Flourescence in Algae

photo taken by Andy captured trhe neon glow illuminating one of Australia's beaches

Diagram 1 : Common clear-water species that produce phycourobilin-rich forms of phycoerythrin have stronger fluorescence with blue excitation.

What is fluorescence?

Fluorescence is the emission of light by a substance that has absorbed light. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region, which gives the fluorescent substance a distinct color that can only be seen when exposed to UV light. 

How to measure fluorescence?

By using a chlorophyll sensor which is known as fluorometer. As all phytoplankton have chlorophyll A, a chlorophyll sensor can be used to detect these organisms in-situ. However, as a chlorophyll sensor assumes all algae and cyanobacteria have the same levels of chlorophyll A, it only provides a rough estimate of biomass. It also cannot be used to identify specific species.

Chlorophyll is measured in micrograms per liter (µg/l). Chlorophyll sensors rely on fluorescence to estimate phytoplankton levels based on chlorophyll concentrations in a sample of water. Fluorescence means that when the chlorophyll is exposed to a high-energy wavelength (approximately 470 nm), it emits a lower energy light (650-700 nm). This returned light can then be measured to determine how much chlorophyll is in the water, which in turn estimates the phytoplankton concentration. These estimates are then used to develop parameter limits for bodies of water. As an example, the New Hampshire Department of Environmental Services provides the following chlorophyll guidelines for river quality: a chlorophyll measurement below 7 µg/l is within a desirable range. 7-15 µg/l is less than desirable, while over 15 µg/l is considered problematic.

Diagram 2: Hand-held fluorometer

(Picture taken from google image)

Diagram 3: Spectroscopy

(Picture taken from google image)

Diagram 4: For fluorescence spectroscopy the equivalent to a single beam spectrometer has a few slight modifications in that the detector is perpendicular to the source, and that there is an additional monochrometer that can be used to vary the wavelength detected. In this fashion, the source light is unable to interfere with the fluorescence light being measured, and the fluorescent light produced can be separated and described as the resulting wavelengths of fluorescence as a function of incident light.

Where do we use fluorometer on?

Plants, algae and phytoplankton

Why do we measure the fluorescence?

• -          Steady state of fluorecence often used for the investigation of energy transfer between    pigments components
• -          To determine the amount of phytoplankton and algae which act as bioindicator.

Diagram 5: A spectacular “red tide” bloom (non-toxic) of Noctiluca scintillans in New Zealand. (Photo by M. Godfrey)

• -               To Prevent Algal Blooms 

An algal bloom is a sudden increase in the concentration of phytoplankton. During a bloom, clear water can become covered with phytoplankton within days. These algal blooms can grow large enough to be seen from a satellite, covering hundreds of square kilometers. Algal blooms come in many colors from green to red, brown, blue, white or purple.

Under the right conditions, algal blooms can last one week to an entire summer, despite the short, few-day life span of phytoplankton ¹¹. A single bloom will only last one to two weeks, as the phytoplankton population will die without the proper oxygen and nutrient levels. However, if the water conditions stay favourable, successive blooms can occur and appear to be one continuous population. Algal blooms are most common in late summer and early fall. 

 

Diagram 6: Fish died due to lack of oxygen ( Google image)

• -                    Oxygen Depletion and Fish Kills

If an algal bloom appears, a fish kill can occur shortly thereafter due to the environmental stresses caused by the bloom. A fish kill, also known as a fish die-off is when a large concentration of fish die. The most common cause of this event is lack of oxygen.