278
P. 5. MEADOWS AND J. I. CAMPBELL
will fluctuate between atmospheric as the advancing tide covers it, up
to about 0.4 atm above atmospheric in a 4 m high tide. Animals that
swim when covered by the tide must therefore swim downwards as the
tide advances and upwards as the tide recedes if they are to maintain
their position, and these changes in swimming behaviour as the tide
rises and falls appear to be, in part at least, dependent on pressure
responses. Corophium volutator has a tidal rhythm of swimming activity
which persists in the laboratory for three days, and the rhythm can be
experimentally entrained by cyclical pressure changes of tidal
amplitude and frequency. Animals swim most actively at the beginning
of the ebb tide, and this agrees with their increased swimming activity
following pressure decrease in the laboratory (Morgan, 1965). The
pycnogonid Nymphon gracile Leach, which lives under stones near
low water, responds in a similar way by swimming more actively if the
pressure is reduced, and, if exposed to cyclical pressure changes of
approximately tidal range, swims most actively during late ebb and low
water (Morgan et al., 1964). These authors’ approach could well be
extended to other species; we wonder, for instance, how animals that
live at the top of the intertidal zone might respond when compared to
Corophiurn which lives over a wide range of shore levels and to
Nymphon which lives at low water. Other investigations on intertidal
animals include those of Enright (1962) on various intertidal Crustacea,
of Rice (1964), on Nymphon and Capella, and of Fincham (1972) on
Marinogammarw, although these authors did not expose their animals
to artificial pressure cycles and their approach is rather more physiological. The general phenomenon of the rhythmic activity shown by a
number of intertidal Crustacsa, aswell as by fish, which willundoubtedly
affect the localized distribution of these species, has been discussed by
Rodriguez and Naylor (1972), and their paper should be referred t o for
further details.
As the tide falls and rises over mud flats and sand banks, horizontal
water currents are generated, the speed of which depends on the local
topography and slope of the beach, and on the tidal range. I n order to
remain in the same position in these circumstances, animals which
make excursions into the overlying water, besides detecting changes in
pressure (see above), should be capable of detecting current flow.
Marinogammarus marinus (Leach) (Fincham, 1972) and Corophium volutator (Meadows, unpublished observations) show responses of this sort
being rheopositive, while Chiton tuberculatus L. an the other hand is
rheonegative (Arey and Crozier, 1919).
Anaerobic conditions often exist under large stones or rocks on a
gravel shore and also a little way below the surface of muddy sediments.
P. 5. MEADOWS AND J. I. CAMPBELL
will fluctuate between atmospheric as the advancing tide covers it, up
to about 0.4 atm above atmospheric in a 4 m high tide. Animals that
swim when covered by the tide must therefore swim downwards as the
tide advances and upwards as the tide recedes if they are to maintain
their position, and these changes in swimming behaviour as the tide
rises and falls appear to be, in part at least, dependent on pressure
responses. Corophium volutator has a tidal rhythm of swimming activity
which persists in the laboratory for three days, and the rhythm can be
experimentally entrained by cyclical pressure changes of tidal
amplitude and frequency. Animals swim most actively at the beginning
of the ebb tide, and this agrees with their increased swimming activity
following pressure decrease in the laboratory (Morgan, 1965). The
pycnogonid Nymphon gracile Leach, which lives under stones near
low water, responds in a similar way by swimming more actively if the
pressure is reduced, and, if exposed to cyclical pressure changes of
approximately tidal range, swims most actively during late ebb and low
water (Morgan et al., 1964). These authors’ approach could well be
extended to other species; we wonder, for instance, how animals that
live at the top of the intertidal zone might respond when compared to
Corophiurn which lives over a wide range of shore levels and to
Nymphon which lives at low water. Other investigations on intertidal
animals include those of Enright (1962) on various intertidal Crustacea,
of Rice (1964), on Nymphon and Capella, and of Fincham (1972) on
Marinogammarw, although these authors did not expose their animals
to artificial pressure cycles and their approach is rather more physiological. The general phenomenon of the rhythmic activity shown by a
number of intertidal Crustacsa, aswell as by fish, which willundoubtedly
affect the localized distribution of these species, has been discussed by
Rodriguez and Naylor (1972), and their paper should be referred t o for
further details.
As the tide falls and rises over mud flats and sand banks, horizontal
water currents are generated, the speed of which depends on the local
topography and slope of the beach, and on the tidal range. I n order to
remain in the same position in these circumstances, animals which
make excursions into the overlying water, besides detecting changes in
pressure (see above), should be capable of detecting current flow.
Marinogammarus marinus (Leach) (Fincham, 1972) and Corophium volutator (Meadows, unpublished observations) show responses of this sort
being rheopositive, while Chiton tuberculatus L. an the other hand is
rheonegative (Arey and Crozier, 1919).
Anaerobic conditions often exist under large stones or rocks on a
gravel shore and also a little way below the surface of muddy sediments.