THE PRESENT STATUS OF SOME ASPECTS OF MARINE WCROBIOL0G)Y
143
the biological differences occurring in the different ecological situations.
Undoubtedly, many terrestrial forms find marine conditions unsuitable
for their existence; but where organisms are isolated close to land
masses it may be difficult to decide whether they are terrestrial contaminants, not adapted to the marine environment and merely surviving,
or species which can grow and multiply in the sea.
The criterion suggested by Butkevich and also by ZoBell for marine
types, viz. their relationship to the concentration and composition of
salt in the medium, corresponding to that of oceanic waters, is not
considered valid (Kriss, 1963). Salinity, at any rate, is not the only
specific feature of marine environments (see below). Moreover, terrestrial
forms exist which can tolerate high salt contents, e.g. in saline soils.
MacLeod and Onofrey (1966) state that true marine bacteria may well
prove to be distinguishable from land forms present as contaminants in
sea water, not by having a requirement for sea water, but rather by
having a readily detectable need for Na+ in the medium for growth.
Kriss (1963) himself lists some of the criteria which he believes would
distinguish marine species, in addition to the one just mentioned of
ZoBell and Butkevich. These are : (1) the ability of marine species to
reproduce in the sea and not just in isolated samples of water where
conditions might be very different from the natural ones ; (2) the finding
of the organism in fairly large numbers, implying growth and multiplication in the open sea where transport from land is impossible;
and (3) the frequency of encounter of the organism aa single cells in the
open sea. Thus, in areas where the concentration of easily assimilable
organic matter necessary for metabolism is very low, such as in the
Arctic and Antarctic Oceans, some marine types grow slowly and hence
are bound to be scarce.
Many believe that there is no absolute proof so far of the existence of
truly marine species, genera, etc. The only group considered truly
marine by Kriss was the new, widely distributed Class of Kraesilnikoviae. Unfortunately, Kriss was never able to cultivate and isolate
these organisms in pure culture in any medium and until this can be
done the Class must remain in doubt, Indeed, the validity of Kra88iEnikoviae has recently been questioned by Sorokin (1963) who showed
that the elements occurring in the slide immersion technique, and from
Which Kriss derived his descriptions, are nothing more than colloblasts of ctenophore tentacles.
It should perhaps just be mentioned that, if life originated in the
Ocean, one might just as well regard the terrestrial types &B being
O%inally marine forms acclimatized to conditions on land; and it
clear that the differences that exist between many of the species
143
the biological differences occurring in the different ecological situations.
Undoubtedly, many terrestrial forms find marine conditions unsuitable
for their existence; but where organisms are isolated close to land
masses it may be difficult to decide whether they are terrestrial contaminants, not adapted to the marine environment and merely surviving,
or species which can grow and multiply in the sea.
The criterion suggested by Butkevich and also by ZoBell for marine
types, viz. their relationship to the concentration and composition of
salt in the medium, corresponding to that of oceanic waters, is not
considered valid (Kriss, 1963). Salinity, at any rate, is not the only
specific feature of marine environments (see below). Moreover, terrestrial
forms exist which can tolerate high salt contents, e.g. in saline soils.
MacLeod and Onofrey (1966) state that true marine bacteria may well
prove to be distinguishable from land forms present as contaminants in
sea water, not by having a requirement for sea water, but rather by
having a readily detectable need for Na+ in the medium for growth.
Kriss (1963) himself lists some of the criteria which he believes would
distinguish marine species, in addition to the one just mentioned of
ZoBell and Butkevich. These are : (1) the ability of marine species to
reproduce in the sea and not just in isolated samples of water where
conditions might be very different from the natural ones ; (2) the finding
of the organism in fairly large numbers, implying growth and multiplication in the open sea where transport from land is impossible;
and (3) the frequency of encounter of the organism aa single cells in the
open sea. Thus, in areas where the concentration of easily assimilable
organic matter necessary for metabolism is very low, such as in the
Arctic and Antarctic Oceans, some marine types grow slowly and hence
are bound to be scarce.
Many believe that there is no absolute proof so far of the existence of
truly marine species, genera, etc. The only group considered truly
marine by Kriss was the new, widely distributed Class of Kraesilnikoviae. Unfortunately, Kriss was never able to cultivate and isolate
these organisms in pure culture in any medium and until this can be
done the Class must remain in doubt, Indeed, the validity of Kra88iEnikoviae has recently been questioned by Sorokin (1963) who showed
that the elements occurring in the slide immersion technique, and from
Which Kriss derived his descriptions, are nothing more than colloblasts of ctenophore tentacles.
It should perhaps just be mentioned that, if life originated in the
Ocean, one might just as well regard the terrestrial types &B being
O%inally marine forms acclimatized to conditions on land; and it
clear that the differences that exist between many of the species