PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
129
A. Living diets
Numerous laboratory studies have shown that many unicellular algae
are used as foods by zooplanktonic animals (see reviews by Marshall and
Orr, 1962; Corner and Cowey, 1964, 1968). In addition, an inverse
relationship has been found between the relative quantities of zooplankton and phytoplankton in a number of sea areas, ranging from
Antarctic waters (Hardy and Gunther, 1935) t o sub-tropical regions
such as the coast of Bermuda (Beers and Herman, 1969; Herman and
Beers, 1969 ; Station " A ", March 196PMarch 1965) : other areas,
with which we shall be dealing in some detail, are the English Channel
(Harvey et al., 1935), Long Island Sound (Riley and Bumpus, 1946)
and Narragansett Bay (Martin, 1965).
The nutritive value of algal diets has been established by studies in
which animals such as Tigriopus californicus (Baker) (Provasoli et al.,
1959), Euterpina mutifrom (Dana) (Neunes and Pongolini, 1965) and
Acartia tonsa Dana (Zillioux and Wilson, 1966) have been reared
through several generations on plant diets. No single species of alga
can support an indefinite number of generations, however, because
apparently none can supply optimal amounts of all the essential
micronutrients.
It has long been known that certain phyla of the zooplankton,
notably the chaetognaths, cnidarians and ctenophores are carnivores ;
and this kind of feeding is now also recognized as characteristic of
certain copepods. Thus, Anraku and Omori (1963) found that Centropages humatus (Lilljeborg) would eat nauplii of Artemia salina (L.) as
well as the diatom Thulmsiosira jluviatilis Hustedt, and that Tortanus
diemudatus (Thompson and Scott) ate only animal food, including other
copepods such as Temora longicornis (Miiller) and PseucEocalanus minutus
(Krsyer). A further example is Euphausia pmifica Hansen, which reduces its feeding on diatoms when Artemia nauplii are present, preferring
the latter as a food (Lasker, 1966). Similarly, Mullin (1966), investigating 19 species of copepod from the Indian Ocean, found that all consumed animal food at least as readily as they fed on phytoplankton,
and several preferred animal food only.
The nutritive value of animal diets has been demonstrated by Lasker
and Theilacker (1965) who reared three species of euphausiid on a diet
of Artemia nauplii alone ; and that of a mixed animal and plant diet
established by Mullin and Brooks (1967) who reared Rhincalanwr
wutus Giesbrecht using Artemia as a dietary supplement for the later
copepodite stages.
129
A. Living diets
Numerous laboratory studies have shown that many unicellular algae
are used as foods by zooplanktonic animals (see reviews by Marshall and
Orr, 1962; Corner and Cowey, 1964, 1968). In addition, an inverse
relationship has been found between the relative quantities of zooplankton and phytoplankton in a number of sea areas, ranging from
Antarctic waters (Hardy and Gunther, 1935) t o sub-tropical regions
such as the coast of Bermuda (Beers and Herman, 1969; Herman and
Beers, 1969 ; Station " A ", March 196PMarch 1965) : other areas,
with which we shall be dealing in some detail, are the English Channel
(Harvey et al., 1935), Long Island Sound (Riley and Bumpus, 1946)
and Narragansett Bay (Martin, 1965).
The nutritive value of algal diets has been established by studies in
which animals such as Tigriopus californicus (Baker) (Provasoli et al.,
1959), Euterpina mutifrom (Dana) (Neunes and Pongolini, 1965) and
Acartia tonsa Dana (Zillioux and Wilson, 1966) have been reared
through several generations on plant diets. No single species of alga
can support an indefinite number of generations, however, because
apparently none can supply optimal amounts of all the essential
micronutrients.
It has long been known that certain phyla of the zooplankton,
notably the chaetognaths, cnidarians and ctenophores are carnivores ;
and this kind of feeding is now also recognized as characteristic of
certain copepods. Thus, Anraku and Omori (1963) found that Centropages humatus (Lilljeborg) would eat nauplii of Artemia salina (L.) as
well as the diatom Thulmsiosira jluviatilis Hustedt, and that Tortanus
diemudatus (Thompson and Scott) ate only animal food, including other
copepods such as Temora longicornis (Miiller) and PseucEocalanus minutus
(Krsyer). A further example is Euphausia pmifica Hansen, which reduces its feeding on diatoms when Artemia nauplii are present, preferring
the latter as a food (Lasker, 1966). Similarly, Mullin (1966), investigating 19 species of copepod from the Indian Ocean, found that all consumed animal food at least as readily as they fed on phytoplankton,
and several preferred animal food only.
The nutritive value of animal diets has been demonstrated by Lasker
and Theilacker (1965) who reared three species of euphausiid on a diet
of Artemia nauplii alone ; and that of a mixed animal and plant diet
established by Mullin and Brooks (1967) who reared Rhincalanwr
wutus Giesbrecht using Artemia as a dietary supplement for the later
copepodite stages.