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Changes in disturbance regimes due to climate change are increasingly challenging the capacity of ecosystems to absorb recurrent shocks and reassemble afterwards, escalating the risk of widespread ecological collapse of current ecosystems and the emergence of novel assemblages 1 – 3 . In marine systems, the production of larvae and recruitment of functionally important species are fundamental processes for rebuilding depleted adult populations, maintaining resilience and avoiding regime shifts in the face of rising environmental pressures 4 , 5 . Here we document a regional-scale shift in stock–recruitment relationships of corals along the Great Barrier Reef—the world’s largest coral reef system—following unprecedented back-to-back mass bleaching events caused by global warming. As a consequence of mass mortality of adult brood stock in 2016 and 2017 owing to heat stress 6 , the amount of larval recruitment declined in 2018 by 89% compared to historical levels. For the first time, brooding pocilloporids replaced spawning acroporids as the dominant taxon in the depleted recruitment pool. The collapse in stock–recruitment relationships indicates that the low resistance of adult brood stocks to repeated episodes of coral bleaching is inexorably tied to an impaired capacity for recovery, which highlights the multifaceted processes that underlie the global decline of coral reefs. The extent to which the Great Barrier Reef will be able to recover from the collapse in stock–recruitment relationships remains uncertain, given the projected increased frequency of extreme climate events over the next two decades 7 . A regional-scale shift in the relationships between adult stock and recruitment of corals occurred along the Great Barrier Reef, following mass bleaching events in 2016 and 2017 caused by global warming.

Phosphorus (P) is essential for life, but most of the global surface ocean is P depleted, which can limit marine productivity and affect ecosystem structure. Over recent decades, a wealth of new knowledge has revolutionized our understanding of the marine P cycle. With a revised residence time (~10–20 kyr) that is similar to nitrate and a growing awareness that P transformations are under tight and elaborate microbial control, the classic textbook version of a tectonically slow and biogeochemically simple marine P cycle has become outdated. P moves throughout the world’s oceans with a higher level of complexity than has ever been appreciated before, including a vast, yet poorly understood, P redox cycle. Here, we illustrate an oceanographically integral view of marine P by reviewing recent advances in the coupled cycles of P with carbon, nitrogen and metals in marine systems. Through this lens, P takes on a more dynamic and connected role in marine biogeochemistry than previously acknowledged, which points to unclear yet profound potential consequences for marine ecosystems, particularly under anthropogenic influence. Phosphorus plays a dynamic and complex role in marine biogeochemistry, which is closely connected to carbon, nitrogen and metal cycling, according to a literature synthesis on recent advances in understandings of the marine phosphorus cycle.

The flow of fresh groundwater may provide substantial inputs of nutrients and solutes to the oceans. However, the extent to which hydrogeological parameters control groundwater flow to the world’s oceans has not been quantified systematically. Here we present a spatially resolved global model of coastal groundwater discharge to show that the contribution of fresh groundwater accounts for ~0.6% (0.004%–1.3%) of the total freshwater input and ~2% (0.003%–7.7%) of the solute input for carbon, nitrogen, silica and strontium. However, the coastal discharge of fresh groundwater and nutrients displays a high spatial variability and for an estimated 26% (0.4%–39%) of the world’s estuaries, 17% (0.3%–31%) of the salt marshes and 14% (0.1–26%) of the coral reefs, the flux of terrestrial groundwater exceeds 25% of the river flux and poses a risk for pollution and eutrophication. The authors here present the global entry of nutrients into marine systems through fresh submarine groundwater discharge to be below 1%. However, they also identify hotspots and argue that about 25% of world’s estuaries are at danger of eutrophication.

Researchers have long attempted to follow animals as they move through their environment. Until relatively recently, however, such efforts were limited to short distances and times in species large enough to carry large batteries and transmitters. New technologies have opened up new frontiers in animal tracking remote data collection. Hussey et al. review the unique directions such efforts have taken for marine systems, while Kays et al. review recent advances for terrestrial species. We have entered a new era of animal ecology, where animals act as both subjects and samplers of their environments. Science , this issue 10.1126/science.1255642 , 10.1126/science.aaa2478 The distribution and interactions of aquatic organisms across space and time structure our marine, freshwater, and estuarine ecosystems. Over the past decade, technological advances in telemetry have transformed our ability to observe aquatic animal behavior and movement. These advances are now providing unprecedented ecological insights by connecting animal movements with measures of their physiology and environment. These developments are revolutionizing the scope and scale of questions that can be asked about the causes and consequences of movement and are redefining how we view and manage individuals, populations, and entire ecosystems. The next advance in aquatic telemetry will be the development of a global collaborative effort to facilitate infrastructure and data sharing and management over scales not previously possible.

Marine ecosystems are experiencing rapid and pervasive changes in biodiversity and species composition. Understanding the ecosystem consequences of these changes is critical to effectively managing these systems. Over the last several years, numerous experimental manipulations of species richness have been performed, yet existing quantitative syntheses have focused on a just a subset of processes measured in experiments and, as such, have not summarized the full data available from marine systems. Here, we present the results of a meta-analysis of 110 marine experiments from 42 studies that manipulated the species richness of organisms across a range of taxa and trophic levels and analysed the consequences for various ecosystem processes (categorised as production, consumption or biogeochemical fluxes). Our results show that, generally, mixtures of species tend to enhance levels of ecosystem function relative to the average component species in monoculture, but have no effect or a negative effect on functioning relative to the ‘highest-performing' species. These results are largely consistent with those from other syntheses, and extend conclusions to ecological functions that are commonly measured in the marine realm (e.g. nutrient release from sediment bioturbation). For experiments that manipulated three or more levels of richness, we attempted to discern the functional form of the biodiversity–ecosystem functioning relationship. We found that, for response variables related to consumption, a powerfunction best described the relationship, which is also consistent with previous findings. However, we identified a linear relationship between richness and production. Combined, our results suggest that changes in the number of species will, on average, tend to alter the functioning of marine ecosystems. We outline several research frontiers that will allow us to more fully understand how, why, and when diversity may drive the functioning of marine ecosystems. Synthesis The oceans host an incredible number and variety of species. However, human activities are driving rapid changes in the marine environment. It is imperative we understand ecosystem consequences of any associated loss of species. We summarized data from 110 experiments that manipulated species diversity and evaluated resulting changes to a range of ecosystem responses. We show that losing species, on average, decreases productivity, growth, and a myriad of other processes related to how marine organisms capture and utilize resources. Finally, we suggest that the loss of species may have stronger consequences for some processes than others.

Recent marine heat waves have caused devastating impacts on marine ecosystems. Substantial progress in understanding past and future changes in marine heat waves and their risks for marine ecosystems is needed to predict how marine systems, and the goods and services they provide, will evolve in the future.

Many estuarine and coastal marine ecosystems have increasingly experienced degradation caused by multiple stressors. Anthropogenic pressures alter natural ecosystems and the ecosystems are not considered to have recovered unless secondary succession has returned the ecosystem to the pre-existing condition or state. However, depending upon the scales of time, space and intensity of anthropogenic disturbance, return along the historic trajectory of the ecosystem may: (1) follow natural restoration though secondary succession; (2) be re-directed through ecological restoration, or (3) be unattainable. In order to address the gaps in knowledge about restoration and recovery of estuarine and coastal ecosystems, this special feature includes the present overview and other contributions to provide a synthesis of our knowledge about recovery patterns, rates and restoration effectiveness. From the 51 examples collated in this contribution, we refine the recovery from the list of stressors into six recovery mechanisms: (1) recovery from sediment modification, which includes all aspects of dredging and disposal; (2) recovery by complete removal of stressors limiting natural ecosystem processes, which includes tidal marsh and inundation restoration; (3) recovery by speed of organic degradation, which includes oil discharge, fish farm wastes, sewage disposal, and paper mill waste; (4) recovery from persistent pollutants, which includes chemical discharges, such as TBT; (5) recovery from excessive biological removal, related to fisheries and (6) recovery from hydrological and morphological modification. Drawing upon experience both from these many examples and from an example of one comprehensive study, we show that although in some cases recovery can take < 5 years, especially for the short-lived and high-turnover biological components, full recovery of coastal marine and estuarine ecosystems from over a century of degradation can take a minimum of 15-25 years for attainment of the original biotic composition and diversity may lag far beyond that period.

Aluminium (Al) is a common chemical element released into the aquatic environment from the Earth’s crust and many anthropogenic activities. It may be present in various dissolved and precipitated forms [Al3+, AlOH2+, Al(OH)2+, Al(OH)03, Al(OH)4−, etc.], which are potentially toxic for organisms. This review summarizes information about the concentrations of Al detected in aquatic ecosystems and its effects on both freshwater and marine organisms (such as growth disturbance, reproduction, and respiration alterations). As the chemistry of Al is different in freshwater and marine systems, we discuss the behaviour of aluminium and its effects on marine or freshwater fauna. Therefore, the solubility of Al, as other metals, is highly pH dependent, which increases when pH decreases. We are assuming that ocean acidification, linked to climate change, would affect the Al bioavailability in the aquatic environment, which may increase its ecotoxicological effects on semi-closed (Bays, Mediterranean Sea, etc.) or closed (lakes, etc.) aquatic ecosystems.

Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, we quantified the effect of fluctuations in food abundance on seabird breeding success. We identified a threshold in prey (fish and rill, termed \"forage fish\") abundance below which seabirds experience consistently reduced and more variable productivity. This response was common to all seven ecosystems and 14 bird species examined within the Atlantic, Pacific, and Southern Oceans. The threshold approximated one-third of the maximum prey biomass observed in long-term studies. This provides an indicator of the minimal forage fish biomass needed to sustain seabird productivity over the long term.

Successfully managing current threats to marine resources and ecosystems is largely dependent on our ability to understand and manage human behavior. In recent times we have seen increased growth in research to understand the human dimension of marine resource use, and the associated implications for management. However, despite progress to date, marine research and management have until recently largely neglected the critically important role of “sense of place,” and its role in influencing the success and efficacy of management interventions. To help address this gap we review the existing literature from various disciplines, e.g., environmental psychology, and sectors, both marine and nonmarine sectors, to understand the ways is which sense of place has been conceptualized and measured. Doing so we draw on three key aspects of sense of place, person, place, and process, to establish a framework to help construct a more organized and consistent approach for considering and representing sense of place in marine environmental studies. Based on this we present indicators to guide how sense of place is monitored and evaluated in relation to marine resource management, and identify practical ways in which this framework can be incorporated into existing decision-support tools. This manuscript is a first step toward increasing the extent to which sense of place is incorporated into modeling, monitoring, and management decisions in the marine realm.