Seagrass Fields

Lore & Background

Seagrasses form dense underwater seagrass meadows which are among the most productive ecosystems in the world. They function as important carbon sinks and provide habitats and food for a diversity of marine life comparable to that of coral reefs. Seagrasses profoundly influence the physical, chemical, and biological environments of coastal waters. Though seagrasses provide invaluable ecosystem services by acting as breeding and nursery ground for a variety of organisms and promote commercial fisheries, many aspects of their physiology are not well investigated. There are 26 species of seagrasses in North American coastal waters. Several studies have indicated that seagrass habitat is declining worldwide. Ten seagrass species are at elevated risk of extinction (14% of all seagrass species) with three species qualifying as endangered. Seagrass loss and degradation of seagrass biodiversity will have serious repercussions for marine biodiversity and the human population that depends upon the resources and ecosystem services that seagrasses provide.

In Their Own Story

The water here is warm and clear, filtered by the sun above into a golden haze that dances across the swaying blades. A school of neon-blue fish darts through the green maze, their movements synchronized like a single living entity. As I drift silently in my rebreather's bubble, the only sound is the rhythmic hiss of air and the soft rustle of vegetation brushing against my suit. It feels less like an alien world and more like a forgotten dream of Earth, a peaceful interlude where the crushing weight of survival momentarily lifts.

Reader's Guide

Seagrasses form important coastal ecosystems. The worldwide endangering of these sea meadows, which provide food and habitat for many marine species, prompts the need for protection and understanding of these valuable resources. Seagrass populations are currently threatened by a variety of anthropogenic stressors. The ability of seagrasses to cope with environmental perturbations depends, to some extent, on genetic variability, which is obtained through sexual recruitment. By forming new individuals, seagrasses increase their genetic diversity and thus their ability to colonise new areas and to adapt to environmental changes. Seagrasses have contrasting colonisation strategies. Some seagrasses form seed banks of small seeds with hard pericarps that can remain in the dormancy stage for several months. These seagrasses are generally short-lived and can recover quickly from disturbances by not germinating far away from parent meadows (e.g., Halophila sp., Halodule sp., Cymodocea sp., Zostera sp. and Heterozostera sp.). In contrast, other seagrasses form dispersal propagules. This strategy is typical of long-lived seagrasses that can form buoyant fruits with inner large non-dormant seeds, such as the genera Posidonia sp., Enhalus sp. and Thalassia sp.

Did You Know?

• Seagrasses are the only embryophytes (land plants) that grow in marine environments.
• There are about 60 species of fully marine seagrasses, belonging to four families: Posidoniaceae, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.
• Seagrasses evolved from terrestrial plants that recolonised the ocean 70 to 100 million years ago.
• The seagrass Posidonia oceanica is one of the oldest and largest species on Earth; an individual can form meadows measuring nearly 15 km wide and can be hundreds to thousands of years old.
• Ten seagrass species are at elevated risk of extinction (14% of all seagrass species), with three species qualifying as endangered.