Salinity is critically important for the health and survival of coral reefs because it directly impacts the symbiotic relationship between corals and the algae living within their tissues.
The Vital Role of Symbiotic Algae
Corals rely heavily on symbiotic algae, known as zooxanthellae, which live inside their tissues. These algae perform photosynthesis, converting sunlight into energy that they share with the coral host. This energy source is crucial for the coral's growth, calcification, and overall survival.
How Salinity Affects Corals and Algae
Maintaining a stable salinity level is essential for this delicate partnership. Changes in salinity, particularly short-term fluctuations, can have dramatic negative effects on the symbiotic algae.
- Impact on Algal Function: Short-term changes in salinity cause dramatic changes in cell respiration and photosynthesis of symbiotic algae [9]. This means the algae struggle to produce the energy that the coral needs.
- Leading to Coral Bleaching: When salinity levels become too low, it creates a stressful environment for the coral and its symbiotic algae. Low salinity environments cause coral bleaching, i.e., a sublethal response of corals involving loss of zooxanthellae [19]. Bleaching occurs when the coral expels the zooxanthellae, leaving the coral white and vulnerable.
While bleaching is a sublethal response, it significantly weakens the coral, making it more susceptible to disease and death if the stressor persists and the algae do not return.
Therefore, stable and appropriate salinity levels are fundamental for maintaining the essential symbiotic relationship that fuels coral growth and supports the entire reef ecosystem.
