Seagrass meadows globally are under pressure with worldwide loss and degradation, but there is a growing recognition of the global importance of seagrass ecosystem services, particularly as a major carbon sink and as fisheries habitat. Estimates of global seagrass spatial distribution differ greatly throughout the published literature, ranging from 177 000 to 600 000 km² with models suggesting potential distribution an order of magnitude higher. The requirements of the Paris Climate Agreement by outlining National Determined Contributions (NDC’s) to reduce emissions is placing an increased global focus on the spatial extent, loss and restoration of seagrass meadows. Now more than ever there is a need to provide a more accurate and consistent measure of the global spatial distribution of seagrass. There is also a need to be able to assess the global spread of other seagrass ecosystem services and in their extension, the values of these services. In this study, by rationalising and updating a range of existing datasets of seagrass distribution around the globe, we have estimated with Moderate to High confidence the global seagrass area to date as 160 387 km², but possibly 266 562 km² with lower confidence. We break this global estimate down to a national level with a detailed analysis of the current state of mapped distribution and estimates of seagrass area per country. Accurate estimates, however, are challenged by large areas remaining unmapped and inconsistent measures being used. Through the examination of current global maps, we are able to propose a pathway forward for improving mapping of this important resource. More accurate measure of global #seagrass distribution, critical for assessing current state and trends

Seagrasses, flowering marine plants that form underwater meadows, play a significant global role in supporting food security, mitigating climate change and supporting biodiversity. Although progress is being made to conserve seagrass meadows in select areas, most meadows remain under significant pressure resulting in a decline in meadow condition and loss of function. Effective management strategies need to be implemented to reverse seagrass loss and enhance their fundamental role in coastal ocean habitats. Here we propose that seagrass meadows globally face a series of significant common challenges that must be addressed from a multifaceted and interdisciplinary perspective in order to achieve global conservation of seagrass meadows. The six main global challenges to seagrass conservation are (1) a lack of awareness of what seagrasses are and a limited societal recognition of the importance of seagrasses in coastal systems; (2) the status of many seagrass meadows are unknown, and up-to-date information on status and condition is essential; (3) understanding threatening activities at local scales is required to target management actions accordingly; (4) expanding our understanding of interactions between the socio-economic and ecological elements of seagrass systems is essential to balance the needs of people and the planet; (5) seagrass research should be expanded to generate scientific inquiries that support conservation actions; (6) increased understanding of the linkages between seagrass and climate change is required to adapt conservation accordingly. We also explicitly outline a series of proposed policy actions that will enable the scientific and conservation community to rise to these challenges. We urge the seagrass conservation community to engage stakeholders from local resource users to international policy-makers to address the challenges outlined here, in order to secure the future of the world’s seagrass ecosystems and maintain the vital services which they supply.

Seagrasses are remarkable plants that have adapted to live in a marine environment. They form extensive meadows found globally that bioengineer their local environments and preserve the coastal seascape. With the increasing realization of the planetary emergency that we face, there is growing interest in using seagrasses as a nature-based solution for greenhouse gas mitigation. However, seagrass sensitivity to stressors is acute, and in many places, the risk of loss and degradation persists. If the ecological state of seagrasses remains compromised, then their ability to contribute to nature-based solutions for the climate emergency and biodiversity crisis remains in doubt. We examine the major ecological role that seagrasses play and how rethinking their conservation is critical to understanding their part in fighting our planetary emergency.

Indonesia's marine ecosystems form a fundamental part of the world's natural heritage, representing a global maxima of marine biodiversity and supporting the world's second largest production of seafood. Seagrasses are a key part of that support. In the absence of empirical data we present evidence from expert opinions as to the state of Indonesia's seagrass ecosystems, their support for ecosystem services, with a focus on fisheries, and the damaging activities that threaten their existence. We further draw on expert opinion to elicit potential solutions to prevent further loss. Seagrasses and the ecosystem services they support across the Indonesian archipelago are in a critical state of decline. Declining seagrass health is the result of shifting environmental conditions due largely to coastal development, land reclamation, and deforestation, as well as seaweed farming, overfishing and garbage dumping. In particular, we also describe the declining state of the fisheries resources that seagrass meadows support. The perilous state of Indonesia's seagrasses will compromise their resilience to climate change and result in a loss of their high ecosystem service value. Community supported management initiatives provide one mechanism for seagrass protection. Exemplars highlight the need for increased local level autonomy for the management of marine resources, opening up opportunities for incentive type conservation schemes.

Seagrass meadows commonly reside in shallow sheltered embayments typical of the locations that provide an attractive option for mooring boats. Given the potential for boat moorings to result in disturbance to the seabed due to repeated physical impact, these moorings may present a significant threat to seagrass meadows. The seagrass Zostera marina (known as eelgrass) is extensive across the northern hemisphere, forming critical fisheries habitat and creating efficient long-term stores of carbon in sediments. Although boat moorings have been documented to impact seagrasses, studies to date have been conducted on the slow growing Posidonia species’ rather than the fast growing and rapidly reproducing Zostera marina that may have a higher capacity to resist and recover from repeated disturbance. In the present study we examine swinging chain boat moorings in seagrass meadows across a range of sites in the UK to determine whether such moorings have a negative impact on the seagrass Zostera marina at the local and meadow scale. We provide conclusive evidence from multiple sites that Zostera marina is damaged by swinging chain moorings leading to a loss of at least 6ha of UK seagrass. Each swinging chain mooring was found to result in the loss of 122m2 of seagrass. Loss is restricted to the area surrounding the mooring and the impact does not appear to translate to a meadow scale. This loss of UK seagrass from boat moorings is small but significant at a local scale. This is because it fragments existing meadows and ultimately reduces their resilience to other stressors. Boat moorings are prevalent in seagrass globally and it is likely this impairs their ecosystem functioning. Given the extensive ecosystem service value of seagrasses in terms of factors such as carbon storage and fish habitat such loss is of cause for concern. This indicates the need for the widespread use of seagrass friendly mooring systems in and around seagrass.

Seagrass ecosystems face widespread threat from reduced water quality, coastal development and poor land use. In recent decades, their distribution has declined rapidly, and in the British Isles, this loss is thought to have been extensive. Given increasing knowledge of how these ecosystems support fisheries production, the understanding of their potential rapid loss, and the difficulty in restoring them, it is vital we develop an understanding of the risks they are under, so that management actions can be developed accordingly. Developing an understanding of their environmental status and condition is therefore critical to their long-term management. This study provided, to our knowledge, the first examination of the environmental health of seagrass meadows around the British Isles. This study used a bioindicator approach and involved collecting data on seagrass density and morphology alongside analysis of leaf biochemistry. Our study provides, to the best of our knowledge, the first strong quantitative evidence that seagrass meadows of the British Isles are mostly in poor condition in comparison with global averages, with tissue nitrogen levels 75% higher than global values. Such poor status places their long-term resilience in doubt. Elemental nutrient concentrations and morphological change suggest conditions of excess nitrogen and probable low light, placing many of the meadows sampled in a perilous state, although others, situated away from human populations were perceived to be healthy. Although some sites were of a high environmental health, all sites were considered at risk from anthropogenic impacts, particularly poor water quality and boating-based disturbances. The findings of this study provide a warning of the need to take action, with respect to water quality and disturbance, to prevent the further loss and degradation of these systems across the British Isles.