CIRCAUJAN YERIODIOITIES IN PI1 YTOPLANKTON
359
siinrchly wts Iiy i t s iiiknsity arid iiction S~JC!CtI' Uln more than by orientiit ion ; rc4wttrrt works are thaw of Rieth (1939) on Hiddulphia sinewi.u
iind Cosc.1:nodint:u.v yravhii, Swift. and 'I'aylor ( 1967) on Pyrocystis lunuln
i
d Kiefer ( 1973) on Lnudrria borealis Gran. Furthermore, the
two former stdieR showed the periodicity to persist under continuous
light or diirkncw. Other workers, although they did not conduct a diel
series, are obviously tiware of the effects of light on chloroplasts (see e.g.
Jenkin's ( 1 937) cliissical paper on Coscinodiscua pxcentricus Ehrenb.) ;
obnorvations l)y Hopkins (19fiS) on ir benthic diatom may also be
roportd hcrw However, no gc*net.trl pattern can be deduced from the
cornprison of the sbovc data : it woeins that both the manner in which
ibnd the tirnc: iLt, which chloroplasts chtrngo their shape and mutual
position depend on cell morphology and specific light sensitivity.
In this connection, but outside the frontiers of marine phytopIaIikton, oiic shouId remember t h e etudies on the chloroplasts of
Acetnbtrlaria und Euglena, namely the diel rhythms of their shape
(Venden I)riwsclit?, 1966b ; Orcivirl-Liifont et al., 1972), division
(Orcivul-I,ibfoiit, ot nl., 1972) and ultrastructure (Vanden Ihiessche and
HilrR, 1972).
xv. ~~~NVIILONMRNTAL FACTORS
'l'he~r~ itrc t w o distjinct reirsons for. paying attention to diel variations
of environmoiit,d factors. Onfa is thnt concentrations and properties
in sea wnt8er cirn change in the course of 24 hours as the result of phytoplankton periodicities. The other is that phytoplankton activities are
subjected to the diel variations occurring in the environment ; in this
connect>ion tb principle which tirises from SynchronouH cultures may be
recalled : not only light, but also temperature and chemioal composition
of the mcdiuni rney set< as synchronizern or " Zeitgober ".
A . l%jh I
Ln syitc o f the f w t that light i H the first factor to be considered
when deirling witch circsdian rhythms, there is still much work to be
done. I t i pai*ticular, stiinulating iirid inhibiting intensities, as well as
:iction spcctrir, in relation to depth and taxonomic composition, offer a
wide field of investigation for every kind of periodicity to be tackled ;
: ~ s an exaniplc, Seliger and Fastie (1968) scrutinized the qualitative
iwd qutuititative changes of illumination at sunset in relation to the
biolumi~ic~sccuc~e cjcle.
As for ~)li('t~o~~~riodisrn (the depeiidence on thylength), scaroely
iillyt
from the relution between the amplitude of the photosynthetic capacity
359
siinrchly wts Iiy i t s iiiknsity arid iiction S~JC!CtI' Uln more than by orientiit ion ; rc4wttrrt works are thaw of Rieth (1939) on Hiddulphia sinewi.u
iind Cosc.1:nodint:u.v yravhii, Swift. and 'I'aylor ( 1967) on Pyrocystis lunuln
i
d Kiefer ( 1973) on Lnudrria borealis Gran. Furthermore, the
two former stdieR showed the periodicity to persist under continuous
light or diirkncw. Other workers, although they did not conduct a diel
series, are obviously tiware of the effects of light on chloroplasts (see e.g.
Jenkin's ( 1 937) cliissical paper on Coscinodiscua pxcentricus Ehrenb.) ;
obnorvations l)y Hopkins (19fiS) on ir benthic diatom may also be
roportd hcrw However, no gc*net.trl pattern can be deduced from the
cornprison of the sbovc data : it woeins that both the manner in which
ibnd the tirnc: iLt, which chloroplasts chtrngo their shape and mutual
position depend on cell morphology and specific light sensitivity.
In this connection, but outside the frontiers of marine phytopIaIikton, oiic shouId remember t h e etudies on the chloroplasts of
Acetnbtrlaria und Euglena, namely the diel rhythms of their shape
(Venden I)riwsclit?, 1966b ; Orcivirl-Liifont et al., 1972), division
(Orcivul-I,ibfoiit, ot nl., 1972) and ultrastructure (Vanden Ihiessche and
HilrR, 1972).
xv. ~~~NVIILONMRNTAL FACTORS
'l'he~r~ itrc t w o distjinct reirsons for. paying attention to diel variations
of environmoiit,d factors. Onfa is thnt concentrations and properties
in sea wnt8er cirn change in the course of 24 hours as the result of phytoplankton periodicities. The other is that phytoplankton activities are
subjected to the diel variations occurring in the environment ; in this
connect>ion tb principle which tirises from SynchronouH cultures may be
recalled : not only light, but also temperature and chemioal composition
of the mcdiuni rney set< as synchronizern or " Zeitgober ".
A . l%jh I
Ln syitc o f the f w t that light i H the first factor to be considered
when deirling witch circsdian rhythms, there is still much work to be
done. I t i pai*ticular, stiinulating iirid inhibiting intensities, as well as
:iction spcctrir, in relation to depth and taxonomic composition, offer a
wide field of investigation for every kind of periodicity to be tackled ;
: ~ s an exaniplc, Seliger and Fastie (1968) scrutinized the qualitative
iwd qutuititative changes of illumination at sunset in relation to the
biolumi~ic~sccuc~e cjcle.
As for ~)li('t~o~~~riodisrn (the depeiidence on thylength), scaroely
iillyt
from the relution between the amplitude of the photosynthetic capacity