CIRCAUIAN I'EBIO1)ICITI ES IN PHYTOPLANKTON
34 I
high light intcnsities. Froin it study on Chlorelln, Stecniann Nielsen and
Jorgcnsen ( 1!W!) inferred thitt " no c+hlorophyll is produced by surface
plankton during the noon period on bright days ", which can explain,
in the hypot,hmis of a continoous grazing rate, the decrease of afternoon
concentrations " often observed in Nature ".
Given the subtlety of the mechunisnis involved in chlorophyll synthesis, initctiv;ttion und destractJion, and considering the possibility
for synthesis to proceed in the (lark, one might expect that chlorophyll
concentration is among the worst indicators of circadian periodicity.
I t is not therefore fiurprising to find that, field data are so diverse
and conflicting thiit reviowing them is : L tedious task, as much in the
writing ILR in thc rei~ding. Fortunately Forsbcrgh ( 1969) has done this
for UH only rccrntly : to the Home fifteen papers he cites, an equal number
mrhy be itlddcd i d summariaetl its follows : afternoon maximum
(Whceler, unpubl., quotcd by Oduni et al., 1958) ; incrcasing conot:ntrittio~ls throughout the day iLnd the rwerNe at night (Ryther P t al.,
1958) ; during i~ cruise (itinerating stations), lower values a t night
(Ltythcr arid Menzel, 1981); petiks ut 18.00 and 06.00 hours (Goering
~t nl., 19fi4) ; some evidonce for il noon mibximum (Shah, 1968, 1969);
diurnd inorause, whether continuous throughout thc day if moderate
illuminat~ion or int+errupt,ed a t noon if bright sunshine (Sournia, 1968) ;
minimum before siinriw itnd an afternoon maximum (Renk and Torbicki, 1 $)7%); 110 obvious die1 pattern (Humphrey, 1960; Alexander and
Corcoritn, 1963 ; Endo, 1067 ; Kitwltrada and h n o , 1968 ; Franceschini
et nl., 1970; (Xooschenko, 197 I : Colton, 1972 ; Krishnamurthy and
L'uroshot,lrttniitii, 1972) : and finidly in lakes : corly morning rnaximum
and 11th afternoon minimum (khimuru, I960), continuous increase
(luring the long mid sunny xumme~ clay in Alaska (MttcIsaac, 1965).
This complementary set of data corroborates Forsbergh's ( 1969)
conclusion that " tho periodicity observed by the various investigators
appears to bc quitc inconsistciit,, mi~xirni~ nnd minima not being limited
to any particular periods of the rliiy ". However, three works covering
ii large number of 'measurrments clescrvc morc emphasis than the rest.
---Forsbcrgh himself (196!)) itnitlys(~tl 47fi surface samples extending
over an annuitl rycle and coveriiig il largr occm arcit; mcrlitin vuluex
(rnther than arithmetic nit:ans) for 24 overlupping &hour intcrvah
were the highest from 08.00 to I A.OO hours and t h e low& from 19.00
t1o 03.00.
-Glooschcnko (1967) devoted n whole thesis to thiR subject,. I n the
0- 15 or 0-25 ni layer, miiximum concentrutions of both chlorophylls
a and c H"X* reiiohed from early evening to midnight, minima occurring
1'2
3 n II 1'2
34 I
high light intcnsities. Froin it study on Chlorelln, Stecniann Nielsen and
Jorgcnsen ( 1!W!) inferred thitt " no c+hlorophyll is produced by surface
plankton during the noon period on bright days ", which can explain,
in the hypot,hmis of a continoous grazing rate, the decrease of afternoon
concentrations " often observed in Nature ".
Given the subtlety of the mechunisnis involved in chlorophyll synthesis, initctiv;ttion und destractJion, and considering the possibility
for synthesis to proceed in the (lark, one might expect that chlorophyll
concentration is among the worst indicators of circadian periodicity.
I t is not therefore fiurprising to find that, field data are so diverse
and conflicting thiit reviowing them is : L tedious task, as much in the
writing ILR in thc rei~ding. Fortunately Forsbcrgh ( 1969) has done this
for UH only rccrntly : to the Home fifteen papers he cites, an equal number
mrhy be itlddcd i d summariaetl its follows : afternoon maximum
(Whceler, unpubl., quotcd by Oduni et al., 1958) ; incrcasing conot:ntrittio~ls throughout the day iLnd the rwerNe at night (Ryther P t al.,
1958) ; during i~ cruise (itinerating stations), lower values a t night
(Ltythcr arid Menzel, 1981); petiks ut 18.00 and 06.00 hours (Goering
~t nl., 19fi4) ; some evidonce for il noon mibximum (Shah, 1968, 1969);
diurnd inorause, whether continuous throughout thc day if moderate
illuminat~ion or int+errupt,ed a t noon if bright sunshine (Sournia, 1968) ;
minimum before siinriw itnd an afternoon maximum (Renk and Torbicki, 1 $)7%); 110 obvious die1 pattern (Humphrey, 1960; Alexander and
Corcoritn, 1963 ; Endo, 1067 ; Kitwltrada and h n o , 1968 ; Franceschini
et nl., 1970; (Xooschenko, 197 I : Colton, 1972 ; Krishnamurthy and
L'uroshot,lrttniitii, 1972) : and finidly in lakes : corly morning rnaximum
and 11th afternoon minimum (khimuru, I960), continuous increase
(luring the long mid sunny xumme~ clay in Alaska (MttcIsaac, 1965).
This complementary set of data corroborates Forsbergh's ( 1969)
conclusion that " tho periodicity observed by the various investigators
appears to bc quitc inconsistciit,, mi~xirni~ nnd minima not being limited
to any particular periods of the rliiy ". However, three works covering
ii large number of 'measurrments clescrvc morc emphasis than the rest.
---Forsbcrgh himself (196!)) itnitlys(~tl 47fi surface samples extending
over an annuitl rycle and coveriiig il largr occm arcit; mcrlitin vuluex
(rnther than arithmetic nit:ans) for 24 overlupping &hour intcrvah
were the highest from 08.00 to I A.OO hours and t h e low& from 19.00
t1o 03.00.
-Glooschcnko (1967) devoted n whole thesis to thiR subject,. I n the
0- 15 or 0-25 ni layer, miiximum concentrutions of both chlorophylls
a and c H"X* reiiohed from early evening to midnight, minima occurring
1'2
3 n II 1'2