1. INTRODUCTION
3
formed the ' net '. The ' krill ' saw this wall of air bubbles, were
frightened into the centre, and then the manoeuvre of the first method
was repeated.
" When the whale lay on its side and shut its mouth the rifled belly
formed an enormous distended bag before it was contracted and the
water pressed out between the whalebone-plates.
" When one saw that enormous bag, which was many times larger
than the real mouth from the gullet to the nose we could understand
that the humpback, fin-back, sei-whale and blue-whale have the rifled
belly from the point of the chin to the middle of the body, solely in
order to be able to take in an enormous quantity of water containing
food. "
Although euphausiids are active swimmers they are members of
the plankton because they are not powerful enough to avoid the effects
of oceanic currents and upwellings that may drift them here and there
in a way that large organisms can avoid by directional swimming.
Euphausiids are associated in the plankton with many of the animals
listed by Scoresby, although now they are known by different names.
Thus, there are found in the net hauls along with the euphausiids
smaller crustaceans, the copepods ; these are usually much more
numerous than the euphausiids and are important food organisms of
many fish and of the euphausiids themselves. Chaetognaths also abound
at certain times of the year and they include small crustaceans in their
diets and themselves can be food for euphausiids. At certain seasons
dinoflagellates, a t others tintinnids, are plentiful and are grazed on by
the euphausiids. The diatoms are also grazed by some species of
euphausiids but herbivorous euphausiids are relatively rare ; they
usually obtain plant material through eating young and adult stages of
copepods and so in turn the whales gain access to the vitamins produced
by the plants.
It is hoped, in this book, to demonstrate how vital are the
euphausiids a t intermediate levels in the marine food chains by reference
to our own studies on the northern species and by drawing from the
large amount of published work on other species. Most of our own
research has been on North Atlantic species and consequently in seeking
examples for general discourse we have tended to quote our own work,
thus accentuating such species as Neganyctiphanes norvegica and
Thysanoessa raschii but every precaution has been taken to ensure that
the relevance, or otherwise, of these examples to euphausiids in general
is pointed out. Marr (1962) has written a large monograph on Euphausia
superba and no attempt is made here to supersede this work ; many of
his conclusions are quoted but it is absolutely necessary for anyone
3
formed the ' net '. The ' krill ' saw this wall of air bubbles, were
frightened into the centre, and then the manoeuvre of the first method
was repeated.
" When the whale lay on its side and shut its mouth the rifled belly
formed an enormous distended bag before it was contracted and the
water pressed out between the whalebone-plates.
" When one saw that enormous bag, which was many times larger
than the real mouth from the gullet to the nose we could understand
that the humpback, fin-back, sei-whale and blue-whale have the rifled
belly from the point of the chin to the middle of the body, solely in
order to be able to take in an enormous quantity of water containing
food. "
Although euphausiids are active swimmers they are members of
the plankton because they are not powerful enough to avoid the effects
of oceanic currents and upwellings that may drift them here and there
in a way that large organisms can avoid by directional swimming.
Euphausiids are associated in the plankton with many of the animals
listed by Scoresby, although now they are known by different names.
Thus, there are found in the net hauls along with the euphausiids
smaller crustaceans, the copepods ; these are usually much more
numerous than the euphausiids and are important food organisms of
many fish and of the euphausiids themselves. Chaetognaths also abound
at certain times of the year and they include small crustaceans in their
diets and themselves can be food for euphausiids. At certain seasons
dinoflagellates, a t others tintinnids, are plentiful and are grazed on by
the euphausiids. The diatoms are also grazed by some species of
euphausiids but herbivorous euphausiids are relatively rare ; they
usually obtain plant material through eating young and adult stages of
copepods and so in turn the whales gain access to the vitamins produced
by the plants.
It is hoped, in this book, to demonstrate how vital are the
euphausiids a t intermediate levels in the marine food chains by reference
to our own studies on the northern species and by drawing from the
large amount of published work on other species. Most of our own
research has been on North Atlantic species and consequently in seeking
examples for general discourse we have tended to quote our own work,
thus accentuating such species as Neganyctiphanes norvegica and
Thysanoessa raschii but every precaution has been taken to ensure that
the relevance, or otherwise, of these examples to euphausiids in general
is pointed out. Marr (1962) has written a large monograph on Euphausia
superba and no attempt is made here to supersede this work ; many of
his conclusions are quoted but it is absolutely necessary for anyone