04 February 2013

Rhossili shellfish strandings

Otter Shells (Lutraria lutraria)
Some pictures from Gordon Howe of the recent shellfish strandings in Rhossili Bay over the last few days; it is worth noting that many of the shells still had the animals inside them.  If anyone can explanation what's been happening it would be interesting to know.

Pod Razors (Pharus legumen
presumably Sand Mason Worms (Lanice conchilega)

7 comments:

Anonymous said...

Could it have something to do with the mineral oil spillage off the South coast Barr?

Wayne Morris said...

There were huge numbers of razor shells along the shoreline at Titchwell, Norfolk on 18-19 January, so it may not be unique to Gower or associated with the oil along the south coast.

Anonymous said...

I saw a similar event last September on this beach after a night of heavy surf. Many seabirds were standing around looking completely stuffed with food.

chris said...

i seem to remember from fishing days,that a strong s to sw blow coupled with big spring tides,can result with various clam species being washed out of their burrows in rhosili bay,transported toward Burry Holmes and eventually washing up on the beach.

Barry Stewart said...

Ivir Rees wrote:

Hi,

I noticed the blog posting on the stranding event at Rhosilli and thought you might like a comment.

Elsewhere on the North Wales and Lancashire coasts this sort of thing occurs from time to time. I know of papers describing such events going back to the 1920s and wrote a paper on the circumstances surrounding such things in Red Wharf Bay in the 1970s.

Basicly it is a wash out event when the swell wave action reaches somewhere that has not been disturbed for at least the life span of the organisms concerned. So it may occur when the swell comes from a slightly unusual direction or the wave base just reaches further down. If there is cold weather this increass the chance of washouts as the burrowing organisms are more sluggish. For example a lot of shallow water benthos was hit in the 1963 winter. Off Rhosilli, as far as I remember the fine sand seabed shelves fairly gently but there is a zone where there is likely to be slightly muddy fine sand carrying an abundance of bivalves such as the Pharus and Lutararia shown on the photos. This zone could well be where the Scoters feed when on this side of Carmarthen Bay. Scoters have been seen taking Pharus and off N Wales we had them concentrating on a patch of Lutraria spat, before they got too big and too deeply dug in. As to the Lanice, they will shed the top of the tubes so masses of these does not mean they have been killed. From the photos I could not identify much else though I did see some Ophiura ophiura. Because of this sort of mass washout the benthos of these intermediate depth sands can vary a lot.

Another circumstance where there can be mass washout mortality is if there is an excess of decaying organic matter such as from a plankton bloom. The depth of the anoxic layer in the sediment gets nearer the surface and the infauna comes out on the surface. But this is normally a summer event. Given recent storms, cold weather and big tides I would hazard a guess at ascribing the event to weather.

Hope this is useful.

Ivor

Barry Stewart said...

Apologies, Ivor not Ivir!

gareth thomas said...

I don't think that it's a coincidence that perhaps thousands of scoters have been frequenting Rhossili bay of late. Obviously attracted by the easy availability of these shellfish, which normally are much less accessible to them.
Ivor's information is most enlightening on this event.