MELBOURNE, Oct. 15 (Xinhua) -- Large predatory fish such as the eastern blue groper are crucial for curbing surges of long-spined sea urchins that threaten kelp forests along Australia's southeast coast, new research shows.
A rapid climate-driven population explosion of long-spined sea urchins along southeastern Australia has stripped kelp forests, leaving vast "urchin barrens" and threatening vital reef ecosystems, according to a statement released Wednesday by Australia's University of Tasmania (UTAS).
The study by Australia's University of New South Wales (UNSW) and UTAS found that big eastern blue groper was responsible for 75 percent of all observed predation events near Sydney, and the other four smaller predatory fishes accounted for the remainder 25 percent.
"Groper larger than 600mm in length was the only predator observed to be capable of consuming sea urchins across the full-size range we studied, from 16 to 110mm in diameter. The other fish only targeted smaller size-classes of urchins," said UNSW PhD candidate Jessica Nguyen.
"Larger urchins are harder to eat, so they tend to be attacked less often," said Associate Professor Scott Ling from the UTAS Institute for Marine and Antarctic Studies, adding fish predatory behavior varied with urchin size.
"We also found smaller urchins were more often attacked from the top, whereas predators had to flip over larger urchins and target the less protected underside around the urchin's mouth," Ling said.
He said predator size and diversity strongly influence urchin control, with large southern rock lobsters identified as the primary urchin predators on Tasmanian reefs, where eastern blue gropers are rare, according to the same predation experiments.
In the Tasmanian experiments, the large bluethroat wrasse, a smaller cousin of the blue groper, were also observed to very occasionally consume small, long-spined urchins, the study shows.
"Protecting and rebuilding all urchin predators, particularly the larger more powerful and longer-lived species, isn't just good for exerting control on urchin populations, it cascades to increase resilience of the whole reef ecosystem," Ling said. ■
