HABITAT SELECTION BY AQUATIC INVERTEBRATES
319
chemical gradient. It also means that even if the settling factor
becomes adsorbed to the cyprid's antennules from solution and the
cyprid then alights on an untreated surface, no settlement follows ; the
chemical must be adsorbed to the surface on which the cyprid alights.
The extrapolation of these results to field conditions is not as yet
possible, except to say that cyprids will only settle after having come
into contact with a chemically suitable surface. Although no other
critical experiments have been conducted, larvae of other sedentary
invertebrates probably react in the same way because a number of
authors think that larvae only respond to chemicals after contact with
treated surfaces (Kampf et al., 1959; Williams, 1964; Wilson, 1953a,
1968).
F. Habitat selection and micro-organisms
1. The microbial fauna of sediments
A large body of work proves that the larvae of benthic marine
invertebrates settle and metamorphose most readily in the presence of
sand or mud from their normal habitat (Mortensen, 1921 ; Wilson, 1932,
1948,1951; Day and Wilson, 1934; Nyholm, 1950; Smidt, 1951; Silh,
1954; Scheltema, 1956, 1961). I n a similar manner the adults of
mobile invertebrates prefer their usual sediments, although few
species have been studied (Meadows, 1964a; Gray, 1966~). We have
already seen how particle size might account for part of this specificity,
but sediments differ in two other important ways: their non-living
organic content, and also the numbers and species of micro-organisms
in or on them, will vary from place to place (Lloyd, 1931 ; McCoy and
Henrici, 1937 ; Zobell, 1938a ; Zobell and Rittenberg, 1938 ; Pearse et al.,
1942; Westeide, 1968; Anderson and Meadows, 1969). These considerations have led to experiments in which sandy sediments, treated
in ways that alter or remove living micro-organisms and non-living
organic material, are offered to larvae for settlement. I n general,
settling larvae find the treated sands far less suitable for metamorphosis
than natural untreated ones (Wilson, 1953a, 1955 ; Scheltema, 1961).
In a similar manner, adults of mobile benthic and interstitial invertebrates avoid treated sands (Wieser, 1956 ;Meadows, 1964a ; Gray, 1966d ;
Marzolf, 1966 ; Sameoto, 1969). The treatments used to render sands
unattractive have included drying, soaking in distilled water or acids,
heating to lOO"C, autoclaving, rtshing and treatment with fixatives and
detergents. None of these treatments, however, distinguishes between
killing micro-organisms, removing all or part of the non-living organia
material, and possible etching of the surfaces of sand grains.
Sands rendered unattractive can have their attractiveness restored
319
chemical gradient. It also means that even if the settling factor
becomes adsorbed to the cyprid's antennules from solution and the
cyprid then alights on an untreated surface, no settlement follows ; the
chemical must be adsorbed to the surface on which the cyprid alights.
The extrapolation of these results to field conditions is not as yet
possible, except to say that cyprids will only settle after having come
into contact with a chemically suitable surface. Although no other
critical experiments have been conducted, larvae of other sedentary
invertebrates probably react in the same way because a number of
authors think that larvae only respond to chemicals after contact with
treated surfaces (Kampf et al., 1959; Williams, 1964; Wilson, 1953a,
1968).
F. Habitat selection and micro-organisms
1. The microbial fauna of sediments
A large body of work proves that the larvae of benthic marine
invertebrates settle and metamorphose most readily in the presence of
sand or mud from their normal habitat (Mortensen, 1921 ; Wilson, 1932,
1948,1951; Day and Wilson, 1934; Nyholm, 1950; Smidt, 1951; Silh,
1954; Scheltema, 1956, 1961). I n a similar manner the adults of
mobile invertebrates prefer their usual sediments, although few
species have been studied (Meadows, 1964a; Gray, 1966~). We have
already seen how particle size might account for part of this specificity,
but sediments differ in two other important ways: their non-living
organic content, and also the numbers and species of micro-organisms
in or on them, will vary from place to place (Lloyd, 1931 ; McCoy and
Henrici, 1937 ; Zobell, 1938a ; Zobell and Rittenberg, 1938 ; Pearse et al.,
1942; Westeide, 1968; Anderson and Meadows, 1969). These considerations have led to experiments in which sandy sediments, treated
in ways that alter or remove living micro-organisms and non-living
organic material, are offered to larvae for settlement. I n general,
settling larvae find the treated sands far less suitable for metamorphosis
than natural untreated ones (Wilson, 1953a, 1955 ; Scheltema, 1961).
In a similar manner, adults of mobile benthic and interstitial invertebrates avoid treated sands (Wieser, 1956 ;Meadows, 1964a ; Gray, 1966d ;
Marzolf, 1966 ; Sameoto, 1969). The treatments used to render sands
unattractive have included drying, soaking in distilled water or acids,
heating to lOO"C, autoclaving, rtshing and treatment with fixatives and
detergents. None of these treatments, however, distinguishes between
killing micro-organisms, removing all or part of the non-living organia
material, and possible etching of the surfaces of sand grains.
Sands rendered unattractive can have their attractiveness restored