Climate change has long been recognised as a significant threat to biodiversity on land, but its profound impact on marine life is now under increased scrutiny. Researchers Barnabas Daru & Brianna Rock, in their recent study published in Nature Plants, turned their attention to the world under the waves, specifically to the globally distributed seagrass meadows. These underwater ecosystems, often overlooked but vital for marine food chains and habitats, face serious reshuffling due to climate change. The surprising twist? Researchers predict an increase in certain types of ‘endemism’ (species unique to a specific location) as seagrass range sizes diminish, dramatically changing diversity across different regions.

Moving beyond the all-too-familiar headlines of shrinking habitats and species loss, Daru and Rock’s research paints a more nuanced picture of what climate change means for the verdant underwater meadows of seagrass.

Their models forecast a general contraction in the geographic ranges of seagrass species due to climate change. Strikingly, over 31% of the seagrass species they studied are predicted to decline by over 10% in their range sizes by mid-century, and these numbers will worsen by the end of the century. Amidst this grim reality, an unexpected phenomenon emerges: as seagrass ranges contract, the unique biodiversity within these areas – known as ‘endemism’ – is projected to increase.

Greater endemism might sound like good news, signifying an increase in species found nowhere else in the world. But it also suggests that the environmental conditions are becoming more hostile for seagrass, endangering these unique communities. Moreover, these changes in endemism are anticipated to manifest differently across various regions, leading to a fascinating, albeit worrying, mix of differentiation and homogenisation in seagrass diversity.

The research also uncovered worrying findings about the future effectiveness of our current conservation efforts. The study revealed that Marine Protected Areas – those parts of the ocean set aside for conservation – are not aligned with the anticipated hotspots of seagrass diversity. As a result, many of the regions forecasted to house diverse and unique seagrass communities may need more protection under current conservation measures.

Seagrasses play a vital role in marine ecosystems, similar to coral reefs and mangroves. They provide food for many marine animals, including endangered species like green sea turtles, manatees, and dugongs both directly and indirectly.

“For example, sharks feed on marine animals that, in turn, may feed directly or indirectly on plants,” said Daru in a press release. “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.”

Seagrasses are an ancient group of plants that originated in the ocean, moved to land, and then returned to the sea roughly 140 million years ago. They offer habitats for many marine creatures and provide valuable ecosystem services, such as sediment stabilisation, carbon sequestration, and water purification. However, these critical habitats are being lost at a startling rate due to human activities like pollution and coastal development, and the impacts of climate change are expected to exacerbate these losses.