In the sheltered parts of many bays, inlets, and estuaries flowering plants called seagrasses establish extensive underwater meadows. Seagrasses are critical in the lifecycles of many fish species with many spending the early part of their life in seagrass beds.

Seagrasses trap soil and other materials washed from the land and bind them together. This stops them from clouding the water and preventing light reaching plants on the bottom.

Seagrasses provide shelter for many marine species. They contribute large amounts of plant material that breaks down to form detritus (a major food source for invertebrates).

In the past three decades, catchments that have been extensively modified for urban or agricultural development leading to a massive decrease in seagrass beds, particularly in bay areas. This decrease means there is reduced habitat for commercially significant fish and internationally important bird species.

As seagrasses can take many decades to recover, loss of this habitat is a community concern.

Animals found in seagrass beds include Banjo Shark (Trygonorrhina fasciata), Cow Fish (Aracana aurita) and Pot-bellied Seahorse (Hippocampus abdominalis). Types of seagrass Narrow Leaf Seagrass (Zosterea nigricaulis) and Broad Leaf Seagrass (Posidonia australis).

Key Threats

• Catchments which result in poor water quality entering the sea containing either large amounts of nutrients like nitrogen that cause algal blooms, or significant loads of sediments that cloud the water
• Oil and chemical pollution
• Fishing or removal of animals and plants
• Marine pests which compete for food or space such as the Northern Pacific Seastar (Asterias amurensis) or the Japanese Kelp (Undaria pinnatifida)
• Boat and anchor damage in shallow areas
• Climate change effects including sea level rise, warming sea surface temperatures, and increasing ocean acidity.

Where to see seagrass beds

• Corner Inlet Marine National Park
• French Island Marine National Park
• Yaringa Marine National Park
• Churchill Island Marine National Park
• Mushroom Reef Marine Sanctuary
• Ricketts Point Marine Sanctuary

Related links

• Museum Victoria’s Marine Life
• Western Port Seagrass Partnership