6. FOOD AND FEEDING
199
species has both the second and third pairs of thoracic limbs greatly
elongated.
It must be borne in mind that when we say these animals are omnivorous we mean that they can feed on a wide range of food obtained by
two or more feeding methods. At certain times and places a species
may feed almost exclusively by one method (and we have suggested
that the present information on Euphausia superba may be a case in
point) but at other times and places the euphausiid may adopt another
method of feeding and so utilize a completely different source of food.
There is some evidence suggesting that some species definitely do have
a more restricted diet than others. Meganyctiphanes norvegica and
Thysanoessa raschii live together in the same deep troughs in the Clyde
sea area but there are differences in their diets. Meganyctiphanes
norvegica has an extremely varied diet whereas Thysanoessa raschii feeds
t o a much greater extent on bottom material. This may be a direct
effect of the two species living in the same environment but this is
thought unlikely because Ponomareva (1955) found that T . raschii in
the Sea of Japan had a much less varied diet than those of T . inermis,
T . longipes, and Euphausia paci$ca. There are one or two peculiar
features of the diet of Meganyctiphanes norvegica and Thysanoessa
raschii in Loch Fyne and other coastal populations of euphausiids will
no doubt be found, on examination, to have comparable dietary
peculiarities. Bracken and midges (Diptera) are characteristic of the
shores of this fjord-like loch and the heavy rainfall locally washes down
much detritus and debris off the land including sporangia of the former
and eggs of the latter. These are found in the stomachs of the euphausiids during the spring and summer months, coinciding with their
appearance ashore.
Discussion of the role of euphausiids in the food chains is reserved
until the last chapter where we shall examine these animals in relation
t o their physical and biological environments.
199
species has both the second and third pairs of thoracic limbs greatly
elongated.
It must be borne in mind that when we say these animals are omnivorous we mean that they can feed on a wide range of food obtained by
two or more feeding methods. At certain times and places a species
may feed almost exclusively by one method (and we have suggested
that the present information on Euphausia superba may be a case in
point) but at other times and places the euphausiid may adopt another
method of feeding and so utilize a completely different source of food.
There is some evidence suggesting that some species definitely do have
a more restricted diet than others. Meganyctiphanes norvegica and
Thysanoessa raschii live together in the same deep troughs in the Clyde
sea area but there are differences in their diets. Meganyctiphanes
norvegica has an extremely varied diet whereas Thysanoessa raschii feeds
t o a much greater extent on bottom material. This may be a direct
effect of the two species living in the same environment but this is
thought unlikely because Ponomareva (1955) found that T . raschii in
the Sea of Japan had a much less varied diet than those of T . inermis,
T . longipes, and Euphausia paci$ca. There are one or two peculiar
features of the diet of Meganyctiphanes norvegica and Thysanoessa
raschii in Loch Fyne and other coastal populations of euphausiids will
no doubt be found, on examination, to have comparable dietary
peculiarities. Bracken and midges (Diptera) are characteristic of the
shores of this fjord-like loch and the heavy rainfall locally washes down
much detritus and debris off the land including sporangia of the former
and eggs of the latter. These are found in the stomachs of the euphausiids during the spring and summer months, coinciding with their
appearance ashore.
Discussion of the role of euphausiids in the food chains is reserved
until the last chapter where we shall examine these animals in relation
t o their physical and biological environments.