5
and is usually so used. Most authors regard the
total seston or plankton as consisting roughly of
net plankton (‘macro-, meso- and some microplankton’) and nannoplankton (some micro-,
nanno- and ultra-plankton).
Amongst the other terms that had been
employed, ‘euplankton’, implying a permanent
planktonic community; ‘meroplankton’, implying organisms with temporary planktonic phases
or stages; and ‘pseudoplankton’, for accidental
plankters, are often useful. The distinction
between the ‘limnoplankton’ of large lakes and
the ‘heleoplankton’ of ponds is useful, and the
term ‘potamoplankton’ for the plankton of rivers
is not infrequently employee. For the other terms,
the philological reader may consult Wilhelmi
( 1917 ) and Naumann ( 1931 ). Multiple prefi xes,
as in ‘eulimnoplankton’, are occasionally useful
but should be employed very discretely.
In brief, the organisms of a lake are conveniently grouped ecologically into those associated with the free water, those associated with
the solid–water interface and those at the surface fi lm.
The free water contains plankton, if not wholly
controlled, in its movements by turbulence, and
nekton, which in a lake can undertake swimming
movements in any direction in spite of turbulence. Most animal plankters are actually nektoplanktonic. The entire mass of suspended matter
in a volume of free water is called seston, the
non-living part, tripton. All of these terms may be
qualifi ed by prefi xes denoting size classes. The
euplankton constitutes the permanently planktonic species, the meroplankton those planktonic
only at certain times in their life histories.
1.6.9 Benthos
The organisms of the solid–water interface are
the ‘benthos’. The following terms appear to be
useful in characterising this assemblage. Benthos
could be classifi ed into the following types:
(a) Rhizobenthos: These are rooted in
substratum.
(b) Haptobenthos: These are adnate to the solid
surfaces.
(c) Herpobenthos: These grow or move through
mud.
(d) Psammon: These grow or move through sand.
(e) Endobenthos: These penetrate a solid
substratum.
When the haptobenthos is well developed, particularly on objects projecting into the free water, it
is called ‘lesion ’, fouling or ‘Bewuchs’. Many merobenthic animals may also be meroplanktonic.
The assemblage of organisms at the surface
fi lm is called ‘pleuston’; the ‘micro-pleuston’ is
often designated as ‘neuston’ and may be ‘hyponeuston’ below the fi lm or ‘epineuston’ above it.
Some large organisms living in air above the fi lm
on which they walk or run are best termed as ‘epipleuston’. Many meropleustonic animals which
reach the surface fi lm from below are adapted to
live at the surface for part of their lives.
The bottom area in contact with the water
exhibits striking zonation .
The following terms are recommended to
describe the zones ordinarily present:
(a) Epilittoral: This zone is completely above the
infl uence of the water.
(b) Supra-littoral: This zone is above the water
but receiving spray.
(c) Eulittoral: This zone lies between the high
and low seasonal levels.
(d) Infra-littoral: This zone is permanently covered but with rooted or adnate macroscopic
vegetation, often divisible into upper (emergent vegetation), middle (fl oating vegetation)
and lower (submerged vegetation).
(e) Littori-profundal: This is a transition zone
with scattered adnate algae.
(f) Profundal: This zone is the bared sediment
below biogeochemical compensation point.
In the terminology of seasonal change, if a
population rises to a maximum and declines
once in an annual cycle, it is monacmic ; if twice,
diacmic , etc.; if many times, polyacmic .
If a species has a single generation per year, it
is called univoltine ; if two bivoltine , etc.; if many,
multivoltine .
If a generation takes two or more years, the
ordinary terms biennial or perennial will be used.
If a bivoltine or multivoltine species changes
its mode of reproduction, ordinarily to produce
1.6 Defi nition of Certain General Ecological Terms
and is usually so used. Most authors regard the
total seston or plankton as consisting roughly of
net plankton (‘macro-, meso- and some microplankton’) and nannoplankton (some micro-,
nanno- and ultra-plankton).
Amongst the other terms that had been
employed, ‘euplankton’, implying a permanent
planktonic community; ‘meroplankton’, implying organisms with temporary planktonic phases
or stages; and ‘pseudoplankton’, for accidental
plankters, are often useful. The distinction
between the ‘limnoplankton’ of large lakes and
the ‘heleoplankton’ of ponds is useful, and the
term ‘potamoplankton’ for the plankton of rivers
is not infrequently employee. For the other terms,
the philological reader may consult Wilhelmi
( 1917 ) and Naumann ( 1931 ). Multiple prefi xes,
as in ‘eulimnoplankton’, are occasionally useful
but should be employed very discretely.
In brief, the organisms of a lake are conveniently grouped ecologically into those associated with the free water, those associated with
the solid–water interface and those at the surface fi lm.
The free water contains plankton, if not wholly
controlled, in its movements by turbulence, and
nekton, which in a lake can undertake swimming
movements in any direction in spite of turbulence. Most animal plankters are actually nektoplanktonic. The entire mass of suspended matter
in a volume of free water is called seston, the
non-living part, tripton. All of these terms may be
qualifi ed by prefi xes denoting size classes. The
euplankton constitutes the permanently planktonic species, the meroplankton those planktonic
only at certain times in their life histories.
1.6.9 Benthos
The organisms of the solid–water interface are
the ‘benthos’. The following terms appear to be
useful in characterising this assemblage. Benthos
could be classifi ed into the following types:
(a) Rhizobenthos: These are rooted in
substratum.
(b) Haptobenthos: These are adnate to the solid
surfaces.
(c) Herpobenthos: These grow or move through
mud.
(d) Psammon: These grow or move through sand.
(e) Endobenthos: These penetrate a solid
substratum.
When the haptobenthos is well developed, particularly on objects projecting into the free water, it
is called ‘lesion ’, fouling or ‘Bewuchs’. Many merobenthic animals may also be meroplanktonic.
The assemblage of organisms at the surface
fi lm is called ‘pleuston’; the ‘micro-pleuston’ is
often designated as ‘neuston’ and may be ‘hyponeuston’ below the fi lm or ‘epineuston’ above it.
Some large organisms living in air above the fi lm
on which they walk or run are best termed as ‘epipleuston’. Many meropleustonic animals which
reach the surface fi lm from below are adapted to
live at the surface for part of their lives.
The bottom area in contact with the water
exhibits striking zonation .
The following terms are recommended to
describe the zones ordinarily present:
(a) Epilittoral: This zone is completely above the
infl uence of the water.
(b) Supra-littoral: This zone is above the water
but receiving spray.
(c) Eulittoral: This zone lies between the high
and low seasonal levels.
(d) Infra-littoral: This zone is permanently covered but with rooted or adnate macroscopic
vegetation, often divisible into upper (emergent vegetation), middle (fl oating vegetation)
and lower (submerged vegetation).
(e) Littori-profundal: This is a transition zone
with scattered adnate algae.
(f) Profundal: This zone is the bared sediment
below biogeochemical compensation point.
In the terminology of seasonal change, if a
population rises to a maximum and declines
once in an annual cycle, it is monacmic ; if twice,
diacmic , etc.; if many times, polyacmic .
If a species has a single generation per year, it
is called univoltine ; if two bivoltine , etc.; if many,
multivoltine .
If a generation takes two or more years, the
ordinary terms biennial or perennial will be used.
If a bivoltine or multivoltine species changes
its mode of reproduction, ordinarily to produce
1.6 Defi nition of Certain General Ecological Terms