The changing foreshore of Mersea Island

by John Llewellyn-Jones

Many years ago in the 1950s as children, and indeed with my own children in the 1980s, we would spend our summer holidays on the lovely sandy beach at the bottom of Seaview Avenue, West Mersea, Essex, where my parents lived. At the top of the beach there was a row of beach huts and the soft golden sand ran down past the high-tide mark and on to what we called the "mud" flats. In fact they were made up of sand, shingle and small patches of mud out to the low spring-tide mark. Every large stone lifted would reveal scurrying baby crabs. We would collect cockles, mussels and winkles to boil in a "billy" can on an open fire made from driftwood found on the beach. We would walk the tide line and across the flats, barefoot, looking for shells and other marine objects

Beach huts at West Mersea

I have included a table of the shells found by us and my mother on the beach in May 1974 (see below). We spent many happy hours wandering over the flats searching for live marine animals and seaweeds. There were chitons (Lepidochiton cinerea Linnaeus, 1767) under the rocks, cockles (Cerastoderma edule Linnaeus, 1758) would squirt water up, giving their position away, and mussel beds on which there was the occasional dog whelk (Nucella lapillus Linnaeus, 1758) drilling one or other of them. In the muddy puddles, if one dug down with one's hands one might find a blunt/truncate gaper (Mya truncata Linnaeus, 1758) or a common gaper (Mya arenaria Linnaeus, 1758) and some Baltic tellins (Macoma balthica (Linnaeus, 1758). If one looked carefully over the muddy areas one might see a star-shaped pattern on its surface. Digging down quite a long way one would find a peppery furrow shell (Scrobicularia plana da Costa, 1778). Here and there on the rocks were a number of seaweeds including Fucus sp. on which the flat periwinkle (Littorina obtusata (Linnaeus, 1758) – there was only one species in the 1970s – could be found feeding. Another algal species, the edible laver (Porphyra umbilicalis Kützing, 1843), was common and red seaweeds were to be found attached to stones in pools. In the small pools one could also see tracks on the muddy surface made by the edible periwinkle (Littorina littorea Linnaeus, 1758) crawling around.

Lepidochiton cinerea (L., 1767)

Littorina obtusata (L., 1758)

This was the situation until the early 1990s when a few large, rather worn but still living specimens of the Pacific oyster (Crassostrea gigas Thunberg, 1793) started to be washed up to the edge of the sandy beach in storms. It was in the early 2000s that the whole situation started to change and the "mud" flats are now almost unrecognisable. Live Crassostrea started reproducing and forming colonies known as "reefs". Mud started to settle between the areas where the reefs were forming at the low-water mark.

Crassostrea gigas Thunberg, 1793

Crassostrea reefs

And then another species, the Quahog (Mercenaria mercenaria Linnaeus, 1758), started appearing and is now common, often being found smashed open on the stones by seagulls. A small band of sandy and stony ground at the bottom of the sandy beach remained and here a third introduction has started to appear, the Asian carpet shell or Manila clam (Tapes philippinarium (Adams & Reeve, 1850).

Mercenaria mercenaria L., 1758

Tapes philippinarium (Adams & Reeve, 1850)

So the situation now is that the cockles have almost gone, the mussel beds have been buried and have gone with the dog whelks, and there are only a few groups of slipper limpets (Crepidula fornicata Linnaeus, 1758) left. The edible winkles have become uncommon, none of them able to cope with the sloppy mud building up between the gigas "reefs". Because a lot of the larger stones have become buried in mud the seaweeds have also disappeared, meaning there is less plant life for the grazers to feed on. The beach huts are still at the top of the sandy beach but the "mud" flats are now covered in gigas reefs and sloppy mud. Crassostrea gigas have very beautiful purple-striped frilly shells which are very sharp-edged. It is therefore either impossible or very difficult indeed to walk over the reefs and certainly not in bare feet or flimsy shoes. Because the shells are so tightly packed and cemented together they are very small and difficult to get at for eating.

Crepidula fornicata L., 1758

Close-up of Crassostrea reef, showing sharp-edged shells

For some years now it has been noticeable that the number of species on the Mersea shore has been reducing. Included in the table below is a list of shells that I made over a day or two in 2010. At first the reduction was thought to be due to the hot cooling water from the Bradwell nuclear power station being pumped into the Blackwater estuary and killing off the marine species living on the flats. But it is now thought that it was more likely to be the highly chlorinated seawater used to keep the huge cooling inlet and outlet pipes extending into the sea, along with the generator castings, free of the barnacles, seaweed and silt which were continually fouling them up. Of course, the sacrifice was the smaller, less adaptable marine animals and molluscs in the area.

I don't believe that the power station is the only problem causing the species diversity reduction over the last few years. The warming of the water, both from the power station and global warming, the chlorination of the seawater and lastly the formation of gigas "reefs" and sloppy mud formation between them have all come together to produce a catastrophic change in the foreshore and its marine life, including molluscs, at West Mersea over the last few years.

The problem, far too late, has at last been recognised by the West Mersea Town Council who in their local newsletter (No. 14, Oct/Nov 2011) made the following statement: "Beware sharp shells". And I quote: "The Mersea beach working group have received complaints regarding the build-up of potentially dangerous rock oyster shells which could harm bathers. Rock oysters or Gigas were first introduced to British waters in the sixties – unlike the natives they grow with their edges pointing upwards. Brightlingsea [a nearby seaside town] Harbour Commissioners have taken action to remove these shells from their beaches."

This was followed in the Courier (Mersea's free magazine) on 18 April 2012 (issue no. 529) by the following article: "Beach cleared of wild oysters". I summarise: "Dredgers started clearing West Mersea beaches of wild oysters, which originated in the Pacific and were introduced in the 1970s by MAFF and have now become a pest and are cutting the feet of bathers and dogs. Natural England considers them to be a pest and with Essex Wildlife Trust have given their backing to this form of removal."

We can only wait and see?

Species	May 1974	July 2010
Lepidochiton cinerea	LC	LO
Patella vulgata	LO	DR
Littorina saxatilis	LO	LR
Littorina littorea	LC	LO
Crepidula fornicata	LC	LO
Littorina obtusata	LO	DR
Gibbula cinerea	LO	DO
Gibbula tumida	DR
Nucella lapillus	LO	DR VOS
Buccinum undatum	DO	DO
Nassarius reticulata	LO	DO
Ocenebra erinacea	DO	DR VOS
Urosalpinx cinerea	LC	DR1
Natica catena	DO
Trivia arctica	DR2
Lora rufa	DO
Lora turricula	DO
Hydrobia ulvae	DO	LC3
Phytia myosotis	LO4
Rissoa membranacea	DO
Turbonilla elegantissima	DO
Cardium edule	LC	LR
Cardium glaucum	DO	DO
Cardium exiguum	DO	DO
Mytilus edulis	LC	LO
Ostrea edulis	DO	DO
Scrobicularia plana	LO	DO
Macoma balthica	LC	DR
Mya arenaria	LO	DO
Mya truncata	LO	DO
Corbula gibba	DR
Spisula solida	DO
Venerupis pullastra	LO	DR
Tapes aurea	DR VOS
Petricola pholadiformis	DO
Barnea parva	DO
Barnea candida	DO
Crassostrea angulata	DO
Crassostrea gigas	DO
Tapes philippinarium	LO
Mercenaria mercenaria	LO

 

Key
L = live
D = dead
C = common

O = occasional
R = rare
VOS = very old shell
Blank = none

Notes
1. Urosalpinx cinerea comes inshore to lay eggs early in the year.
2. Trivia arctica may have come from the Red Crag at Walton-on-the-Naze.
3. Hydrobia ulvae was living in the small piece of salt marsh behind the beach.
4. Phytia myosotis was living under the Suaeda fruticosa at the top of the beach.

This article by John Llewellyn-Jones was first published in our magazine Pallidula in October 2012.