276
P. s. MEADOWS AND J. r. CAMPBELL
animal’s biology. The cumacean Cumella vulgaris Hart prefers two size
ranges : (a) under 150 pm (unsieved) in which it feeds as a deposit feeder
on fine organic debris; and (b) 150-300 pm in which it feeds as an
epistrate feeder scraping material from the surface of individual sand
grains. There are no published investigations of animals from other
phyla, although unpublished experiments by Meadows, Tevendale and
Thompson show that the polychaete Nereis prefers finer sands as it
moves through sediments.
Lagoon sands, and this presumably applies to intertidal sands as
well, vary in volume of capillary water they take up (Webb, 1958b).
The h e r the sand, the more water it holds until at below 200 pm quicksands form; furthermore, mixtures of different particle sizes have a
lower porosity than either size separately. In a later paper Webb
(1969) directed his attention to the different ways in which sand grains
can pack together. During compression from loose packing t o close
packing, the geometry of the lattice that the particles form moves
through three phases, changing abruptly from one to the next. Webb
(1969) has begun to analyse how animals that live in sand respond to
these characteristics and the results are promising. More recently,
Morgan (1970), although he does not refer to Webb’s papers, has
attempted to analyse how similar parameters affect the particle size
preferences of the amphipod Pectenogammarw planicrurus Reid. He
argues convincingly that the particular grade of sand preferred by
Pectenogammarus is determined by the size of the ‘‘ throats ” connecting
the voids between sand particles; in smaller grain sizes the throats
are also smaller and the animals cannot enter or move through these.
In fact it would appear that the maximum diameters of the animals
compare closely with the calculated diameters of the throats of the
samples they select.
There are a number of other intertidal variables that are less
obvious but nevertheless may prove significant to animals as they
select habitats on beaches.
The depth of sand over rock, mud, or gravel varies on different
parts of a shore, and Chapman and Newell (1949) concluded from an
ecological survey that this was the main factor governing the
distribution of Arenicola marina (L.) on a muddy shore at Whitstable.
That this might be so had, however, been shown experimentally long
before by Reid (1929). I n the laboratory Arenicota would not burrow
into sand containing 2% ferric oxide; if the sand containing ferric
oxide was covered by ordinary sand, animals burrowed down to the
ferric oxide layer and then burrowed horizontally. Similar results were
obtained by using CaCO,, MgCO,, Kaolin, clay or kieselguhr. Reid‘s
general conclusion was that sub-surface layers of sand whiah were
P. s. MEADOWS AND J. r. CAMPBELL
animal’s biology. The cumacean Cumella vulgaris Hart prefers two size
ranges : (a) under 150 pm (unsieved) in which it feeds as a deposit feeder
on fine organic debris; and (b) 150-300 pm in which it feeds as an
epistrate feeder scraping material from the surface of individual sand
grains. There are no published investigations of animals from other
phyla, although unpublished experiments by Meadows, Tevendale and
Thompson show that the polychaete Nereis prefers finer sands as it
moves through sediments.
Lagoon sands, and this presumably applies to intertidal sands as
well, vary in volume of capillary water they take up (Webb, 1958b).
The h e r the sand, the more water it holds until at below 200 pm quicksands form; furthermore, mixtures of different particle sizes have a
lower porosity than either size separately. In a later paper Webb
(1969) directed his attention to the different ways in which sand grains
can pack together. During compression from loose packing t o close
packing, the geometry of the lattice that the particles form moves
through three phases, changing abruptly from one to the next. Webb
(1969) has begun to analyse how animals that live in sand respond to
these characteristics and the results are promising. More recently,
Morgan (1970), although he does not refer to Webb’s papers, has
attempted to analyse how similar parameters affect the particle size
preferences of the amphipod Pectenogammarw planicrurus Reid. He
argues convincingly that the particular grade of sand preferred by
Pectenogammarus is determined by the size of the ‘‘ throats ” connecting
the voids between sand particles; in smaller grain sizes the throats
are also smaller and the animals cannot enter or move through these.
In fact it would appear that the maximum diameters of the animals
compare closely with the calculated diameters of the throats of the
samples they select.
There are a number of other intertidal variables that are less
obvious but nevertheless may prove significant to animals as they
select habitats on beaches.
The depth of sand over rock, mud, or gravel varies on different
parts of a shore, and Chapman and Newell (1949) concluded from an
ecological survey that this was the main factor governing the
distribution of Arenicola marina (L.) on a muddy shore at Whitstable.
That this might be so had, however, been shown experimentally long
before by Reid (1929). I n the laboratory Arenicota would not burrow
into sand containing 2% ferric oxide; if the sand containing ferric
oxide was covered by ordinary sand, animals burrowed down to the
ferric oxide layer and then burrowed horizontally. Similar results were
obtained by using CaCO,, MgCO,, Kaolin, clay or kieselguhr. Reid‘s
general conclusion was that sub-surface layers of sand whiah were