ECOLOGICAL STUDIES AT LOIJGH INE
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prawns visited the sites, especially when the crabs were feeding, and
some were seen to seize fragments of mussel. There was a strongly
marked maximum of crustacean visitors during the hours of darkness.
Carcinus was much more plentiful at East Goleen than a t Glannafeen
Quay, whereas Portunus was much more plentiful at Glannafeen. Indeed, only a single specimen of Portunus was seen at East Goleen, and
subsequent investigation has failed to record Portunus puber in this
area. The results suggest that Portunus puber can eat Mytilus of all
sizes, but that Carcinus meanas only eats small ones. They favour the
hypothesis that large Mytilus can survive in the Goleen because
Portunus puber rarely occurs there, and small mussels lie within the
clusters and are thus protected from Carcinus. I n those parts of the
Lough where Portunus puber is common, however, Mytilus is scarce
o r absent.
4. Crabs and Mussels in Cages
(a) Carcinus maenas with Mytilus edulis. A series of galvanized wire
cages (coated with polyurethane, mesh 5 mm) was set up in the shallow
sublittoral. Each experimental cage contained one Carcinus and six
Mytilus and each control cage contained six Mytilus only; various sizes
of Carcinus were combined with various sizes of Mytilus. The large
Mytilus (length over 45 mm) were immune to all of the Carcinus tested
(up to 57 mm in width of carapace) for the period of the experiment,
which was one week, but two out of thirty-six medium-sized mussels and
nineteen small ones were opened or broken, including some placed with
small crabs.
(b) Portunus puber with Myti1u.s edulis. A Portunus puber having a
carapace 82 mm wide was successively given a series of Mytilus of
different sizes. Mussels of length 39, 50 and 60 mm were broken within
24 h of presentation; one 70 mm long survived after three days. Another
Portunus puber, having a carapace width of 84 mm, failed to damage
mussels 59 mm long, but subsequently broke up and cleaned out specimens of 40, 41, 45 and 50 mm in length.
(c) Cancer pagurus with Mytilus edulis. Two edible crabs, themselves
not by any means fully grown (width of carapace 88 and 120 mm), were
able to destroy mussels of the largest size.
c. T H A I S ( N U C E L L A ) L A P I L L U S
1. Distribution and Shell Form
Thais (Nucella) lapillus occurs between tide marks on the exposed
rocky coast such as a t Carrigathorna and on the south side of Bullock
Island. Here it preys upon mussels and presumably on barnacles as
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prawns visited the sites, especially when the crabs were feeding, and
some were seen to seize fragments of mussel. There was a strongly
marked maximum of crustacean visitors during the hours of darkness.
Carcinus was much more plentiful at East Goleen than a t Glannafeen
Quay, whereas Portunus was much more plentiful at Glannafeen. Indeed, only a single specimen of Portunus was seen at East Goleen, and
subsequent investigation has failed to record Portunus puber in this
area. The results suggest that Portunus puber can eat Mytilus of all
sizes, but that Carcinus meanas only eats small ones. They favour the
hypothesis that large Mytilus can survive in the Goleen because
Portunus puber rarely occurs there, and small mussels lie within the
clusters and are thus protected from Carcinus. I n those parts of the
Lough where Portunus puber is common, however, Mytilus is scarce
o r absent.
4. Crabs and Mussels in Cages
(a) Carcinus maenas with Mytilus edulis. A series of galvanized wire
cages (coated with polyurethane, mesh 5 mm) was set up in the shallow
sublittoral. Each experimental cage contained one Carcinus and six
Mytilus and each control cage contained six Mytilus only; various sizes
of Carcinus were combined with various sizes of Mytilus. The large
Mytilus (length over 45 mm) were immune to all of the Carcinus tested
(up to 57 mm in width of carapace) for the period of the experiment,
which was one week, but two out of thirty-six medium-sized mussels and
nineteen small ones were opened or broken, including some placed with
small crabs.
(b) Portunus puber with Myti1u.s edulis. A Portunus puber having a
carapace 82 mm wide was successively given a series of Mytilus of
different sizes. Mussels of length 39, 50 and 60 mm were broken within
24 h of presentation; one 70 mm long survived after three days. Another
Portunus puber, having a carapace width of 84 mm, failed to damage
mussels 59 mm long, but subsequently broke up and cleaned out specimens of 40, 41, 45 and 50 mm in length.
(c) Cancer pagurus with Mytilus edulis. Two edible crabs, themselves
not by any means fully grown (width of carapace 88 and 120 mm), were
able to destroy mussels of the largest size.
c. T H A I S ( N U C E L L A ) L A P I L L U S
1. Distribution and Shell Form
Thais (Nucella) lapillus occurs between tide marks on the exposed
rocky coast such as a t Carrigathorna and on the south side of Bullock
Island. Here it preys upon mussels and presumably on barnacles as