340
AldAIN SOURNIA
peak in ronwntrat,ion occiii*red ut 4 m dcpth around 4 p.m. when
division riit~c wus 1‘1ose t o z t ~
(src NtLuwerck’s Fig. 49).
(2) It, h n n been often argued that zooplankton grazing could be
responsible for thc diel vwitit ions of phytoplankton vertical distribution.
Meusu reinelits sliould ba nmde to substantiate this statement.
(3) Akinina (1989) points out that vertical changes can be explained
by the nocturnd increase of sinking ratt?, in addition to grazing pressure at, night and miiximum division rate during the day (the latter
poilit is fiir from being the rule : see above). Actually, future work will
htive t,o i~ssess tlio relutivc effects of “ passive ” and ‘I active” diephcerncnts; in this connection Eppley d d. (1968b) presented expcrimcmtd evidence that downward niigrtition in Cach,onina is much
faster t8hnn its passive sinking rate, some geottbctism being involved.
(4) Physi(*iil fiietors also aiuy intcrfwc. For instance, tidal transport
in n Jiiiriaica bay led to the fulliicious interpretation of an upward
nocturnal movement of P?yrodiniurrb (Carpenter and Seliger, 1968 ;
Seliger and McRlroy, 1968).
Tho benefi t e and ecological significance of vertical migration of
phytoplankton are questionable. According to Eppley ef d. (196Sb),
thcre is a doublc survival value : an increased photosyntliesis in surface
waters during tlic &by, :md R better tissimilntion of nutrients in deep
layers :It night.
VI. CHLOROPHYLL A CONTENT
Rime chlorophyll is both t i significant puriimeter and a handy tool
in primiiry podwtivity studies, diel variations of its concentration
hwvc~ been drscribad in a consided)le number of papers-greater, as
a mutter of fact, t‘hiin those c1t:tiling with numcrical abundance of
species, the cstiniation of which is much morc timu connuming.
I ~ b o n ~ t o r y
work on phytoplanktc?rs grown in light/dark cycle8
does not suggest any gc?neraI pcriot1ic:ity for chlorophyll concentratione.
Sometimeg pigmcmt ooiitetit increiw+cs in light only ; this w w the w t ~ e
for tlic green alga Dunnlielln (Eppley ant1 Coatsworth, 1966) and for
the diatoms Nlceletonema (Jsrgensen, 1966) and IMyZum (Epploy et nl.,
1067). More often, pigment synthesis is carried on also during a part of
the dark period, a s observed on the diatoms Ph&dydum
(Palmer
et al., I !)84), Ilitylum and Nitzmhia ( f’aasche, 1968), on Comolithue
(Pansche, 1967: Eppley d d., 1971) or on the red-alga Porphyridium
(Gense e l al., 19GY) ; maximum concentrations may even be recorded
in darknrss (Uno, 1971 : I’hueodact!/lum). Large-volume shipboard
cultures did not, show any periodicity (Eppley et al., 1972).
Pigment synthesis can be inhibited and bleaching can occur at
AldAIN SOURNIA
peak in ronwntrat,ion occiii*red ut 4 m dcpth around 4 p.m. when
division riit~c wus 1‘1ose t o z t ~
(src NtLuwerck’s Fig. 49).
(2) It, h n n been often argued that zooplankton grazing could be
responsible for thc diel vwitit ions of phytoplankton vertical distribution.
Meusu reinelits sliould ba nmde to substantiate this statement.
(3) Akinina (1989) points out that vertical changes can be explained
by the nocturnd increase of sinking ratt?, in addition to grazing pressure at, night and miiximum division rate during the day (the latter
poilit is fiir from being the rule : see above). Actually, future work will
htive t,o i~ssess tlio relutivc effects of “ passive ” and ‘I active” diephcerncnts; in this connection Eppley d d. (1968b) presented expcrimcmtd evidence that downward niigrtition in Cach,onina is much
faster t8hnn its passive sinking rate, some geottbctism being involved.
(4) Physi(*iil fiietors also aiuy intcrfwc. For instance, tidal transport
in n Jiiiriaica bay led to the fulliicious interpretation of an upward
nocturnal movement of P?yrodiniurrb (Carpenter and Seliger, 1968 ;
Seliger and McRlroy, 1968).
Tho benefi t e and ecological significance of vertical migration of
phytoplankton are questionable. According to Eppley ef d. (196Sb),
thcre is a doublc survival value : an increased photosyntliesis in surface
waters during tlic &by, :md R better tissimilntion of nutrients in deep
layers :It night.
VI. CHLOROPHYLL A CONTENT
Rime chlorophyll is both t i significant puriimeter and a handy tool
in primiiry podwtivity studies, diel variations of its concentration
hwvc~ been drscribad in a consided)le number of papers-greater, as
a mutter of fact, t‘hiin those c1t:tiling with numcrical abundance of
species, the cstiniation of which is much morc timu connuming.
I ~ b o n ~ t o r y
work on phytoplanktc?rs grown in light/dark cycle8
does not suggest any gc?neraI pcriot1ic:ity for chlorophyll concentratione.
Sometimeg pigmcmt ooiitetit increiw+cs in light only ; this w w the w t ~ e
for tlic green alga Dunnlielln (Eppley ant1 Coatsworth, 1966) and for
the diatoms Nlceletonema (Jsrgensen, 1966) and IMyZum (Epploy et nl.,
1067). More often, pigment synthesis is carried on also during a part of
the dark period, a s observed on the diatoms Ph&dydum
(Palmer
et al., I !)84), Ilitylum and Nitzmhia ( f’aasche, 1968), on Comolithue
(Pansche, 1967: Eppley d d., 1971) or on the red-alga Porphyridium
(Gense e l al., 19GY) ; maximum concentrations may even be recorded
in darknrss (Uno, 1971 : I’hueodact!/lum). Large-volume shipboard
cultures did not, show any periodicity (Eppley et al., 1972).
Pigment synthesis can be inhibited and bleaching can occur at