Starfish washed up on the shore in their thousands have fallen foul of extreme weather and dredging by fishermen, naturalists said yesterday.

On two separate occasions recently beachwalkers have had to pick their way past piles of dead starfish stranded on beaches in Kent and Sussex.

Thousands of the echinoderms were washed up almost two weeks ago on the stretch of coast between Pegwell Bay and Sandwich in Kent, and several hundred more were found at Black Rock on Brighton beach at the weekend.

Ecologists from the Environment Agency were called in to investigate the mass deaths and concluded that each stranding had a different cause.

The estimated 500 common starfish (Asterias rubens) found at Brighton were thought to have lost their grip on the seabed and were swept to their deaths during the recent storms.

The several thousand starfish found on the Kent coast are believed to have been killed by fishermen as they dredged the sea floor for shellfish.

Mussels are the favourite food of starfish, which can gather at shellfish beds in groups of more than a million. Dredging equipment often dislodges them.

Ian Humpheryes, a marine ecologist for the Environment Agency, said it was unlikely that disease or starvation had killed the starfish.

He concluded that in both cases the bodies of the common starfish were washed up on a single tide, whereas disease and starvation would have taken place over time, meaning that bodies would have washed up over many tides.

Storms are usually cited as the cause of mass deaths of starfish, which are generally recorded at least once every two years.

In the case of the Brighton stranding, the discovery of hundreds of bodies fits the theory that the deaths were caused by the recent extreme weather and the unusually high spring tide. Storms and spring tides both work to weaken the grip of starfish clinging to rocks on the seabed.

The stranding in Kent ten days earlier took place before the storms and the weather was too calm for it to be a likely cause of the deaths. Shellfish dredgers were also known to be operating in the area at the time.

Mr Humpheryes said that while both strandings were “significant events” the overall starfish population was unlikely to be badly affected by the losses.

“It probably won’t even dent the population,” he said. “It’s a shame to see them dead on the shore like this but there are countless other common starfish in our waters. They are a favourite seaside animal – the ladybirds of the sea.”

A single starfish can produce 1.5 million eggs and “literally billions” of larvae are produced each year.

To eat a mussel a starfish will pull apart the two halves of the shell until there is a tiny opening. It then pushes its inverted stomach through the gap, allowing its digestive juices to ooze out and turning the flesh of the mussel into a more edible mush.

Times recommends

• Energy-saving ideas from switched-on professor
• Rooks are as clever with tools as chimpanzees
• Burping of the lambs blows roast off menu