THE IIIOLOQY OF PELAGIC SHRIMPS IN THE OCEAN
309
are frequently restricted to one ocean, or even to one particular area
of water off a single coast of one ocean.
0. The body lengths of pelagic shrimps range from 10 to 100 mm,
although a few species grow up to 130-180 mm. The epipelagic
and upper mesopelagic species are, tmnspcwent or semitransparent
with orange or red c:hromat,~irhor.('K Imt all spciw living in tho
uppermost 600-700 m depth by tl;iy h;ive iL more or less uniform
pigmentation that varies from deep-red to scarlet. Special adaptations
for the pelagic existence are observed in Revera1 species. Many shrimps
possess various types of luminescent organs and are capable of luminous
secretion.
7. Pelagic shrimps are good swimmers, and their distribution is
usually uneven both vertically and horizontally. Unless the distributional and biological characteristics of the individual species are
known, an accurate quantitative analysis of shrimp populations is
difficult.
8. The shrimp biomass is large in inshore waters and localities
over the continental slope. It decreases with increasing distance from
the coast. The biomass is particularly great in water where the bottom
slopes steeply away close to the shore and strong upwelling is frequently
observed. The role of shrimps in the zooplankton community is
considerable in subtropical and tropical regions. Shrimps generally
form about 10% of the total zooplankton biomass and of 15-25% of
the micronekton biomass in the uppw 1 000-m stratum ; on weight
basis they arc comparable to t h e euphausiids and the fkh.
9. Pelagic shrimps are distributed from the surface to at least
4 000-6 000 m depth, but the distribution is concentrated in the depths
where the food supply is greatest. They form a comparatively thin
layer in shallower depths in poorly productive areas, whereas they
occur in much thicker layers in the productive areas. The shrimp
biomass attains the maximum in 1 000-3 000 m depths in the subarctic
region of the North Pacific. The largest concentration of shrimp ix
seen at 200-500 m in the areas between 30'N and lO"N, whereas in
the equatorial region the role of shrimps in the 1 000-2 000 m appears
to be the greatest.
10. Besides the food supply, the vertical distribution of xhrimps is
principally modified by light penetration and temperaturc.
11. There is a tendency for the population maxima of congeneric
species to occur at different depths at one locality.
12. Diurnal vertical migration seems to occur in all epi- and
mesopelagic shrimps. The amplitude of migration in the majority of
A.M.B.-12
I I
309
are frequently restricted to one ocean, or even to one particular area
of water off a single coast of one ocean.
0. The body lengths of pelagic shrimps range from 10 to 100 mm,
although a few species grow up to 130-180 mm. The epipelagic
and upper mesopelagic species are, tmnspcwent or semitransparent
with orange or red c:hromat,~irhor.('K Imt all spciw living in tho
uppermost 600-700 m depth by tl;iy h;ive iL more or less uniform
pigmentation that varies from deep-red to scarlet. Special adaptations
for the pelagic existence are observed in Revera1 species. Many shrimps
possess various types of luminescent organs and are capable of luminous
secretion.
7. Pelagic shrimps are good swimmers, and their distribution is
usually uneven both vertically and horizontally. Unless the distributional and biological characteristics of the individual species are
known, an accurate quantitative analysis of shrimp populations is
difficult.
8. The shrimp biomass is large in inshore waters and localities
over the continental slope. It decreases with increasing distance from
the coast. The biomass is particularly great in water where the bottom
slopes steeply away close to the shore and strong upwelling is frequently
observed. The role of shrimps in the zooplankton community is
considerable in subtropical and tropical regions. Shrimps generally
form about 10% of the total zooplankton biomass and of 15-25% of
the micronekton biomass in the uppw 1 000-m stratum ; on weight
basis they arc comparable to t h e euphausiids and the fkh.
9. Pelagic shrimps are distributed from the surface to at least
4 000-6 000 m depth, but the distribution is concentrated in the depths
where the food supply is greatest. They form a comparatively thin
layer in shallower depths in poorly productive areas, whereas they
occur in much thicker layers in the productive areas. The shrimp
biomass attains the maximum in 1 000-3 000 m depths in the subarctic
region of the North Pacific. The largest concentration of shrimp ix
seen at 200-500 m in the areas between 30'N and lO"N, whereas in
the equatorial region the role of shrimps in the 1 000-2 000 m appears
to be the greatest.
10. Besides the food supply, the vertical distribution of xhrimps is
principally modified by light penetration and temperaturc.
11. There is a tendency for the population maxima of congeneric
species to occur at different depths at one locality.
12. Diurnal vertical migration seems to occur in all epi- and
mesopelagic shrimps. The amplitude of migration in the majority of
A.M.B.-12
I I