The decline of an endangered species of coral in Port Stephens and Brisbane Water poses a threat to the coastal food web, including fish such as bream and tarwhine, University of Newcastle research has found.
A research paper published on Tuesday, titled What eats a cauliflower coral?, expanded on findings that the soft coral had declined by about 90 per cent since records were kept.
Cauliflower coral [scientific name Dendronephthya australis] is found along the southern shore of the Port Stephens estuary, between Fly Point and Corlette Point - including off Nelson Bay.
It is also found in Brisbane Water on the Central Coast, near Ettalong and Lobster Beach, but it may have been wiped out there in recent floods.
Dr Vincent Raoult said the coral's "alarming decline" could have "potential negative flow-on effects for our coastal food webs".
Dr Raoult said honours student Hannah Finlay-Jones found no fish fed on the corals. "But interestingly, she found all these small organisms got most of their nutrition from them," he said.
"Those smaller organisms, like little crustaceans, are important food species for a lot of commercially important species of fish, particularly bream and tarwhine."
Ms Finlay-Jones also examined the species of fish associated with the coral, compared to seagrass habitat. Seagrass plays an important role in fish nurseries.
"It turned out soft corals have a similar number of species associated with them," Dr Raoult said.
A previous study, from 2016, warned that cauliflower coral was under increasing threat from sand inundation "caused by a combination of complex factors such as ongoing erosion at Shoal Bay and past nourishment there, stabilisation of Zenith Beach sand dunes and interaction of wave climate changes".
That study said large patches of the coral off Nelson Bay could be protected through habitat management, such as "no-anchoring areas or sanctuary zones".
This would have reduced effects including fishing line entanglement.
The Port Stephens marine park protected seagrass, but not the cauliflower coral.
The coral remains under threat from sand movement, boat anchoring and mooring. Given its critical role in the ecosystem's health, the researchers recommended action to ensure it does not become extinct in the region.
Research into cauliflower coral was initially done by Dr David Harasti, senior marine scientist in fisheries research with the NSW Department of Primary Industries.
Dr Harasti originally studied the coral because it was associated with White's seahorse, a threatened species.
His research led him to realise that the coral in Port Stephens was declining fast.
The coral was identified as a critical habitat for these seahorses. As the coral declined, so did the seahorses.
A previous four-year study also found that the Port Stephens marine park led to the decline of White's seahorse.
The seahorse's major predators - such as octopus, flathead and scorpionfish - were more common at four marine park sites around Nelson Bay.
