How do the only flowering plants in the sea cope with being buried?

Researchers from Edith Cowan University within the larger WAMSI Westport Marine Science Program investigated how seagrasses cope with burial from dredging. Seagrasses are the only flowering plants to occur in the ocean and are beneficial as they provide habitat and food for many economically valuable species and also improve water quality. Seagrasses have high light requirements and so they tend to occur in the shallows along our coastlines. Their habitats generally coincide with urbanisation and coastal developments, such as ports and harbours. Dredging associated with these developments can affect seagrasses directly by reducing light or indirectly by burial as the sediment settles on the seagrass. Seagrasses can also be naturally buried with ocean movement causing sediment to be transported, but we don’t fully understand how much the plants can tolerate (also known as a threshold) before their growth and survival is adversely affected.

The goal of researchers was to acquire scientific evidence that supports how much and how long dredging can occur for whilst minimising or avoiding impacts to seagrasses. Individuals of the seagrass Posidonia sinuosa were collected in the Cockburn Sound area as this is the dominant species. Plants were put into aquarium tanks in a greenhouse at Edith Cowan University (below).

Researchers take measurements of seagrass Posidonia sinuosa to assess how it responds to different burial treatments.

Plants within each tank were not buried (control) or buried under 2, 4, 8 or 16cm of dredge spoil (below).

Seagrass Posidonia sinuosa under 16cm burial treatment of dredge spoil.

Preliminary analysis of the data suggests that burial levels of 8 and 16cm negatively impacted the seagrass P. sinuosa in a mesocosm setting,as plants under these treatments had lower growth and survival. Even after these burial treatments were removed, plants were not able to recover. This research will help inform mitigation planning and the long-term management of Cockburn Sound.

Authors: Edith Cowan University – Chanelle Webster, Nicole Said, Tash Dunham, Aaron Bywater and Kathryn McMahon

Photo credits: Edith Cowan University – Chanelle Webster, Nicole Said, Tash Dunham, Aaron Bywater and Kathryn McMahon