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Question

Difficulty: MediumEcological Functions, Nutrient Cycles and Ecological Succession

Which of the following represents the correct chronological sequence of seral stages during primary hydrarch ecological succession (hydrosere) in a newly formed freshwater lake, from the initial pioneer stage to the terrestrial community?

  1. 1Phytoplankton stage
  2. 2Submerged plant stage
  3. 3Floating plant stage
  4. 4Reed-swamp stage
  5. 5Scrub stage

Answer

The correct chronological sequence of seral stages in primary hydrarch succession (hydrosere) is: Phytoplankton stage → Submerged plant stage → Floating plant stage → Reed-swamp stage → Scrub stage.
Primary hydrarch succession begins in a water body with microscopic phytoplankton as pioneers. Organic matter accumulation progressively shallow-up the basin, allowing rooted submerged plants to take root, followed by floating plants, amphibious reed-swamp plants, woody scrubs, and ultimately a terrestrial climax forest.

Step-by-Step Solution

1
Identify the pioneer community in an aquatic basin
The Phytoplankton stage is the pioneer stage consisting of unattached microscopic algae that colonize open water.
Pioneer species must be able to survive in deep, open aquatic environments without rooted anchorage.
2
Trace the early rooted submerged and floating vegetation stages
Dead phytoplankton create organic mud, allowing the Submerged plant stage (e.g., Vallisneria) followed by the Floating plant stage (e.g., Nymphaea) to form.
As organic matter and silt reduce water depth, light penetration and substrate depth favor rooted species.
3
Trace the transition from aquatic to semi-terrestrial and land vegetation
Decreasing water levels lead to the amphibious Reed-swamp stage, followed by soil drying which enables the Woody Scrub stage.
Transpiration by amphibious plants rapidly dries out the wetland, allowing terrestrial shrubs and eventually climate-adapted trees to replace aquatic species.

Key Concept

Hydrarch Ecological Succession (Hydrosere)
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Topics

Ecological Functions, Nutrient Cycles and Ecological Succession