Monday, 24 December 2012

Western rock lobster dines on time

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wester rock_lobster“The western rock lobster fishery is the largest single species fishery in Australia so it’s important to know whether fishing impacts can cascade down to lower trophic levels.”—John Dumas. Image: Claire RossTHE strong predator–prey relationship between lobsters and crustaceans could impact on areas where lobsters are heavily fished, including WA’s south-west coast, according to a recent study.

Strong preference for decapod prey by the western rock lobster (Panulirus cygnus) a collaboration between the University of WA’s Oceans Institute and Centre for Marine Futures and the UK’s Plymouth Marine Laboratory, explored which group of animals may be affected if lobster populations decrease.

While the research was laboratory-based, author John Dumas says future studies could translate the findings in the field to see whether lobsters are controlling populations of certain species of crustaceans.

“The western rock lobster fishery is the largest single species fishery in Australia so it’s important to know whether fishing impacts can cascade down to lower trophic levels,” he says.

Prey preferences of small, medium and large lobsters were investigated through feeding trials to identify size-associated differences.

But investigating prey preference was not a simple matter of providing lobsters with different prey and observing their selections, Mr Dumas says.

“The experiment is done in two stages,” he says. “Firstly, prey is offered individually to lobsters to measure the rate each prey type is consumed.

“Prey types are then offered simultaneously and the consumption rate of each prey type is again measured—the comparison of the consumption ratio between the two stages is statistically tested using a chi-squared test.”

It was found lobsters preferred crabs and mussels while medium and small lobsters preferred crabs over mussels, gastropods and sea urchins, suggesting strong predator–prey interactions between lobsters and crabs may occur in the wild.

“The main reason behind differences in diet is the handling time required to capture and consume prey,” Mr Dumas says.

“Large lobsters are stronger than smaller lobsters and we found, for a given prey type, smaller lobsters would take longer to eat the prey because it’s harder for them to break the shells or carapaces.

“Smaller lobsters will find easier prey to eat—even for the same prey type, such as mussels, they will target smaller mussels with thinner and weaker shells.”

Mr Dumas also explored whether prey choice was influenced by diet quality.

Crustaceans were found to have the lowest protein quality and were preferred by lobsters, which makes him believe prey choice is more greatly influenced by handling time.

“In the wild, lobster diet is also found to be different between juveniles and mature lobsters,” Mr Dumas says.

“But I believe it’s because they live in different habitats with a different abundance of prey, hence prey availability influences what they eat.”

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