Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 km ² yr ⁻¹ since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% yr ⁻¹ before 1940 to 7% yr ⁻¹ since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.

Angiosperms are the cornerstone of most terrestrial ecosystems and human livelihoods^1,2. A robust understanding of angiosperm evolution is required to explain their rise to ecological dominance. So far, the angiosperm tree of life has been determined primarily by means of analyses of the plastid genome^3,4. Many studies have drawn on this foundational work, such as classification and first insights into angiosperm diversification since their Mesozoic origins^5–7. However, the limited and biased sampling of both taxa and genomes undermines confidence in the tree and its implications. Here, we build the tree of life for almost 8,000 (about 60%) angiosperm genera using a standardized set of 353 nuclear genes⁸. This 15-fold increase in genus-level sampling relative to comparable nuclear studies⁹ provides a critical test of earlier results and brings notable change to key groups, especially in rosids, while substantiating many previously predicted relationships. Scaling this tree to time using 200 fossils, we discovered that early angiosperm evolution was characterized by high gene tree conflict and explosive diversification, giving rise to more than 80% of extant angiosperm orders. Steady diversification ensued through the remaining Mesozoic Era until rates resurged in the Cenozoic Era, concurrent with decreasing global temperatures and tightly linked with gene tree conflict. Taken together, our extensive sampling combined with advanced phylogenomic methods shows the deep history and full complexity in the evolution of a megadiverse clade.

Seagrasses are important marine foundation species that are reported to be declining worldwide, with almost 15% of species considered threatened. Seagrasses are highly productive plants that reconfigure water flow and influence nutrient cycling, as well as provide critical habitat for a wide array of fish and invertebrate species. Yet, many of these seagrass‐dependent species, including economically important fishes and invertebrates, are themselves in danger of overexploitation or extinction. In fact, there is on average more than one threatened associated species for every seagrass species across the globe. Links between threatened seagrasses and their dependent communities illustrate the importance of an ecosystem‐based management approach that incorporates interdependencies and facilitation among species.

Disturbance and habitat destruction due to human activities is a pervasive problem in near-shore marine ecosystems, and restoration is often used to mitigate losses. A common metric used to evaluate the success of restoration is the return of ecosystem services. Previous research has shown that biodiversity, including genetic diversity, is positively associated with the provision of ecosystem services. We conducted a restoration experiment using sources, techniques, and sites similar to actual large-scale seagrass restoration projects and demonstrated that a small increase in genetic diversity enhanced ecosystem services (invertebrate habitat, increased primary productivity, and nutrient retention). In our experiment, plots with elevated genetic diversity had plants that survived longer, increased in density more quickly, and provided more ecosystem services (invertebrate habitat, increased primary productivity, and nutrient retention). We used the number of alleles per locus as a measure of genetic diversity, which, unlike clonal diversity used in earlier research, can be applied to any organism. Additionally, unlike previous studies where positive impacts of diversity occurred only after a large disturbance, this study assessed the importance of diversity in response to potential environmental stresses (high temperature, low light) along a water–depth gradient. We found a positive impact of diversity along the entire depth gradient. Taken together, these results suggest that ecosystem restoration will significantly benefit from obtaining sources (transplants or seeds) with high genetic diversity and from restoration techniques that can maintain that genetic diversity.

This study assessed metabolism, growth, and survival of two seagrass species at three different seawater temperatures (27°C, 30°C, and 33°C) under saturating (400 µmol photons m^‐2 s^‐1) and limiting (40 µmol photons m^‐2 s^‐1) light over 1 month. Halodule uninervis grown at 33°C was within its physiological optimum temperature range, exhibiting 2.3× higher photosynthetic rates than at 27°C, and increased net shoot carbon (C) production (up to 10× higher) at saturating light levels. In contrast, 33°C exceeded the optimum temperature threshold for Zostera muelleri, resulting in critical metabolic imbalances with large reductions in photosynthesis and increases in leaf respiration. This led to substantially lower growth rates (0‐2% of those at 27°C) and lower final biomass (only 10% of that at 27°C) in the 33°C treatment after 1 month. This decline at higher temperatures occurred at both light levels, but it was more severe in limiting light, where the C balance went into deficit. H. uninervis in the Great Barrier Reef (GBR) exists well within its optimal temperature range and should continue to thrive at projected future temperatures, at least under saturating light levels. In contrast, Z. muelleri currently exists near its upper thermal threshold, and future temperature increases of the magnitude investigated here would likely lead to the contraction of the range of this species from the northern GBR ‐ potentially by more than 1000 km. This could have ecologically significant ramifications, because Z. muelleri is often the only GBR species that currently inhabits muddy estuarine areas, which are critical fisheries habitats.