THE PRODUCTION OF MARINE PLANKTON
119
divided into the macrobenthic plants which are the typical large seaweeds which occur fixed to rocks around the coast, particularly in temperate regions of the world, and the microbenthic algae. The fixed seaweeds appear to form dense forests in regions where they are abundant,
and it might be felt that they make a very appreciable contribution to
the production of organic matter in the 8 8 8 3 . Equally conspicuous in
certain shallow marine regions are a few species of flowering plants,
such as Zostera, Ruppia, and Thalausia, which grow successfully in
fairly soft bottoms of sandy mud. Less obrious but of considerable
importance are the microbenthic algae which occur as single celled
diatoms and flagellates on rocks, muds and sands, and also on the
fronds of the larger seaweeds.
All plants require light as an energy source for the synthetic process.
Benthic forms are thus limited to a fairly shallow layer on the coasts.
The macrophytes are especially typical fringi ng the continental shelves
in temperate latitudes, but they are relatively uncommon in tropical
regions, and do not persist very far into really high latitudes. Around
island fringes, especially oceanic islands, the benthic algae have very
little foothold, but in shallow areas, constant turbulence and increased
turbidity sharply cut down light penetration, thus reducing the level a t
which these fixed benthic plants can live. Off north-western Europe
macrophytes may persist to a depth of some 30 metres; in clear waters
as off California or in the Mediterranean, somewhat deeper.
In shallow, muddy areas such as the sheltered Danish fjords, the
fixed algae and Zostera zones may not exceed 10 or 15 metres. Since the
average depth of the world’s oceans is approximately 3 800 metres, the
very small contribution of benthic plants to the production of the oceans
as a whole is only too obvious. Wood (1963a) quoting Braarud suggests
that the macrophytes may contribute some 2 94. Ryther (1 963) however
has recently suggested that we may be under-estimating the role of the
benthic algae in productivity and that they may contribute to the
particulate organic matter even some distance offshore.
Apart from macrophytes, the algal microbenthos on the bottom
deposit may add significantly to inshore production. Grrantved (1960)
has investigated the productivity of microbenthos and phytoplankton
in very shallow Danish fjords. For the more productive season March to
October phytoplankton production amounted to only approximately a
quarter that of the bottom microflora which consisted mainly of benthic
diatoms. In a further study Grrantved (1962) has investigated the production of microbenthos on exposed tidal flats. The plant population
was again mostly benthic diatoms attached to sand grains, though some
plankton cells descended to the bottom and were able to live for a time.
There was a marked seasonal variation in production but again the
119
divided into the macrobenthic plants which are the typical large seaweeds which occur fixed to rocks around the coast, particularly in temperate regions of the world, and the microbenthic algae. The fixed seaweeds appear to form dense forests in regions where they are abundant,
and it might be felt that they make a very appreciable contribution to
the production of organic matter in the 8 8 8 3 . Equally conspicuous in
certain shallow marine regions are a few species of flowering plants,
such as Zostera, Ruppia, and Thalausia, which grow successfully in
fairly soft bottoms of sandy mud. Less obrious but of considerable
importance are the microbenthic algae which occur as single celled
diatoms and flagellates on rocks, muds and sands, and also on the
fronds of the larger seaweeds.
All plants require light as an energy source for the synthetic process.
Benthic forms are thus limited to a fairly shallow layer on the coasts.
The macrophytes are especially typical fringi ng the continental shelves
in temperate latitudes, but they are relatively uncommon in tropical
regions, and do not persist very far into really high latitudes. Around
island fringes, especially oceanic islands, the benthic algae have very
little foothold, but in shallow areas, constant turbulence and increased
turbidity sharply cut down light penetration, thus reducing the level a t
which these fixed benthic plants can live. Off north-western Europe
macrophytes may persist to a depth of some 30 metres; in clear waters
as off California or in the Mediterranean, somewhat deeper.
In shallow, muddy areas such as the sheltered Danish fjords, the
fixed algae and Zostera zones may not exceed 10 or 15 metres. Since the
average depth of the world’s oceans is approximately 3 800 metres, the
very small contribution of benthic plants to the production of the oceans
as a whole is only too obvious. Wood (1963a) quoting Braarud suggests
that the macrophytes may contribute some 2 94. Ryther (1 963) however
has recently suggested that we may be under-estimating the role of the
benthic algae in productivity and that they may contribute to the
particulate organic matter even some distance offshore.
Apart from macrophytes, the algal microbenthos on the bottom
deposit may add significantly to inshore production. Grrantved (1960)
has investigated the productivity of microbenthos and phytoplankton
in very shallow Danish fjords. For the more productive season March to
October phytoplankton production amounted to only approximately a
quarter that of the bottom microflora which consisted mainly of benthic
diatoms. In a further study Grrantved (1962) has investigated the production of microbenthos on exposed tidal flats. The plant population
was again mostly benthic diatoms attached to sand grains, though some
plankton cells descended to the bottom and were able to live for a time.
There was a marked seasonal variation in production but again the