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Jersey's mammoth tides
By James McLachlan
Marine biologist Andrew Syvret explains why Jersey has such huge tides and how important the island is to marine life in the English Channel.
Rock pools are teeming with hidden life
Jersey may be a small island, but can boast some of the biggest tides in the world. When it recedes, the immense body of water that surrounding us seems to melt into the horizon, only to surge back to shore with alarming speed.†
These huge shifts have caught out many unsuspecting tourists and locals who, while investigating the myriad of rock pools at low water, have suddenly found themselves cut off from dry land.
But what causes the vast differences between high and low water?
Jersey marine biologist Andrew Syvret explained there is a common misunderstanding about how the tides work.
He said: “People think the tide rises and falls in the English Channel; that it floods and empties.
“The reality is you have a huge see-saw of water, with high tide at one end and low tide at the other. This massive bulge of water moves backwards and forwards twice each day.
“When it arrives in our corner of the English Channel this bulge of water really hasn’t got anywhere to go. We then find ourselves in a giant anti clockwise tidal gyre – a great whirlpool.”
North V South
Jersey’s north and south coast could not be more different. On the north, the sea sweeps up and crashes dramatically into the high cliffs. There are no such histrionics in the south, as the sea retreats over a gentle slope to reveal vast areas of rock and rock pools.
One such place is La Rocque, on the south-east coast. Here the pools which form at low tide give sanctuary to small fish and sea creatures.
Mr Syvret said: “These very shallow pools with a sandy bottom are incredibly important. You can think of these as incubators or nursery areas.
Low tide at La Rocque
“In the summer, they are three to four degrees warmer than the surrounding ocean, so a lot of small animals will begin their life here. They will use the sanctuary of these pools to grow as fast as they can.”
The pools provide the perfect hideaway for sea bass, sole and small turbot, as well as a plethora of crustaceans.
Although an invasive species, the rafts of Japweed which are strewn across the island’s beaches has both a positive and negative effect on indigenous marine life.
My Syvret said: “This stuff in particular is a negative in some respects, because it is shading out other species. But it does provide an incredible canopy at low tide for prawns, small fish and molluscs.”
The rocks, too, disguise an abundance of life not apparent at first glance and the creatures which live beneath are important to the whole region.†††
Mr Syvret said: “You’ve got snakelocks anemones, squat lobsters, a gang of shore crabs, pipefish tucked away and, of course, the molluscs that incrust the rocks.
“I have described the Violet Bank, the Minkies and the offshore reefs around Jersey as the engine room of the English channel.
Mr Syvret uses the Chancre, also known the Brown crab, as an example.
He said: “Historically, we would refer to them as Guernsey crabs, because to get a large chancre you would have to buy it from Guernsey.
“What tends to happen is they start their life here, grow to a certain size, and then go off in search of deeper water.
Sea birds snacking on marine life
“We are regularly broadcasting animals to the wider English Channel. We find ourselves in a corner which is absolutely vital to the functioning of the whole English Channel.”
last updated: 21/04/2009 at 14:27
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