 435–460More LessSediments covering Arctic continental shelves are uniquely impacted by ice processes. Delivery of sediments is generally limited to the summer, when rivers are ice free, permafrost bluffs are thawing, and sea ice is undergoing its seasonal retreat. Once delivered to the coastal zone, sediments follow complex pathways to their final depocenters—for example, fluvial sediments may experience enhanced seaward advection in the spring due to routing under nearshore sea ice; during the open-water season, boundary-layer transport may be altered by strong stratification in the ocean due to ice melt; during the fall storm season, sediments may be entrained into sea ice through the production of anchor ice and frazil; and in the winter, large ice keels more than 20 m tall plow the seafloor (sometimes to seabed depths of 1–2 m), creating a type of physical mixing that dwarfs the decimeter-scale mixing from bioturbation observed in lower-latitude shelf systems. This review summarizes the work done on subtidal sediment dynamics over the last 50 years in Arctic shelf systems backed by soft-sediment coastlines and suggests directions for future sediment studies in a changing Arctic. Reduced sea ice, increased wave energy, and increased sediment supply from bluffs (and possibly rivers) will likely alter marine sediment dynamics in the Arctic now and into the future.
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Feedbacks Regulating the Salinization of Coastal Landscapes
Vol. 17 (2025), pp. 461–484More LessThe impact of saltwater intrusion on coastal forests and farmland is typically understood as sea-level-driven inundation of a static terrestrial landscape, where ecosystems neither adapt to nor influence saltwater intrusion. Yet recent observations of tree mortality and reduced crop yields have inspired new process-based research into the hydrologic, geomorphic, biotic, and anthropogenic mechanisms involved. We review several negative feedbacks that help stabilize ecosystems in the early stages of salinity stress (e.g., reduced water use and resource competition in surviving trees, soil accretion, and farmland management). However, processes that reduce salinity are often accompanied by increases in hypoxia and other changes that may amplify saltwater intrusion and vegetation shifts after a threshold is exceeded (e.g., subsidence following tree root mortality). This conceptual framework helps explain observed rates of vegetation change that are less than predicted for a static landscape while recognizing the inevitability of large-scale change.
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The Desiccation and Catastrophic Refilling of the Mediterranean: 50 Years of Facts, Hypotheses, and Myths Around the Messinian Salinity Crisis
Vol. 17 (2025), pp. 485–509More LessAccording to some authors, the Messinian salinity crisis was ended by a giant waterfall or megaflood 5.33 million years ago, when the Atlantic Ocean reconnected in a catastrophic way with the desiccated Mediterranean, creating the Strait of Gibraltar. An erosional surface deeply cutting upper Miocene or older rocks and sealed by lower Pliocene sediments is the geological feature that inspired this fascinating hypothesis. The hypothesis, which recalls several ancient myths, is well established in the scientific community and often considered to be a fact. However, several studies are suggesting that the Atlantic–Mediterranean connection through the Strait of Gibraltar was probably active before and during the entire Messinian salinity crisis. This allows us to consider the possibility that long-lived, more gradual physical processes were responsible for the evolution of the strait, opening the idea of a nondesiccated Mediterranean Sea.
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A Global Inventory of Natural and Synthetic Estrogens in Aquatic Systems
Vol. 17 (2025), pp. 511–536More LessEstrogens are a group of endocrine disruptors that are recognized as a threat to the world's ecosystems and are easily transported through aquatic systems from mainly anthropogenic sources. To illustrate this growing problem, we have compiled a global overview of measured concentrations of natural and synthetic estrogens restricted to freshwater systems (lakes, rivers, and lagoons) and marine coastal and open ocean environments, focusing on estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2). We found that the cumulative risk quotient is high at 65% of 400 sampled sites, highlighting that estrogen pollution is a major environmental concern. Our investigation revealed that almost no information is available on the concentration levels of E1, E2, E3, and EE2 for the open ocean areas. However, their occurrence in all systems, including open seas, suggests that estrogens are not completely degraded during transport to and within the environment and may be more persistent than previously thought.
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How Big Is Big? The Effective Population Size of Marine Bacteria
Vol. 17 (2025), pp. 537–560More LessGenome-reduced bacteria constitute most of the cells in surface-ocean bacterioplankton communities. Their extremely large census population sizes (Nc) have been unfoundedly translated to huge effective population sizes (Ne)—the size of an ideal population carrying as much neutral genetic diversity as the actual population. As Ne scales inversely with the strength of genetic drift, constraining the magnitude of Ne is key to evaluating whether natural selection can overcome the power of genetic drift to drive evolutionary events. Determining the Ne of extant species requires measuring the genomic mutation rate, a challenging step for most genome-reduced bacterioplankton lineages. Results for genome-reduced Prochlorococcus and CHUG are surprising—their Ne values are an order of magnitude lower than those of less abundant lineages carrying large genomes, such as Ruegeria and Vibrio. As bacterioplankton genome reduction commonly occurred in the distant past, appreciating their population genetic mechanisms requires constraining their ancient Ne values by other methods.
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How Viruses Shape Microbial Plankton Microdiversity
Vol. 17 (2025), pp. 561–576More LessOne major conundrum of modern microbiology is the large pangenome (gene pool) present in microbes, which is much larger than those found in complex organisms such as humans. Here, we argue that this diversity of gene pools carried by different strains is maintained largely due to the control exercised by viral predation. Viruses maintain a high strain diversity through time that we describe as constant-diversity equilibrium, preventing the hoarding of resources by specific clones. Thus, viruses facilitate the release and degradation of dissolved organic matter in the ocean, which may lead to better ecosystem functioning by linking top-down to bottom-up control. By maintaining this equilibrium, viruses act as a key element of the adaptation of marine microbes to their environment and likely behave as a single evolutionary unit.
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Beyond Meta-Omics: Functional Genomics in Future Marine Microbiome Research
Vol. 17 (2025), pp. 577–592More LessWhen President Bill Clinton and Francis Collins, then the director of the National Human Genome Research Institute, celebrated the near completion of the human genome sequence at the White House in the summer of 2000, it is unlikely that they or anyone else could have predicted the blossoming of meta-omics in the following two decades and their applications in modern human microbiome and environmental microbiome research. This transformation was enabled by the development of high-throughput sequencing technologies and sophisticated computational biology tools and bioinformatics software packages. Today, environmental meta-omics has undoubtedly revolutionized our understanding of ocean ecosystems, providing the genetic blueprint of oceanic microscopic organisms. In this review, I discuss the importance of functional genomics in future marine microbiome research and advocate a position for a gene-centric, bottom-up approach in modern oceanography. I propose that a synthesis of multidimensional approaches is required for a better understanding of the true functionality of the marine microbiome.
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Metabolic Flux Modeling in Marine Ecosystems
Helen Scott, and Daniel SegrèVol. 17 (2025), pp. 593–620More LessOcean metabolism constitutes a complex, multiscale ensemble of biochemical reaction networks harbored within and between the boundaries of a myriad of organisms. Gaining a quantitative understanding of how these networks operate requires mathematical tools capable of solving in silico the resource allocation problem each cell faces in real life. Toward this goal, stoichiometric modeling of metabolism, such as flux balance analysis, has emerged as a powerful computational tool for unraveling the intricacies of metabolic processes in microbes, microbial communities, and multicellular organisms. Here, we provide an overview of this approach and its applications, future prospects, and practical considerations in the context of marine sciences. We explore how flux balance analysis has been employed to study marine organisms, help elucidate nutrient cycling, and predict metabolic capabilities within diverse marine environments, and highlight future prospects for this field in advancing our knowledge of marine ecosystems and their sustainability.
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