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Limiting Factors for Algae

If you placed a small sample of algae in an appropriate growth medium with access to sunlight, you would observe that after an initial lag period, growth would be very rapid, the population doubling in size in a matter of days. This period of logarithmic growth would eventually slope off, then begin to decline. By carefully observing growth under different conditions, scientists are able to identify the factors limiting the growth of organisms.

Sunlight
- Algae are photosynthetic and require sunlight to grow. Within a given area, even with a theoretically unlimited supply of all other nutrients, an algal colony can only grow so large before the algae are competing with one another for sunlight. Suspended solid particles can limit algae growth by blocking sunlight. Algae can also lose precious sunlight to dissolved organic pigments. Though translucent, unlike solid particles, these effectively tint the water, absorbing some frequencies of light and reducing the amount of light available for algal photosynthesis.
Nitrogen
- Nitrogen is the most significant limiting factor for algal growth in most marine environments. Algae need it to survive, but its supply is limited, especially in the middle of the oceans. The large amount of nitrogen present in waste produced by human industry and agriculture drives most algal blooms. Algae living in coastal areas, which formerly had a limited supply of nitrogen, now prosper from an essentially unlimited supply. They grow unchecked until they begin to die from overcrowding and competition for sunlight.
Phosphorus
- Phosphorus is the primary limiting factor for fresh water algae. High concentrations of phosphates, much of it from cleansers and detergents that end up in our waterways, spur the algal blooms in lakes and rivers. The abundant presence of an otherwise limiting nutrient stimulates prolific algae growth. Decomposition of this overgrowth by aerobic bacteria depletes the water of oxygen, killing animals that require dissolved oxygen. Anaerobic bacteria decompose these animals, producing toxic by-products that kill even more animals, in a destructive chain reaction.
Iron
- A 2006 NASA study found that iron was a surprisingly significant growth factor for algae. Scientists were well aware that algae required some iron for growth, but they had considered nitrogen and phosphorus dependence to be far more significant. They expected the unavailability of these nutrients to limit growth before limited iron had any effect. The study identified limiting nutrient growth factors for algae growing in the tropical Pacific. It concluded that while nitrogen was the most significant limiting factor in the northern portion of the tropical Pacific, iron was the limiting nutrient in the rest of the region.

Nature