Zooplankton
105
horizontal daytime tow-nets. Some of them have mentioned the limitations
and insufficiency of this method because a significant part of the reef
zooplankton is composed of demersal and meroplanktonic forms, which
hide in the bottom biotopes during daytime and move to the water column
only at night (Renon 1977). Therefore, the daytime tow-nets employed in
those studies were not suitable for providing a real picture. Another method
was used by Johannes et al. (1970). They fixed plankton nets up the reef flat
surface in a direction meeting the incoming current. But the zooplankton
biomasses they thus obtained were negligible - 5 mg m -3 in daytime and
only 8 mg m -3 at night. This method was obviously invalidated by
disregarding the ability of demersal animals to move on the solid surface and
so to crawl out from the net.
New developments in methodology were the use of nocturnal tows up the
bottom by scuba divers (Emery 1968; von Hentig 1971; Hickel 1972; Porter
1974b) and airlift to get samples of demersal zooplankton (Emery 1968).
Later various traps were used, similar to those which are employed by
entomologists to collect flying insects emerging from water or from the soil
(Porter and Porter 1977; Alldredge and King 1977; Mc William et al. 1981;
Sale et al. 1976; Riitzler et al. 1980). But, actually, trap data cannot give
adequate quantifications of zooplankton number and biomass (Hobson and
Chess 1979). The traps catch and accumulate an excess of holoplanktonic
zooplankters or mysids, which use the trap as shelter. Thus the use of traps
could lead to overstimating holoplanktonic zooplankters or underestimating
a portion of demersal animals, like some of the gammarids, which do not
rise far from the bottom even at night, or like animals with negative
phototaxis. The author used a simple but from his viewpoint representative
method of collecting quantitative samples of zooplankton by passing 100250 I of water, taken at night from the boat with a bucket, through .the
plankton net. This method was especially efficient in shallows over the reef
where it was difficult to catch zooplankton with the aid of a net, especially at
night.
As regards the microzooplankton, including planktonic animals less than
0.2 mm in size, the early researchers have used for this purpose methods
which were not actually quantitative meaning the sedimentation method for
the counting of planktonic ciliates, or the method of catching them and also
the larvation with the plankton nets. Recently, new methods were offered
and used, which made a real quantifications of the main groups of microzooplankton possible. The fraction of larger eucariotic microzooplankton -
the larvaton (40-200 size) - has been counted quantitatively by the author
in 3-1 samples concentrated by reverse filtration through 2-4 J.l Nuclepore
filters into a volume of 30 ml, and then - by sedimentation after a weak
Utremol fixation - into a volume of 5 ml. Another method used by the
author was the direct epifluorescence microscopic counting of these microzooplankters stained with acridine orange on the black Nuclepore filters
(4 J.l pore size). The ciliates could be quantitatively counted in fresh intact
105
horizontal daytime tow-nets. Some of them have mentioned the limitations
and insufficiency of this method because a significant part of the reef
zooplankton is composed of demersal and meroplanktonic forms, which
hide in the bottom biotopes during daytime and move to the water column
only at night (Renon 1977). Therefore, the daytime tow-nets employed in
those studies were not suitable for providing a real picture. Another method
was used by Johannes et al. (1970). They fixed plankton nets up the reef flat
surface in a direction meeting the incoming current. But the zooplankton
biomasses they thus obtained were negligible - 5 mg m -3 in daytime and
only 8 mg m -3 at night. This method was obviously invalidated by
disregarding the ability of demersal animals to move on the solid surface and
so to crawl out from the net.
New developments in methodology were the use of nocturnal tows up the
bottom by scuba divers (Emery 1968; von Hentig 1971; Hickel 1972; Porter
1974b) and airlift to get samples of demersal zooplankton (Emery 1968).
Later various traps were used, similar to those which are employed by
entomologists to collect flying insects emerging from water or from the soil
(Porter and Porter 1977; Alldredge and King 1977; Mc William et al. 1981;
Sale et al. 1976; Riitzler et al. 1980). But, actually, trap data cannot give
adequate quantifications of zooplankton number and biomass (Hobson and
Chess 1979). The traps catch and accumulate an excess of holoplanktonic
zooplankters or mysids, which use the trap as shelter. Thus the use of traps
could lead to overstimating holoplanktonic zooplankters or underestimating
a portion of demersal animals, like some of the gammarids, which do not
rise far from the bottom even at night, or like animals with negative
phototaxis. The author used a simple but from his viewpoint representative
method of collecting quantitative samples of zooplankton by passing 100250 I of water, taken at night from the boat with a bucket, through .the
plankton net. This method was especially efficient in shallows over the reef
where it was difficult to catch zooplankton with the aid of a net, especially at
night.
As regards the microzooplankton, including planktonic animals less than
0.2 mm in size, the early researchers have used for this purpose methods
which were not actually quantitative meaning the sedimentation method for
the counting of planktonic ciliates, or the method of catching them and also
the larvation with the plankton nets. Recently, new methods were offered
and used, which made a real quantifications of the main groups of microzooplankton possible. The fraction of larger eucariotic microzooplankton -
the larvaton (40-200 size) - has been counted quantitatively by the author
in 3-1 samples concentrated by reverse filtration through 2-4 J.l Nuclepore
filters into a volume of 30 ml, and then - by sedimentation after a weak
Utremol fixation - into a volume of 5 ml. Another method used by the
author was the direct epifluorescence microscopic counting of these microzooplankters stained with acridine orange on the black Nuclepore filters
(4 J.l pore size). The ciliates could be quantitatively counted in fresh intact