('1RCAI)IAN PERIOI)ICITl IS IN PHYTOPLANKTON
345
Naples and HrtwtLii (Uoty et a/., l!)(i7 or Newhouse, 1967 or Newhouse
et d., 1067) showed u phwe-shil't of ttbout six hours, maximum occurring
in the afternoon tmd minimum at, t h e end of the night. According to
the tu~thors, this feature would be typical of neritic waters as opposed
to tho open ocean; more recent diLta collected by Newhouse and
Knuuer (quotcd in Malone, 1971) from both oceanic and neritic
station8 in tht. tropical Pacific corroborate this pattern. However, all
the other cyclcf~ reported from neritio r~reaa belong to the '' type "rhythm (q. Yentsch and Ryther, 1M7 ; Lorenzen, 1963; Endo, 1967,
1070 ; 'I'tiylor rmd Hughes, 1967 ; Sournin, unpubl.) and, furthermore,
some cxeunio datu published by Doty's group itself also seem to eshibit an ufbrnoon peak (Newhouse, 1968, Table 2 or Uoty, 1969,
'I'able 3). A unifying explanation for these conflicting facts may be
that, a~ Rhown hy Malono (1971), the timing of the maximum-whether
mid-morning or mid-ufternoon--would depend both on size composition of the phytoplnnktere (nano- or microplankton) and availability
of nutrients.
The original data of Doty and Oguri (1957) exhibited the same
periodicity for surface samples and for 20-m samples. Later work
gave evidence that, the rhithm extends throughout the whole euphotic
Ittyer, though the amplitude probably decreases with increasing depth
(McAllister, 1963; Sournitt, 1967; Endo, 1970); it might also be that
the phasing is deltiyed cit'depth, the peak at the 1 light level being
observed it few hours after the surface maximum (Sournia, 1967).
No attempt hus been made a t ~ e a
to determine whether the rhythm
persists under continuous light or darkness (this could be done by illuminating or darkening a large body of wat4er). However, laboratory
work has demonstrated clenrly that t h e phenomenon does persist
under constant conditions, preferably under continuous dim light (to
mnie extent also in darkness, but definitely not in bright light), or, in
other words, that the rhythm is endogenous ; organisms studied first
were freshwater algae (0.g. Pirson et al., 1954; Schsn, 1955), then
(I'onyaulux (Hastings and Astrnohan, I969 ; Hweeney, 1960 ; Hastings
cC nl., 19(il), Yltneodactylztm (Palmer P# al., 1964) and four diatoms or
dinoflagell~~tca in a mixed culture (Honjo and Hanaoka, 1961)) ; some
trends for JL persisting rhythm in darkness we found in the experiments
on DunaEir~EZa, conducted by Yentwh ant1 Reichert (1963 ; Bee their
Pig. 3). The girmt iinicollul~r green-algri Acetnbrrluviu may be included
(Swweney ixnd H~LXO, 1961 ; Richter, 1963; Terborgh and McLeod,
1967, and others). In fact hoth exogenous and endogenous componsnts
should be taken into account (Ohle, 1961), as it generally happens with
circadian rhythms (see a180 below : " Mechanisms ").
345
Naples and HrtwtLii (Uoty et a/., l!)(i7 or Newhouse, 1967 or Newhouse
et d., 1067) showed u phwe-shil't of ttbout six hours, maximum occurring
in the afternoon tmd minimum at, t h e end of the night. According to
the tu~thors, this feature would be typical of neritic waters as opposed
to tho open ocean; more recent diLta collected by Newhouse and
Knuuer (quotcd in Malone, 1971) from both oceanic and neritic
station8 in tht. tropical Pacific corroborate this pattern. However, all
the other cyclcf~ reported from neritio r~reaa belong to the '' type "rhythm (q. Yentsch and Ryther, 1M7 ; Lorenzen, 1963; Endo, 1967,
1070 ; 'I'tiylor rmd Hughes, 1967 ; Sournin, unpubl.) and, furthermore,
some cxeunio datu published by Doty's group itself also seem to eshibit an ufbrnoon peak (Newhouse, 1968, Table 2 or Uoty, 1969,
'I'able 3). A unifying explanation for these conflicting facts may be
that, a~ Rhown hy Malono (1971), the timing of the maximum-whether
mid-morning or mid-ufternoon--would depend both on size composition of the phytoplnnktere (nano- or microplankton) and availability
of nutrients.
The original data of Doty and Oguri (1957) exhibited the same
periodicity for surface samples and for 20-m samples. Later work
gave evidence that, the rhithm extends throughout the whole euphotic
Ittyer, though the amplitude probably decreases with increasing depth
(McAllister, 1963; Sournitt, 1967; Endo, 1970); it might also be that
the phasing is deltiyed cit'depth, the peak at the 1 light level being
observed it few hours after the surface maximum (Sournia, 1967).
No attempt hus been made a t ~ e a
to determine whether the rhythm
persists under continuous light or darkness (this could be done by illuminating or darkening a large body of wat4er). However, laboratory
work has demonstrated clenrly that t h e phenomenon does persist
under constant conditions, preferably under continuous dim light (to
mnie extent also in darkness, but definitely not in bright light), or, in
other words, that the rhythm is endogenous ; organisms studied first
were freshwater algae (0.g. Pirson et al., 1954; Schsn, 1955), then
(I'onyaulux (Hastings and Astrnohan, I969 ; Hweeney, 1960 ; Hastings
cC nl., 19(il), Yltneodactylztm (Palmer P# al., 1964) and four diatoms or
dinoflagell~~tca in a mixed culture (Honjo and Hanaoka, 1961)) ; some
trends for JL persisting rhythm in darkness we found in the experiments
on DunaEir~EZa, conducted by Yentwh ant1 Reichert (1963 ; Bee their
Pig. 3). The girmt iinicollul~r green-algri Acetnbrrluviu may be included
(Swweney ixnd H~LXO, 1961 ; Richter, 1963; Terborgh and McLeod,
1967, and others). In fact hoth exogenous and endogenous componsnts
should be taken into account (Ohle, 1961), as it generally happens with
circadian rhythms (see a180 below : " Mechanisms ").