272
J. A. KITCHINO AND F. J. EBLING
of the Carrigathorna type were found at each site, but only one of the
Barloge type was found broken. We concluded that a significant proportion of the losses of Thais from Carrigathorna was due to preferential predation, probably by Portunus puber (mainly) and Carcinus
maenas, since we were able t o trap these species of crab in the area.
6. Survival of Thais in L q h Ine
Thais only occurs sparsely within the lough, at a small number of
localities, and it does not seem to make use of the abundant supply of
Mytilus, either in the Goleen or in the North Basin. Our first experiments
showed that Thais from Carrigathorna rapidly disappeared after transfer to the Goleen and adjacent south shore; the last experiment has
shown that both types are susceptible to predators in the Goleen.
In the first experiment two hundred specimens from Carrigathorna
were distributed, on a dense belt of Mytilus in the lower littoral region,
along about 12 m of rocky and boulder-strewn shore on the east side of
the Goleen. During the following eight days, they disappeared entirely
from the Mytilus zone, and only one Mytilus was found to have been
attacked by a Thaia. Some Thais were attacked by predators, but the
survivors moved upwards out of the Mytilus zone, as far as the Pelvetia
zone and even higher.
As it seemed possible that the tendency of Thais to move up the
shore might be due to some unfavourable chemical condition in the
Goleen, a second experiment was carried out in which one hundred
Thais were transferred to East Goleen and one hundred to a steep site on
the south shore of the lough. Many pieces of broken Thais shell were
found at both stations and there was a heavy fall in numbers during the
PIG. 65. Survival of Thais (Nucella) lapillus (both types) and Ocenebra erinacea in cages
with Carcinus maenas. Each column shows the results of a single experiment in which
twenty Thais from the Rapids, twenty Thais irom Carrigathorna and in some cases ten
or twenty Ocenebra were put in a cage with a single Carcinus. The size of the crab
(carapace width) is shown at the head of the column; the 31, 65 and 76 mm crabs were
females, the remainder were males. The sizes of the molluscs (overall height) can be read
from the vertical scales.
The number of days each mollusc survived may be read from left to right against
horizontal scales for each experiment. Lethal damage during the experiment is indicated
by symbols, explained in the key. A few molluscs were lost (record ends without symbol);
some shells were empty from start of experiment (dotted lines); c, shell chipped; r, removed for unspecified reason.
A control experiment, in which twenty T h i 8 of each type were put in a cage without
a crab, was set up contemporaneously with the experiments using crabs sized 42,44,45,
52, 66, 66, 59 and 65 mm. One very small Thais of the Rapids type and two of the
Carrigathorna type were noted as missing in the course of the experiment; all other
molluscs survived. I n another control experiment set up at the same time as the experiment with crabs, sized 31, 66 and 75 mm, twenty Thais of each type and ten Ocenebra
survived alive and intact.
J. A. KITCHINO AND F. J. EBLING
of the Carrigathorna type were found at each site, but only one of the
Barloge type was found broken. We concluded that a significant proportion of the losses of Thais from Carrigathorna was due to preferential predation, probably by Portunus puber (mainly) and Carcinus
maenas, since we were able t o trap these species of crab in the area.
6. Survival of Thais in L q h Ine
Thais only occurs sparsely within the lough, at a small number of
localities, and it does not seem to make use of the abundant supply of
Mytilus, either in the Goleen or in the North Basin. Our first experiments
showed that Thais from Carrigathorna rapidly disappeared after transfer to the Goleen and adjacent south shore; the last experiment has
shown that both types are susceptible to predators in the Goleen.
In the first experiment two hundred specimens from Carrigathorna
were distributed, on a dense belt of Mytilus in the lower littoral region,
along about 12 m of rocky and boulder-strewn shore on the east side of
the Goleen. During the following eight days, they disappeared entirely
from the Mytilus zone, and only one Mytilus was found to have been
attacked by a Thaia. Some Thais were attacked by predators, but the
survivors moved upwards out of the Mytilus zone, as far as the Pelvetia
zone and even higher.
As it seemed possible that the tendency of Thais to move up the
shore might be due to some unfavourable chemical condition in the
Goleen, a second experiment was carried out in which one hundred
Thais were transferred to East Goleen and one hundred to a steep site on
the south shore of the lough. Many pieces of broken Thais shell were
found at both stations and there was a heavy fall in numbers during the
PIG. 65. Survival of Thais (Nucella) lapillus (both types) and Ocenebra erinacea in cages
with Carcinus maenas. Each column shows the results of a single experiment in which
twenty Thais from the Rapids, twenty Thais irom Carrigathorna and in some cases ten
or twenty Ocenebra were put in a cage with a single Carcinus. The size of the crab
(carapace width) is shown at the head of the column; the 31, 65 and 76 mm crabs were
females, the remainder were males. The sizes of the molluscs (overall height) can be read
from the vertical scales.
The number of days each mollusc survived may be read from left to right against
horizontal scales for each experiment. Lethal damage during the experiment is indicated
by symbols, explained in the key. A few molluscs were lost (record ends without symbol);
some shells were empty from start of experiment (dotted lines); c, shell chipped; r, removed for unspecified reason.
A control experiment, in which twenty T h i 8 of each type were put in a cage without
a crab, was set up contemporaneously with the experiments using crabs sized 42,44,45,
52, 66, 66, 59 and 65 mm. One very small Thais of the Rapids type and two of the
Carrigathorna type were noted as missing in the course of the experiment; all other
molluscs survived. I n another control experiment set up at the same time as the experiment with crabs, sized 31, 66 and 75 mm, twenty Thais of each type and ten Ocenebra
survived alive and intact.