PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
145
20.4:l at the first station and 20.0:l a t the other, both values being
markedly higher than that of 16.0 :1 originally suggested by Fleming
(1940).
X. NITROGEN AND PHOSPHORUS EXCRETION BY ZOOPLANKTON
Curl ( 1962), discussing zooplankton production in Continental
Shelf waters south of New York, wrote that ( ( The cotninunity metabolism of carbon only will be examined, inasmuch as the iieccssrwy data
on nitrogen and phosphorus metabolism in marine anim& is almost
totally non-existent.” In recent years, numerous studies of this problem
have been made, stimulated mainly by the relevance of nitrogen and
phosphorus metabolism to the vital question of nutrient regeneration
(Ketchum, 1962), and the relation of nitrogen metabolism in particular
to the important problem of protein synthesis (Gerking, 19G2 ; Cowey
and Corner, 1963b).
A. Nitrogen excretion
The first attempt t o measure nitrogen excretion by zooplankton
seems t o have been that of Harris (1959) who estimated the quantities
of ammonia excreted by catches of mixed zooplankton taken in Long
Island Sound. The animals were placed in freshly collected sea water
in the dark and the amount of ammonia excreted was determined as
the difference between the levels present in the sea water at the start and
end of a 4-h period. I n most of Harris’s experiments the zooplankton
consisted mainly of Acurtia clausi, and the results he obtained with
these animals showed that they excreted on average 43.1 pg N/mg dry
body weightlday. Earlier, Harris and Riley (1956) found that body
nitrogen in zooplankton from Long Island Sound accounted on average
for 8.91 yo of the dry weight : accordingly, the animals studied by Harris
(1959) excreted the equivalent of 48% of their body nitrogen daily.
These tneasurements were made during spring (April 6-May 27) when a
significant amount of particulate mate-ial was present in the unfiltered
seawater and available t o the animals during the excretion experiments.
As no allowance was made for the possible uptake of excretion products
by this particulate material present as a food, Harris may have underestimated the total amount of ammonia excreted.
A different approach to the problem of nitrogen excretion was made
by Cowey and Corner (1963b) who measured the average daily reduction
in the levels of 16 amino acids in Galanus helgolandicus when the
animal was starved over a period of 10 days. Measurements were made
in both summer and winter, the daily fall in amino acids in the summer
animals representing 2.1% of the total and the corresponding value
145
20.4:l at the first station and 20.0:l a t the other, both values being
markedly higher than that of 16.0 :1 originally suggested by Fleming
(1940).
X. NITROGEN AND PHOSPHORUS EXCRETION BY ZOOPLANKTON
Curl ( 1962), discussing zooplankton production in Continental
Shelf waters south of New York, wrote that ( ( The cotninunity metabolism of carbon only will be examined, inasmuch as the iieccssrwy data
on nitrogen and phosphorus metabolism in marine anim& is almost
totally non-existent.” In recent years, numerous studies of this problem
have been made, stimulated mainly by the relevance of nitrogen and
phosphorus metabolism to the vital question of nutrient regeneration
(Ketchum, 1962), and the relation of nitrogen metabolism in particular
to the important problem of protein synthesis (Gerking, 19G2 ; Cowey
and Corner, 1963b).
A. Nitrogen excretion
The first attempt t o measure nitrogen excretion by zooplankton
seems t o have been that of Harris (1959) who estimated the quantities
of ammonia excreted by catches of mixed zooplankton taken in Long
Island Sound. The animals were placed in freshly collected sea water
in the dark and the amount of ammonia excreted was determined as
the difference between the levels present in the sea water at the start and
end of a 4-h period. I n most of Harris’s experiments the zooplankton
consisted mainly of Acurtia clausi, and the results he obtained with
these animals showed that they excreted on average 43.1 pg N/mg dry
body weightlday. Earlier, Harris and Riley (1956) found that body
nitrogen in zooplankton from Long Island Sound accounted on average
for 8.91 yo of the dry weight : accordingly, the animals studied by Harris
(1959) excreted the equivalent of 48% of their body nitrogen daily.
These tneasurements were made during spring (April 6-May 27) when a
significant amount of particulate mate-ial was present in the unfiltered
seawater and available t o the animals during the excretion experiments.
As no allowance was made for the possible uptake of excretion products
by this particulate material present as a food, Harris may have underestimated the total amount of ammonia excreted.
A different approach to the problem of nitrogen excretion was made
by Cowey and Corner (1963b) who measured the average daily reduction
in the levels of 16 amino acids in Galanus helgolandicus when the
animal was starved over a period of 10 days. Measurements were made
in both summer and winter, the daily fall in amino acids in the summer
animals representing 2.1% of the total and the corresponding value