HABITAT SELECTION BY AQUATIU INVERTEBRATES
289
and so we can argue, in the same way as when considering anaerobic
conditions, that it might be advantageous for planktonic animals which
shun the very bright surface layers to become photopositive if they
pass across the thermocline. There is no clear evidence of this however ;
in fact the hemipteran Ranatra fusca P.B., although hardly
planktonic, shows exactly the opposite response (Holmes, 1905),
but so do Volvox and Pandorina colonies and they are planktonic
(Mast, 1919). The only investigations on preferred temperatures we
know of are by McGinnis (191 1) on Branchipus (= Eubranchipus)
serratus Forbes, by Ackefors and Rosen (1970) on Podon polyphemoides Leuckart (Cladocera) by Costa ( 1966b) on Caridina pristis
Roux and C. simoni Bouvier (Atyidae, Decapoda), and by Gebczyhski
(1965) who demonstrated species differences in the preferences of the
snails Planorbis corneus rubra L. (17-19 "C) and Limnea stagnalis L.
(12-13 "C) which agreed with their usual habitats.
Many planktonic Crustacea (Yerkes, 1899, 1900; Towle, 1900; Loeb,
1906a, b; Dice, 1914) and some other planktonic animals (Mast,
1919 ; Pause, 1919) are photopositive. Hutchinson (1967, chapter 25)
reviews these responses in detail. Siebeck (1968), in a comprehensive
paper, presents evidence that planktonic Crustacea avoid the shore by
a horizontal migration because the shore looks dark. Migration is
particularly noticeable when the horizon is hilly or has a high elevation.
His elegant apparatus could easily be adapted for marine use. The light
responses of planktonic animals in fresh water are therefore likely to
play a large part in maintaining them at the water surface and away
from the shore line. In the sea, many planktonic larvae are photopositive during their early life and then photonegative as settlement
and metamorphosis approaches, and in this way species are dispersed.
The only example of a similar behaviour in fresh water is of
Chironomus gregarius (= C . thummi Kieffer) larvae (Pause, 1919). It
would be worth while examining the planktonic larvae of the bivalve
mollusc Dreissena polymorpha (Pallas).
As one might expect, animals that live on the bottom of lakes and
rivers are usually photonegative. The following groups have been
studied : planarians (Loeb, 1894; Hesse, 1897 ; Parker and Burnett,
1900; Ullyott, 1936a, b), gastropods (Walter, 1906), bivalves (Allen,
1923), leeches (Gee, 1913), amphipods (Holmes, 1901; Loeb, 1904;
Wolsky and Huxley, 1932), isopods (Banta, 1910; Janzer and Ludwig,
1952), mayfly and dragonfly nymphs (Wodsedalek, 1911; Curtis Riley,
1912; Allee and Stein, 1918; Hughes, 1966), chironomid larvea (McLachIan, 1969), caddis fly larvae (Lehmann, 1972). On the other hand,
species that are found on lighter parts of the bottom, on a sunlit gravel
289
and so we can argue, in the same way as when considering anaerobic
conditions, that it might be advantageous for planktonic animals which
shun the very bright surface layers to become photopositive if they
pass across the thermocline. There is no clear evidence of this however ;
in fact the hemipteran Ranatra fusca P.B., although hardly
planktonic, shows exactly the opposite response (Holmes, 1905),
but so do Volvox and Pandorina colonies and they are planktonic
(Mast, 1919). The only investigations on preferred temperatures we
know of are by McGinnis (191 1) on Branchipus (= Eubranchipus)
serratus Forbes, by Ackefors and Rosen (1970) on Podon polyphemoides Leuckart (Cladocera) by Costa ( 1966b) on Caridina pristis
Roux and C. simoni Bouvier (Atyidae, Decapoda), and by Gebczyhski
(1965) who demonstrated species differences in the preferences of the
snails Planorbis corneus rubra L. (17-19 "C) and Limnea stagnalis L.
(12-13 "C) which agreed with their usual habitats.
Many planktonic Crustacea (Yerkes, 1899, 1900; Towle, 1900; Loeb,
1906a, b; Dice, 1914) and some other planktonic animals (Mast,
1919 ; Pause, 1919) are photopositive. Hutchinson (1967, chapter 25)
reviews these responses in detail. Siebeck (1968), in a comprehensive
paper, presents evidence that planktonic Crustacea avoid the shore by
a horizontal migration because the shore looks dark. Migration is
particularly noticeable when the horizon is hilly or has a high elevation.
His elegant apparatus could easily be adapted for marine use. The light
responses of planktonic animals in fresh water are therefore likely to
play a large part in maintaining them at the water surface and away
from the shore line. In the sea, many planktonic larvae are photopositive during their early life and then photonegative as settlement
and metamorphosis approaches, and in this way species are dispersed.
The only example of a similar behaviour in fresh water is of
Chironomus gregarius (= C . thummi Kieffer) larvae (Pause, 1919). It
would be worth while examining the planktonic larvae of the bivalve
mollusc Dreissena polymorpha (Pallas).
As one might expect, animals that live on the bottom of lakes and
rivers are usually photonegative. The following groups have been
studied : planarians (Loeb, 1894; Hesse, 1897 ; Parker and Burnett,
1900; Ullyott, 1936a, b), gastropods (Walter, 1906), bivalves (Allen,
1923), leeches (Gee, 1913), amphipods (Holmes, 1901; Loeb, 1904;
Wolsky and Huxley, 1932), isopods (Banta, 1910; Janzer and Ludwig,
1952), mayfly and dragonfly nymphs (Wodsedalek, 1911; Curtis Riley,
1912; Allee and Stein, 1918; Hughes, 1966), chironomid larvea (McLachIan, 1969), caddis fly larvae (Lehmann, 1972). On the other hand,
species that are found on lighter parts of the bottom, on a sunlit gravel