184
J . E. 0 . RAYMONT
Although a species such as Calunus appears to feed on a wide variety
of phytoplankton there may be some selection. Harvey (1937) found
that the copepod selected Lauderia in preference to Chaetoceros or
Nitzschia. Mullin (1963) tested 4 species of Calunus on 8 different food
species of phytoplankton. The larger-celled species were selected; from
a mixture of 5 food species, the smaller nanoplankton algae contributed
less than 6% to the diet. Petipa (1959) claims a considerable degree of
food selection for Acartia spp. from the Black Sea.
Less is known of the diet of other groups, but among the euphausids
Euphausia superba (Barkley, 1940) appears to be exclusively a herbivore, feeding on diatoms, probably selecting the smoother celled,
smaller species. On the other hand, species of Thysanoessa and Meganyctiphanes are believed by Einarsson (1945) to be essentially detritus
feeders or carnivores. Work in the Clyde sea area (Macdonald, 1927;
Mauchline, 1959) suggests that Meganyctiphanes is largely a filter feeder
in the smaller stages, while the larger older forms are mainly carnivorous on copepods and on other zooplankton; some detritus appears to
be taken.
Some mysids filter phytoplankton effectively, and in shallow water
may live on bottom material and detritus. Bathypelagic species are
usually regarded as mainly carnivorous though some detritus is
probably eaten. Ostracods were also thought to be filter feeders, but
Cannon (1931; 1940) has shown that whereas Cypridina is a filter feeder,
the large Gigantocypris mfilleri is apparently carnivorous. Loosanoff and
his colleagues have investigated the food of bivalve larvae, especially
those of Crassostrea and Venus mercenaria (Loosanoff and Davis, 1963).
Food for young larval molluscs must be of suitable size; usually algal
cells greater than lop in diameter cannot be ingested, but size is not the
only factor. Thus bacteria and certain flagellates will not promote good
growth in oyster larvae. Davis (1953) showed that 9 species of bacteria
and 1 species of flagellate failed to produce growth, although 5 other
flagellate species (Dicrateria, Hemiselmis, Isochrysis, Chromulina and
Pyramimonm) all gave good growth. The requirements even changed
with the age of oyster larvae. The larvae of Venus mercenaria appear to
be able to grow on Chlorellu and even on some bacterial cultures which
are unsuitable for oyster larvae. However, for many bivalve larvae a
mixture of Momchrysis and Isochrysis appears to be most suitable (cf.
also Walne, 1963).
The specific food requirements of cirripede larvae have also been
investigated. Early work suggested that diatoms and flagellates might
be utilized, but the work of Costlow and Bookhout (1967, 1958) indicated that algal (Chlanzydomonas) food needed to be supplemented with
a little animal (Arbacia eggs) material. Moyse (1963) has recently added
J . E. 0 . RAYMONT
Although a species such as Calunus appears to feed on a wide variety
of phytoplankton there may be some selection. Harvey (1937) found
that the copepod selected Lauderia in preference to Chaetoceros or
Nitzschia. Mullin (1963) tested 4 species of Calunus on 8 different food
species of phytoplankton. The larger-celled species were selected; from
a mixture of 5 food species, the smaller nanoplankton algae contributed
less than 6% to the diet. Petipa (1959) claims a considerable degree of
food selection for Acartia spp. from the Black Sea.
Less is known of the diet of other groups, but among the euphausids
Euphausia superba (Barkley, 1940) appears to be exclusively a herbivore, feeding on diatoms, probably selecting the smoother celled,
smaller species. On the other hand, species of Thysanoessa and Meganyctiphanes are believed by Einarsson (1945) to be essentially detritus
feeders or carnivores. Work in the Clyde sea area (Macdonald, 1927;
Mauchline, 1959) suggests that Meganyctiphanes is largely a filter feeder
in the smaller stages, while the larger older forms are mainly carnivorous on copepods and on other zooplankton; some detritus appears to
be taken.
Some mysids filter phytoplankton effectively, and in shallow water
may live on bottom material and detritus. Bathypelagic species are
usually regarded as mainly carnivorous though some detritus is
probably eaten. Ostracods were also thought to be filter feeders, but
Cannon (1931; 1940) has shown that whereas Cypridina is a filter feeder,
the large Gigantocypris mfilleri is apparently carnivorous. Loosanoff and
his colleagues have investigated the food of bivalve larvae, especially
those of Crassostrea and Venus mercenaria (Loosanoff and Davis, 1963).
Food for young larval molluscs must be of suitable size; usually algal
cells greater than lop in diameter cannot be ingested, but size is not the
only factor. Thus bacteria and certain flagellates will not promote good
growth in oyster larvae. Davis (1953) showed that 9 species of bacteria
and 1 species of flagellate failed to produce growth, although 5 other
flagellate species (Dicrateria, Hemiselmis, Isochrysis, Chromulina and
Pyramimonm) all gave good growth. The requirements even changed
with the age of oyster larvae. The larvae of Venus mercenaria appear to
be able to grow on Chlorellu and even on some bacterial cultures which
are unsuitable for oyster larvae. However, for many bivalve larvae a
mixture of Momchrysis and Isochrysis appears to be most suitable (cf.
also Walne, 1963).
The specific food requirements of cirripede larvae have also been
investigated. Early work suggested that diatoms and flagellates might
be utilized, but the work of Costlow and Bookhout (1967, 1958) indicated that algal (Chlanzydomonas) food needed to be supplemented with
a little animal (Arbacia eggs) material. Moyse (1963) has recently added