280
P. S. MEADOWS AND J. I. CAMI'BELL
positive in water and photonegative and geopositive in air (Meadows
and Reid, 1966; Barnes et al., 1969). Small animals differ from large
ones when selecting substrates ; they burrow more readily and are less
likely to leave their burrows (Meadows and Reid, 1966; Meadows, 1967).
Corophium is also gregarious (Meadows, 1964b and unpublished observations) and is sensitive to pressure changes. Animals sometimes leave
their burrows when covered by the rising tide (Vader, 1964), although
they are most likely to do so after high tide, as the tide and pressure
begin to fall (Morgan, 1965). We see from this, that although it is usually
necessary to study one variable at a time in experiments, if we are to
understand how a species' behaviour determines its distribution, many
variables must be tested in turn. Having undertaken a series of experiments of this sort, one should then consider how the variables interact
with each other to alter behaviour; are swimming Corophium, for
instance, always photopositive at all salinities? We know very little of
these interactions, although they could be investigated by suitably
designed factorial experiments (c.f. LaRow, 1970 ; Gale, 1971).
The intertidal environment, therefore, is a fluctuating one, where
animals have to react to a number of variables that alter quickly.
What work there is suggests that intertidal species utilize information
from many of these variables. Perhaps the most important area for
future study is in a detailed approach to other intertidal species
similar to that adopted by Gamble, McLusky, Meadows and Morgan.
More information about the way intertidal animals respond to fluctuations of, say, pressure or humidity or immersion and emersion would
also be useful, because it would help in understanding the way in which
many species stay at one level on the shore as the environment
fluctuates around them.
B. Marine animals
The marine environment is very large in comparison to the intertidal zone, and is usually a great deal more uniform at least over
horizontal distances of a mile or so. However with increasing depth,
light intensity and pressure change rapidly (Nicol, 1967, p. 19, 22). We
shall therefore consider firstly light and pressure responses, and then
outline what little is known of the detection of salinity differences, of
gravity, and of sediment depth and particle size.
There are many detailed studies on the light responses of marine
invertebrates (c.f. Mast, 1911). In his comprehensive review of the
light responses of larvae of 141 species of benthic marine invertebrates,
Thorson (1964) states that 82% are photopositive, 12% indifferent
and 6% photonegative during early larval life. As the larvae approach
P. S. MEADOWS AND J. I. CAMI'BELL
positive in water and photonegative and geopositive in air (Meadows
and Reid, 1966; Barnes et al., 1969). Small animals differ from large
ones when selecting substrates ; they burrow more readily and are less
likely to leave their burrows (Meadows and Reid, 1966; Meadows, 1967).
Corophium is also gregarious (Meadows, 1964b and unpublished observations) and is sensitive to pressure changes. Animals sometimes leave
their burrows when covered by the rising tide (Vader, 1964), although
they are most likely to do so after high tide, as the tide and pressure
begin to fall (Morgan, 1965). We see from this, that although it is usually
necessary to study one variable at a time in experiments, if we are to
understand how a species' behaviour determines its distribution, many
variables must be tested in turn. Having undertaken a series of experiments of this sort, one should then consider how the variables interact
with each other to alter behaviour; are swimming Corophium, for
instance, always photopositive at all salinities? We know very little of
these interactions, although they could be investigated by suitably
designed factorial experiments (c.f. LaRow, 1970 ; Gale, 1971).
The intertidal environment, therefore, is a fluctuating one, where
animals have to react to a number of variables that alter quickly.
What work there is suggests that intertidal species utilize information
from many of these variables. Perhaps the most important area for
future study is in a detailed approach to other intertidal species
similar to that adopted by Gamble, McLusky, Meadows and Morgan.
More information about the way intertidal animals respond to fluctuations of, say, pressure or humidity or immersion and emersion would
also be useful, because it would help in understanding the way in which
many species stay at one level on the shore as the environment
fluctuates around them.
B. Marine animals
The marine environment is very large in comparison to the intertidal zone, and is usually a great deal more uniform at least over
horizontal distances of a mile or so. However with increasing depth,
light intensity and pressure change rapidly (Nicol, 1967, p. 19, 22). We
shall therefore consider firstly light and pressure responses, and then
outline what little is known of the detection of salinity differences, of
gravity, and of sediment depth and particle size.
There are many detailed studies on the light responses of marine
invertebrates (c.f. Mast, 1911). In his comprehensive review of the
light responses of larvae of 141 species of benthic marine invertebrates,
Thorson (1964) states that 82% are photopositive, 12% indifferent
and 6% photonegative during early larval life. As the larvae approach