11. ECOLOGY OP DTSTRlBUl'fON
329
The euphausiid communities of the different sea areas will now be
discussed and any problems peculiar to each area mentioned.
North Atlantic species, north of about 40"N
Resident species
norvegica; Thysanoessa inermis, T . longicaudata, T . raschii.
Southerly guests throughout much of the area
Bentheuphausia amblyops; Euphausia krohnii; Nematoscelis
megalops; Nematobrachion boopis; Stylocheiron maximum, S. longicorne, X. elongatum.
Southerly guests in southern regions only
Thysanopoda aequalislT. subaequalis, T . cornuta; Euphausia
brevis; Thysanoessa gregaria; Nematoscelis microps; Stylocheiron
suhmii, 8. abbreviatum.
There are, therefore, only six species that live and breed in the North
Atlantic, Meganyctiphanes norvegica being the largest and the commonest
in many areas but frequently occurring along with the smaller Thysano&sa raschii in coastal waters and with T . inermis in more offshore
regions. Of the six species, T . inermis and T . raschii have their centres
of distribution farthest to the north while Nyctiphanes couchii has its
farthest to the south; the former two species breed north of Iceland
and off West Greenland. Einarsson (1945) has drawn a very clear
representation of the horizontal and vertical distribution of these
species in a section going southwards from Iceland (Fig. 121). This
figure is, of course, diagrammatic and the species are not so discretely
distributed as indicated but the main centres of population occur as
shown. Nyctiphanes couchii replaces Thysanoessa raschii in more
southern areas, these species both living in coastal regions but also
extending to slope regions. Thysanoessa inermis also occurs in the
coastal zone but tends to be found more frequently offshore than the
previous two species, while Meganyctiphanes norvegica occurs above
the continental slope although it is present with these other species in
coastal areas with depths greater than 100-200m. The two species,
Thysanopoda acutifrons and Thysanoessa longicaudata, live in oceanic
areas, the former at greater depths than the latter. Einarsson (1945)
has shown that the spawning areas of these species are much more
restricted than the total geographical area of occurrence. This is
illustrated by Meganyctiphanes norvegica which is distributed throughout the greater part of the North Atlantic yet has " centres of
spawning ". These centres are located in the Gulf of Maine, south and
Thysanopoda acutifrons; Nyctiphanes couchii; Meganyctiphanes
329
The euphausiid communities of the different sea areas will now be
discussed and any problems peculiar to each area mentioned.
North Atlantic species, north of about 40"N
Resident species
norvegica; Thysanoessa inermis, T . longicaudata, T . raschii.
Southerly guests throughout much of the area
Bentheuphausia amblyops; Euphausia krohnii; Nematoscelis
megalops; Nematobrachion boopis; Stylocheiron maximum, S. longicorne, X. elongatum.
Southerly guests in southern regions only
Thysanopoda aequalislT. subaequalis, T . cornuta; Euphausia
brevis; Thysanoessa gregaria; Nematoscelis microps; Stylocheiron
suhmii, 8. abbreviatum.
There are, therefore, only six species that live and breed in the North
Atlantic, Meganyctiphanes norvegica being the largest and the commonest
in many areas but frequently occurring along with the smaller Thysano&sa raschii in coastal waters and with T . inermis in more offshore
regions. Of the six species, T . inermis and T . raschii have their centres
of distribution farthest to the north while Nyctiphanes couchii has its
farthest to the south; the former two species breed north of Iceland
and off West Greenland. Einarsson (1945) has drawn a very clear
representation of the horizontal and vertical distribution of these
species in a section going southwards from Iceland (Fig. 121). This
figure is, of course, diagrammatic and the species are not so discretely
distributed as indicated but the main centres of population occur as
shown. Nyctiphanes couchii replaces Thysanoessa raschii in more
southern areas, these species both living in coastal regions but also
extending to slope regions. Thysanoessa inermis also occurs in the
coastal zone but tends to be found more frequently offshore than the
previous two species, while Meganyctiphanes norvegica occurs above
the continental slope although it is present with these other species in
coastal areas with depths greater than 100-200m. The two species,
Thysanopoda acutifrons and Thysanoessa longicaudata, live in oceanic
areas, the former at greater depths than the latter. Einarsson (1945)
has shown that the spawning areas of these species are much more
restricted than the total geographical area of occurrence. This is
illustrated by Meganyctiphanes norvegica which is distributed throughout the greater part of the North Atlantic yet has " centres of
spawning ". These centres are located in the Gulf of Maine, south and
Thysanopoda acutifrons; Nyctiphanes couchii; Meganyctiphanes