279
producers. Finally, some systems may exhibit a very large biomass of cells> 5 j.tm, often
pertaining to species avoided by grazers (e.g. Phaeocystis, Gyrodiniurn aureolurn; Holligan,
1987). This would be the case of "exceptional" blooms (sensu Tett, 1987), where
phytoplankton biomass in surface waters may reach > 100 mg m- 3 in terms of chlorophyll a
concentration.
Using the various possible combinations of phytoplankton production and standing stock, as
dominated by large or small cells or resulting from a combination of various cell sizes, it is
possible to design a typology of pelagic marine ecosystems, as shown in Fig. 3. This figure
schematizes the five possible patterns linking standing stock to production of phytoplankton.
In any given environment, some types of pelagic ecosystems may exist for only part of the
year and, in some cases, two or perhaps several types may coexist in the same general area.
It will be shown that this typology has an operational character, since the production of small
vs. large cells is under hydrodynamic control (e.g. Legendre and Le Fevre, 1989), while the
size-distribution of the standing stock is influenced by ecosystem structure, as well as by
phytoplankton production. The relationship between the size-distributions of phytoplankton
production and standing stock appears to be a fundamental characteristic of the structure of
the overall pelagic ecosystem, with consequences for fisheries and for the export and
sequestration of biogenic carbon.
TYPE 1. PRODUCTION AND STANDING STOCK DOMINATED BY LARGE CELLS
Large and small cells develop together in most planktonic ecosystems, as in the classical case
of temperate waters where plankton production undergoes a well-marked annual cycle (see
Type 3 below). Large cells, generally consisting of diatoms, are favoured at the initial stages
of species succession, when the nutrient supply is abundant and vertical mixing (one form of
"auxiliary energy" sensu Margalef, 1978) is strong enough to maintain non-motile cells in the
euphotic layer, while other types of large cells, together with small ones, take over when the
environment becomes hydrodynamical\y less energetic. Primary production dominated by (and
thus biomass consisting mainly of) large cells generally corresponds to a diatom bloom,
especially in a transient situation that does not allow the further stages of the succession to
take place. Such a bloom will occur when a major change in hydrographic conditions (a strong
producers. Finally, some systems may exhibit a very large biomass of cells> 5 j.tm, often
pertaining to species avoided by grazers (e.g. Phaeocystis, Gyrodiniurn aureolurn; Holligan,
1987). This would be the case of "exceptional" blooms (sensu Tett, 1987), where
phytoplankton biomass in surface waters may reach > 100 mg m- 3 in terms of chlorophyll a
concentration.
Using the various possible combinations of phytoplankton production and standing stock, as
dominated by large or small cells or resulting from a combination of various cell sizes, it is
possible to design a typology of pelagic marine ecosystems, as shown in Fig. 3. This figure
schematizes the five possible patterns linking standing stock to production of phytoplankton.
In any given environment, some types of pelagic ecosystems may exist for only part of the
year and, in some cases, two or perhaps several types may coexist in the same general area.
It will be shown that this typology has an operational character, since the production of small
vs. large cells is under hydrodynamic control (e.g. Legendre and Le Fevre, 1989), while the
size-distribution of the standing stock is influenced by ecosystem structure, as well as by
phytoplankton production. The relationship between the size-distributions of phytoplankton
production and standing stock appears to be a fundamental characteristic of the structure of
the overall pelagic ecosystem, with consequences for fisheries and for the export and
sequestration of biogenic carbon.
TYPE 1. PRODUCTION AND STANDING STOCK DOMINATED BY LARGE CELLS
Large and small cells develop together in most planktonic ecosystems, as in the classical case
of temperate waters where plankton production undergoes a well-marked annual cycle (see
Type 3 below). Large cells, generally consisting of diatoms, are favoured at the initial stages
of species succession, when the nutrient supply is abundant and vertical mixing (one form of
"auxiliary energy" sensu Margalef, 1978) is strong enough to maintain non-motile cells in the
euphotic layer, while other types of large cells, together with small ones, take over when the
environment becomes hydrodynamical\y less energetic. Primary production dominated by (and
thus biomass consisting mainly of) large cells generally corresponds to a diatom bloom,
especially in a transient situation that does not allow the further stages of the succession to
take place. Such a bloom will occur when a major change in hydrographic conditions (a strong