Seagrass in the Tin Can Bay inlet.
Seagrass in the Tin Can Bay inlet. Craig Warhurst

Fears Cyclone Marcia damaged seagrass

THERE are fears over how Cyclone Marcia and localised flooding will damage seagrass, which is a vital food source for many other marine species.

Freshwater run-off from agricultural land and flooded rivers and creeks could cause poor water quality in Queensland bays and damage seagrass beds, James Cook University tropical water and aquatic ecosystem scientist Michael Rasheed said.

"If there is lots of dirty water sitting around for a long time, it could start to die," he said.

Dr Rasheed said long dirty flood water in bays and off the coast would limit seagrass's access to light.

Seagrass played a critical role in the marine food chain, Dr Rasheed said.

It provided food for fish, prawns, crabs, turtles and dugongs - a species that almost exclusively relies on seagrass.

Larger animals such as other fish and sharks are attracted to seagrass beds for forage fish to survive.

An example of the importance of seagrass was revealed in the 1990s in Hervey Bay.

Fishers started spotting dead dugongs in the bay in 1992.

The Mary River flooded twice in one month that year, carrying silt into the sea. The seagrasses were killed because of extended periods of clouded water.

Without their seagrass food source, the dugongs died.

Dr Rasheed said seagrass off Gladstone also was being monitored because of similar scares.

But it is a different story in Shoalwater Bay, where Cyclone Marcia hit as a category five. Dr Rasheed said the past seagrass mapping occurred in the bay in the late 1990s.

He said it would be difficult to determine exactly how badly seagrass was affected from Cyclone Marcia and flooding because seagrass was not closely monitored in Queensland.