Seagrass meadows are unique marine flowering plants that form expansive underwater ecosystems. Unlike seaweeds, which are algae, seagrasses possess true roots, stems, and leaves, and they produce flowers and seeds. These submerged plant communities are considered fundamental to the health of coastal marine environments.
Worldwide Distribution
Seagrass meadows are found in coastal waters across every continent except Antarctica. Their presence extends from tropical and subtropical regions to temperate zones. These underwater habitats typically thrive in shallow, sheltered coastal areas, including bays, estuaries, and lagoons.
The total area covered by seagrass meadows is estimated to be around 160,000 to 266,000 square kilometers. Over 70 species of seagrass exist worldwide, inhabiting 159 countries. This broad distribution underscores their adaptability to various marine conditions.
Ideal Growth Conditions
They depend on clear, shallow waters that allow sufficient sunlight to penetrate for photosynthesis. While many species are found in depths of a few meters, some can grow as deep as 90 meters. Seagrasses generally need between 4% and 36% of surface irradiance to survive.
These plants typically anchor themselves in soft, sandy, or muddy bottoms. Seagrasses thrive in marine saltwater or brackish conditions, which are mixtures of fresh and salt water. Most species grow well within a salinity range of 10 to 30 practical salinity units (PSU), but they can tolerate a broader range of 5 to 45 PSU.
Temperature also plays a role in their distribution. Temperate seagrass species typically prefer optimal growth temperatures between 10°C and 25°C, while tropical and subtropical species thrive in warmer waters, with optimal ranges between 23°C and 32°C. Seagrasses generally prefer sheltered areas with low wave action.
Key Global Hotspots
Significant seagrass meadows are found in several regions around the world. The Caribbean Sea is home to extensive meadows, including those off the coasts of Florida, Mexico, and Belize. Florida boasts some of the nation’s largest seagrass resources.
The Indo-Pacific region contains a high diversity of seagrass species and vast meadows. Australia’s Shark Bay is particularly notable, hosting one of the world’s largest seagrass banks, covering approximately 1,030 square kilometers. Other significant areas in this region include Southeast Asian coastlines, such as those in Indonesia, the Philippines, and Cambodia.
The Mediterranean Sea is another important hotspot, characterized by its endemic Posidonia oceanica seagrass. These meadows cover a significant area within the Mediterranean basin. Posidonia oceanica forms dense underwater prairies along the coasts of countries including France, Italy, Croatia, Greece, Spain, and Tunisia.