It is a type of succession that happens in water. This kind of change does not always lead to the development of land communities from aquatic communities. If the body of water is big and deep, or if the waves are strong and there are other strong physical forces at work, the succession leads to a stable aquatic community in which any big changes are hard to notice.
Succession can only be seen when plant communities move into small, shallow, man-made ponds, lakes, etc., where waves speed up the process by allowing soil to wash away from the center to the edges. So, the process of filling up also happens quickly, and the body of water disappears within a few years.
Figure 1 shows the different kinds of plants that grow at different depths in a pond. There are floating plants in the middle, rooted hydrophytes in the shallows, amphibious plants in the mud around the edges, and trees growing in dry areas.
7 successional stages of hydrosere Figure 1: Zonation of aquatic vegetation (Hydrophytes) along a pond and river banks. Note the changes in vegetation with water depth.
1. Phytoplankton stage
At the beginning of the succession process (Figure 2), spores of algae are brought into the body of water. Simple forms of life that float in water, like bacteria, algae, and many other aquatic plants and animals (called phytoplankton and zooplankton, respectively), were the first to settle. Due to their different ways of living, all of these organisms add a lot of organic matter and nutrients to the pond, and when they die, they sink to the bottom and form a layer of muck.
2. Submerged stage
The stage after phytoplankton is the submerged plant stage. When a thin layer of loose mud forms on the bottom of the pond, some submerged plants with roots start to grow on this new surface. The submerged aquatic vegetation grows in ponds or lakes where the water is at least 10 feet deep. Elodia, Potamogeton, Myriophyllum, Ranunculus, Utricularia, Ceratophyllum, Vallisnena, Chara, etc., are some of the pioneers.
These plants grow together in a tangled mass that changes the environment in a big way. When these plants die, their dead parts sink to the bottom of lakes and ponds. The pieces of soil that have been worn away and other things that have been moved also end up at the bottom. This slowly brings the water level up in ponds and lakes. As this process of stratification goes on, the body of water gets shallower and shallower, making it less suitable for the plants that live under the water and more suitable for other plants.
3. Floating stage
When the water gets to about 4 to 8 feet deep, the plants that are under the water start to move away from their original places and the plants that float start to grow in that area. At first, plants that grow underwater and plants that grow on the surface grow together. Over time, however, the plants that grow underwater are completely replaced. The area’s most tolerant species are able to reproduce and keep going. Their big leaves that float on the surface of the water block light from getting to the deeper layers of water.
This could be one of the main reasons why plants that live in water die. Because plant communities and the water environment are always interacting, the habitat changes both physically and chemically. More soil and dead plant parts brought there by water and air settle at the bottom. So, the substratum goes up in a straight line. Nelumbmm, Trapa, Pistia, Nymphaea, Limnanthemum, etc. are all important floating plants that take the place of submerged plants.
Figure 2: Community succession in an open pond
4. Reed-swamp stages
When the water in ponds and lakes gets too shallow (one to three feet) and the environment changes so much that floating plants can’t live there anymore, other plants that do well in the new environment will move in. Under these conditions, floating plants start to die off slowly, and their places are taken by amphibious plants that can live well in both water and air. Bothrioclova, Typha, Phragmites (Reed), etc. are all good examples.
The leaves of these plants stick out well above the surface of the water, and their roots are usually either in mud or in water. The foliage leaves form a cover over the plants that are submerged or floating, blocking the light from getting to the plants underneath. Under these conditions, neither plants that sink or float can live. Adding more soil and dead plants to the bottom makes the water level lower and the habitat less good for the plants that are already there.
When the bottom is very close to the water’s surface, secondary species like Polygonum, Sagittaria, and others start to grow there. Later, they also cause reactions that make the habitat less good for most of the existing species, which leads to the next step in the successional process.
5. Sedge Marsh stage
At the end of the filling process, the soil is muddy and may be too dry for the plants that were already there. Now, plants that have done well in the new environment are starting to show up in the community that was already there. Members of the cyperaceae and grameae families are important plants that do well in wet places. The first plants to move into a marshy area are species of sedge (Carex) and rush (Juncus), as well as species of Themeda, Iris, Dichanthium, Eriophorum, Cymbopogon, Campanula, Mentha, Caltha, Gallium, Teucrium, Cicuta, etc.
Because these plants grow best in marshes, they change the habitats in a number of ways. They take in and release (transpire) a lot of water, and they also catch and collect plant debris and soil particles carried by the wind and water. Because of this, the environment becomes dry, which may make it impossible for normal hydrophytes to grow. Slowly, the mesophytes start to grow, and after some time, they completely replace the sedge plants.
6. Woodland stage
At first, there are some shrubs, and then, as time goes on, there are medium-sized trees. This is called an open woodland. More shade is made by these plants, which also take in and release (transpire) a lot of water. So, they make the environment drier. Under the trees and bushes, you can also grow herbs that like to be in the shade. Plants like Buteazon, Acacia, Cassia, Terminalia, Salix, Cephalanthus, and others stand out in a woodland community.
7. Climax forest
After a very long time, the hydrosere could cause climax vegetation to grow. As humus and soil particles slowly build up, they raise the level of the soil above the water level. This makes the habitat much drier and more airy. In this kind of environment, a mesophytic forest grows, which is a well-adapted plant community that takes care of itself, reproduces itself, and is mostly made up of woody trees.
All kinds of plants can be found in the climax forest. Herbs, bushes, mosses, and plants that like to grow in the shade are their own communities. Trees are the most important plants, and they control all the other plants. Microorganisms like bacteria, fungi, and others are more common in the climax vegetation. They change the environment in ways that make the soil full of organic matter. At the climax stage, the plant community and its environment work together perfectly.
Now, it’s clear that the whole sere is a complex that is always changing, but only slowly. These changes are caused by biotic, topographic, or climatic factors. The process is very slow and can’t be seen in nature. The climax stage may not happen for thousands of years. One can still see the order of the hydrosere as he moves from the deepest part of the lake or pond to the shallower edge.