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| Strange Molluscs |
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| Created by jonmakeham on 11 Feb
2001 23:40:02 |
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| 1 |
Date Posted: 11 Feb 2001 23:40:02
by jonmakeham
  
I have been
rockpooling and keeping records on my finds at Hannafore
Point,
West Looe, Cornwall for some seven years now. This is a rocky
reef approx. 2km x 1km at extreme low water and is the richest
shore
habitat that I have ever come across in the UK.
I paid
my first visits of the year to the shore for the very low tides
this weekend, and found, as well as the usual collection of
fauna, some
unusual discoveries.
First were some ten adult,
live specimens of the Great Scallop Pecten
Maximus, which, to my
knowledge, is never found on shore. These were
quite viable, and
have two in one of my tanks to prove it. It is
probable that
storms dredged these up offshore and dumped them on the
reef,
although I have not seen this happen before.
Two specimens (small
- carapace 15mm long) of the swimming crab
Liocarcinus arcuatus
were found living under rocks on the middle shore.
This species,
which is distinctive and easy to recognise, is supposed to
be
exclusively sublittoral.
More interesting, and puzzling, were my
finds of the large top shell
Gibbula magus. Worn shells
occasionally turn up on Cornish coasts, and I
was very surprised
to find in excess of twenty live specimens, with
brilliant
coloration, living on the middle to lower shore. More evidence
of
their abundance was found in the form of literally hundreds of small
hermit crabs living in discarded and obviously fairly fresh
shells of
the species. The hermit crabs, empty shells and live
animals gave the
impression that this was one of the more common
gastropod species on the
lower shore. Given that the species is
not generally regarded as common,
and is strictly sublittoral,
this is puzzling? Any ideas? Anyone else
seen this? Anyone
interested?
Jon.
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| 2 |
Date Posted: 12 Feb 2001 08:04:15
by Anne
I am, and are pearl
bearing specimens of mussels and clams etc among them,.
the rise
in sea temperatures and density change with influx of phytoplankton
and zooplankton because of upwellings along the Cornish coast
because of
global warming - the El Ninio effect and the
Milankovitch cycles are bound to
affect the species noted as
they are seeking the richest fragments and
together are food web
cousins. Did you take pictures of this migrated
group?
Paula
|
| 3 |
Date Posted: 12 Feb 2001 09:17:45
by Mike
Noren
On Sun, 11 Feb 2001
23:44:53 -0000, you wrote:
...
: First were some ten adult,
live specimens of the Great Scallop Pecten
: Maximus, which, to
my knowledge, is never found on shore.
...
: Two specimens
(small - carapace 15mm long) of the swimming crab
: Liocarcinus
arcuatus were found living under rocks on the middle shore.
:
This species, which is distinctive and easy to recognise, is
supposed to
: be exclusively sublittoral.
:
: More
interesting, and puzzling, were my finds of the large top shell
: Gibbula magus. Worn shells occasionally turn up on Cornish
coasts, and I
: was very surprised to find in excess of twenty
live specimens
The scallop and the swimming crab are not uncommon
creatures, they
just normally live subtidally.
I'm not sure I
know exactly which species G. magus is - I've never
been any darn
good at telling the various Gibbulas apart - but it's
supposed to
be found in your area.
To me, several possibilities suggest
themselves:
1) There's been an episode of unusual larval
settlement due to unusual
environmental factors, e.g. unusually
high or low temperature, or
unusual currents. This happens all
the time - locally, for instance,
the bivalve Gari fervensis is
unable to reproduce, and may yet be
fairly common some years due
to larvae drifting in from the
south-west.
2) If this is an
area where salinity might be depressed or temperature
elevated,
low salinity or high temperature may have previously
prohibited
these species from entering. Unusual weather or changes
in
currents may have caused cooler and/or more saline deep water,
with
associated fauna, to reach shore. This scenario is probably
less
likely given that scallops and snails aren't particularly
mobile,
meaning that these conditions would have had to persist
for quite some
time.
3) A key predator of these species has
disappeared from the area, or
been greatly reduced in number,
allowing these species to persist
where previously they could
not. Given these species, I'd guess that
that predator would
likely be shore crab, gulls, or humans
4) Translocation by
humans. Diving or sampling close to marine biology
stations is
usually guaranteed to turn up species not normally found
in the
area, or found in much deeper water.
5) Unusually powerful storms
have physically disloged these organisms
and moved them into more
shallow water than they're usually found.
This is not uncommon,
although usually deeper water organisms die due
to heat and/or
lower salinity and/or predation when they find
themselves in
shallow water.
There's probably other explanations, but these are
the ones I can
think of offhand.
: Jon.
Michael Norén,
Doctoral student,
Stockholm University and Tel: Int +46 (0)8 5195
5163
Swedish Museum of Natural History, Fax: Int +46 (0)8 5195
5181
"Nihil umquam facile"
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| 4 |
Date Posted: 12 Feb 2001 10:10:40
by Anne
OS
>"More
interesting, and puzzling, were my finds of the large top
shell
>Gibbula magus. Worn shells occasionally turn up on
Cornish coasts, and I
>was very surprised to find in excess of
twenty live specimens, with
>brilliant coloration, living on
the middle to lower shore. More evidence
>of their abundance
was found in the form of literally hundreds of small
>hermit
crabs living in discarded and obviously fairly fresh shells
of
>the species. The hermit crabs, empty shells and live
animals gave the
>impression that this was one of the more
common gastropod species on the
>lower shore. Given that the
species is not generally regarded as common,
>and is strictly
sublittoral, this is puzzling? Any ideas? Anyone else
>seen
this? Anyone interested?"
Hi Jon,
regarding your queries
on G. magus, whilst i am not very familiar with the
species
myself, heres what Fretter & Graham* have to say on its
habitat...
according to Fretter & Graham, whilst being
mainly infralittoral, not being
uncommon on muddy gravel to a
depth of 70m, occasional specimens may be
found at LWST and there
are localities such as some southern shores of Co.
Galway where
intertidal specimens are common.Though apparently
these
intertidal animals are more squat than those from deeper
waters which are
also mre frequently spiny.
They occur on rock
and weed and under stones, requiring some shelter. They
do not
like reduced salinity.
hope this of some
help
anne
* Fretter, V. & Graham A. 1977. The
Prosobranch molluscs of Britain and
Denmark, part 2-Trochacea,
Supplement 3. The Journal of Molluscan
Studies.
Anne O' Shaughnessy
Zoology
Dept.
Martin Ryan Institute,
National University of Ireland,
Galway.
Tel: +353 91 524411 ext; 3219
Fax: +353 91
525005
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| 5 |
Date Posted: 12 Feb 2001 19:24:41
by Cedric
d'Udekem d'Acoz
Dear Jon,
As
concerns Liocarcinus arcuatus, I would like to inform you that it is
not
uncommon on some shores on the French coasts of the English
Channel. It is
however frequently overlooked. The species stays
burried in the sediment
during the day and is more easily caught
at night (with a shrimp net),
especially in Zostera
meadows.
Actually, there are several decapod crustaceans
which are found (and are
sometimes common) on the shore on the
French coasts of the English Channel
and which have never been
recorded intertidally around the British Isles. I
do not know if
they have been overlooked or if they are really absent from
the
shore. The more important tides on the French side of the Channel
could
be a possible explanation.
The most surprising case
concerns Macropodia deflexa. It is said to be
strictly subtidal
around the British Isles while it is the commonest
intertidal
Macropodia species on the westen half of French part of
the
Channel (the species is absent both intertidally and
subtidally in the
Easternmost part of the
Channel).
Gibbula magus is also common on many shores of the
French part of the
Channel.
If I well remember, I have
also seen Pecten maximus on the shore on the
French part of the
Channel, but it was long ago.
Kind regards,
Cédric
d'Udekem d'Acoz
----- Original Message -----
From:
Jon Makeham <jon-makeham@beeb.net>;
To:
<glaucus@smartgroups.com>;
Sent:
Sunday, February 11, 2001 11:44 PM
Subject: [glaucus] Strange
Molluscs
I have been rockpooling and keeping records on
my finds at Hannafore
Point, West Looe, Cornwall for some seven
years now. This is a rocky
reef approx. 2km x 1km at extreme low
water and is the richest shore
habitat that I have ever come
across in the UK.
I paid my first visits of the year to the
shore for the very low tides
this weekend, and found, as well as
the usual collection of fauna, some
unusual
discoveries.
First were some ten adult, live specimens of the
Great Scallop Pecten
Maximus, which, to my knowledge, is never
found on shore. These were
quite viable, and have two in one of
my tanks to prove it. It is
probable that storms dredged these up
offshore and dumped them on the
reef, although I have not seen
this happen before.
Two specimens (small - carapace 15mm
long) of the swimming crab
Liocarcinus arcuatus were found living
under rocks on the middle shore.
This species, which is
distinctive and easy to recognise, is supposed to
be exclusively
sublittoral.
More interesting, and puzzling, were my finds of
the large top shell
Gibbula magus. Worn shells occasionally turn
up on Cornish coasts, and I
was very surprised to find in excess
of twenty live specimens, with
brilliant coloration, living on
the middle to lower shore. More evidence
of their abundance was
found in the form of literally hundreds of small
hermit crabs
living in discarded and obviously fairly fresh shells of
the
species. The hermit crabs, empty shells and live animals gave
the
impression that this was one of the more common gastropod
species on the
lower shore. Given that the species is not
generally regarded as common,
and is strictly sublittoral, this
is puzzling? Any ideas? Anyone else
seen this? Anyone
interested?
Jon.
|
| 6 |
Date Posted: 12 Feb 2001 19:25:55
by jonmakeham
----- Original
Message -----
From: <Rainforestanne@aol.com>;
To:
<glaucus@smartgroups.com>;
Sent:
Monday, February 12, 2001 8:04 AM
Subject: Re: [glaucus] Strange
Molluscs
> I am, and are pearl bearing specimens of
mussels and clams etc among
them,.
> the rise in sea
temperatures and density change with influx
of
phytoplankton
> and zooplankton because of upwellings
along the Cornish coast because of
> global warming - the El
Ninio effect and the Milankovitch cycles are bound
to
>
affect the species noted as they are seeking the richest fragments
and
> together are food web cousins. Did you take pictures of
this migrated
group?
> Paula
Pictures of which
group? I found isolated specimens, and these are well
known
species. Can photograph recovered animals in my aquarium if this
helps
anybody.
Jon.
>
>
>
>
>
If you want to share pictures, use the calendar, or hold a
questionnaire
> visit http://uk.groups.yahoo.com/group/Glaucus
>
>
To leave the group, email: glaucus-unsubscribe@smartgroups.com
>
|
| 7 |
Date Posted: 12 Feb 2001 22:37:58
by Anne
Thank you and most
appreciated.
Paula
|
| 8 |
Date Posted: 16 Feb 2001 19:40:31
by Nicolas Jouault
Nick from Jersey
16-2-01
Re; live specimens of the Great Scallop Pecten
Maximus, I have found the odd one occassionally in the past. On
the last
spring tide a work colleague reported collecting a dozen
or more on the
south east coast of jersey, his mate had similiar
amount two days following.
I have also had reports in past of
collections of dozen plus in St. Aubins
bay. I would say finding
them on the shore on a spring tide is not unusual
in Jersey.
regards Nick
Author wrote:
> I have been rockpooling
and keeping records on my finds at Hannafore
> Point, West
Looe, Cornwall for some seven years now. This is a rocky
>
reef approx. 2km x 1km at extreme low water and is the richest shore
> habitat that I have ever come across in the UK.
> I
paid my first visits of the year to the shore for the very low tides
> this weekend, and found, as well as the usual collection of
fauna, some
> unusual discoveries.
> First were some
ten adult, live specimens of the Great Scallop Pecten
>
Maximus, which, to my knowledge, is never found on shore. These were
> quite viable, and have two in one of my tanks to prove it.
It is
> probable that storms dredged these up offshore and
dumped them on the
> reef, although I have not seen this
happen before.
> Two specimens (small - carapace 15mm long) of
the swimming crab
> Liocarcinus arcuatus were found living
under rocks on the middle shore.
> This species, which is
distinctive and easy to recognise, is supposed to
> be
exclusively sublittoral.
> More interesting, and puzzling,
were my finds of the large top shell
> Gibbula magus. Worn
shells occasionally turn up on Cornish coasts, and I
> was
very surprised to find in excess of twenty live specimens, with
> brilliant coloration, living on the middle to lower shore.
More evidence
> of their abundance was found in the form of
literally hundreds of small
> hermit crabs living in
discarded and obviously fairly fresh shells of
> the species.
The hermit crabs, empty shells and live animals gave the
>
impression that this was one of the more common gastropod species on
the
> lower shore. Given that the species is not generally
regarded as common,
> and is strictly sublittoral, this is
puzzling? Any ideas? Anyone else
> seen this? Anyone
interested?
> Jon.
|
| 9 |
Date Posted: 19 Feb 2001 09:11:14
by Grainne
Hello Nick &
Jon,
I have a quick question Nick. Are there scallop farmers
in the area you are
talking about? If there are it may account
for the large numbers at certain
times due to a release of spatt
or a broken cage resulting in a release
event. I have never seen
Pecten maximus in large congregations in the wild,
just the
occasional individual so I'd be interested to know. Also
what
size range where the animals, adult of
juvenile?
Grainne.
At 19:40 16/02/01 +0000, you
wrote:
>Nick from Jersey 16-2-01
>Re; live specimens of
the Great Scallop Pecten
>Maximus, I have found the odd one
occassionally in the past. On the last
spring tide a work
colleague reported collecting a dozen or more on the
south east
coast of jersey, his mate had similiar amount two days
following.
I have also had reports in past of collections of dozen plus
in
St. Aubins bay. I would say finding them on the shore on a
spring tide is
not unusual in Jersey. regards
Nick
>
>Author wrote:
>> I have been
rockpooling and keeping records on my finds at Hannafore
>> Point, West Looe, Cornwall for some seven years now.
This is a rocky
>> reef approx. 2km x 1km at extreme low
water and is the richest shore
>> habitat that I have ever
come across in the UK.
>> I paid my first visits of the
year to the shore for the very low tides
>> this weekend,
and found, as well as the usual collection of fauna, some
>> unusual discoveries.
>> First were some ten
adult, live specimens of the Great Scallop Pecten
>>
Maximus, which, to my knowledge, is never found on shore. These were
>> quite viable, and have two in one of my tanks to prove
it. It is
>> probable that storms dredged these up
offshore and dumped them on the
>> reef, although I have
not seen this happen before.
>> Two specimens (small -
carapace 15mm long) of the swimming crab
>> Liocarcinus
arcuatus were found living under rocks on the middle shore.
>> This species, which is distinctive and easy to
recognise, is supposed to
>> be exclusively
sublittoral.
>> More interesting, and puzzling, were my
finds of the large top shell
>> Gibbula magus. Worn shells
occasionally turn up on Cornish coasts, and I
>> was very
surprised to find in excess of twenty live specimens, with
>> brilliant coloration, living on the middle to lower
shore. More evidence
>> of their abundance was found in the
form of literally hundreds of small
>> hermit crabs living
in discarded and obviously fairly fresh shells of
>> the
species. The hermit crabs, empty shells and live animals gave the
>> impression that this was one of the more common
gastropod species on the
>> lower shore. Given that the
species is not generally regarded as common,
>> and is
strictly sublittoral, this is puzzling? Any ideas? Anyone else
>> seen this? Anyone interested?
>>
Jon.
>
>
>
>
>If you want to share
pictures, use the calendar, or start a questionnaire
>visit http://uk.groups.yahoo.com/group/Glaucus
>
>To
leave the group, email: glaucus-unsubscribe@smartgroups.com
>
>
Grainne
Mooney
Executive Officer
BESS Faculty Office
Arts
Building
Trinity College, Dublin 2, Ireland
Tel:
6082456/6081840
Fax: 671 5269
E-mail: gmooney@tcd.ie
|
| 10 |
Date Posted: 19 Feb 2001 10:59:40
by Andy
Horton
Hello,
It is
the scallop dredging season - scallop dredging may go on for the
whole
of the year?
Now, adult scallops have a limited
vision and maybe they just swam (is this
the right term?) out of
the way and ended up on the beach?
I like them in cream
sauce, and farmed ones (in bags?) taste the best (no
grit in
them).
Cheers
Andy Horton
(Sussex)
Author
wrote:
> Hello Nick & Jon,
> I have a quick question
Nick. Are there scallop farmers in the area you are
> talking
about? If there are it may account for the large numbers at
certain
> times due to a release of spatt or a broken cage
resulting in a release
> event. I have never seen Pecten
maximus in large congregations in the wild,
> just the
occasional individual so I'd be interested to know. Also
what
> size range where the animals, adult of
juvenile?
> Grainne.
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