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Difficulty: Very hardEnergy Flow, Food Chains, and Ecological Pyramids

In a tropical mangrove estuarine ecosystem, solar energy fixed during primary productivity flows through a sequential food chain. Consider the following four organisms inhabiting this ecosystem:

Arrange these organisms in order from HIGHEST to LOWEST available energy (kJ⋅m−2⋅yr−1kJ \cdot m^{-2} \cdot yr^{-1}) present at their respective trophic levels.

  1. 1Red mangrove tree (*Rhizophora mangle*)
  2. 2Mangrove tree crab (*Aratus pisonii*)
  3. 3Mangrove snapper (*Lutjanus griseus*)
  4. 4Osprey (*Pandion haliaetus*)

Answer

Red mangrove tree (*Rhizophora mangle*) → Mangrove tree crab (*Aratus pisonii*) → Mangrove snapper (*Lutjanus griseus*) → Osprey (*Pandion haliaetus*)
Energy flow through an ecosystem is unidirectional and non-cyclic. According to the Second Law of Thermodynamics and the 10% energy transfer rule, metabolic respiration, excretion, and heat dissipation result in inevitable energy losses at each step. Consequently, the total available energy per unit area per year strictly decreases from primary producers at the base (Red mangrove tree) to primary consumers (Mangrove tree crab), secondary consumers (Mangrove snapper), and tertiary consumers (Osprey).

Step-by-Step Solution

1
Identify the trophic level and ecological role of each listed organism.
Red mangrove is a primary producer (T1), Mangrove tree crab is a primary consumer (T2), Mangrove snapper is a secondary consumer (T3), and Osprey is a tertiary consumer (T4).
Determining trophic position is essential for establishing the sequence of energy transfer.
2
Apply the principles of ecological energy flow and thermodynamic laws across trophic levels.
Energy flow is strictly unidirectional, with roughly 80% to 90% of available energy lost as heat and metabolic work at each transfer step.
The Second Law of Thermodynamics dictates that energy transformation is inefficient, causing available energy to decrease progressively from lower to higher trophic levels.
3
Sequence the organisms from highest available energy (T1) to lowest available energy (T4).
The correct order from highest to lowest available energy is Red mangrove tree → Mangrove tree crab → Mangrove snapper → Osprey.
Primary producers hold the highest energy budget, while apex predators at the top of the food chain receive the least.

Key Concept

Unidirectional Energy Transfer and Thermodynamic Dissipation in Trophic Pyramids
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Topics

Energy Flow, Food Chains, and Ecological Pyramids

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