The Tiny Plant Wanderers

At least a few among us have a bucket list with visualising the bioluminescent “sea sparkle”. This bioluminescence is often because of the blooming of Noctiluca scintillans, a free￾living marine dinoflagellate. Dinoflagellates belong to one class of phytoplankton.

Phytoplankton, the plants made to wander, are the foundations of the aquatic food web and are responsible for the majority of the transfer of carbon dioxide from the atmosphere to the ocean. The growth of the phytoplankton requires the presence of sunlight and the inorganic nutrients such as nitrates, phosphates and sulphur. Water temperature, salinity, water depth, wind, predators grazing on them, are the other influencing factors for their growth (Lindsey & Scott, 2010). When there is an abundance of these inorganic nutrients, the growth of the plankton moves into an exponential phase resulting in a plankton bloom and when the levels of the nutrients lower, the bloom crashes. The above mentioned bioluminescent “sea sparkle” is one such example of the plankton bloom. Red tide is another textbook example of the plankton bloom. Now the question arises, what are the causes of the bloom, what is its ecological relevance and how the changing climate is affecting the growth and distribution of the phytoplankton? As mentioned above, increased nutrient concentration is the reason for the plankton bloom but nowadays anthropogenic factors are predominantly responsible for this increasing nutrient concentration. Agricultural run￾off, fertilizers, high concentration of sewage enhances the nutrient distribution and spikes the plankton growth. As a result, the underlying aquatic fauna and flora are deprived of oxygen and other nutrients. The plankton bloom increases the biological oxygen demand (BOD) of water. Some blooms can be very harmful if there is any production of biotoxin involved as in the case of red tide. Red tide can result in massive fish mortality and may cause illness in people directly or indirectly. After a massive bloom, the lake or ocean floor is filled with the sunken dead phytoplankton resulting in a dead zone. This can deplete the oxygen in the water further and may suffocate the animal life. El Niño Southern Oscillations climate pattern has the biggest influence on the year to year differences in global phytoplankton productivity. It is to be noted that, in high latitudes, blooms peak during spring and summer. In subtropical oceans, populations drop off in summer and in lower latitudes, seasonal blooms are often linked to monsoon related changes in winds. But because of climate change, everything has been juggled upa bit. Intensity, as well as the composition of phytoplankton, has been shifted.

A critical understanding of this changing pattern today is essential for making predictions about the changing of massive ecosystems in the future. Quantification of chlorophyll-a is a study to estimate the phytoplankton abundance in the ocean as chlorophyll-a is its predominant pigment. Chlorophyll-a concentration can be estimated from the satellite data. Recently, a team of Indian scientists from the Indian National Centre for Ocean Information Services (INCOIS) measured the same in the Bay of Bengal (India Science Wire, 2020). The data for the trend of chlorophyll-a analysis was collected by relying on United States National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, onboard Aqua satellite acquiring data in 36 spectral bands (India Science Wire, 2020). One of the most widely used studies for the plankton is by collecting the water sample, identification and finally calculating its diversity and abundance. Integration of Imaging Flow CytoBot (IFCB), a submersible imaging flow cytometer has enabled automated phytoplankton identification, classification and genus- (or species-) specific cell abundance estimation done in a very short time. It has allowed monitoring of high-frequency variability in phytoplankton diversity and distribution. Estimates of marine inherent optical properties (IOP play a crucial role in estimating phytoplankton pigments) can be generated from ocean colours measured from the satellite. This can provide a daily, global synoptic view of spectral waterleaving reflectances (Werdell et al., 2018). Dimethyl sulphide (DMS), a gas produced by phytoplankton rapidly breaks down in the atmosphere. Aerosols formed from the resulting sulphur form clouds when water condenses around them. The North Atlantic Aerosols and Marine Ecosystem Study (NAAMES) is a five-year investigation supported by the NASA Earth Venture Suborbital Programme for resolving key processes controlling marine ecosystems and aerosols that are essential to our understanding of the Earth System and future change (Lineberry, 2017). The organisms you cannot even see have a huge impact on the vital processes of the planet. We still have to apply a systems approach for sustained global ocean observation for understanding the ocean ecosystem. Global Ocean Observing System (GOOS) has become a critical and strategic tool in addressing the plankton bloom as a global community (Anderson et al., 2019). A more widespread interaction between the communities across the globe is necessary to build ecological models to understand the impact of these tiny microscopic organisms in order to address the changing climate.

REFERENCES

1) Lindsey, R., Scott, M. (2010, July 13). What are Phytoplankton?. Retrieved on October 10, 2020 from https://earthobservatory.nasa.gov/features/Phytoplankton

2) Deccan Chronicle. (2019, June 19). ‘Algal bloom’ behind sea foam in Kollam. Retrieved on October 10, 2020 from www.deccanchronicle.com/nation/current-affairs/190619/algal-bloombehind-sea-foam-in-kollam.html

3) India Science Wire. New study helps monitor trendsin phytoplankton biomass in Bay of Bengal. Retrieved on October 10, 2020 from www.downtoearth.org.in/news/wildlife-biodiversity/newstudy-helps-monitor-trendsin-phytoplankton-biomass-inbay-of-bengal-73377

4) Werdell, P. J., McKinna, L. I. W., Boss, E., Ackleson, S. G., Craig, S. E., Gregg, W. W., … Zhang, X. (2018). An overview of approaches and challenges for retrieving marine optical prop erties from ocean color remote sensing. Progress in Oceanography, 160, 186–212. https://doi.org/https://doi.org/10.1016/j.pocean.2018.01.001

5) Lineberry, D. Tiny organisms, giant impact. Retrieved on October 10, 2020 from https://climate.nasa.gov/news/2621/tiny-organisms-giant-impact/

6) Anderson, C. R., Berdalet, E., Kudela, R. M., Cusack, C. K., Silke, J., O’Rourke, E., … Morell, J. (2019). Scaling Up From Regional Case Studies to a Global Harmful Algal Bloom Observing System. Frontiers in Marine Science, Vol. 6, p. 250. Retrieved from https://www.frontiersin.org/article/10.3389/fmars.2019.00250