HABITAT SELECTION BY AQUATIC INVERTEBRATES
357
have been investigated. Some intertidal invertebrates maintain
themselves in one position on the shore as the tide moves over
them, while others move up and down with the advancing or
receding water’s edge ; in most cases the patterns of behaviour
determining these distributions are not understood.
( b ) There is in general less experimental evidence for habitat
selection by sublittoral marine invertebrates. The light and
pressure responses of planktonic species are well known ;
however, the responses of benthic invertebrates to temperature,
salinity, currents, gravity, density discontinuities and to the
characteristics of sediments (packing, depth, surface charge,
particle size), have rarely been recorded.
(c) Many freshwater invertebrates choose their habitats by
responding to current speed, to light, to the nature ofthe bottom,
and to contact with solid objects. Less is known of their
temperature, humidity, or salinity preferences, or of their
reactions to anaerobic conditions and pH changes, or of the
preferences of burrowing animals for varying depths of
sediment.
Responses to ions and organic molecules in
solution and to the packing characteristics of sediments have not
been studied.
(d) Interstitial animals (invertebrates and Protozoa) live in the
spaces between grains in freshwater, intertidal, and marine
sandy sediments. Their behaviour suggests that temperature,
light, salinity, oxygen content, sand permeability, pore size and
particle size, play a significant part in their selection of
habitats.
3. The maintenance of parasitic and in particular of commensal
associations in the marine environment has received much attention,
but little is known of freshwater associations, or of the way any of these
associations are initiated. The responses of commensals to their nonbiological environment appear to be similar to free living animals,
and most associations depend on specific chemical stimuli detected at a
distance from or on contact with the host. The nature of the chemicals
is not known. A few commensals can live with more than one host
species ; their specificity to and success on the different hosts is not clearly
understood.
4. Aquatic invertebrates respond to information from a number of
sources in their biological environment.
(a) The behaviour of the larvae of marine benthic invertebrates at
settlement is very similar and is described. The responses of
A . M . B . - ~ ~
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357
have been investigated. Some intertidal invertebrates maintain
themselves in one position on the shore as the tide moves over
them, while others move up and down with the advancing or
receding water’s edge ; in most cases the patterns of behaviour
determining these distributions are not understood.
( b ) There is in general less experimental evidence for habitat
selection by sublittoral marine invertebrates. The light and
pressure responses of planktonic species are well known ;
however, the responses of benthic invertebrates to temperature,
salinity, currents, gravity, density discontinuities and to the
characteristics of sediments (packing, depth, surface charge,
particle size), have rarely been recorded.
(c) Many freshwater invertebrates choose their habitats by
responding to current speed, to light, to the nature ofthe bottom,
and to contact with solid objects. Less is known of their
temperature, humidity, or salinity preferences, or of their
reactions to anaerobic conditions and pH changes, or of the
preferences of burrowing animals for varying depths of
sediment.
Responses to ions and organic molecules in
solution and to the packing characteristics of sediments have not
been studied.
(d) Interstitial animals (invertebrates and Protozoa) live in the
spaces between grains in freshwater, intertidal, and marine
sandy sediments. Their behaviour suggests that temperature,
light, salinity, oxygen content, sand permeability, pore size and
particle size, play a significant part in their selection of
habitats.
3. The maintenance of parasitic and in particular of commensal
associations in the marine environment has received much attention,
but little is known of freshwater associations, or of the way any of these
associations are initiated. The responses of commensals to their nonbiological environment appear to be similar to free living animals,
and most associations depend on specific chemical stimuli detected at a
distance from or on contact with the host. The nature of the chemicals
is not known. A few commensals can live with more than one host
species ; their specificity to and success on the different hosts is not clearly
understood.
4. Aquatic invertebrates respond to information from a number of
sources in their biological environment.
(a) The behaviour of the larvae of marine benthic invertebrates at
settlement is very similar and is described. The responses of
A . M . B . - ~ ~
13