Question

Difficulty: MediumEcological Succession

Match each seral stage of hydrarch succession (hydrosere) in a freshwater habitat on the left with its corresponding characteristic vegetation or ecological role on the right.

  • Phytoplankton stageMicroscopic algae such as diatoms and green algae that initiate organic mud deposition on the bare water bottom
  • Submerged macrophyte stageRooted aquatic plants like Vallisneria and Hydrilla that trap sediment and further raise the water bed
  • Floating macrophyte stageRooted plants with broad surface leaves like Nymphaea (water lily) that cut off light to underwater vegetation
  • Reed-swamp stageEmergent amphibious species like Typha and Phragmites that produce heavy organic debris and build up marshy soil

Answer

Phytoplankton stage pairs with microscopic algae; Submerged macrophyte stage pairs with rooted aquatic plants like Vallisneria; Floating macrophyte stage pairs with broad surface-leaved plants like Nymphaea; Reed-swamp stage pairs with emergent amphibious plants like Typha.
In hydrarch primary succession, microscopic phytoplankton act as pioneers in deep water. As organic debris accumulates on the bed, submerged plants establish, followed by floating-leaved species that block sunlight, and finally emergent reed-swamp plants that convert shallow waters into wet soil.

Step-by-Step Solution

1
Identify the pioneer community of a hydrosere.
The pioneer stage consists of unattached microscopic producers (phytoplankton) that start organic sedimentation.
Deep open water bodies lack soil anchorages for rooted plants initially.
2
Trace the sequence of rooted vegetation growth as water depth decreases.
Fully submerged rooted species grow first, followed by floating-leaved species as mud layers thicken, and finally emergent amphibious reeds near the water edges.
Each community alters light penetration and substrate depth, facilitating the establishment of the next seral stage.

Key Concept

Hydrarch succession stages (hydrosere)
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