MASS STRANDING IN TORBAY
by Chris Proctor
On Sunday the 12th September 1993 south-west England was hit by a deep depression moving in from the Atlantic. The resulting gale was not particularly heavy (wind speeds of 60 mph were reported at Berry Head that evening), but the wind direction was unusual. The position of the depresson, with it's centre to the south of Britain, meant that the wind blew from the east, straight into Torbay. Most gales in this part of the country are caused by depressions passing to the north and blow from the south-west, leaving the bay sheltered. Conditions were spectacular. At Hope's Nose a 3 metre swell broke over the rocks, producing plumes of spray perhaps 10 metres high. A heavy surf was breaking on the beaches at Paignton and even in the most sheltered corners of Torbay the sea was rough. The following day the wind veered to the northeast and abated somewhat: by Tuesday the 14th the gale had ended.
The direction from which this gale blew meant that it's full force was felt along a stretch of coast normally sheltered from heavy weather. In several ports in the southwest, there was extensive damage to boats in normally sheltered anchorages. Little damage was reported in Torbay (except the iron railings beside the Shoalstone open air swimming pool which were swept away), but the effect on marine life was spectacular. Over the next few days I visited the beaches between Broadsands in the south and Torre Abbey Sands to the north to see what had been washed up. At all the beaches visited large amounts of material had come ashore, but by far the most impressive stranding was at Preston Sands just north of Paignton. Here the beach was an amazing sight. Much of it was buried under piles of weed, and near the north end massive drifts of dead animals, mostly molluscs, had accumulated. A wide variety of animals had been washed up: the more interesting species are discussed in detail below.
From the nearby rocks came thousands of Common Mussels,
Mytilus edulis, and a variety of other animals, mostly common shore
inhabitants such as Shore and Edible Crabs Carcinus
maenas and Cancer pagurus, and
the Green Sea Urchin Psammechinus miliaris. A few were probably
derived from rocks below low tide mark, including a Ballan
Wrasse Labrus bergylta, and the tail end of a Spiny Squat-Lobster
Most of the stranded animals, however, came from the sandy seabed offshore
from the beach. These were much more exciting since many of them were sublittoral
species not normally found on the shore and included burrowing forms rarely
or never seen by divers. Most obvious were bivalve molluscs. The beach
was littered with thousands of Otter Shells Lutraria lutraria
and Razor Shells Ensis siliqua.
Scallops and Necklace Shells
The otter shells in particular excited much interest and virtually everyone I spoke to on the beach commented on them, many saying they had never seen them before. They are deep burrowers, maintaining contact with the surface by their massive non-retractible siphons, and are normally safe from storms. Their presence in such numbers showed that the waves had eroded deeply into the seabed, exposing and washing them out. Other bivalves washed up included another deep burrower, the Blunt Gaper Mya truncata, fair numbers of the spectacular Red Nose or Spiny Cockle Acanthocardia tuberculata with its vivid scarlet foot, and the little circular white bivalve Mysia undata. About half a dozen other species were present in smaller numbers.
Together with the bivalves were the burrowing gastropods which prey
on them. The commonest was the Large Necklace Shell Lunatia catena,
some of which were still alive and would probably have been worth collecting
for aquarium study. Also present were two burrowing predatory opisthobranchs.
I found several dozen Philine aperta in pools near low water
mark, looking rather repulsive like small grey slugs.
Other burrowers included a variety of echinoderms. Most familiar was
the Heart Urchin Echinocardium cordatum
which frequently washes up in Torbay and occurs on the shore in some places.
A few were freshly dead, but most were empty tests which had lost their
spines, probably individuals which had died some time ago and remained
buried in the sand until washed out by the storm.
Another group of species comprised animals which had lived on the surface of the sand. Prominent were Queen Scallops Aequipecten opercularis, and one or two Great Scallops Pecten maximus. Many of the Queen Scallops supported tangled masses of the calcareous tube worm Serpula vermicularis. Serpula was also present encrusting old whelk shells with Slipper Limpets Crepidula fornicata and a few Saddle Oysters Anomia ephippium. These shells had probably been inhabited by large hermit crabs: had they been empty it is unlikely they would have stayed on the surface of the sand long enough to gain such a rich encrusting fauna. The most likely inhabitant of these large shells would be Pagurus bernhardus, and this species was indeed present in fair numbers, although mostly as smaller individuals. Two smaller species were also present: Pagurus prideauxi with its symbiont anemone Adamsia palliata and the left clawed hermit crab Diogenes pugilator.
True Crabs (Brachyura)
True crabs were well represented with 9 species washed up, including
most of the common shore forms. Several species characteristic of sandy
bottoms were present.
Other beaches produced much less variety than Preston sands, but some
new species were found. At Goodrington Sands few otter or razor shells
had been washed up, but there were plenty of spiny cockles. At Broadsands
at the southwest corner of Torbay burrowing fauna was conspicuously scarce.
There were many sagartiid anemones here, which had probably been living
attached to stones and shells covered by a thin layer of sand. The real
interest was opisthobranch molluscs. In addition to a few Sea Hares
punctata and large numbers of Philine aperta, hundreds
of another shelled opisthobranch, Akera bullata had been
stranded. These have a very delicate translucent brown shell that is so
thin it can bend without breaking. Akera is known to occur in plagues
in some years: presumably this was such an aggregation, possibly to breed
- there were many spawn ribbons washed up with them, though these might
have belonged to a different species.
At the northwest corner of Torbay at Torre Abbey Sands, there were many
live Heart Urchins Echinocardium cordatum,
and the small Sand Crab Portumnus latipes, like a swimming
crab with a very narrow carapace.
Sea Bed Erosion
Looking at the distribution of the stranded animals some patterns are
obvious, but there are also some puzzles. Clearly Preston Sands took the
brunt of the weather, with deep erosion of the sea bed which dug out even
the deepest burrowers. To the south the depth of erosion decreased, so
that at Goodrington only shallow burrowers such as spiny cockles were washed
up in any numbers and at Broadsands the stranded fauna comprised mainly
surface dwellers. The level of Broadsands beach actually rose, burying
a patch of stones near the south end. At Torre Abbey Sands some erosion
took place, exposing the forest bed and digging out many heart urchins.
Use these links if your are familiar with the scientific classifications of marine life