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Harmful phytoplankton blooms indicate the existence of allelopathic interactions

Suparna Mandal

Agricultural Sciences Unit, Indian Statistical Institute
203, B.T.Road, Calcutta 700108, INDIA
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Although phytoplankton species composition and biomass are fundamental parameters in food web ecology, chemical interactions (allelopathic) among phytoplankton have been largely overlooked. Harmful phytoplankton blooms are a serious ecological and socio-economic problem. We have therefore studied the allelopathic interaction of such harmful bloom. In the present study we have put our emphasis to observe the effects of harmful phytoplankton on planktonic blooms and succession. We have studied the variation of marine plankton of Bay of Bengal at Digha, Talsari and Sankarpur, (West Bengal, India) throughout two years along with hydro chemical parameters. In our study, 88 phytoplankton species were identified. of those 53 are from diatoms followed by 9 of green algae, 7 of blue greens and 19 of dinoflagellates. The dominant phytoplankton species are Asterionella, Biddulphia, Chaetoceros, Coscinodiscus, Ditylum, Nitzschia, Ceratium, Noctiluca etc. Field data indicates that harmful phytoplankton, Noctiluca scintillans releases toxic chemicals that may control the succession and blooms of two dominant diatom species namely Coscinodiscus excentricus and Coscinodiscus oculus iridis. C.excentricus is highly sensitive to Noctiluca toxin, but C. oculus iridis shows concentration dependant activity. We therefore conclude that allelopathy of blooming phytoplankton play an important role in plankton ecology.

Media Summary

Harmful phytoplankton, Noctiluca scintillans controls the succession and blooms of Coscinodiscus excentricus and Coscinodiscus oculus iridis .C.excentricus is highly sensitive to Noctiluca toxin whereas C.oculus iridis shows a concentration dependent response.

Key Words

Harmful phytoplankton, succession, blooms, Coscinodiscus excentricus, Coscinodiscus oculus irridis, Noctiluca scintillans.


Harmful Algal Blooms has received considerable and interactions among these organisms are the subject of many studies (Rice, 1984; Anderson and Garrison, 1997). However, the role of allelopathy on those interactions is not well understood. To investigate the role of allelopathy in phytoplankton interactions, it is important to study the variation of plankton population for longer term. As Inderjit and Dakshini (1994) pointed out to get an in-depth insight into algal allelochemical interactions, it is important to generate data on bloom formation, algal succession and their physical and chemical effects on the substratum. Our present work deals with the study of variation of marine plankton community of Bay of Bengal at Digha, Talsari and Sankarpur region throughout two years (2002-2003) to gain a clear understanding about interactions between different marine plankton species. Harmful phytoplankton plays a role in changing/moulding the plankton community. In this regard, an attempt has been made to identify the effect of such harmful algal species on succession and blooms of other phytoplankton species. Our emphasis was on the Harmful Phytoplankton Species, Noctiluca scintillans belonging to the group Dinoflagellates of the Division Dinophyta. The other two phytoplanktons we have chosen are Coscinodiscus excentricus and Coscinodiscus oculus irridis belonging to the group Diatom of the Division Bacillariophyta. This two dominant diatom species occur throughout the year and produces the base of the aquatic food web.


The study area extends from Talsari (Orissa, India) to Digha Mohana (West Bengal). Geographically the area is situated between 2137′ Northern Latitude and 8725′ Eastern Longitude to 2142′ Northern Latitude to 8731′ Eastern Longitude (Figure 1).

Figure 1. Map of Coastal Region of West Bengal and part of Orissa, India. (Source : CIFRI, Barrackpore, India)

The study was carried out from January 2002 to December 2003 and frequency of sampling was every fortnight. Samplings were done aboard a 10-meter fishing vessel. Plankton samples were collected both from the surface and subsurface water (1-2 meter depth) by horizontal plankton tow with 20-micron mesh net and 0.3m in diameters. The collected samples were preserved in 3% formaldehyde in seawater. Counting phytoplankton was made under microscope using Sedgewick-Rafter counting cell and are expressed in nos./liter. Identification of plankton community was done following Davis (1955), Newell and Newell (1979) and Tomas (1997). Surface water samples were collected from each station and physio-chemical properties (viz. Water temperature, pH, salinity, dissolved oxygen and conductivity), recorded. Mettler-Toledo MX300 X-matepro of Switzerland measured water temperature, pH and conductivity of surface water. Salinity was measured by using Salinity Refractometer. The dissolved Oxygen content of the sample water was estimated by standard Winklers method as given by Strickland and Parsons (1969).


A total of 216 samples were collected in 36 sample days. The present study shows that the presence of 88 phytoplanktonic species, including 53 diatoms, and 7 blue green algae (Cyanophyceae), 9 green algae (Chlorophyceae) and 19 Dinoflagellates in the coastal water chosen (Table 1)

Table 1. List of total phytoplankton species found in Bay of Bengal at Digha-Talsari-Sankarpur Region during 2002 to 2003.



Blue Green Algae

Green Algae

Amphora ovalis

Ceratium candelabrum

Anabaena sp

Asterococcus limneticus

Asterionella formosa

Ceratium extensum

Chroococcus gigantens

Chlorella sp

Asterionella japonica

Ceratium falcatus

Holopedium irregulare

Closterium sp

Bacteriastrum delicatulum

Ceratium furca

Nodularia hawaiiensis

Coelastrum microporum

Bacteriastrum hyalina

Ceratium fusus

Oscillatora limosa

Netrium digitus

Bellerochea sp

Ceratium lineatum

Skujaella thiebauti

Pediastrum sp

Biddulphia alternans

Ceratium longipes

Spirulina sp

Planktosphaeria gelatinosa

Biddulphia aurita

Ceratium macroceros


Scenedesmus sp

Biddulphia favus

Ceratium setaceum


Tetraedron sp

Biddulphia mobiliensis

Ceratium tripos


Biddulphia regia

Dinophysis acuta


Biddulphia sinensis

Exuviella sp


Campylodiscus cribrosus

Gymnodinium sp


Cerataulina bergonii

Noctiluca scintillans


Chaetoceros danicum

Peridinium divergens


Chaetoceros decipiens

Peridinium globulum


Chaetoceros densum

Peridinium granii


Chaetoceros laciniosus

Peridinium oratum


Chaetoceros teres

Prorocentrum sp


Corethron sp


Coscinodiscus excentricus


Coscinodiscus oculus iridis


Coscinosira oestrupi


Ditylum brightwelli


Ditylum sol


Eucampia zoodiacus


Fragilaria ocenica


Gyrosigma sp


Halosphaera viridis


Hemiaulus hauckii


Lauderia borealis


Leptocylindricus danicus


Lithodesmium undulatum


Navicula sp


Nitzschia closterium


Nitzschia seriata


Paralia sulcata


Phaeocystis sp


Planktoniella sol


Pleurosigma sp


Rhizosolenia alata


Rhizosolenia setigera


Rhizosolenia shrubsolei


Rhizosolenia stolterfothi


Skeletonema costatum


Stephanodiscus astraea


Stephanopyxis turris


Striatella sp


Surirella sp


Synedra utermohlii


Thalassiosira decipiens


Thalassionema nitzschioides


Thalassiothrix nitzschioides


Noctiluca scintillans shows five peaks (i.e. occurring in larger number) over the year (Figure 2). First smaller peak (30896 no./m3) was recorded on 28.02.02, second slightly larger peak (69909 no./m3), on 27.06.02, third very smaller peak (8114 no./m3) on 13.08.02, fourth large peak (226754 no./m3) on 23.10.02 and last peak (79786 no./m3) on 19.12.02. From our field data, it is indicated that Noctiluca scintillans might produce some toxin and that have a direct effect on Coscinodiscus excentricus and Coscinodiscus oculus iridis. C. excentricus is highly sensitive to Noctiluca toxins but C. oculus iridis shows concentration-dependent activity. At first time peak of Noctiluca (30896 no./m3), the blooms of C. excentricus completely disappear but C.oculus iridis can withstand that toxin level. At the time of fourth large peak of Noctiluca (226754 no./m3), C. oculus iridis are unable to resist at level and both species completely disappear at that time.

The interactions of these three species do not match well with the hydrological parameters. C. excentricus shows inverse relation with salinity but C.oculus iridis shows parallel relation with salinity(Figure3).

We are unable to describe these three species interactions by hydrological parameters but these interactions obtained from our data shows that harmful phytoplankton may play a role in succession and blooms of other phytoplankton species.


Harmful phytoplankton certainly plays an important role in the blooms and succession. Probably the main reason behind population succession and blooms are due to the toxin produced by harmful phytoplankton. When blooms of a particular harmful phytoplankton occur, the cumulative effect of the entire toxin released may affect the other organisms, causing mass mortality. Bloom of toxic phytoplankton depends on the effects observed and not necessarily because of a large biomass.

From our field data, it is indicated that Noctiluca scintillans might produce some toxin and that have a direct effect on Coscinodiscus excentricus and Coscinodiscus oculus iridis. Coscinodiscus excentricus is highly sensitive to Noctiluca toxins but Coscinodiscus oculus iridis shows concentration-dependent activity. The hydrological parameter that we have studied does not play any direct role in these three species interactions but it may help in species succession. Harmful phytoplankton controls the community structure and planktonic blooms.To establish the fact firmly, it is necessary to identify the toxic chemical and find out the amount of doses is required for the termination of planktonic blooms in a specified area. Our future work will be in this direction.


Anderson, D.M. and Garrison, D.J. 1997. The ecology and oceanography of harmful algal blooms. Limnology and Oceanography 42: 1009-1035.

Davis, C.C. (1955). The marine and fresh water plankton. Michigan State Univ. Press.

Inderjit and Dakshini, K.M.M. (1994). Algal allelopathy. Botanical Review. 60, 182,

Newell, G.E. and Newell, R.C. Marine plankton. A practical guide. 5th Edition. Hatchinson and Co.

Rice, E.L. (1984). Allelopathy 2nd Edition, Academic Press, London.

Tomas, C.R. (1997). Identifying marine diatoms and dinoflagellates. A P San Diego, C.A.

Strickland, J.D.H. and Parsons, T.R. (1969). A practical handbook of sea water analysis Bull. 167. Fisheries Research Board of Canada.

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