HABITAT SELECTION BY AQUATIU INVERTEBRATES
273
of reviews covering these subjects already (Allen, 1966; CloudsleyThompson, 1962; Knight-Jones and Morgan, 1966; Korringa, 1957);
neither have we referred t o the original literature on the responses of
marine larvae to their physical environment at settlement since the
subject is adequately covered by Williams (1964, 1952).
11. THE PHYSIOAL AND CHEMICAL ENVIRONMENT
A . Intertidal animals
Animals on intertidal shores are exposed to a wide range of environmental variables. On a hot summer’s day tide pool temperatures are
likely, even in temperate climates, to reach 3O-4OoC, while during cold
winter spells temperatures may fall below 0°C. Fresh water flowing
over a beach will expose animals in its path to salinity fluctuations of
0-33%, during a single tidal cycle, and the beach itself is exposed to air
twice a day as the tide rises and falls. Animals living on the shore must,
therefore, be able to respond to fluctuations in their environment,
particularly of temperature, salinity and humidity, if they are to
maintain themselves in one position.
Little is known of local fluctuations in temperature on the shore or
of the temperature preferences of animals that live there. Temperatures
in tide pools (Pyefinch, 1943; Ganning, 1967) and sediments (Johnson,
1965) change from hour to hour, and presumably animals must react
to them. Two tide pool copepods studied by Ganning and Wulff (1966)
and Ganning (1967) showed temperature preferences which accorded
with their distribution.
Salinity can fluctuate widely on beaches, and there is some evidence
that intertidal Crustacea are capable of selecting specific salinities in
which to live. Ligia baudiniana Milne-Edwards survives longer in air
over damp sand, than in sea water, and longer in sea water than in
distilled water (Barnes, 1932). However, if offered a choice, it prefers
filter paper moistened with 1O-25% sea water, rather than 100%
sea water or distilled water (Barnes, 1938). Its behaviour and survival
will, therefore, tend to limit it to the upper shore in areas where damp
sand flanks freshwater rivulets. Other crustaceans also show salinity
preferences (Gross, 1955, 1957; Teal, 1958; Lagerspetz and Mattila,l961;
Ganning, 1967; McLusky, 1970), but nothing is known of intertidal
organisms from other phyla.
As the tide recedes across intertidal beaches, the humidity in and
around heaps of stones and at the surface of and within sandy sediments
will fall from 100% R.H. to lower values, only to move back again as
the tide rises. Isopod and amphipod Crustacea (Lagerspetz, 1963 ;
273
of reviews covering these subjects already (Allen, 1966; CloudsleyThompson, 1962; Knight-Jones and Morgan, 1966; Korringa, 1957);
neither have we referred t o the original literature on the responses of
marine larvae to their physical environment at settlement since the
subject is adequately covered by Williams (1964, 1952).
11. THE PHYSIOAL AND CHEMICAL ENVIRONMENT
A . Intertidal animals
Animals on intertidal shores are exposed to a wide range of environmental variables. On a hot summer’s day tide pool temperatures are
likely, even in temperate climates, to reach 3O-4OoC, while during cold
winter spells temperatures may fall below 0°C. Fresh water flowing
over a beach will expose animals in its path to salinity fluctuations of
0-33%, during a single tidal cycle, and the beach itself is exposed to air
twice a day as the tide rises and falls. Animals living on the shore must,
therefore, be able to respond to fluctuations in their environment,
particularly of temperature, salinity and humidity, if they are to
maintain themselves in one position.
Little is known of local fluctuations in temperature on the shore or
of the temperature preferences of animals that live there. Temperatures
in tide pools (Pyefinch, 1943; Ganning, 1967) and sediments (Johnson,
1965) change from hour to hour, and presumably animals must react
to them. Two tide pool copepods studied by Ganning and Wulff (1966)
and Ganning (1967) showed temperature preferences which accorded
with their distribution.
Salinity can fluctuate widely on beaches, and there is some evidence
that intertidal Crustacea are capable of selecting specific salinities in
which to live. Ligia baudiniana Milne-Edwards survives longer in air
over damp sand, than in sea water, and longer in sea water than in
distilled water (Barnes, 1932). However, if offered a choice, it prefers
filter paper moistened with 1O-25% sea water, rather than 100%
sea water or distilled water (Barnes, 1938). Its behaviour and survival
will, therefore, tend to limit it to the upper shore in areas where damp
sand flanks freshwater rivulets. Other crustaceans also show salinity
preferences (Gross, 1955, 1957; Teal, 1958; Lagerspetz and Mattila,l961;
Ganning, 1967; McLusky, 1970), but nothing is known of intertidal
organisms from other phyla.
As the tide recedes across intertidal beaches, the humidity in and
around heaps of stones and at the surface of and within sandy sediments
will fall from 100% R.H. to lower values, only to move back again as
the tide rises. Isopod and amphipod Crustacea (Lagerspetz, 1963 ;