ECOLOQICAL STUDIES AT LOUQH INE
285
we hope that in the end we shall be able to treat quantitatively at least
one community at Lough Ine. So far we are only in a position to make
qualitative suggestions about the food chains of the Paracentrotusdominated community of the shallow sublittoral, and to describe diurnal
migrations which probably play an important part in controlling encounters with predators. A full account of this work is published elsewhere (Ebling et al., 1966).
The ultimate source of food for the Paracentrotus community consists of algae growing upon the rocks and eaten by grazing animals, and
of plankton eaten by filter feeders. The most important grazers are
Paracentrotus and Gibbula cineraria, of which Paracentrotus undoubtedly determines the character of the community. It maintains the rock
bare of algae by its constant grazing, and from observations of Paracentrotus transferred to new sites we infer that it spreads as far as is
necessary for it to maintain itself on regenerating algal growth in the
occupied area, supplemented by virgin growth cropped around the margins. The chief filter feeders are Anornia and Chlamys varia; both are
plentiful in shallow areas of the North Basin, but the former is by far
the more important. Small specimens of the starfish Marthasterias and
Asterias reside within the Paracentrotus community in certain areas.
They are found especially on shores which slope steeply and are heaped
with boulders, including most of the areas newly dominated by Paracentrotus in 1964 (see below). The larger specimens of these starfish do
not, within our experience, come up into the Paracentrotus community.
The shore crab Carcinus inhabits the community in the North Basin,
and Portunus puber and (less frequently) Cancer pagurus visit it mainly
in the South Basin. Birds destroy some Paracentrotus and remove starfish in the shallowest part of the Paracentrotus-dominated areas.
From the local abundance of Anoinia in areas of the North Basin free
from starfish, it is likely that in the South Basin the numbers of Anomia
are, in fact, controlled by predators and not by the supply of planktonic
food. Similarly, from the density of Paracentrotus and Gibbula in shallow
parts of the North Basin, where abundant algae surround the Paracentrotus-dominated areas, we may infer that food supply does not limit
the population of grazers. Thus the numbers of these grazers are probably controlled by predators. The fragile young Paracentrotus develop
under boulders around the margins of the lough, where presumably they
find relative safety from predators. We believe that as they grow they
emerge and spread downwards as far as their food requirements make
necessary and predators permit. The larger they grow, the less vulnerable they become, but in venturing deeper they may expose themselves
to greater danger.
Areas dominated by Paracentrotus are almost bare of animal and plant
285
we hope that in the end we shall be able to treat quantitatively at least
one community at Lough Ine. So far we are only in a position to make
qualitative suggestions about the food chains of the Paracentrotusdominated community of the shallow sublittoral, and to describe diurnal
migrations which probably play an important part in controlling encounters with predators. A full account of this work is published elsewhere (Ebling et al., 1966).
The ultimate source of food for the Paracentrotus community consists of algae growing upon the rocks and eaten by grazing animals, and
of plankton eaten by filter feeders. The most important grazers are
Paracentrotus and Gibbula cineraria, of which Paracentrotus undoubtedly determines the character of the community. It maintains the rock
bare of algae by its constant grazing, and from observations of Paracentrotus transferred to new sites we infer that it spreads as far as is
necessary for it to maintain itself on regenerating algal growth in the
occupied area, supplemented by virgin growth cropped around the margins. The chief filter feeders are Anornia and Chlamys varia; both are
plentiful in shallow areas of the North Basin, but the former is by far
the more important. Small specimens of the starfish Marthasterias and
Asterias reside within the Paracentrotus community in certain areas.
They are found especially on shores which slope steeply and are heaped
with boulders, including most of the areas newly dominated by Paracentrotus in 1964 (see below). The larger specimens of these starfish do
not, within our experience, come up into the Paracentrotus community.
The shore crab Carcinus inhabits the community in the North Basin,
and Portunus puber and (less frequently) Cancer pagurus visit it mainly
in the South Basin. Birds destroy some Paracentrotus and remove starfish in the shallowest part of the Paracentrotus-dominated areas.
From the local abundance of Anoinia in areas of the North Basin free
from starfish, it is likely that in the South Basin the numbers of Anomia
are, in fact, controlled by predators and not by the supply of planktonic
food. Similarly, from the density of Paracentrotus and Gibbula in shallow
parts of the North Basin, where abundant algae surround the Paracentrotus-dominated areas, we may infer that food supply does not limit
the population of grazers. Thus the numbers of these grazers are probably controlled by predators. The fragile young Paracentrotus develop
under boulders around the margins of the lough, where presumably they
find relative safety from predators. We believe that as they grow they
emerge and spread downwards as far as their food requirements make
necessary and predators permit. The larger they grow, the less vulnerable they become, but in venturing deeper they may expose themselves
to greater danger.
Areas dominated by Paracentrotus are almost bare of animal and plant