Threats to Seagrasses

Seagrass ecosystems are under intensifying pressure from a combination of localised human activities and global climate shifts. The degradation and loss of seagrass habitats can have far-reaching ecological consequences, particularly for migratory marine species that depend on connected coastal habitats for feeding, breeding, and movement. Habitat fragmentation can disrupt critical migration corridors, isolate populations, accelerating localised extinctions. 

 

Water Quality Degradation 

Seagrasses have exceptionally high light requirements, often needing between 10% and 30% of surface light levels to sustain healthy growth. Declining water quality is therefore one of the most significant threats to seagrass ecosystems. 

  • Nutrient Enrichment and Cultural Eutrophication: Excessive nutrient inputs from agriculture, aquaculture, urban runoff, and untreated wastewater triggers rapid blooms of microalgae and epiphytes. These organisms reduce water clarity and cover seagrass blades, limiting sunlight available for photosynthesis and reducing seagrass productivity. 
  • Increased Sedimentation and Turbidity: Deforestation, coastal development, land clearing, and unsustainable land management increase the amount of sediment runoff entering coastal waters. This suspended sediment reduces light penetration and can smother seagrass plants, forcing meadows to decline or retreat to shallower waters. 
  •  

Coastal Development and Physical Disturbance 

Direct physical disruption causes immediate habitat loss and breaks up continuous meadows into small, exposed patches. 

  • Dredging & Land Reclamation: Port development, coastal engineering, and land reclamation activities can remove, bury, or damage productive seagrass habitats, while causing long-term turbidity downstream.  

  • Anchoring, Propeller Scarring, and Destructive Fishing Practices: Bottom-trawling fishing gear, commercial anchoring, and vessel propeller paths damage seagrass meadows by cutting deep tracks through root and rhizome networks. Recovery from such disturbances can be slow, particularly where repeated impacts occur or where environmental conditions limit regrowth.  

     

Climate Change and Thermal Stress 

Global climate shifts introduce severe environmental stress that compound existing local pressures. 

  • Marine Heatwaves: Prolonged periods of anomalous sea surface temperatures exceed the physiological tolerance of key seagrass species, causing reduced growth, loss of productivity, and, in severe cases, large-scale meadow die-offs.  

  • Sea-Level Rise and Coastal Squeeze: As sea-levels rise, seagrass habitats may naturally migrate shoreward in response to changing light conditions and water depths. However, where coastlines are heavy modified with or seawalls, ports, or urban development, the habitat is trapped, resulting in “coastal squeeze” and a net loss of habitat. 

     

Extreme Weather Events 
Increasingly frequent and intense storms can uproot seagrass plants, alter sediment dynamics, and damage extensive areas of habitat, particularly when ecosystems are already stressed by other environmental pressures. 

 

Implications for Migratory Species 

The loss and fragmentation of seagrass meadows can disrupt critical feeding grounds and movement corridors used by migratory species, including dugongs, sea turtles, fish, and invertebrates. Because many of these species move across national boundaries, local habitat degradation can have regional consequences, highlighting the need for coordinated conservation action among Range States. 

 

Transboundary Conservation Tools 

Reversing these trends requires coordinated, science-based policies across all Signatory States of the CMS Dugong MOU. Range States can utilize international frameworks and collaborative tools to align their local management plans with global targets: 

  • International Frameworks & Policies: Review official guidelines, resolutions, and regional conservation targets on the Convention on Migratory Species (CMS) main portal to align national policies with international biodiversity commitments.