STINGRAYS are being researched as a keystone species in WA’s Ningaloo, where they are playing an important ecological role “modifying physical and biological habitats through their foraging and predation”.
In a paper published last year in journal Marine and Freshwater Research, Murdoch University PhD student Owen O’Shea quantified the effects of bioturbation by stingrays (Pastinachus atrus, Himantura spp. Taeniura lymma and Urogymnus asperrimus) on flat sands of Ningaloo reef.
The length, breadth and depth of 108 feeding pits created by stingrays were measured daily over three 7-day periods.
“Stingrays create big depressions in the sand and anywhere you get lots of rays that feed, you’ll see these quite obvious depressions on the bottom.,” Dr O’Shea says.
“The way they feed is by sitting on the sand beating their pectoral wings and jetting water into the sediment, which creates these excavations or pits.
“We saw these pits on an enormous scale and randomly sampled areas within this intertidal zone at Ningaloo reef—measuring pits for their volume to see how much sediment the rays were displacing,” he says.
This bioturbation allows the stingrays to access the animals living in the sand (infauna).
“The other thing about them doing so is they’re providing secondary predation opportunities for other predators species.”
Mr O’Shea says these factors class stingrays as a functional or ‘keystone’ species in these ecosystems and that ecological management plans need to look more closely at stingrays.
“[The rays] exert a top down control on the food chains at lower levels. Through their feeding and bioturbation they also modify the physical habitat. So the comings-and-goings of infauna and the shifting sands of the ecosystems and specific habitats are largely determined by stingrays,” he says.
He hopes application of this research can be reverted back to a management objective.
“Ultimately, the importance of this research is that it’s highlighting a fairly critical process from a lesser known and less iconic species,” Mr O’Shea says.
“So when looking at ecosystem based approaches to management, instead of primarily looking at when the whale sharks or the manta rays come, it might be appropriate to look at where there are large concentrations of stingrays. The processes and the function they fulfill in these ecosystems has been completely overlooked.”
Mr O’Shea is furthering this research and aims to paint a broad ecological, biological and demographic picture of the Ningaloo stingrays.
