Light
17
As mentioned above, in an artificially illuminated environment it is
not
ordinarin possible to reproduce annual or seasonal cycles of
light intensity and character, for reasons of equipment complexity.
It is therefore usual to try to reproduce only that part of the cycle
which best conforms to the aquarist’s requirements.
Wherever
light falls something living will usually develop. In
aquatic environments, algae of various types will appear, either on
fixed surfaces or floating free in the water, and it can be said«that,
unless some regulating factor is at work, all illuminated environments tend towards a situation in which all of the available light is
being used up by the algae. In an aquarium this produces the ‘pea—
soup effect”, which is obviously undesirable. Algal growth is generally
limited by plants of a higher order which can absorb or shield out
much of the light; by various aquatic animals such as snails and baby
fish which eat certain types of algae ; and by artificial methods such as
filtration (see p. 78) which physically remove some types, especially
the free-floating kinds. Thus, in a planted aquarium, we must ensure
that the plants selected dominate the algae present and discourage
too much new algal growth. Algae should not be eliminated alto—
gether, even if this were possible: they are a very necessary feature
of all artificial environments which are meant to be natural rather
than sterile. F urthermore, algae is at present the only readily avail—
able plant growth for many marine environments.
Where algae live in association with more desirable plants they
must be kept in a secondary position. To achieve full growth of the
major plants, the light available to them and their population in the
environment must be such as to represent that time in the cycle of
the wild environment when the plants are at their best. If we illustrate
the seasonal changes in a natural, planted pond it may help to clarify
the situation (see Figure 3).
In winter the pond is in a static condition in which plant growth
is either stationary or reduced to dormant root—stocks in the base
medium. Temperatures are at their lowest, daylight is dim and does
not last long, and any animals present are inactive and do not feed
enough to provide any appreciable wastes. Spring comes, daylight
and temperature increase, the animals ‘wake up’ and feed and produce wastes, and a plant—oriented condition develops. Those plants
which may have retained their last year’s growth will now carry on,
but the other plants whose old growth is non—existent or useless
exist only as root—stock in the base medium. These plants need to
grow all the way from the bottom to the surface or near it to make
the most efficient use of light, and this takes some time especially
17
As mentioned above, in an artificially illuminated environment it is
not
ordinarin possible to reproduce annual or seasonal cycles of
light intensity and character, for reasons of equipment complexity.
It is therefore usual to try to reproduce only that part of the cycle
which best conforms to the aquarist’s requirements.
Wherever
light falls something living will usually develop. In
aquatic environments, algae of various types will appear, either on
fixed surfaces or floating free in the water, and it can be said«that,
unless some regulating factor is at work, all illuminated environments tend towards a situation in which all of the available light is
being used up by the algae. In an aquarium this produces the ‘pea—
soup effect”, which is obviously undesirable. Algal growth is generally
limited by plants of a higher order which can absorb or shield out
much of the light; by various aquatic animals such as snails and baby
fish which eat certain types of algae ; and by artificial methods such as
filtration (see p. 78) which physically remove some types, especially
the free-floating kinds. Thus, in a planted aquarium, we must ensure
that the plants selected dominate the algae present and discourage
too much new algal growth. Algae should not be eliminated alto—
gether, even if this were possible: they are a very necessary feature
of all artificial environments which are meant to be natural rather
than sterile. F urthermore, algae is at present the only readily avail—
able plant growth for many marine environments.
Where algae live in association with more desirable plants they
must be kept in a secondary position. To achieve full growth of the
major plants, the light available to them and their population in the
environment must be such as to represent that time in the cycle of
the wild environment when the plants are at their best. If we illustrate
the seasonal changes in a natural, planted pond it may help to clarify
the situation (see Figure 3).
In winter the pond is in a static condition in which plant growth
is either stationary or reduced to dormant root—stocks in the base
medium. Temperatures are at their lowest, daylight is dim and does
not last long, and any animals present are inactive and do not feed
enough to provide any appreciable wastes. Spring comes, daylight
and temperature increase, the animals ‘wake up’ and feed and produce wastes, and a plant—oriented condition develops. Those plants
which may have retained their last year’s growth will now carry on,
but the other plants whose old growth is non—existent or useless
exist only as root—stock in the base medium. These plants need to
grow all the way from the bottom to the surface or near it to make
the most efficient use of light, and this takes some time especially