Seagrasses face an uncertain future due to climate change

Lying beneath our coastal waters, seagrasses represent a crucial yet overlooked member of the marine food chain. These vast meadows perform a variety of functions that benefit both the planet and humanity. 

Seagrass meadows produce oxygen, absorb carbon dioxide, provide sustenance and shelter for various marine organisms, and significantly contribute to the global marine food chain. However, according to a recent study conducted by Stanford researchers, these ecosystems may be at risk of vanishing due to the impacts of climate change.

Oceans are estimated to absorb about 80% of the excess heat generated by greenhouse gas emissions, which will pose severe challenges to marine species. What remains less known, however, is how seagrasses, a fundamental group in the marine food chain, will adapt or survive. 

“The simple question we ask in this paper is, ‘How will seagrasses – which are a foundational group in the marine food chain – respond to climate change?'” said study lead author Barnabas Daru, a professor in the Stanford School of Humanities and Sciences.

Why are seagrass meadows important?

Seagrasses are an ancient group of plants that first originated in the ocean, colonized the land, and then returned to the sea around 140 million years ago. These unique ecosystems offer grazing grounds for herbivores such as endangered green sea turtles, manatees, and parrotfish. 

They also provide shelter for shrimp, marine invertebrates, and fish, while simultaneously serving as nurseries for approximately 20% of the world’s major commercial fisheries.

Many marine organisms depend directly on seagrasses for their survival. However, their influence extends further, offering indirect benefits to a wider array of species. 

“For example, sharks feed on marine animals that, in turn, may feed directly or indirectly on plants,” explained Professor Daru. “If anything affects these foundational species at the beginning of the food chain, it will have cascading effects on other organisms that depend on them high up in the food chain, including humans.”

How the study was conducted 

Given the expansive distribution of seagrasses, spanning roughly 116,000 square miles of coastline across 191 countries and all continents save for Antarctica, modeling the impacts of climate change on these plants is indeed a colossal task. To tackle this, the researchers began by mapping the location and abundance of seagrass species using about a century’s worth of samples gathered from coastal ecosystems. 

The team used field data and information from public seagrass databases, such as the Global Biodiversity Information Facility and Seagrass-Watch. To compensate for uneven sampling, the researchers used data from extensively sampled regions, like North America and Europe, to predict seagrass habitats for under-sampled areas like Southeast Asia and the Indo-Pacific.

The researchers then developed global “snapshots” of current oceanic climate and two future timeframes, 2040-2050 and 2090-2100, based on geophysical and environmental data from the Bio-ORACLE website. They modeled four different scenarios for each time period, ranging from a “best-case” climate with low greenhouse gas concentrations, to a “worst-case” scenario characterized by high greenhouse gas concentrations. 

Each of these scenarios took into account crucial variables like sea temperature, salinity, and sea current speed that significantly influence seagrass growth, distribution, and photosynthesis.

To project future seagrass populations and distributions, Daru and Rock applied a computer model that correlated observed species occurrences to each climate scenario. 

What the researchers learned 

The analysis revealed that even under the best-case scenario, seagrasses will face significant reductions in species diversity and composition. Disturbingly, these reductions were observed in every modeled scenario, including the best-case one. 

“It probably means that ‘the best’ is still not enough,” said Professor Daru. “We have to be more intentional in how conservation efforts are prioritized and this sort of analysis points to the places where these efforts should be done.”

Significant declines were particularly notable in areas referred to as hotspots that are currently outside the existing marine protected areas network. This observation shows that even the currently designated marine protected areas may not be sufficient to prevent the projected decline of seagrass populations. 

According to the experts, this is a stark reminder that the current strategies in place to protect these essential ecosystems may not be adequate to ensure their survival in the face of mounting climate change pressures.

Potential consequences 

“One of the signatures of this modern era of profound human impact on the environment is not even the loss of species, but the reorganization of biotic communities,” said Professor Daru. 

He further warned that the homogenization of seagrass communities could lead to a loss of their distinctiveness and uniqueness, making them more susceptible to disease and extreme weather events. This would not only impact the vital ecosystem services that these communities provide but also the diverse marine life that depends on them.

A change in seagrass communities could force marine animals that rely on specific seagrasses to either adapt to less favored species or relocate if their preferred seagrass is lost, resulting in a reduction of their fitness and survival.

Conservation efforts are urgently needed

Despite these grim projections, the study does not necessarily spell doom and gloom for seagrass meadows. Professor Daru noted that the research has also identified hotspots of change in species diversity and phylogenetic diversity. These areas represent priority regions for conservation efforts. 

“Our goal, our hope is that by pointing policymakers and conservationists to focus on these hotspots, marine protection will be increased in these areas and the future of seagrasses will – to some extent – be safeguarded,” he expresses.

This groundbreaking research was made possible through the support of the U.S. National Science Foundation. The study underlines the critical role seagrasses play in marine ecosystems and the need for a focused and intentional approach towards their conservation, particularly in the face of climate change. 

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