Long‐term declines and recovery of meadow area across the world’s seagrass bioregions

Abstract

As human impacts increase in coastal regions, there is concern that critical habitats that provide the foundation of entire ecosystems are in decline. Seagrass meadows face growing threats such as poor water quality and coastal development. To determine the status of seagrass meadows over time, we reconstructed time series of meadow area from 175 studies that surveyed 547 sites around the world. We found an overall trajectory of decline in all seven bioregions with a global net loss of 5602 km2 (19.1% of surveyed meadow area) occurring since 1880. Declines have typically been non‐linear, with rapid and historical losses observed in several bioregions. The greatest net losses of area occurred in four bioregions (Tropical Atlantic, Temperate North Atlantic East, Temperate Southern Oceans and Tropical Indo‐Pacific), with declining trends being the slowest and most consistent in the latter two bioregions. In some bioregions, trends have recently stabilised or reversed. Losses, however, still outweigh gains. Despite consistent global declines, meadows show high variability in trajectories, within and across bioregions, highlighting the importance of local context. Studies identified 12 different drivers of meadow area change, with coastal development and water quality as the most commonly cited. Overall, however, attributions were primarily descriptive and only 10% of studies used inferential attributions. Although ours is the most comprehensive dataset to date, it still represents only one‐tenth of known global seagrass extent, with conspicuous historical and geographic biases in sampling. It therefore remains unclear whether the bioregional patterns of change documented here reflect changes in the world's unmonitored seagrass meadows. The variability in seagrass meadow trajectories, and the attribution of change to numerous drivers, suggest we urgently need to improve understanding of the causes of seagrass meadow loss if we are to improve local‐scale management.

Effects of Seagrass Wasting Disease on Eelgrass Growth and Belowground Sugar in Natural Meadows

“…Globally, seagrasses are declining under pressure from coastal development, climate change, and disease (Orth et al, 2006;Waycott et al, 2009;Dunic et al, 2021). To sustain and conserve these crucial habitats and their ecosystem services, we must determine the impacts of disease on eelgrass health.…”

Seagrass Meadows Provide a Significant Resource in Support of Avifauna

“…With each generation, the concept of a healthy ecosystem shifts, depending on their perceived baseline. In many parts of the world there is extensive evidence that vast amounts of seagrass have disappeared and with it the support it provided for fish stocks and biodiversity [5,62]. Factors driving this loss range from poor water quality, to coastal development, land reclamation and boating and fishing impacts [4].…”

“…Given the wide variety of food sources provided by this productive habitat, it is no surprise that seagrass meadows support an equally wide array of grazers and predators. However, despite its importance for sustaining biodiversity and many other ecosystem services [3], the global distribution of seagrass is a fraction of what was historically present [4,5]. Recent estimates from where records exist indicate that at least 20% of the world's seagrass has been lost [5].…”

“…However, despite its importance for sustaining biodiversity and many other ecosystem services [3], the global distribution of seagrass is a fraction of what was historically present [4,5]. Recent estimates from where records exist indicate that at least 20% of the world's seagrass has been lost [5]. Seagrasses also provide other services in the coastal zone such as preventing coastal erosion, storing and trapping carbon [6] and filtering the water column [7].…”

A Biophysical Model and Network Analysis of Invertebrate Community Dispersal Reveals Regional Patterns of Seagrass Habitat Connectivity

“…Pollution can also create barriers to dispersal through increased mortality during dispersal (Puritz and Toonen, 2011), and identifying reductions in connectivity will be crucial for understanding the broader regional effects to what may initially seem like a localized problem (Jonsson et al, 2020). In addition, seagrass worldwide is being lost at an alarming rate (Waycott et al, 2009;Dunic et al, 2021), and the consequences of habitat loss for biodiversity will depend on the specific connectivity characteristics of the remaining habitat (Thompson et al, 2016). By quantifying the contribution of each meadow or set of meadows to network connectivity, we can predict the consequences of losing a seagrass meadow.…”