AN ANALYTICAL STUDY OF THE PHYTOPLANKTON BLOOMS ALONG THE INDIAN COASTS FROM 1963 TO 1982 NOTA CIENTÍFICA

Trabajo recibido el 25 de agosto de 1983 y aceptado para su publicación el 10 de noviembre de 1983.

RESUMEN

INTRODUCCIÓN

Marine Phytoplankton organisms are minute algae suspended in the sea, drifting or floating within the currents and usually remaining near the surface. They are extremely varied in their morphology and physiology to adopt themselves to the environment. The process of rapid reproduction of phytoplankton reaching a peak and then dying down is called blooming or flowering. The blooms are mainly constituted by diatoms, dinoflafellates and blue-green algae. One manifestation of bloom is red tide. Many red tides are non-toxic but only few red tides caused by certain dinoflagellates are toxic. Under certain círcunstances one or a few species of Phytoplankton muytiply to such a degree to doscolour the water. The colour of the water at the time of bloom may be red, brown, yellow and green. Catastrophic mortality of marine life and paralytic shellfish poison in humans are caused by the production of toxins.

There have been many studies on phytoplankton blooms in the world oceans, but some of the more important self contained studies in the important oceans during the recent years are as follows: Wood (1965) and Bowman and Lancaster (1965) observed blooms ofTrichodesmium erythraeumin the Pacific Ocean, Sato, et al. (1966) noted red tide ofTrichodesmium in north eastern Brazil and related it to Tamandare fever.

Prakash and Taylor (1966) studied red water due to Gonyaulax acatenella in the strait of Georgia and its relation to paralytic Shellfish toxicity. Wood (1968) pointed out that bloom ofGonyaulax tamarensis was the cause of mortalities and poisoning in the North Sea.

Robinson (1968) studied red tide of Gonyaulax tamarensis off the North East Coast of England. Red water due toNoctiluca was studied by Le Fevre and Grall (1970) of the Western coast of Britany, Fung and Trott (1973) in Hong Kong. Blasco (1977) observed that the predominant organism in a red water dinoflagellate bloom off Baja California were Gonyaulax Polyedra, Ceratium furca and Gymnodinium sp Dodge (1977) noted a bloom ofDinophysis in the North Sea. Shimizu (1983) notedDinophysis fortii cause diarrahetic Shellfish poisoning (DSP). Neurotic Shellfish Poisoning (NSP) by Gymnodinium breve. It was believed that NSP originates from a newly identified dinoflagellate Gambierdiscus toxicus.

The coastal belt in India bordering Bay of Bengal, Arabian Sea and Indian Ocean roughly extended about 6000 KM. In fact along the Indian coast some stray observations on Phytoplankton blooms otherwise called as red water phenomena were reported as early as 1930 onwards. Though there were some sporadic publications are available pertaining to different types of blooms, but no specific studies were undertaken in relation to marine fish production. Some of the studies reviewed in the following pages are of isolated observations made by individual authors. For the sake of convenience the studies along the Indian coast are grouped under two headings.

East coast of India of Bay of Bengal

West coast of India of Arabian Sea.

In the East Coast of India ie. Bay of Bengal Raghu Prasad (1953, 1958) observed red water phenomenon caused byNoctiluca in the Palk Bay and Mandapam and there was an inverse relationship between Pelagic fishery andNoctiluca.Raghu Prasad and Sayaraman (1954) reported lethal reactions on Plankton caused by swarms of dinoflagellates. They have also observed varying intensities of diatom peaks occur followingNoctiluca bloom. Raghu. Prasad (1956) noted that the bloom ofRhizosolenia alata andRhizosolenia imbricataoccured March 1950 and February 1951 respectively. Subba Rao (1969) observed extensive discoloration of coastal waters off Waltair due toAsterionella japonica bloom. Ramamurthy (1968, 1970 A and B and 1973) recorded blooms ofTrichodesmium in PortoNovo waters. Santha Joseph (1975) observed swarming of Noctiluca miliaris in August 1966, August 1967 and May 1968 in Vellar Estuary. The cell counts ofNoctiluca during the bloom periods ranged from 6,500 cells/10 ml to 28,500 cells/ 10 ml.

In the west coast of India ie. Arabian Sea, Bhimachar and George (1950) observed an abrupt set back in the fisheries of Malabar and Kanara coast due to red water phenomenon which in turn caused by Noctilucta., Gymnodinium, Coscinodiscusand Dinophysis. Though no mortality was observed, but they reported the fishes avoided that area. Prakash and Sarma (1964) recorded the presence of Gonyaulax polygramma from the west coast of India off Cochin and there was virtual exclusion of Zooplankton. The bloom was non-toxic. No fish mortality was reported, according to the author the cell counts was 10,828,000 cells/litre. Prabhu et al. (1965) noticed an extensive greenish yellow patches ofTrichodesmium erythraeum and Trichodesmium hildebrontii in Ullal (Mangalore). Oil sardine and Mackerel were landed in good quantities preceding algal bloom. At the time of bloom there were no catches of fish.

Revival of catches started after the bloom.Trichodesmium cell counts varied from 2,600-1,03,000 per ml. Nagabhushanam (1967) observed adverse effects to Tuna fisheries due toTrichodesmium erythraeum bloom in Minicoy Island. Colour of the water was deep brownish and it had a distinct iodoform odour. Qasim (1970) noted Trichodesmium bloom in Laccadive Island. Prabhu.et al. (1971) pointed out that the bloom of Trichodesmium has got adverse effect on the oil sardine fishery off Mangalore. Ramamurthy et al. (1972) studied bloom of Trichodesmium erythraeum in the waters of the Goa coast. No mortality of fish or other organisms was associated with this bloom. Phytoplanktons and Zooplanktons were sparse. This bloom was succeeded by the bloom of centric and pennate diatoms and it consisted of Asterionella sp., Thalassiothrix sp., Coscinodiscus sp., Melosira sp., Stephanopyxis sp., cell counts ranged from 36-338 (cells/0.1 ml) . Devassy (1974) reported Fragilaria oceanica deve the dominant component in a mixed bloom of diatoms and a blue green algae which occured near Mangalore. He also reportedNitzschia andSkeletonema blooms from Cochin backwater. Devassyet al. (1978) notedTrichodesmiumphenomenon in near shore water of Goa and reported that Phytoplanktons and Zooplanktons were fairly abundant. Verlancar (1978) studied blooms of Trichodesmium erythraeum at several places along the southwest coast of India during March 1977. Swarming of Physaliacoincided with the bloom. Although the bloom occurred in great profusion along the South west coast of India, 1977 catches of both oil sardines and Mackerel were good almost throughout the west coast. Devassyet al. (1979) studied the succession of organisms followingTrichodesmium phenomenon when theTrichodesmium bloom was on the decline a mixed diatom bloom consisting largely of Chaetoceros appeared. This was followed by swarming of Cladocerans. It was succeeded byNoctilucaand then by copepods and carnivores. Venugopal et. al (1979) reported occurrence of discoloured water off Cochin and Quilon associated with swarming of Noctiluca miliaris. The cell counts varied from 2.4 X 10 5 - 4.1 X 10 5/m³ at Quilon and Cochin 1976, 3.01 X 105 - 7.71 X 10 5/m³ at Cochin 1977.

To study the Phytoplankton blooms along the Indian coast the following field survey and Laboratory methods are employed. To study in field condition smaller 32' fishing boats as well as exploratory trawlers were used to study the occurrence of blooms at different points of Bay of Bengal and Arabian Sea. The blooms were observed by the skipper and fishing second hands and the messages were passed on to the authors pertaining to the duration and location. Samples were collected in the bloom patches and also in the non-bloom patches. The length and breadth of the blooms and locality of the arca were also noted. The mortality of fishes if any was estimated on the basis of visual observations. Cell counts were made in the laboratory by using binocular microscope of per ml. of sample. The food items in each fish stomach were studied on the basis of rough counts and judgement visually. Due regard being taken of the size of the organisms as well as their abundance. The data compiled on the basis of information received from the skipper, at different centres and the same has been processed with reference to Marine Fish Production.

It is interesting to compare the bloom of different types in relation to toxicity and marine fish production. The Table No. 1 shows the seasonal occurrence of various Phytoplankton blooms during the last two decades (1963-1982). Chidambaram. (1942) found out that due toTrichodesmiumabundance the fish may react negatively to it. He also found this alga.e as an occasional item, of food of the Mackerel, Oil sardine and other lesser Sardines. Chacko (1942), Chidambaram, and Unny (1944) have recorded mortality among marine animals including fishes in the Gulf of Mannar. In these cases mortality was caused by asphyxiation and also by putrefaction. Bhimachar and George (1950) reported that, there was abrupt set back in the fisheries of the Malabar and Kanara coast due to the swarming of Noctiluca. Raghu Prasad (1953, 1958) observed in the Palk Bay and Mandapam that red water Phenomena caused byNoctiluca are inimical to fisheries and an inverse relationship exists between swarm of Noctiluca and Pelagic fishery. Prakash and Sarma (1964) also observed a similar bloom due to G.Polygramma along the south west coast of India. According to them. the fishing log of R. V. Kalava that fish seemed to be avoided the above bloom arca but reappeared again in the same arca after some days. Prabhuet al. (1965) studiedTrichodesmiumbloom and it was noted that Sardines and Mackerel were landed in good quantities preceding algal bloom. At the time of bloom there were no catches of fishes and revival of fish landings occured after the bloom. Adverse effect to Tuna fishery at the time of bloom ofTrichodesmium was reported by Nagabhushanam (1967) but the overhaul annual landings of Tuna were not affected. Prabhu et al. (1971) discussed theTrichodesmium bloom of Mangalore and found the bloom had an adverse effect on the oil sardine fishery. However the total annual Sardine landings did not show any fluctuations due to the above adverse effect.

However contradictory to the above observations Devanesan (1932) observed in the Gulf of Mannar that theTrichodesmium form the chief food of Sardine. The same author (1942) observed that Trichodesmium favoured as food of S. gibbosa in Krusadai Islands and fishery depends to a certain extent on the abundance of the alga. Subrahmanyam (1959) observed that the bloom ofFragilaria could be used as an indicator of the abundance of oil sardine and the sequence of appearence and disappearance of fishes were related to the water movements and phytoplankton blooms. These studies were further confirmed by Ramamurthy (1970 B) . According to him. no mortality of fish or other organisms associated due to Trichodesmiumbloom and thus non toxicity of Trichodesmium bloom was due to the production of some kind of ectocrines produced by theTrichodesmium filaments. At the time of bloom some of the pelagic fishes like Hilsa kanagurta andRastrelliger kanagurta were landed abundantly and were consumed in unusually in large amount by the Sea gull Laurus brunicephalus.

Ramamurthy et al. (1972) further confirmed along the Goa coast that no mortality of fish or other organism associated duringTrichodesmium bloom and there were no reports of ill effects or fishery food poisoning but the other Phytoplankton and Zooplankton were sparse. Nair (1973) observed the presence of large numbers ofTrichodesmium filaments in the stomach contents of the oil sardine. Devassy et al. (1978) also reported that Phytoplanktons and Zooplanktons were fairly abundant at the time ofTrichodesmium bloom. Verlancar (1978) studied bloom ofTrichodesmium erythraeum at several places along the southwest coast of India and it was seen that there were good catches of oil sardine and Mackerel throughout the west coast.

The study in the past reveals that the Trichodesmium bloom occured annually whereas the Noctiluca bloom appeared at irregular intervals. The diatom blooms of types mentioned in Table 1 appeared at irregular intervals though not annually. The bloom ofGonyaulax occured only once in two decades, i.e. 1963.

In the present study the bloom ofCeratium occured annually from 1980 to 1982 during Febraury to March. The Trichodesmium bloom though it was not observed in 1980 but was observed in 1981 and 1982 during March to April. The bloom ofAsterionella occured in 1981 and 1982 from june to July.Noctiluca bloom occurred only in August 1981.Peridinium bloom noted only in May 1982 and theSkeletonema bloom occurred in October to November 1982. It may be seen that the above observations were restricted along south west coast of India, however reports (personal communication) from the other areas reveal the above blooms also appeared in central west coast of Arabian Sea and also along the south east coast of Bay of Bengal. On close observations of the Table No. 1 though the occurrence of Phytoplankton blooms and marine fish production do not show any linear or inversal relationship but some conclusions can be drawn on the forming of Phytoplankton blooms and the marine fish production. In the past two decades the peak marine fish production was observed in 1975 and 1978 though Trichodesmium blooms appeared during the respective years as primary and secondary peaks. The tertiary peak observed in 1979, wherein there seemed to be no report of occurrence of any bloom. In 1976, 1977 and 1981 though there were occurrence ofNoctilucablooms, but nevertheless the marine fish production did not show any significant fluctuation. From the foregoing discussion it can be concluded some of the Phytoplankton blooms occurring along the Indian coast of Arabian Sea and Bay of Bengal have some indirect short term influences on pelagic fishes. One of the short term effect is the pelagic fishes like Sardines and Mackerel avoided certain dense areas of bloom temporarily. The movement of shoals were observed many times by the skippers of many vessels. However such short term movements will not have any significance on the annual total marine fish production. It may be noted also there was no reported out break of PSP (Paralytic Shellfish Poisoning) or DSP (Diarrahetic Shellfish, Poisoning) seems to the reported along the Indian coast either during the pre-bloom period or during the post bloom period.

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