Crossing Jersey’s Intertidal Reef to the Seymour Tower

Along the south-east coast of Jersey, stretching from St Helier to Gorey, the seabed is so shallow that at low tide an area of 17.5 square kilometres becomes exposed, making this one of the largest intertidal reefs in the world. Because of this, the area was declared a wetland of international importance in 2000, under the terms of the Ramsar Convention. (In 1971, the city of Ramsar in northern Iran, was the venue for an inter-governmental conference, the purpose of which was to provide a framework for action to ensure the conservation and wise use of wetland resources.)

Seymour Tower and Intertidal Reef (photo: Anthony Toole)

Seymour Tower and Intertidal Reef (photo: Anthony Toole)

At La Roque, on the south-east corner of the island I joined a group led by Trudie and Keith, of Jersey Walk Adventures. About two kilometres from the coast, the Seymour Tower stood on its craggy plinth, separated from us by an expanse of sand and mud flats, pools and channels and rock platforms. Some in our party accepted the offer of gumboots, others of us decided we could put up with wet feet.

Crossing the Reef

Our guides took us first to the holding cages that contained thousands of oysters, harvested from the beds that lay in deeper waters. The oysters would be held here for a time before being transferred to tanks exposed to ultra-violet light prior to being sent to markets, mostly in France. There were European oysters in the pools, but the farmed ones were American Pacific. Farther out among the rocks were poles festooned with mussels. Farming of shellfish is an important aspect of Jersey’s economy, providing employment and contributing to the local cuisine.

In Your Bucket Because…

  • The Jersey coast is a wetland of international importance for its marine life.
  • As the intertidal range is the second largest in the world, there are few places where on can walk a comparable distance from the mainland coast.
  • The rock pools are a wildlife wonderland for children to explore.

We continued through calf-deep pools and over fields of serrated, knotted and bladder wrack, kelp and carrageen. Trudie pointed out examples of velvet horn seaweed and coralline algae, and tempted us to taste sea lettuce and other rock pool delicacies. She also found a piece of seaweed clustered with small colonies of star sea squirt (botryllus schlosseri), and in one pool, a snake locks sea anemone.

Snakelocks Sea Anemone (photo: Anthony Toole)

Snakelocks Sea Anemone (photo: Anthony Toole)

Life in the Rock Pools

The pools and channels held myriad shells, tops, limpets, periwinkles, whelks and the occasional ormer and oyster, half of them abandoned, half still occupied. In one pool, we saw a limpet being predated by a whelk. The roof of a small grotto, formed by boulders, was coated with a layer of orange sponges. A series of incongruous tracks across gravel beds, some of them several metres long, led to stones that had been dragged along by currents acting on bunches of seaweed rooted to them.

Among the sand ripples were concentrations of what appeared to be dark green algae, but which on closer examination, proved to consist of millions of tiny mint sauce worms (symsagittifera roscoffensis) that obtained their nutrition and their colour from a symbiotic alga. Each worm contained around 25000 algal cells.

Star Sea Squirt (photo: Anthony Toole)

Star Sea Squirt (photo: Anthony Toole)

We came to a rock on which a large letter P was carved. This, said Keith, dated from 1740, when, following a dispute, the rights to harvest seaweed were granted to the Paine family. Evidence of much earlier, probably seasonal human activity had been found in butchered mammoth bones dating back to Neolithic times, when the land bridge still existed and forests of alder and birch covered the area.

At the Seymour Tower

As we approached the Seymour Tower, a waterspout appeared over the sea to the south. Seeming to form in a lower stratum of cloud, this atmospheric vortex, an ocean variety of tornado, reached up to a higher, broader cumulus, and hovered there for several minutes before slowly fading.

The Tower itself was built as a defensive structure during the 18th century, and stands on a tall, granite shelf. It is reached by means of a rough-hewn staircase, and contains seven bunk beds and a stove, with fridge and lighting powered by roof-mounted solar panels. It can be booked by groups of people who are happy to spend a night cut off from the land by the high tides.

We climbed to the roof, where Trudie hoisted the Jersey pennant while we enjoyed the quite stunning view back over the rocky expanse to the coast. Despite its sometimes being compared to a moonscape, we had found it to be a magical region, teeming with a huge variety of marine life.


  • Flights to St Helier can be arranged from most British airports.
  • Walks to the Seymour Tower may be undertaken privately or under the guidance of Jersey Walk Adventures. The latter would be advisable as the guides have knowledge of the tides.
  • If you wish to spend a night in the Seymour Tower, then this can only be done with a qualified guide. Bookings can be made through Jersey Heritage.

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