THE PRODUCTION OF MARINE PLANKTON
143
showed considerable seasonal variations. Values quoted by Provasoli
(1963) include 2.8-3.4 g C/m3 for the Black Sea with a marked seasonal
variation, and up to 4.(igC/m7 in the Ihltic. Inshore regions may have
very high values; even 8.0g C/mJ in the Wadd:n Sea (Duursma, 1961).
If photosynthetic organisms can make use, a t least temporarily, of
some of this vast reserve of dissolved organic substance, it can play a
significant part in particulate production. Eut the possible heterotrophic powers of phytoplankton must be also considered in relation to
the important observations of Bernard (19!i3; 1963), Bernard and
Lecal (1960) and of Kimball et al. (1963) that considerable populations
of photosynthetic organisms may apparently exist in some seas, such
‘ as the Mediterranean and parts of the Indian Ocean, a t depths well
below the euphotic zone. Many of these algae are not dying populations
which have descended into the deep layers, but are in healthy condition
and are actively living at these depths. Wood (1963a and c), Bernard,
as well as Kimball et al., have all suggested that such organisms must be
living heterotrophically at such great depths. Though coccolithophores
often tend to dominate these deeper-sea populakions, other algal groups,
diatoms, flagellates, and dinoflagellates, are also represented. Especially
in such seas where primary production in the euphotic zone may not be
very high, and therefore the amount of particulate matter reaching
deep water may be much reduced, productioi due t o this deep-living
phytoplankton may be extraordinarily significant to the whole economy
of the deeper layers.
Apart from the possibility that some pl1,ytoplankton may utilize
dissolved carbon and nitrogen, certain species are known to have
definite demands for specific organic constituents. Organic substances
may be important as chelating substarices m d a number of marine
phytoplankton forms are now known to have specific vitamin requirements. Among the many growth-promoting and growth-inhibiting substances in sea water, Belser (1959) demonstrated 10 growth-promoting
substances on a marine bacterium of which three, biotin, uracil, and
isoleucine appeared frequently in sea water s#tmples. Other substances
have been recently assayed (Belser, 1963). Collier (1953) and Wangersky
(1952) both reported the presence of ascorbic acid in sea water, and later
studies by Collier et al. (1956) suggested that nicotinamide as well as
ascorbic acid could affect the growth of marine species. Harvey (1955)
suggested that cystine was necessary for the growth of some diatoms,
and Provasoli et al. (1957) indicated that divalent sulphur is probably
necessary, a point which has also been recently taken up by Curl
(1962a) for the growth of Skeletonenza. Wood (l”963b) lists several
organic substances which influence photosynthesis and growth of
flagellates and diatoms. At this stage we crinnot list all the organic
143
showed considerable seasonal variations. Values quoted by Provasoli
(1963) include 2.8-3.4 g C/m3 for the Black Sea with a marked seasonal
variation, and up to 4.(igC/m7 in the Ihltic. Inshore regions may have
very high values; even 8.0g C/mJ in the Wadd:n Sea (Duursma, 1961).
If photosynthetic organisms can make use, a t least temporarily, of
some of this vast reserve of dissolved organic substance, it can play a
significant part in particulate production. Eut the possible heterotrophic powers of phytoplankton must be also considered in relation to
the important observations of Bernard (19!i3; 1963), Bernard and
Lecal (1960) and of Kimball et al. (1963) that considerable populations
of photosynthetic organisms may apparently exist in some seas, such
‘ as the Mediterranean and parts of the Indian Ocean, a t depths well
below the euphotic zone. Many of these algae are not dying populations
which have descended into the deep layers, but are in healthy condition
and are actively living at these depths. Wood (1963a and c), Bernard,
as well as Kimball et al., have all suggested that such organisms must be
living heterotrophically at such great depths. Though coccolithophores
often tend to dominate these deeper-sea populakions, other algal groups,
diatoms, flagellates, and dinoflagellates, are also represented. Especially
in such seas where primary production in the euphotic zone may not be
very high, and therefore the amount of particulate matter reaching
deep water may be much reduced, productioi due t o this deep-living
phytoplankton may be extraordinarily significant to the whole economy
of the deeper layers.
Apart from the possibility that some pl1,ytoplankton may utilize
dissolved carbon and nitrogen, certain species are known to have
definite demands for specific organic constituents. Organic substances
may be important as chelating substarices m d a number of marine
phytoplankton forms are now known to have specific vitamin requirements. Among the many growth-promoting and growth-inhibiting substances in sea water, Belser (1959) demonstrated 10 growth-promoting
substances on a marine bacterium of which three, biotin, uracil, and
isoleucine appeared frequently in sea water s#tmples. Other substances
have been recently assayed (Belser, 1963). Collier (1953) and Wangersky
(1952) both reported the presence of ascorbic acid in sea water, and later
studies by Collier et al. (1956) suggested that nicotinamide as well as
ascorbic acid could affect the growth of marine species. Harvey (1955)
suggested that cystine was necessary for the growth of some diatoms,
and Provasoli et al. (1957) indicated that divalent sulphur is probably
necessary, a point which has also been recently taken up by Curl
(1962a) for the growth of Skeletonenza. Wood (l”963b) lists several
organic substances which influence photosynthesis and growth of
flagellates and diatoms. At this stage we crinnot list all the organic