How it Works
The simulation integrates a 4-level nutrient-phytoplankton-zooplankton-fish-apex (NPZFA) model using Euler integration. Nutrients are supplied externally at rate I and recycled from dead biomass. Phytoplankton grow on nutrients via Michaelis-Menten kinetics and are grazed by zooplankton. Each level eats the one below and is eaten by the one above, following Lotka-Volterra-style terms with efficiency factors.
The particle visualization on the left shows relative population sizes as animated plankton, fish, and predator icons. The time-series chart on the right tracks all populations over 500 time steps.
dP/dt = r·N·P/(K+N) - g·P·Z - m_P·P
dZ/dt = e·g·P·Z - p·Z·F - m_Z·Z
dF/dt = e·p·Z·F - q·F·A - m_F·F - fishing·F
dA/dt = e·q·F·A - m_A·A
e = trophic efficiency (10%), g,p,q = predation rates
Frequently Asked Questions
What is a trophic web?
A trophic web (food web) describes the feeding relationships in an ecosystem. Each trophic level represents a position in the energy transfer chain: producers (phytoplankton) → primary consumers → secondary consumers → apex predators.
What is the Lotka-Volterra model?
The Lotka-Volterra equations model predator-prey dynamics: prey grows logistically and is consumed by predators; predators grow by consuming prey and die at a natural rate. The system produces characteristic oscillations in both populations.
What role do phytoplankton play in the ocean?
Phytoplankton are microscopic algae that form the base of most marine food webs. They perform about half of Earth's photosynthesis, fixing CO₂ into organic matter that fuels higher trophic levels and drives the biological carbon pump.
What is the 10% rule in ecology?
The 10% rule states that on average only about 10% of energy is transferred from one trophic level to the next. The rest is lost as heat through respiration, excretion, and decomposition, limiting the number of viable trophic levels to 4–5.
How does nutrient cycling work in the ocean?
Dead organisms and excreta sink and are decomposed by bacteria, releasing dissolved inorganic nutrients (nitrogen, phosphorus) that fuel phytoplankton growth. Upwelling brings nutrient-rich deep water to the surface, completing the cycle.
What causes trophic cascades?
A trophic cascade occurs when changes at one level ripple through the food web. For example, removing apex predators (sharks) releases pressure on fish, which then over-graze zooplankton, causing phytoplankton blooms and hypoxic dead zones.
What is eutrophication?
Eutrophication is the excessive enrichment of water with nutrients, typically nitrogen and phosphorus from agricultural runoff. This causes algal blooms that deplete oxygen when they decompose, creating dead zones harmful to marine life.
How does climate change affect ocean food webs?
Warming oceans stratify more strongly, reducing nutrient upwelling and phytoplankton productivity. Ocean acidification affects calcifying organisms. Range shifts and phenological mismatches disrupt predator-prey timing across trophic levels.
What is carrying capacity in ecology?
Carrying capacity (K) is the maximum population size an environment can sustain indefinitely given available resources. When populations exceed K, resource limitation, disease, or predation reduce them back toward equilibrium.
What is the biological carbon pump?
The biological carbon pump is the process by which phytoplankton fix atmospheric CO₂ through photosynthesis and sequester carbon to the deep ocean via sinking organic particles. It removes about 10 GtC per year from the atmosphere.