PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
141
The levels vary considerably, nitrogen ranging from 1.34% (Pleurobruchia pileus (0. F. Muller) to l l . l y o (Calanus finmarchicus) and
phosphorus from 0.23% (Pleurobrachia pileus) to 1.70% (Balanus
balanoides L.). On the other hand, nitrogen values obtained for certain
groups of animals, such as copepods, are fairly similar, although the
data apply to material collected from sea areas with different hydrographic and nutrient conditions. For example, Harris and Riley
(1956) found that nitrogen accounted for 10.9yo and phosphorus
0.82% dry body weight of mixed zooplankton, mainly copepods,
from Long Island Sound; and Beers (1966) obtained corresponding
values of 12.2 and 0.79% respectively for copepods from the Sargasso
Sea.
The data of Beers (1966) confirm earlier observations by Curl
(1962) in showing that nitrogen and phosphorus content varies with the
wateriness ” of the animal. Thus, nitrogen accounts for 9-1 1 % dry
weight in copepods and euphausiids-mysids (wet weight : dry weight
ratio = 6-3-7.4 :I), 6 4 % in chaetognaths (wet weight : dry weight
ratio = 14.7 : I ) and 1-4% in siphonophores (wet weight: dry weight
ratio = 25 :I). Likewise, the phosphorus content of copepods is much
higher that that of “ watery ” forms such as siphonophores and hydromedusae. Seasonal values for nitrogen and phosphorus were more
constant for animals with lower water content. For example, in
euphausiids-mysids, nitrogen varied from 9.43 to 10.46% dry body
weight and phosphorus from 1.39 to 1.60% throughout the year ; but
in ‘‘ watery ” forms, such as siphonophores, the range for nitrogen was
0-98-4-36% and that for phosphorus O-05-O~18~o.
In the study by Beers (1966) the species composition and relative
proportions of different stages of a particular group could have altered
between monthly hauls, and this may account for the absence of any
obvious seasonal trend in the levels of nitrogen and phosphorus.
Evidence of seasonal changes is better sought using a particular stage
of a single species, as was done by Orr (1934) with stage V Calanus
jinmarchicus from the Clyde sea-area. Orr’s data, recalculated in terms
of dry body weight, are presented in Table VII and show that levels of
nitrogen slowly increased from November to March. With the onset of
the spring diatom increase, they then rose markedly to a maximum
before falling throughout summer and winter to a minimum in October.
Further evidence consistent with these findings is provided by Butler
et al. (1969) who showed, using a mixture of Calanusfinmarchicus and
Calanus helgolaizdicus from the Clyde sea-area, that females and stage
V contained more nitrogen and phosphorus in spring than in autumn
(see Tablc VI) ; also, Conover and Corner (1968) found that in Metridia
( 6
141
The levels vary considerably, nitrogen ranging from 1.34% (Pleurobruchia pileus (0. F. Muller) to l l . l y o (Calanus finmarchicus) and
phosphorus from 0.23% (Pleurobrachia pileus) to 1.70% (Balanus
balanoides L.). On the other hand, nitrogen values obtained for certain
groups of animals, such as copepods, are fairly similar, although the
data apply to material collected from sea areas with different hydrographic and nutrient conditions. For example, Harris and Riley
(1956) found that nitrogen accounted for 10.9yo and phosphorus
0.82% dry body weight of mixed zooplankton, mainly copepods,
from Long Island Sound; and Beers (1966) obtained corresponding
values of 12.2 and 0.79% respectively for copepods from the Sargasso
Sea.
The data of Beers (1966) confirm earlier observations by Curl
(1962) in showing that nitrogen and phosphorus content varies with the
wateriness ” of the animal. Thus, nitrogen accounts for 9-1 1 % dry
weight in copepods and euphausiids-mysids (wet weight : dry weight
ratio = 6-3-7.4 :I), 6 4 % in chaetognaths (wet weight : dry weight
ratio = 14.7 : I ) and 1-4% in siphonophores (wet weight: dry weight
ratio = 25 :I). Likewise, the phosphorus content of copepods is much
higher that that of “ watery ” forms such as siphonophores and hydromedusae. Seasonal values for nitrogen and phosphorus were more
constant for animals with lower water content. For example, in
euphausiids-mysids, nitrogen varied from 9.43 to 10.46% dry body
weight and phosphorus from 1.39 to 1.60% throughout the year ; but
in ‘‘ watery ” forms, such as siphonophores, the range for nitrogen was
0-98-4-36% and that for phosphorus O-05-O~18~o.
In the study by Beers (1966) the species composition and relative
proportions of different stages of a particular group could have altered
between monthly hauls, and this may account for the absence of any
obvious seasonal trend in the levels of nitrogen and phosphorus.
Evidence of seasonal changes is better sought using a particular stage
of a single species, as was done by Orr (1934) with stage V Calanus
jinmarchicus from the Clyde sea-area. Orr’s data, recalculated in terms
of dry body weight, are presented in Table VII and show that levels of
nitrogen slowly increased from November to March. With the onset of
the spring diatom increase, they then rose markedly to a maximum
before falling throughout summer and winter to a minimum in October.
Further evidence consistent with these findings is provided by Butler
et al. (1969) who showed, using a mixture of Calanusfinmarchicus and
Calanus helgolaizdicus from the Clyde sea-area, that females and stage
V contained more nitrogen and phosphorus in spring than in autumn
(see Tablc VI) ; also, Conover and Corner (1968) found that in Metridia
( 6