160
E. D. 8. CORNER AND ANTHONY 0. DAVIES
quantity of phosphorus excreted is much less than that of nitrogen : yet,
when excretion rates are expressed in terms of body phosphorus and
body nitrogen, the proportion of body phosphorus lost daily is notably
higher than that of body nitrogen. Generally, the turnover of both
nitrogen and phosphorus by the animals is a rapid process, substantial
quantities of dissolved nitrogen and phosphorus being returned to the
sea water. Some ecological consequences of this are now considered.
D. Nutrient regeneration
Several attempts have been made to assess the extent to which the
excretion products of zooplankton supply nutrients required by the
phytoplankton on which the animals feed. Thus, Harris (1959) computed the utilization of ammonia, nitrite and nitrate by plants in Long
Island Sound as the amounts brought to the surface by vertical turbulence together with the small inorganic stock already present in the
water. The sum of these quantities was 0.085 pg-atom N/1 at a mean
depth of 7 m. The quantity of ammonia excreted by the animals was
calculated from the average zooplankton population (about 0.1 1 mg
dry weight/l) and the average excretion of ammonia (2.6 pg-atom
N/mg dry weight/day) as 0-285 pg-atom N/1. The total amount of
inorganic nitrogen consumed by the plants was therefore 0.370 pg-atom
N/1, of which 77% was contributed by zooplankton. Balance sheets
for nitrogen utilization and regeneration covering two further yearn
were also provided by Harris who found that ammonia excreted by
zooplankton accounted for 66% of the phytoplankton requirement in
one and 43% in the other. The remainder was presumed to represent
regeneration by bacteria and other organisms too small t o be captured
quantitatively in the plankton nets.
Martin (1968)) assuming a phytoplankton production rate of 10%
daily, calculated that the Skeletonemu population in Narragansett Bay
during spring required 1-89 pg-atom N/l/day. The regeneration of
ammonia by the zooplankton was calculated as the product of the
average excretion rate and the average biomass as 0.048 pg-atom N/1/
day, only 2.54% ofthe daily nitrogen requirement of the phytoplankton.
On the other hand, during the autumn, when the phytoplankton
population was much lower and nitrogen excretion by the animals
much higher, the zooplankton were estimated to supply 181.7% of the
daily needs of the phytoplankton. This excess ammonia apparently
accumulated and contributed to the autumn maximum of nitrogen
found in the sea.
Martin applied similar methods in estimating the extent to which
zooplankton excretion supplied the daily plant requirement for inor-
E. D. 8. CORNER AND ANTHONY 0. DAVIES
quantity of phosphorus excreted is much less than that of nitrogen : yet,
when excretion rates are expressed in terms of body phosphorus and
body nitrogen, the proportion of body phosphorus lost daily is notably
higher than that of body nitrogen. Generally, the turnover of both
nitrogen and phosphorus by the animals is a rapid process, substantial
quantities of dissolved nitrogen and phosphorus being returned to the
sea water. Some ecological consequences of this are now considered.
D. Nutrient regeneration
Several attempts have been made to assess the extent to which the
excretion products of zooplankton supply nutrients required by the
phytoplankton on which the animals feed. Thus, Harris (1959) computed the utilization of ammonia, nitrite and nitrate by plants in Long
Island Sound as the amounts brought to the surface by vertical turbulence together with the small inorganic stock already present in the
water. The sum of these quantities was 0.085 pg-atom N/1 at a mean
depth of 7 m. The quantity of ammonia excreted by the animals was
calculated from the average zooplankton population (about 0.1 1 mg
dry weight/l) and the average excretion of ammonia (2.6 pg-atom
N/mg dry weight/day) as 0-285 pg-atom N/1. The total amount of
inorganic nitrogen consumed by the plants was therefore 0.370 pg-atom
N/1, of which 77% was contributed by zooplankton. Balance sheets
for nitrogen utilization and regeneration covering two further yearn
were also provided by Harris who found that ammonia excreted by
zooplankton accounted for 66% of the phytoplankton requirement in
one and 43% in the other. The remainder was presumed to represent
regeneration by bacteria and other organisms too small t o be captured
quantitatively in the plankton nets.
Martin (1968)) assuming a phytoplankton production rate of 10%
daily, calculated that the Skeletonemu population in Narragansett Bay
during spring required 1-89 pg-atom N/l/day. The regeneration of
ammonia by the zooplankton was calculated as the product of the
average excretion rate and the average biomass as 0.048 pg-atom N/1/
day, only 2.54% ofthe daily nitrogen requirement of the phytoplankton.
On the other hand, during the autumn, when the phytoplankton
population was much lower and nitrogen excretion by the animals
much higher, the zooplankton were estimated to supply 181.7% of the
daily needs of the phytoplankton. This excess ammonia apparently
accumulated and contributed to the autumn maximum of nitrogen
found in the sea.
Martin applied similar methods in estimating the extent to which
zooplankton excretion supplied the daily plant requirement for inor-