Question

Limiting factor for the growth of aquatic organisms is
A. $C{O_2}$
B. ${O_2}$
C. Mineral elements
D. All of the above

Answer 1

Hint: A variable that causes a significant change is referred to as a limiting factor. In an ecosystem, the features from the environment that help in limiting the growth, abundance, or distribution of an organism or a population of organisms are referred to as limiting factors.

Complete answer:
1. $C{O_2}$ acts as a limiting factor in photosynthesis. The atmospheric concentration of $C{O_2}$ is very low and hence its increase in concentration up to a small percentage can cause an increase in the fixation rates. Crossing the level may be damaging over longer periods.
2. Oxygen content, nutrient availability, salinity, the temperature of sunlight is some of the main limiting factors for growth in an aquatic environment.
3. From the atmosphere and via production by phytoplankton, oxygen enters the aquatic ecosystem.
4. Water temperatures influence the dissolved oxygen concentrations which are derived from the atmosphere.
5. When the level of dissolved oxygen is below 3 ppm fish and many other consumers including zooplankton will die.
6. The oxygen that helps the aquatic organisms to survive is known as dissolved oxygen. This oxygen does not produce bubbles and it is not a constituent of the water molecule. It is dissolved in water and is invisible to our eyes.
7. This makes oxygen a very important limiting factor for growth in aquatic organisms.

Thus, the limiting factor for the growth of aquatic organisms is (B), i.e., ${O_2}$.

Note: Thus, dissolved oxygen is an essential component for the survival of many aquatic organisms including fish, invertebrates, bacteria, and plants. Fish obtain oxygen through gills while plants require oxygen for respiration when they are unable to photosynthesize.