Seagrass has signs of new growth

The DPI has not shared the same concerns of residents about the future of seagrass in Port Stephens.
The DPI has not shared the same concerns of residents about the future of seagrass in Port Stephens.

CONCERN for the health of the Port's waterways is not shared by seagrass experts from the Department of Primary Industry.

In response to the Examiner's article last week on fears of declining seagrass in the Port, Tim Glasby, principal research scientist at the DPI's Marine Ecosystems Unit, said while there was evidence of it occurring, there were also signs of new growth.

"Seagrasses are protected in NSW and play important roles in recycling nutrients, trapping and stabilising sediments and storing carbon," Dr Glasby said.

"The species that has declined in abundance in Port Stephens is zostera capricorni, commonly called eelgrass, starting around 2010 in parts of the upper estuary, west of Soldiers Point.

"There have been more declines in the last 12 months or so, particularly around Tea Gardens and along part of the southern shore of the port.

"In many shallow areas such as along Bagnalls Beach, the zostera has thinned out considerably, but there is evidence of new growth."

Dr Glasby said scientists were not sure of the causes for the zostera decline, but suspects it might be heavy rainfall.

"We are starting to do experiments to examine the tolerance of zostera to low salinity, due to heavy rainfall, and in particular to repeated events over short periods," he said.

"Heavy rainfall can potentially kill the grass in shallow water by decreasing the salinity, but it can also kill zostera in deeper water by turning the water brown and hence reducing light levels.

"Zostera that grows closer to the ocean is less likely to be affected by freshwater inputs, which might explain why we have not seen reductions east of Nelson Bay marina."

Dr Glasby said the seagrass could re-establish from fragments of plants or from seeds.

"One of the triggers for germination of seeds is low salinity and low water temperatures, which is why zostera is well adapted to germinate after heavy rainfall, particularly in winter."