Nashad Musaliyarakam

Nashad Musaliyarakam Nansen Environmental Research Centre and Department of Marine Biology, Microbiology & Biochemistry, University of Science and Technology, India. Wikipage: hƩ p://www.nf-pogo-alumni.org/~Nashad+Musaliyarakam

On the Occurrence of Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea)

During the last several decades, harmful algal bloom (HAB) events have been observed in more locaƟ ons than ever before, throughout the coast of India. There have been 39 causaƟ ve species responsible for blooms of which NocƟ luca scinƟ llans and Trichodesmium erythraeum are the most common. ReporƟ ng of massive fi sh mortality in Indian waters has been associated with the blooming of Cochlodinium polykricoides, Karenia mikimotoi, K. brevis, Trichodesmium erythraeum, T. thiebauƟ i and ChaƩ onella marina. Occurrences of these blooms are coincided with South west monsoon and North east monsoon. Around eighty blooms were recorded during the period 1998-2012. PotenƟ ally toxic microalgae recorded from the Indian waters were Alexandrium spp., Gymnodinium spp., Coolia monoƟ s, Prorocentrum lima, Dinophysis spp., and Pseudo-nitzchia spp. (Padmakumar et al., 2012). The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India observed on 30 th April 2014 is accounted. It is a marine cyanobacterium, an important nitrogen fi xer in the sea. It is one of the common bloom forming species found in the tropical and sub-tropical waters, parƟ cularly in the eastern tropical Pacifi c and Arabian sea (Westberry et al., 2006). Trichodesmium normally occurs in macroscopic bundles or trichomes and blooms formed by it are oŌ en extremely patchy with yellowish brown color. The blooms appeared during relaƟ vely high temperature condiƟ ons (30.5 - 31.8 °C) when coastal water salinity was greater than 31 psu (31.47 - 33.82). A signifi cant reducƟ on in nitrate concentraƟ on was noƟ ced during the bloom period, whereas relaƟ vely high concentraƟ ons of phosphate were observed. DO concentraƟ on ranged from 6.4 - 8.0 mg L -1 . These condiƟ ons favor abrupt increases in Trichodesmium density (2.16 - 2.32 10 6 fi laments L -1 ), contribuƟ ng 99.58% to total plankton community. Blooms consƟ tuted both individual trichomes and colonial forms although later dominated up to 95%. Low zooplankton biomass was found in bloom area with respect to non blooming regions. HarpacƟ coid copepods were dominated followed by Chaetognatha. Trichodesmium is not a food source for most of the zooplankton and this may have been the reason for the low mesozooplankton biomass in the mixed layer.

References

Padmakumar, K.B.; Menon, N.R.; Sanjeevan, V.N., 2012. Is occurrence of Harmful Algal Blooms in the Exclusive Economic Zone of India on the rise? InternaƟ onal journal of oceanography. Vol. 2012, ArƟ cle ID 263946, 7 pp. Westberry, T.K.; Siegel, D.A., 2006. SpaƟ al and temporal distribuƟ on of Trichodesmium blooms in the world’s oceans. Global Biogeochem Cyc les 20:GB4016.

Trichodesmium bloom - off Calicut, Kerala, India and at 10X magnifi caƟ on (Trichodesmium erytraeum)

Details of the locaƟ on and nutrients of the bloom site