Physical factors affecting algae | Effect of Substrate, Pressure, Temperature, Illumination on the distribution of Algae.

  Physical factors affecting algae

Algae are thalloid plants. It depends on many biotic and abiotic factors that can affect the rate of growth and development in algae. In this article, we will consider the effect of some abiotic factors or physical factors that are abiotic in nature on algae. There are four important physical factors that can really affect the rate of growth and development in algae:

1. Substrate
2. Pressure
3. Temperature
4. Illumination

Substrate:

• The substrate is any kind of substance or surface through which algae can attach with the help of its rhizoids (mostly). 
• Examples of the substrates include solid rock, boulders, pebbles, sand, mud, or peat are some basic substrates that help algae in anchorage and general distribution of algal flora.
• The presence of different algal species can be affected by the impact of the rocky coast's slope angle and cracks in rocks in the area.
• Similarly, the geological nature of rocks may also be important. For example, soft rocks or sand may rarely carry any algae.

Pressure:

• Water is also an abiotic factor that can affect the growth of algae because all kinds of algae need water to live their lives. 
• Some of them grow near water bodies but most of the algae are found inside water bodies like rivers, oceans, etc. 
• Algae can tolerate high pressure of oceanic water but there is a limit to this tolerance and in this way, pressure is an important factor that can affect the algae. 
• The pressure of water determines the lower limit to which any species of algae will go deep in water. 
• The algae have gas vesicles in them. With the help of these gas vesicles algae shows a floatation mechanism. This floatation mechanism helps algae to keep themselves near the surface of the water. 
• This is brought about by the pressure of the gas inside the vesicle or bladder.
• The shape of the bladder appears to be related to the water depth for any algae. 

During the day due to the production of oxygen, the pressure in the bladder increases, and algae tend to come on the upper surface while during the night this pressure decreases and the algae go deep into the water.

Temperature:

• Temperature is an abiotic modifying factor for the growth of algae. 
• Algae modify themselves according to external temperature. 
• These modifications can lead to some adaptations or changes in the physiology of algae, some seasonal migrations shown by algae,  or the way of reproduction in algae.
• The increase or decrease in temperature about its optimum range of temperature in algae has a negative effect on the rate of photosynthesis and respiration because these processes are dependent on the surrounding's temperature.
• High temperature results in the breakdown of photosynthetic apparatus while cold temperature slows the process of metabolism.
• Seasonal migration is also a modifying factor. Species may be abundant in the region where the temperature is favorable for their growth during any period of the year.
• Temperature variations also affect the production of gametes and their fertilization. For example, in Phaeophyta, the formation of gametes and their fertilization is optimum at 2-6 C and rarely above 16. 

Illumination:

Light is also a very important factor because it is essential for photosynthesis.

Changes in light can affect the algal distribution.

Quality of light: 

The quality or color of light greatly determines the photosynthetic rate in the algae. The hypothesis that “the color of algae (type of pigments present in algae) is complementary to the incident light” is of great significance. 

The following examples can be helpful to understand this hypothesis:

• In Chlorophyta, the light-absorbing pigments are green (chlorophyll and carotenoids). The absorption of light and maximum rate of photosynthesis occur in red and blue regions of the light spectrum.
• In seawater, red and much of the blue regions are rapidly eliminated. So the chlorophytes found at any depth would be expected to have a very low rate of photosynthesis.
• In brown algae, there is increased absorption in the green region due to the presence of fucoxanthin. Phaeophytes living at any depth where the light spectrum is predominantly green, photosynthesis is not limited.
• In the Rhodophyta, the phycobiliproteins are pinkish and absorb light in the green-yellow region. The phycobiliproteins transfer their absorbed energy to the chlorophyll so that light not predominantly absorbed by the chlorophyll is utilized in photosynthesis.

Quantity of light: 

• With increasing depth of water, the quantity of light available for photosynthesis is reduced. 
• Algae living in supralittoral or littoral zones show different photosynthetic responses than those found in the sublittoral zone. 
• For example, many of the deep-growing algae are fully light-saturated at a quite low amount of available light (1/10th of full sunlight). 
• The incident light is cut down considerably even at a depth of one meter, while at a two-meter depth, only 25% of the surface light can penetrate. 
• Similarly, the turbidity of water also affects the rate of photosynthesis and the light compensation point.