Beneath Saudi waters, seagrass anchors life and resilience

DHAHRAN: Carpeting the Kingdom’s two coasts — from the Red Sea in the west to the Arabian Gulf in the east— green seagrass meadows are among the most vital ecosystems, supporting biodiversity and serving as indicators of marine health. Beyond their ecological role, they offer a mesmerizing underwater spectacle.

Despite their name, seagrasses are not true grasses (Poaceae); they are fully submerged marine flowering plants.

“Seagrass meadows act as natural filters that help maintain the clear waters coral reefs depend on. Their leaves slow water movement, allowing sediments and suspended particles to settle before reaching nearby habitats, like reefs. At the same time, seagrasses absorb excess nutrients from the water and sediments,” Susana Carvalho, research associate professor of Marine Science at KAUST, told Arab News.

Research shows that seagrass ecosystems can reduce harmful bacteria and pathogens, with waters flowing through these meadows containing fewer human-derived bacteria. Areas rich in seagrass experience significantly lower levels of coral and fish disease.

"In this way, seagrasses do more than filter the water, they can actively improve reef health and resilience, while also benefiting human health that depends on clean coastal ecosystems,” Carvalho added.

The Red Sea presents a striking paradox: one of the saltiest seas on Earth, yet exceptionally clear.

“Despite its high salinity and warm temperatures, the Red Sea supports an extraordinary diversity of marine life, much of which is unique to the region. In fact, the Red Sea has high levels of endemism, meaning many species occur nowhere else on Earth,” Carvalho said. “What might appear to be harsh conditions can actually create unique opportunities for organisms that have adapted to them over thousands of years.”

Clear waters provide a major ecological advantage. “Because seagrasses are plants, they rely on sunlight for photosynthesis. Clear water allows light to penetrate much deeper than in many coastal regions around the world, where turbidity limits their growth. As a result, Red Sea seagrasses —which are important ecosystem engineers — can grow at depths of up to about 70 meters, forming extensive underwater meadows. They contribute to the biodiversity hotspot the Red Sea is known for, while supporting coastal protection, carbon sequestration, and fisheries.”

“Seagrasses in the Red Sea, and also in the Arabian Gulf, grow in one of the warmest and saltiest marine environments on Earth. Many species can maintain photosynthesis and growth at temperatures that would stress seagrasses elsewhere,” Carvalho said.

“This tolerance is partly due to physiological and biochemical adaptations that help them cope with thermal stress. They are also supported by an extensive underground network of roots and rhizomes, which anchors the plants in shifting sediments, recycles nutrients, and allows them to spread horizontally across the seabed. This clonal growth enables seagrass meadows to recover after disturbances and form large, stable habitats, if disturbances do not persist.”

Mapping these meadows for marine spatial planning is challenging.

“Many seagrass meadows are surprisingly difficult to detect, particularly through satellite imagery. They often occur in shallow or turbid waters, and their spectral signature can easily be confused with seaweeds or other underwater vegetation. Satellite tracking of animals such as sea turtles can help scientists identify feeding areas, which often leads to the discovery of previously unmapped seagrass beds. For a country like Saudi Arabia, where coastal development and conservation are both priorities, accurate maps of seagrass habitats help ensure that important nursery areas for fisheries and valuable blue-carbon ecosystems are considered in planning decisions,” Carvalho said.

The 2019 book Oceanographic and Biological Aspects of the Red Sea highlights this complexity. In the chapter “Seagrass distribution, composition and abundance along the Saudi Arabian coast of Red Sea,” researchers note: “Seagrasses rank among the most productive ecosystems with important implications in climate change mitigation. Tropical and subtropical seas hold the largest seagrass species richness. A total of 12 different seagrass species have been reported from the Red Sea. However, there is little information on seagrass diversity and distribution along the Saudi Arabian coast of the Red Sea. The Red Sea is a unique, semi-enclosed, and youthful ocean basin (approx. 2,000 km long, 355 km wide) characterized by high water temperatures, extreme salinity, and high evaporation rates, functioning as a ‘natural laboratory.’”

Restoring degraded seagrass meadows in the Red Sea faces a major obstacle: limited data.

“One of the main challenges in advancing seagrass restoration is knowledge — or the lack of it,” Carvalho acknowledged. “Before any restoration project begins, it is essential to understand whether a particular area historically supported seagrass or other target species and why it disappeared. Same applies to trying to introduce a species where it never existed.”

In 2025, the National Center for Wildlife launched a comprehensive monitoring plan targeting seagrasses, particularly in the Red Sea, to boost biodiversity and carbon storage. Surveys at 64 coastal locations assessed species health, while water temperature changes were monitored at 37 sites to gauge impacts on wildlife. 

NCW CEO Mohammed Qurban said the study “aligned with the green development goals of Saudi Arabia, which promote environmenefddetal sustainability in the Kingdom.”

While less visually flamboyant than coral reefs, seagrass meadows are indispensable.

“Seagrass meadows are among the most valuable ecosystems on Earth. They serve as nursery habitats where many fish and invertebrates that later live on coral reefs spend their early life stages. They also provide food for iconic Red Sea species such as green turtles and dugongs, stabilize sediments, improve water clarity, and store large amounts of carbon in their soils,” Carvalho concluded.