UNDERSTANDING OLIGOTROPHIC OCEANS : CAN THE EASTERN
MEDITERRANEAN BE A USEFUL MODEL ?
T.BERMAN 1 , Y.AZOV 1 and D.TOWNSEND 2
lIsrael Oceanographic & Limnological Research Co.,.
P.O. Box 8030, Haifa, Israel
2. 1
b
B~ge ow La oratory for Ocean Sciences, West Boothbay Harbor,
Mai~e 04575, USA.
This paper will pose some general questions concerning marine ecosystems in the
light of major discoveries and observations in the past decade. More specifically
we shall apply these to oligotrophic seas and present some preliminary data to
support the suggestion that the Eastern Mediterranean Basin may serve as a convenient
model for the study of such environments.
The following points should be considered (not necessarily in order of precedence).
1) It has become increasingly evident that a very significant portion of phytoplankton biomass and photosynthetic activity in the open ocean, especially in oligotrophic regions, is associated with organisms smaller than 3 pm or even 1 ~m (Johnson
and Sieburth 1979; Waterbury et al. 1979; Li et ~. 1983). Many of these small
phytoplankters are blue-greens (Cyanobacteria), an algal division which was previously
believed to be rather poorly represented in the pelagic flora. Often these ultra
(or pico) phytoplankton are relatively more numerous towards the bottom of the euphotic zone or in deep chlorophyll maxima (see below) and there is some evidence that
they' are adapted to low light in the green region of the spectrum (Platt et al. 1983;
Glover et al. 1984). Fundamental, unresolved, questions concerning these organisms
are: what are their growth rates in situ and what organisms are capable of grazing
on them?
2) The possible functions of the heterotrophic protozoa, until recently a Comparatively neglected component of the plankton, have been attracting increasing research scrutiny (Banse 1982; Sherr and Sherr 1983). Microciliates such as tintinnids
have been found to be major grazers of phytoplankton in some areas (Rassoulzadegan
and Eti~nne 1981; Capriulo and Carpenter 1983) and the smaller microflagellates may
be important consumers of bacteria and ultraphytoplankton (Fenchel 1982; Sherr and
Sherr 1983; Sherr et ~. 1983). As yet, however, there are few reliable data on the
amounts of carbon biomass which are grazed by the heterotrophic microzooplankton or
the extent to which these organisms in their turn serve as prey. Growth efficiencies
are a basic but as yet, an almost unknown parameter which are required for understanding the ecological roles of these protozoans.
MEDITERRANEAN BE A USEFUL MODEL ?
T.BERMAN 1 , Y.AZOV 1 and D.TOWNSEND 2
lIsrael Oceanographic & Limnological Research Co.,.
P.O. Box 8030, Haifa, Israel
2. 1
b
B~ge ow La oratory for Ocean Sciences, West Boothbay Harbor,
Mai~e 04575, USA.
This paper will pose some general questions concerning marine ecosystems in the
light of major discoveries and observations in the past decade. More specifically
we shall apply these to oligotrophic seas and present some preliminary data to
support the suggestion that the Eastern Mediterranean Basin may serve as a convenient
model for the study of such environments.
The following points should be considered (not necessarily in order of precedence).
1) It has become increasingly evident that a very significant portion of phytoplankton biomass and photosynthetic activity in the open ocean, especially in oligotrophic regions, is associated with organisms smaller than 3 pm or even 1 ~m (Johnson
and Sieburth 1979; Waterbury et al. 1979; Li et ~. 1983). Many of these small
phytoplankters are blue-greens (Cyanobacteria), an algal division which was previously
believed to be rather poorly represented in the pelagic flora. Often these ultra
(or pico) phytoplankton are relatively more numerous towards the bottom of the euphotic zone or in deep chlorophyll maxima (see below) and there is some evidence that
they' are adapted to low light in the green region of the spectrum (Platt et al. 1983;
Glover et al. 1984). Fundamental, unresolved, questions concerning these organisms
are: what are their growth rates in situ and what organisms are capable of grazing
on them?
2) The possible functions of the heterotrophic protozoa, until recently a Comparatively neglected component of the plankton, have been attracting increasing research scrutiny (Banse 1982; Sherr and Sherr 1983). Microciliates such as tintinnids
have been found to be major grazers of phytoplankton in some areas (Rassoulzadegan
and Eti~nne 1981; Capriulo and Carpenter 1983) and the smaller microflagellates may
be important consumers of bacteria and ultraphytoplankton (Fenchel 1982; Sherr and
Sherr 1983; Sherr et ~. 1983). As yet, however, there are few reliable data on the
amounts of carbon biomass which are grazed by the heterotrophic microzooplankton or
the extent to which these organisms in their turn serve as prey. Growth efficiencies
are a basic but as yet, an almost unknown parameter which are required for understanding the ecological roles of these protozoans.