ECOLOGICAL STUDIES AT LOUGH INE
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Paracentrotus, about 30% in the cage with three Paracentrotus, and no
growth of macroscopic algae in the cage with six Paracentrotus.
These observations establish that there is an inverse correlation between the occurrence of Paracentrotus and algae. The field experiments
involving clearance and transfer of Paracentrotus and the experiments
with cages suggest that this inverse relationship in distribution arises
because Paracentrotus destroys algae as fast as they grow. Examination
of the sedentary fauna of Curlew Bay shows that the grazing activity
of Paracentrotus also prevents the establishment of other parts of the
fauna especially associated with algae, namely the gastropods Rissoa
parva and Bittium reticulaturn, and the amphipod Caprella acanthifera.
F. DISTRIBUTION O F CRABS
We have already seen that the distribution of intertidal mussels in a
limited area of Lough Ine is negatively correlated with the distribution
of certain crabs, and our observations and experiments on Thais and
on Paracentrotus have suggested that crabs may play a similar part in
determining their distribution. A necessary link in our chain of evidence
is a knowledge of the distribution of crabs. We have investigated this
in four ways (Muntz et al., 1965). First, we have used beds of intact or
crushed mussels as ground bait at various selected stations and we have
observed the visitors with a view box; second, we have fished from a
rowing boat a t night, luring the crabs out of their crevices by dangling
a crushed mussel on a string; third, skin diving has been carried out by
day in a limited number of places; fourth, traps have been laid. The
traps were of conventional design, but made of mesh polythene, and
were baited with fresh fish, crushed mussels or tinned fish cat food.
They were always put down in the afternoon well before dusk and
taken up on the following morning long after dawn.
The results of trapping are shown in Fig. ' i d ; these distributions are
confirmed by the other methods which we used. C'arcinus maenas is
common intertidally all around the lough. It is abundant sublittorally
close inshore in the North Basin and in the Goleen. It is common intertidally among rocks at Harbour, but seems to be scarce sublittorally in
the south-east corner of the lough. Portunus puber is not found anywhere in large numbers, but occasional specimens are taken in shallow
water in many parts of the lough, and the crab was regularly found in
small numbers at all stations in the south-east corner of the South
Basin, where the Rapids join the lough. It is abundant in Barloge
Creek, which possibly acts as a source of replenishment for the lough.
Portunus puber is virtually absent from three much studied areas,
namely North Wall, the Goleen, and the inner part of Curlew Bay.
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281
Paracentrotus, about 30% in the cage with three Paracentrotus, and no
growth of macroscopic algae in the cage with six Paracentrotus.
These observations establish that there is an inverse correlation between the occurrence of Paracentrotus and algae. The field experiments
involving clearance and transfer of Paracentrotus and the experiments
with cages suggest that this inverse relationship in distribution arises
because Paracentrotus destroys algae as fast as they grow. Examination
of the sedentary fauna of Curlew Bay shows that the grazing activity
of Paracentrotus also prevents the establishment of other parts of the
fauna especially associated with algae, namely the gastropods Rissoa
parva and Bittium reticulaturn, and the amphipod Caprella acanthifera.
F. DISTRIBUTION O F CRABS
We have already seen that the distribution of intertidal mussels in a
limited area of Lough Ine is negatively correlated with the distribution
of certain crabs, and our observations and experiments on Thais and
on Paracentrotus have suggested that crabs may play a similar part in
determining their distribution. A necessary link in our chain of evidence
is a knowledge of the distribution of crabs. We have investigated this
in four ways (Muntz et al., 1965). First, we have used beds of intact or
crushed mussels as ground bait at various selected stations and we have
observed the visitors with a view box; second, we have fished from a
rowing boat a t night, luring the crabs out of their crevices by dangling
a crushed mussel on a string; third, skin diving has been carried out by
day in a limited number of places; fourth, traps have been laid. The
traps were of conventional design, but made of mesh polythene, and
were baited with fresh fish, crushed mussels or tinned fish cat food.
They were always put down in the afternoon well before dusk and
taken up on the following morning long after dawn.
The results of trapping are shown in Fig. ' i d ; these distributions are
confirmed by the other methods which we used. C'arcinus maenas is
common intertidally all around the lough. It is abundant sublittorally
close inshore in the North Basin and in the Goleen. It is common intertidally among rocks at Harbour, but seems to be scarce sublittorally in
the south-east corner of the lough. Portunus puber is not found anywhere in large numbers, but occasional specimens are taken in shallow
water in many parts of the lough, and the crab was regularly found in
small numbers at all stations in the south-east corner of the South
Basin, where the Rapids join the lough. It is abundant in Barloge
Creek, which possibly acts as a source of replenishment for the lough.
Portunus puber is virtually absent from three much studied areas,
namely North Wall, the Goleen, and the inner part of Curlew Bay.
E