Reef-building corals are found only in areas where algae can survive. The algae, especially Zooxanthellae, are more efficient than the coral-eating phytoplankton. Although phytoplankton is the primary source of food for the reef organisms, their population in a typical aquarium is extremely low, that is, it gets consumed faster than it can be produced. Although they can be cultured, the process is expensive, and the product shelf life is limited. Research indicates that even if phytoplanktons are ingested, they are not digested and regurgitated (Sorokin 23).
Corals depend exclusively on phytoplankton and algae for feeding. The algae include; zooxanthellae algae, coralline algae, and turf algae. Zooxanthellae algae are of immense importance in the survival of corals. They live inside the coral polyps forming a symbiotic relationship with the polyps. The algae shelters within the coral tissue while the coral receives energy from the coral’s photosynthetic process. The corals get 85% of their total energy from Zooxanthellae and the remaining from the metabolisms of the coral nutrients. The Zooxanthellae use the sunlight on the reef as their prime source of energy and pass 95% of their photosynthesis products to their coral host. The host coral provides the algae with nutrients: phosphates, nitrogenous products, and carbon dioxide. The algae protect the corals from strong UV radiation by shading the delicate inner soft layers of the coral tissues and absorbing the light energy (Fabricius 32).
The presence of these algae also provides some limiting factors. The algae provide competition to the coral animals by competing for the available resources hence the coral may become undernourished. The increase in Zooxanthellae algae causes the corals to be darker, and become deep brown. This hinders the natural vivid, pigments of the coral. The algae affect where the corals grow; hence reef-building corals grow, not below 150ft and where they can receive sunlight easily (Sorokin 29).