Blooming of the dinoflagellates Noctiluca scintillans was observed at Kollam Bay, Kerala during September

2003 (bloom-1) and Cochlodinium sp. in September 2004 (bloom-2) with cell densities of 9.8 x 104 and

1.4 x 105 cells l-1 respectively. These caused 27% and 100% mortality of the farmed pearl oyster Pinctada

fucata in the raft farms of Central Marine Fisheries Research Institute moored in the Bay. The mortality of

the pearl oysters can be attributed to the high dissolved ammonia 14.9 μmol l-1 during bloom-1 and high

dissolved ammonia (14.7 μmol l-1) and total suspended solids (154.8 mg l-1) during bloom-2. These

instances of harmful algal blooms (HAB) indicate that precautionary management protocols should be

developed to relocate the farm stock to overcome such natural causes to prevent economic loss to farmers

Alloycious, P S

Jenni, B

Joseph, Mathew

Jugnu, R

Kripa, V

Mohamed, K S

Radhakrishnan, P

Velayudhan, T S

CMFRI Digital Repository

213Journal of the Marine Biological Association of India (2007)Mortality of farmed peal oyster and Noctiluca bloomsJ. Mar. Bio . Ass. India, 49 (2) : 213 - 218, July - December 2007IntroductionThough algal blooms in coastal waters are anatural phenomenon, recent studies indicate thatthey have increased in frequency and geographicdistribution over the past few decades. Ho andHodgkiss (1991) in a review on the red tides insubtropical coastal waters from 1928 to 1989showed that the number of blooms increased from1 or 2 every 10 year at the beginning of the periodto over 220 between 1980 and 1989.  Of the harmfulalgae, the species most often reported (Jugnu, 2006)from Indian waters is the dinoflagellate Noctilucaspecies which is a large (200 µm to >1 mm)unarmoured dinoflagellate widely distributed inthe subtropical and tropical waters.  Noctilucablooms have been reported and studied in thecoastal waters along the southwest coast of India(Bhimachar and George, 1950; Devassy and Nair,1987; Katti et al., 1988; Mathew et al., 1988;Nayak et al., 2000; Eashwar et al., 2001;Mohammed, 2003).The naked flagellate Cochlodinium sp. is alsoknown to form blooms and cause fish kills (Whyteet al., 2001; Vicente et al., 2002).  The presentinvestigation reports on the occurrence of Noctilucascintillans and Cochlodinium sp. blooms at KollamBay in the central Kerala coast and the associatedmortality of pearl oysters stocked in a raft farm.This is the first instance of large scale mortality offarmed pearl oysters due to harmful algal bloom(HAB) along the west coast of India.Material and MethodsThe pearl oyster farm of Central MarineFisheries Research Institute (CMFRI) is located inthe Kollam Bay, an artificially created semi-enclosed bay in central Kerala. As a part of thedemonstration and improvement of pearl culturetechnology under the National AgricultureTechnology Project (NATP), wooden rafts (5 x 5m)were moored in the bay since 2001 and pearl oysterswere suspended from the raft in net and plasticcages.  The monthly variations in hydrologicalparameters at the farm site were studied by takingwater samples from the farm site at a depth of 1.5m using 10 l Niskin bottles. Water temperature wasMortality of farmed pearl oyster Pinctada fucata (Gould, 1850) due to theblooming of Noctiluca scintillans and Cochlodinium sp. at Kollam Bay, KeralaK. S. Mohamed*, V. Kripa, R. Jugnu, P. Radhakrishnan, P. S. Alloycious, J. Sharma, M.Joseph and T. S. VelayudhanCentral Marine Fisheries Research Institute, PO Box 1603, Cochin - 682 018, Kerala, India.*E-mail: ksmohamed@vsnl.comAbstractBlooming of the dinoflagellates Noctiluca scintillans was observed at Kollam Bay, Kerala during Septem-ber 2003 (bloom-1) and Cochlodinium sp. in September 2004 (bloom-2) with cell densities of 9.8 x 104 and1.4 x 105 cells l-1 respectively.  These caused 27% and 100% mortality of the farmed pearl oyster Pinctadafucata in the raft farms of Central Marine Fisheries Research Institute moored in the Bay.  The mortality ofthe pearl oysters can be attributed to the high dissolved ammonia 14.9 µmol l-1 during bloom-1 and highdissolved ammonia (14.7 µmol l-1) and total suspended solids (154.8 mg l-1) during bloom-2.  Theseinstances of harmful algal blooms (HAB) indicate that precautionary management protocols should bedeveloped to relocate the farm stock to overcome such natural causes to prevent economic loss to farmers.Key words: Noctiluca scintillans, Cochlodinium sp., harmful   algal blooms (HAB), farmed pearl oysters214Journal of the Marine Biological Association of India (2007)K. S. Mohamed et al.recorded by a thermometer with 0.5°C precisionand salinity by a refractometer. The total suspendedsolids (TSS) estimation was carried outgravimetrically after desiccation (105°C, 24 h)using an electronic balance (accuracy ± 0.1 mg).Chlorophyll pigments, ammonia and nutrients viz.,nitrate, nitrite, and phosphate were measured usinga spectrophotometer (Strickland and Parsons, 1972).In the third week of September 2003, a deeporange colouration, indicative of an algal bloom(bloom 1), was observed at Kollam bay with theintensity of the colouration increasing towards theshore line. On 10th September 2004 also adiscolouration in the seawater (dirty yellow colour)with higher intensity occurred at the same site(bloom-2). To study the causative organism andthe intensity of the bloom, water samples (10 l)were collected from the site on the bloom day andfixed with 4% formalin and brought to thelaboratory for enumeration. Quantitative estimationof phytoplankton was done by sedimentationmethod (Utermohl, 1958).  Enumeration was donein triplicates and the average count ofphytoplankton was expressed in cells l-1. Thesecond bloom persisted and spread southwardalong the southwest coast.Results and DiscussionThe water samples collected from the siteduring bloom-1 showed the presence of the toxicdinoflagellate N. scintillans (Fig. 1A) at a densityof 9.8 x 104 cells l-1.  Apart from this, the diatomCoscinodiscus sp. and Gyrosigma balticum atdensities of 5 and 3 cells l-1 respectively wererecorded. A complete absence of otherphytoplankton in the bloom area was noted in thesamples taken. During bloom-2, the density ofCochlodinium sp. (Fig. 1B) was much higher at 1.4x 105 cells l-1. A few cells of the toxicdinoflagellate, Gymnodinium sp. were alsoobserved.  While the first bloom subsided withina day, the second bloom lasted for nearly threeweeks. Bloom-2 spread to regions further south ofKollam and species such as theholococcolithophore, Helladosphaera sp.(Ramaiah, et al., 2005) bloomed during the laterstages.  During 23-26 September 2004, a study(Ramaiah et al., 2005) in this region showed thatthe abundance of Helladosphaera sp. was in excessof 1.8 x 106 cells l-1.  During bloom-2 an unusualand strong stench was reported from the coast offKollam and Vizhinjam and several childrencomplained of nausea, chest pain and bouts ofbreathlessness.  However, there were no humanfatalities.The pearl oysters (Pinctada fucata, n = 5000)suspended in the plastic and lantern cages in thewooden raft of CMFRI in the bay were affected bybloom-1 and a mortality of 27% of oysters oflength range 48-80 mm was recorded.  Mortality ofa few farmed green mussels, Perna viridis, wasobserved in the adjacent raft.  The intensity ofbloom-2 was much more severe and it was observedthat the mantles of the oysters were shrunken andthe meat was flaccid (Fig.1C).  Complete mortalityof the stock (n= 5500) of pearl oysters of lengthrange 40 to 80 mm was noted within 24 hours ofthe bloom (Fig. 1D). The pearl oysters were highlysusceptible to Cochlodinium sp. unlike N.scintillans. Mortality of farmed pearl oysters dueto the blooms of N. scintillans and Cochlodiniumsp. were not observed previously in the Indianwaters but similar mortality of farmed pearl oystersdue to the bloom of Trichodesmium sp. was reportedin the pearl farm of CMFRI at Veppalodai alongthe southeast coast (Alagarswami, 1991).  Jugnu(2006) reported on the large scale mortality ofgreen mussels along Calicut coast due to the bloomof the raphidophyte Chatonella marina and on themortality of farmed shrimps and fishes along VypinIsland in central Kerala due to the bloom ofGymnodinium sp.  Along the British Columbiacoast, bloom of Cochlodinium polykrikoides at adensity of 6 x 104 cells ml–1 caused substantialmortality to the farmed salmon with lossesestimated at Canadian $2 million (Whyte et al.,2001).   They observed that the fishes stoppedfeeding when cell counts exceeded 500 cells ml–1.Recently blooms of Cochlodinium sp. also led tofish kills at Iligan bay, Philippines (Vicente et al.,2002).Both the present HABs were observed duringSeptember and instances of similar Noctiluca215Journal of the Marine Biological Association of India (2007)Mortality of farmed peal oyster and Noctiluca bloomsblooms along the west coast of India were reportedbetween August and November (Mathew et al.,1988) which marked the end of upwelling alongthe coast. Sreekumaran et al. (1992) observed thatalong the west coast of India regular blooms ofNoctiluca sp. occur during or immediately afterthe onset of the monsoon following an increase inphytoplankton population.  Jugnu (2006) alsofound that blooms of Noctiluca sp. occurred atChombala in north Kerala and Vizhinjam in southKerala in the monsoon months preceded by rainsand diatom maxima. During the blooms of N.scintillans in August 2003 at Vizhinjam, theseawater was golden yellow colour near the shorewith a frothy appearance along the shoreline.Noctiluca was present at a density of 1.02 x 10 5cells l-1 in the sea and at a lesser density of 5.5 x104 cells l-1 in the Vizhinjam bay (Jugnu, 2006).Shetty et al. (1988) observed a cell density of 8.2x 109 cells m-3, Venugopal  et al. (1979) accountedfor a cell density of 3-7.7 x10 5 cells m-3  whereas,Nayak et al. (2000) recorded a cell density of 1.56x 10 6 cells m-3 of the same species at differentcentres along the west coast of India. Rich foodsupply is basically necessary for the species toreproduce massively, but suitable temperature andFig. 1. (A) Noctiluca scintillans cell from bloom-1; (B) Cochlodinium cells in chain and pairs frombloom-2; (C) A view of the clogged gills, shrunken mantle and flaccid meat of the farmed pearl oysterPinctada fucata killed by bloom-2 of Cochlodinium sp; (D) A view of the dead shells of pearl oystersstocked in cages in the raft farm of CMFRI at Kollam bay.216Journal of the Marine Biological Association of India (2007)K. S. Mohamed et al.stable weather without heavy rain also appear to befavourable factors.In Kollam Bay during bloom-1, the pigmentschlorophyll a and c content of the seawater wereestimated as 1.14 and 0.019 mg m-3 while chl bwas absent. Chl a and c values were lower in thepreceding and succeeding months with values of0.05  and 0.04 mg m-3 in August and 0.65 and 0.07mg m-3 in October (Table 1). Compared to the pre-bloom-2 period (August 2004), the concentrationof chlorophyll pigments was low during bloomperiod and post-bloom period of September andOctober (Table 1) indicating a departure from thenormal.  The major physicochemical and biologicalparameters measured before, during and after thebloom are given in Table 1.The atmospheric temperature, sea surfacetemperature, salinity and pH did not show muchdifference. However, considerable differences ofphysicochemical parameters were observed.  Thetotal suspended solids increased from 24.8 inAugust to 27.2 mg l-1 during bloom-1 and againdecreased to 23.9 mg l-1 in the following month.During bloom-2 the TSS level reached 154.8 mgl-1 and decreased to 16.8 mg l-1subsequently.Ammonia concentrations were also comparativelyvery high during both the blooms.  Ammonia whichwas nil in August 2003 increased to 14.9 µmol l-1during bloom-1. During bloom-2 also a hike inammonia level was noted.  A high value of ammoniaof 82 µg at.l-1 was observed by Nayak et al. (2000)during N. scintillans bloom off Mangalore.Dissolved phosphate, nitrite and nitrate valuesshowed a marginal increase during bloom-1 whilethe increase was considerably higher duringbloom-2 of 2004.  According to Della-Cruz et al.(2000), N. scintillans is an indicator of coastaleutrophication, in New South Wales coastal waterswhere the frequency of occurrence has increased inrecent years with increasing nutrient load.  Theyalso observed that extensive red tides of Noctilucaoften succeeded diatom blooms, specificallyThalassiosira sp.Table 1. Environmental parameters and cell densities during the blooms of the dinoflagellates Noctiluca scintillans andCochlodinium sp. at Kollam Bay, Kerala  Parameters Bloom-1 Bloom-2Pre-bloom Bloom Post-bloom Pre-bloom Bloom Post-bloomAugust 03 September 03 October 03 August 04 September 04 October 04Noctiluca scintillans (cells l-1 ) 0 9.8 x 104 0 0 0 0Cocholdinium sp. count (cells l-1 ) 0 0 0 0 1.2 x 10 5 0Atmospheric temperature  (o C) 27 28 29 27 28 29Sea surface temperature  (o C) 28 29 29 25 27 27Salinity  (ppt) 32 33 34 35 33 33pH 8.1 8.1 8.1 7.9 7.4 7.8Dissolved oxygen (mg l-1) 5.8 4.8 4.9 3.8 * 6.5Total suspended solids (mg l-1) 24.8 27.2 23.9 31 154.82 16.8Ammonia (µmol l –1 ) negligible 14.9 5.7 7.18 14.72 5.03Phosphate (µmol l –1 ) 1.24 1.7 0.93 negligible 15.95 12.62Nitrate (µmol l –1 ) 0.06 0.08 0.06 0.7 2.4 0.55Nitrite (µmol l –1 ) 2.1 0.24 0.93 8.37 24.52 14.89Chlorophyll a (mg m-3) 0.05 1.14 .65 2.4 1.2 0.2Chlorophyll b (mg m-3) 0.03 0 0 0 0.21 0.05Chlorophyll c (mg m-3) 0.04 0.019 0.07 0.27 0.47 0.06*could not be estimated due to discoloration of sample water217Journal of the Marine Biological Association of India (2007)Mortality of farmed peal oyster and Noctiluca bloomsRamaiah et al. (2005) who made a detailedstudy of bloom-2 about two weeks after the bloomoccurred in Kollam found the holococcolithophore,Helladosphaera sp. as the main species in thebloom, besides a dozen other species of diatoms.However, they did not record Cochlodinium sp.Species successions are common in long-durationalgal blooms (Smayda and Reynolds, 2001).Ramaiah et al. (2005) also suggested thatoccurrence of such blooms during Septemberindicates that several physical processes must havehelped the holococcolithophores to bloom. Theyreported that the minimum de-tided sea level (i.e.sea level from which tidal variations have beenremoved) was recorded by the tide gauge in CochinPort area on September 6, 2004, and from this theyconcluded that when the thermocline is shallowthe region becomes vulnerable to events that canbring high quantities of nutrients to the surface.This would have resulted in the right conditionsfor the algal blooms to develop.The large scale mortality of pearl oysters is awarning that precautionary management measuresmust be taken to protect the farmed stock.  Whenaquaculture programs are planned, facilities mustbe developed to relocate the pearl oyster stock inshore based collapsible pools with good aerationin clean filtered seawater for 2 to 3 days in suchexigencies so that the mortality of high valuedfarm stock and economic losses can be avoided.AcknowledgementsThe authors are thankful to the Director, CMFRIand to Dr. K. K. Appukuttan, Head, MolluscanFisheries Division for facilities and encouragement.Dr. C. P. Gopinathan, former Principal Scientist,CMFRI helped to confirm plankton speciesidentity.  They are grateful to the fishermen ofKollam Bay for the timely alert on the bloom inthe farm area.ReferencesAlargaswami, K. 1991. Production of cultured pearls. IndianCouncil of Agricultural Research, New Delhi. 112 pp.Bhimachar, B. S. and P. C. George. 1950.  Abrupt setbackin the fisheries of the Malabar and Kanara coasts andred water phenomenon and their probable cause. Proc.Ind. Acad. Sci., 31: 339-350.Della-Cruz, J., A. Penelope, L. Randall and I. Suthers.2000. Noctiluca scintillans - An indicator of coastaleutrophication? In: HAB Ninth conference Tasmania,2000.  www.utas.edu.au /docs/ plant science/HAB2000/ abstracts/docs.Devassy, V. P. and S. R. S. Nair. 1987. Discolouration ofwaters and its effect on fisheries along the Goa coast.Mahasagar, 20:121-128.Eashwar, M. T., Nallathambi, K. 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Keddy.2001. First record of blooms of Cochlodinium sp.(Gymnodiniales, Dinophyceae) causing mortality toaquacultured salmon on the west coast of Canada.Phycologia, 40: 298-304.Received: 12 March 2008Accepted: 28 March 2008

Mortality of farmed pearl oyster Pinctada fucata (Gould, 1850) due to the blooming of Noctiluca scintillans and Cochlodinium sp. at Kollam Bay, Kerala

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Mortality of farmed pearl oyster Pinctada fucata (Gould, 1850) due to the blooming of Noctiluca scintillans and Cochlodinium sp. at Kollam Bay, Kerala

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