152
J . E . a. RAYMONT
When such density differences restrict vertical transport of nitrate
and phosphate to the euphotic zone, regeneration processes in the photosynthetic stratum itself may be of the greatest significance, in that
excretory material and some organic detritus can be converted relatively
rapidly to inorganic phosphorus and nitrogen, mainly as ammonia, so
keeping some phytoplankton growth continuing. Rates are the major
factors and there appears to be variation between nitrogen and phosphorus regeneration (cf. Harris, 1959; Vaccaro, 1963; Pomeroy et al.,
1963; Hoffman, 1956; Menzel and Ryther, 1964; McAllister et al., 1961;
Antia et al., 1963). Nitrate regeneration appears to be especially slow.
In any event, regeneration usually is insufficient, and with the restriction in vertical transport of nutrients, a reduction in primary production
typically occurs during the summer months. With the autumn breakdown of the seasonal thermocline and the consequent increased supply
of essential nutrients to the euphotic zone, an increased production again
leads to the so-called “autumn peak”, but this is usually short-lived
owing to the rapidly decreasing light.
Too often this picture of a spring and autumn peak in phytoplankton
with a smaller and variable production over summer (cf. Fig. 7) has
-
lee. I Jon. I Feb. I Mar. 1 Apr. I May 1 June 1 July I Auq. 1 Sep. I Oct. 1 Nov. I Dc
FIG. 7. Diagrammatic representation of the seasonal cycles in light, nitrate and phosphate, and phytoplankton in a typical northern temperate sea. (Reprinted from Plankton
and Productivity i n the Oceans, Raymont 1963, Pergamon Press).
been based on estimates of standing crop of phytoplankton rather than
on rates of primary production, though the few seasonal estimates of
productivity such as those of Ryther and Yentsch (1958), Anderson
(1964), Steele (1958) and Steele and Baird (1961) confirm the high rate
in spring and the lowering of rate in summer. The large densities of
zooplankton over summer may reduce the phytoplankton standmg
J . E . a. RAYMONT
When such density differences restrict vertical transport of nitrate
and phosphate to the euphotic zone, regeneration processes in the photosynthetic stratum itself may be of the greatest significance, in that
excretory material and some organic detritus can be converted relatively
rapidly to inorganic phosphorus and nitrogen, mainly as ammonia, so
keeping some phytoplankton growth continuing. Rates are the major
factors and there appears to be variation between nitrogen and phosphorus regeneration (cf. Harris, 1959; Vaccaro, 1963; Pomeroy et al.,
1963; Hoffman, 1956; Menzel and Ryther, 1964; McAllister et al., 1961;
Antia et al., 1963). Nitrate regeneration appears to be especially slow.
In any event, regeneration usually is insufficient, and with the restriction in vertical transport of nutrients, a reduction in primary production
typically occurs during the summer months. With the autumn breakdown of the seasonal thermocline and the consequent increased supply
of essential nutrients to the euphotic zone, an increased production again
leads to the so-called “autumn peak”, but this is usually short-lived
owing to the rapidly decreasing light.
Too often this picture of a spring and autumn peak in phytoplankton
with a smaller and variable production over summer (cf. Fig. 7) has
-
lee. I Jon. I Feb. I Mar. 1 Apr. I May 1 June 1 July I Auq. 1 Sep. I Oct. 1 Nov. I Dc
FIG. 7. Diagrammatic representation of the seasonal cycles in light, nitrate and phosphate, and phytoplankton in a typical northern temperate sea. (Reprinted from Plankton
and Productivity i n the Oceans, Raymont 1963, Pergamon Press).
been based on estimates of standing crop of phytoplankton rather than
on rates of primary production, though the few seasonal estimates of
productivity such as those of Ryther and Yentsch (1958), Anderson
(1964), Steele (1958) and Steele and Baird (1961) confirm the high rate
in spring and the lowering of rate in summer. The large densities of
zooplankton over summer may reduce the phytoplankton standmg