Jellyfish blooms are regarded by some as an ecological menace, but they may sound the dinner gong for the commercially valuable Norway lobster. Recently, a team of scientists from Heriot-Watt University in Edinburgh have photographed the tasty crustacean in the waters off western Norway chowing down on jellyfish carcasses, suggesting that they could form a major part of its diet.

The 25-cm (10-in) Norway lobster (Nephrops norvegicus), also known as the Dublin Bay prawn, langoustine, or scampi, is the most important commercial crustacean in Europe, responsible for revenues of £78 million (US$105 million) to Scotland alone. They're remarkably abundant in the north-eastern Atlantic and parts of the Mediterranean, and they're cheaper than the larger common lobster. Each year 60,000 tonnes of them are hauled in with half taken in British waters.

It's known that these lobsters enjoy living on muddy bottoms, where they hunt for fish and worms, but it wasn't known until now that they have a taste for jellyfish – a fact that could have a large potential impact if it turns out that jellyfish blooms are actually a potential sustainable food source for the lobsters.

The discovery was made in 2016 when the Heriot-Watt team led by Dr Andrew Sweetman lowered a cage containing two defrosted helmet jellyfish carcasses and a pair of underwater cameras to a depth of over 250 m (820 ft) in the Sognefjorden, the largest and deepest fjord in Norway. Along with the usual scavengers, the scientists were surprised to find Norway lobsters decimating the carcasses.

"The Norway lobsters' feasting was fast and furious," says Sweetman. "In both deployments, they located the jellyfish in under 25 minutes, scared the other scavengers away almost immediately and consumed over 50 percent of the carcass.

"We looked at the nutritional value of the jellyfish, along with average Norway lobster energy intakes in the Firth of Clyde, and found that just one of these jellyfish could satisfy the lobster's energy requirements for up to three months.

"Jellyfish have historically been considered a 'dead end' in the marine food chain, and it was only in 2012 that we discovered that anything was using it as a food source. To discover that it's a potentially huge food source for one of the Atlantic and North Sea's most commercially important catches is really interesting, and raises questions about how jellyfish could contribute to sustainable commercial fishing."

The team expects the lobsters in Scotland to react similarly to the ones in Norway and believes that the fall of dead jellyfish to the sea bottom could be a major food source for the crustaceans that will help to offset the effect of jellyfish blooms.

"An interesting next step would be to find out how the Norway lobster are using the energy from the jellyfish," says Sweetman. "New techniques mean we could label jellyfish tissue with an isotope and trace it in the lobster – so we could actually tell whether it was going into reproductive cells, or helping general growth. That would be really fascinating"

The research was published in Nature Scientific Reports.

Source: Heriot-Watt University