Plants As Tools And Pests

In many situations, plants are a vital tool used both by man and in nature for ecological purposes. Fast-growing plants are often used to remove wastes from water, allowing the cleanup of polluted waterways or to prevent toxic algal blooms from occurring in nutrient-rich areas. Aquarists use plants as a form of filtration, both in aquariums and ponds. Some special pond filters are designed to house a bed of aquatic or marginal plants that remove nutrients and toxic metals from the water, preventing algae and improving the water quality for the fish.

However, in the last few decades, the increase in the use of plants for commercial and ecological purposes and by aquarists has had its drawbacks. Any natural habitat that has not been significantly altered has a natural balance between all the plants, animals, and organisms that inhabit it. Thousands of years of natural selection have ensured that the plants and animals that live there will exist happily alongside the other inhabitants. If a plant or animal from another place is introduced into that habitat, three things could happen. The first, and most likely, is that the new species will not survive and simply dies out within a few years or less. The second is that it may survive, reproduce, and sustain a level population alongside the existing species, although this is unlikely. The third possibility is that it may survive, reproduce, and increase its population. During this time, it will compete with native species for resources, and if it has a significant advantage, it may out-compete them and drive them out The balance of nature In the area can be seriously disturbed in this way.

This can happen when commercially grown plants are introduced into local rivers, ponds, lakes, and waterways. The species that are introduced are called alien species and if they survive and spread, have the potential to kill off native species. This may have secondary effects, such as starving native animals of food sources, altering the composition of the substrate, blocking up waterways, and removing potential nesting or breeding sites.

An aquarium is an enclosed environment, and providing the chosen plants remain in it, there is no danger to local rivers and waterways. However, if plants are discarded in such locations, there is a great risk of introducing alien plants. The consequences of this can be ecologically catastrophic, so aquarists must behave responsibly. Any waste plants should be destroyed.

How Many Alien Species Are There

Below: Many Cryptocoryne spp. grow in conditions that other plants do not favor. However, their slow-growing nature may mean that alien species could compete with them for light and nutrients.

Alien Aquatic Plants

Left: In the right conditions, one species of aquatic plant (here water hyacinth, Eichhornia crassipes) will spread and dominate a large stretch of water, allowing little else to grow. This can be advantageous or detrimental, depending on the effect on the environment.

Below: Many Cryptocoryne spp. grow in conditions that other plants do not favor. However, their slow-growing nature may mean that alien species could compete with them for light and nutrients.

reproduce out of water. Bog plants usually have slightly thicker leaves, because their thicker cuticle helps to prevent the leaves from drying out when the water level drops. As we have seen, some plants produce differently shaped leaves, depending on whether they are submerged or out of water.

Fast-flowing streams

In small streams there is little room for plant growth, minimal substrate, high oxygenation, and few nutrients, but often plenty of light. These conditions are not ideal for aquatic plants and the growth of substantial, large-leaved plants is not usually possible. Carbon dioxide levels are usually low in such conditions, and the strong light is not as useful as you might expect, because photosynthesis is limited by carbon dioxide levels. Often, water movement is quite strong, making stemmed plants prone to damage. Therefore, smaller plants are often found in fast-flowing

Right: Cryptocoryne species are ideally suited to the shallow depths of tropical streams. They flourish in specific environments where other plants would fail to grow.

Right: Cryptocoryne species are ideally suited to the shallow depths of tropical streams. They flourish in specific environments where other plants would fail to grow.

Shallow Stream Co2 Planted Tank

streams, since they do not require large amounts of substrate or nutrients for growth. Mosses and hairlike plants, such as Eleocharis sp., thrive in this environment, as do plants that root to wood and rocks, such as Java fern (Microsorium sp.j.

River plants

Rivers have a wide range of habitats throughout their length, so classifying plants as "adapted for river life" would be futile. Most aquatic plants come from various areas of rivers. Echlnodorus sp. are often found growing above water in the middle of shallow rivers, or along the edges of deeper rivers. In these situations they can take advantage of the combination of nutrients from the riverbed, stronger lighting above water, and carbon dioxide from the atmosphere. Cryptocorynes and slow-growing plants

Light zones of a river

Once the water gets a little deeper, plants grow longer roots and thicker stems. They produce large aquatic and aerial leaves, which can use strong light and C02 from the surface.

Toward the center, the water is faster flowing and the light is bright. The plants here have flexible stems that bend with the flow, so aerial leaves are rarely produced.

In slow-moving, shallow water, shaded by overhanging vegetation, plants are small and slow growing, needing little rooting depth and less light.

In a typical river or large stream, there are zones of light and water depth where different plants grow.

Water Lettuce AquariumPistia Stratiotes Aquarium

Left: Water lettuce (Pistia stratiotes) will grow to significantly different sizes depending on its environment. In the aquarium, the leaves will grow up to 2 in (5 cm), whereas in an open stretch of water, they will grow more than three times bigger.

Many aquatic plants are naturally bog plants with a submerged leaf form, and although they grow and reproduce perfectly well underwater, in their natural habitats they are usually found growing above water in marshy conditions or very shallow water. Lobelia cardinalis is often sold both as a pond marginal plant and an aquatic plant. In the aquarium it is a short plant (usually 6 in [15 cm], but up to 12 in [30 cm]), with fleshy leaves of a light green to purple-red color. When grown as a bog plant it reaches over 36 in (90 cm) in height and produces numerous red flowers set against beetroot-red leaves.

Below: The conditions that plants encounter in the aquarium are different from those found in nature. They respond by producing different leaf shapes, colors, and sizes to adapt to the aquarium environment. The results can be stunning, even though the display does not recreate the natural world.

are found near the edges, where they are often shaded by overhanging vegetation. Stem plants are also found toward the edges, but normally at a depth of at least 16-20 in (40-50 cm). Floating plants are not as common and are found only in the wider, open, and slow-moving sections.

Growth in nature and aquarium

The growth of plants is affected a great deal by their environment, and many plants appear quite different when grown in the aquarium compared to their wild counterparts. In the aquarium there is generally less available substrate, no seasonal variations, different light conditions, and variable water qualities. All these factors cause aquarium plants to grow slightly differently than they would in nature. In many cases, plants in the aquarium will not grow as large as in the wild. A notable example is the water lettuce (Pistia stratiotes). In the aquarium it produces compact leaves, normally up to about 2 in (5 cm) across. However, in its natural environment or in ponds, the leaves are much larger and fleshier, growing up to 6 in (15 cm) in diameter.

Water quality and filtration

Pure water is made up from two hydrogen molecules and one oxygen molecule (H20). However, the water in which you house living aquatic organisms such as fish and plants is much more than a simple combination of molecules. Water can be described as hard or soft, alkaline or acid, and acts as a carrier for a wealth of minerals, nutrients, toxins, bacteria (both beneficial and harmful), and pollutants. Providing good water quality means ensuring that all these factors are at the correct level, so that the water in the aquarium is not only safe for fish and plants, but actively encourages their health and growth.

There are many different interactions between chemicals and minerals that alter the properties of water. To make things even more complicated, both plants and fish are found in many different habitats, each with their own water quality parameters. However, the basic principles of water quality and filtration are universal and apply to all aquarium environments. Other than the functions of nutrients, which are described on pages 66-77, all the important aspects of water quality and filtration in a planted aquarium are included in this chapter.


In all aquariums, you can employ four types of filtration in one way or another: mechanical, biological, chemical, and sterilization. The function of filtration in the aquarium is to remove or neutralize substances that may be harmful, and to remove visible debris from the water. In nature, a combination of naturally occurring bacteria, organisms, and vegetation provide the waste disposal means to keep water quality stable and pollutants at a minimal level. In the aquarium, the ratio of plants and fish to the volume of water is far higher than in nature. This means that there is more waste to be removed than the natural processes can cope with. Artificial filtration is therefore essential if you are to maintain a healthy aquarium.

Mechanical filtration is the physical removal of matter from the water. In most cases, mechanical filtration simply removes visible debris and performs a purely aesthetic function. Generally speaking, mechanical filtration is achieved by passing water through a sponge, or series of sponges, to trap debris. The sponges can then be removed and cleaned. In the planted aquarium, mechanical filtration is important because it removes suspended debris that may otherwise collect in the

Below: These angelflsh (Pterophyllum scalare) from South American rivers enjoy the same warmth and soft water conditions as many popular aquarium plants.

Below: These angelflsh (Pterophyllum scalare) from South American rivers enjoy the same warmth and soft water conditions as many popular aquarium plants.

Aquarium Plants South America

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