Hydrosere and Stages of Hydrosere

Hydrosere also known as hydarch succession, is the series of gradual change in biotic community that takes place within aquatic environments, eventually leading to the formation of climax land community.

When the body of water is large and deep, or when strong wave action and other powerful physical forces are present, succession leads to a stable aquatic community with minimal noticeable changes over time.

Hydrosere becomes noticeable primarily in small, shallow, artificial ponds or lakes, where wave action accelerates the process by eroding soil toward the edges.

Rapid erosion of soil hastens the filling process, leading to the disappearance of the body of water within a few years which in turn leads to replacement of water community by land plant communities. This type of succession may not always direct aquatic communities toward becoming land-based communities.

Stages of Hydrosere (Aquatic Succession)

• Phytoplankton stage
• Submerged stage
• Floating stage
• Reed-swamp stages
• Sedge-Marsh stage
• Woodland stage
• Climax forest stage

Phytoplankton Stage

• In the early stages of succession, algal spores enter the water body. Simple life forms, such as bacteria, algae, and other aquatic plants (phytoplankton) along with floating animals (zooplankton), act as pioneer colonizers.
• Through their life processes and eventual decomposition, these organisms contribute significant amounts of organic matter and nutrients, which settle at the bottom of the pond, forming a layer of muck.

Submerged Stage

• The phytoplankton stage is succeeded by the submerged plant stage.
• Once a layer of loose mud forms at the pond’s bottom, rooted submerged hydrophytes start to establish on this new substrate.
• This submerged vegetation typically appears in areas of ponds or lakes where the water depth is around 10 feet or more.
• Typical pioneer species include Elodea, Potamogeton, Myriophyllum, Ranunculus, Utricularia, Ceratophyllum, Vallisneria, Chara, and others.

• These plants create dense masses that significantly impact the habitat. When they die, their remains settle at the bottom of ponds or lakes, along with eroded soil particles and other transported materials.
• This accumulation gradually raises the pond or lake bottom, making the water shallower over time.
• As the stratification continues, conditions become less favorable for submerged vegetation but increasingly suitable for other types of plants.

Floating Stage

• As the water depth decreases to around 4 to 8 feet, the submerged vegetation begins to disappear, and floating plants gradually take over the area.
• Initially, submerged and floating plants grow together, but over time, the floating plants fully replace the submerged ones.
• The hardiest species in the area reproduce and establish themselves. Their broad leaves floating on the surface reduce light penetration to the deeper water layers.

• This reduced light penetration is likely a major factor in the decline of submerged plants.
• Ongoing interactions between plant communities and the aquatic environment lead to both chemical and physical changes in the habitat.
• More soil, along with plant remains, accumulates at the bottom, gradually raising the substrate vertically.
• Key floating plants that replace submerged vegetation include Nelumbo, Trapa, Pistia, Nymphaea, and Limnanthemum.

Reed-Swamp Stage

• As ponds and lakes become very shallow, with water depths of one to three feet, the habitat changes to a point where it is less suitable for floating plants.
• This shift allows other plants better adapted to the new environment to establish themselves. Gradually, the floating plants disappear, replaced by amphibious plants capable of thriving in both aquatic and aerial conditions.
• Key examples include Bothrioclova, Typha, and Phragmites (Reed).

• The foliage of these plants extends well above the water’s surface, with their roots typically anchored in the mud or submerged in the water.
• These leaves create a canopy over submerged and floating plants, blocking the light needed by those below. As a result, neither submerged nor floating plants can survive.
• Additionally, the continued accumulation of soil and plant debris at the bottom further reduces water depth, making the habitat increasingly unsuitable for the plants that were previously present.

• As the bottom approaches the water’s surface, secondary species like Polygonum and Sagittaria begin to appear.
• Over time, these plants trigger changes that make the habitat less suitable for many of the existing species, leading to the next step in the succession process.

Sedge-Marsh Stage

• The filling process eventually creates marshy soil, which may be too dry for the plants of the previous community.
• As a result, plants that are better suited to the new habitat begin to appear alongside the existing plants in a mixed state.
• Key plants adapted to marshy environments include members of the Cyperaceae and Poaceae families. Early invaders of the marshy area include species like Carex (sedge), Juncus (rushes), Themeda, Iris, Dichanthium, Eriophorum, Cymbopogon, Campanula, Mentha, Caltha, Gallium, Teucrium, and Cicuta.

• These plants thrive in the marshes, significantly altering the habitat in various ways.
• They absorb and transpire large amounts of water, while also trapping and accumulating plant debris, as well as wind- and water-borne soil particles.
• This leads to the development of a drier habitat, which may become unsuitable for the growth of typical hydrophytes.
• Over time, mesophytes begin to appear, eventually replacing the sedge vegetation entirely.

Woodland Stage

• Initially, some shrubs and later medium-sized trees form an open vegetation or woodland.
• These plants provide more shade and absorb and transpire large amounts of water, making the habitat drier.
• Shade-loving herbs may also grow beneath the trees and shrubs.
• Notable plants in the woodland community include species of Butea, Acacia, Cassia, Terminalia, Salix, and Cephalanthus.

Climax Forest Stage

• After a long period, the hydrosere can progress to the formation of climax vegetation. As soil levels rise significantly above the water level due to the gradual buildup of humus and soil particles, the habitat becomes drier and better aerated.
• In this environment, a stable, self-sustaining, and self-reproducing plant community, primarily consisting of woody trees, forms as a mesophytic forest.

• In the climax forest, a variety of plant types coexist, including herbs, shrubs, mosses, and shade-loving plants, each forming their own communities.
• Trees are the dominant species, controlling the entire vegetation.
• Bacteria, fungi, and other microorganisms are abundant in the climax vegetation, interacting with the habitat and enriching the soil with organic materials.
• At this stage, a perfect balance is achieved between the plant community and the habitat.

The entire sere is a complex, ongoing process of gradual change driven by biotic, topographic, or climatic factors. It is a slow process that is not easily observed in nature and may take thousands of years to reach the climax stage. However, sequence of hydrosere can be observed in a lake or pond, from the deepest areas towards the shallower edges.

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