The oceans are home to thousands of microscopic

algae which constitute the base of the marine

food web. These phytoplankton are essential for the

production of biomass at all levels of the food web

and thus play an important role in ocean’s ecology

Jugnu, R

Kripa, V

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C M Y K3Table 1  Regression coefficients and goodness of fit for relationships between SBI and catchS. No Relationship Regression coefficients Goodness of fit (R2) Remarks1 L mean and catch y = -13663x + 384834 0.1738 Poor fit – no relationship2 L range and catch y = 1E-05x + 5.6383 0.2129 Poor fit – no relationship3 L min and catch y = -1E-05x + 13.634 0.4596 Moderately good relationship4 L max and catch y = 6E-07x + 19.108 0.0033 Poor fit – no relationshipThese results are in contrast to what has beenobserved for temperate water stocks, where adecrease in mean length and maximum length cansignify adverse fishing effects on the population.  Inthe case of oil sardine, L mean was not a good predictorof stock health, probably because of the fast growthrate and the presence of multiple broods in thepopulation.  The L min was however a reasonably goodpredictor of recruitment success and eventually agood fishery.  The use of SBI in tropical fish stocksneeds to be evaluated for more number of speciesbefore definite conclusions can be drawn. A recentstudy on demersal fish stocks of northwest Africa alsoshows that changes in size structure is not  a suitableindicator for the effects of fishing in areascharacterized by faster growth rates, small sizes, highspecies diversity and complex interrelationships, suchas the tropics.This work was carried out under an AP CessFund project on ‘Assessing the impact of fisherieson the biodiversity of marine fish resources ofsouthwest coast of India’ and one of the targets ofthe projects was to evaluate the usefulness of SBIfor assessing the impact of fishing on fish populations.Prevalence of non toxic and harmful algal blooms along Kerala coastJugnu R and V.KripaCentral Marine Fisheries Research Institute, KochiThe oceans are home to thousands of microscopicalgae which constitute the base of the marinefood web. These phytoplankton are essential for theproduction of biomass at all levels of the food weband thus play an important role in ocean’s ecology.Beneficial phytoplankton blooms defined as –‘aUse of Size-based Indicators in Indian oil sardine (Sardinella longiceps) fisheryFig.4. Striking inverse relationship between L minand catch of oil sardineFig.5. Scatter plot showing inverse relationshipbetween Lmin and catch4 Marine Fisheries Information Service T&E Ser., No. 195, 2008significant population increase during which the bloomand the subordinate species within the communityhave equivalent ecological and physiological valence’,are thus intrinsically beneficial to food web processesas they channel carbon or energy into the marine foodweb. There are, however a few dozen of algal specieswhose blooms are associated with some adverseimpacts. According to International Council For theExploration of Seas (1984), exceptional blooms havebeen defined as ‘those which are noticeable,particularly to the general public, directly or indirectlythrough their effects such as visible discolouration ofthe water, foam production, fish or invertebratemortality or toxicity to humans’. Species abundancedata is considered crucial, as it gives valuableinformation on quantitative and qualitative changesin the relative frequency of occurrence of exceptional/harmful algal species.Study SiteA continuous study is thus essential forunderstanding the bloom dynamics of a region. Acontinuous and regular phytoplankton monitoring wasdone at two sites, one each along the north and southcoasts of Kerala. Sites were selected on the basis ofprevious records of harmful algal bloom occurrences.Vizhinjam in Trivandrum district, situated in theextreme southwest coast of India (Lat 80 22' N, Long76o 56' E) was selected as sampling station alongsouth Kerala. A natural bay (Vizhinjam bay) is presentin the region formed by two rock promontories,Mathalipuram on the west and Kottapuram in the east,which makes the area an enclosed water bodyfacilitating fishing and mariculture operations.Samples were collected from two sites at Vizhinjam,one from within the bay and the other from theadjacent sea. Chombala in Calicut district (Lat 11043' N, Long 75o 33' E) was selected as the samplingsite in the north coast of Kerala. Samples werecollected from a depth of 8 meters at a distance ofabout 3 kilometers from the shore, at Chombala andVizhinjam sea. In the bay, the depth was 6 meters.Sampling was done at a monthly frequency at boththese stations for a period of two years, Chombalafrom October 2001 to September 2003 and atVizhinjam from October 2001 to August 2003.Sampling could not be done during September 2003at Vizhinjam, as the sea was very rough due tonortheast monsoon winds.Harmful algae in the communityTwelve species with known records of toxicity-Noctiluca scintillans, Gymnodinium mikimotoi,Prorocentrum lima, Prorocentrum micans, Dinophysiscaudate, Dinophysis acuminata, Dinophysis miles,Pseudo-nitzschia sp, Pseudo-nitzschia pungens,Chattonella marina, Ceratium fusus andTrichodesmium sp. were identified to occur along theKerala coast. Of these Prorocentrum lima andChattonella marina were unique to Chombala andCeratium fusus and Dinophysis miles to Vizhinjam.Pseudo- nitzschia spp., a major causative agentin Amnesic Shellfish Poisoning (ASP) was also notedat both the sites. Mouse bioassay showed thepresence of a water soluble toxin in the month in whichthe species was present in the community.Occurrence of algal bloomsSeventeen algal blooms were recorded along theKerala coast during the study period. At Chombala,there were 9 algal blooms of which 7 were diatomblooms. Two of them were caused by the speciesCoscinodiscus asteromphalus (53,000 and 4,10,000cells l-1), and one each by C.janischii (35,000 cells l-1),Thalassiothrix frauenfeldii (88,500 cells l1),Thalassionema nitzchioides (3,75,600 cells l-1) andPleurosigma normanii (26,40,000 cells l-1) and 2 dueto the harmful alga Chattonella marina (17 x104 and13.5x106 cells l-1).In the coastal waters of Vizhinjam, 7 blooms wererecorded, of which 6 were diatom blooms. Three ofthe blooms were caused by Chaetoceros curvisetus(1x105 –1.82x107 cells l-1) and one each by C. eibinii(82 to 85x105 cells l-1), Fragilaria oceanica (46,000and 498000 cells l-1) and Coscinodiscus sublineatus(82,850 and 128500 cells l-1)  and one harmful bloomcaused by the dinoflagellate Noctiluca scintillans(102000 and 55000 cells l-1). The harmfuldinoflagellate D. caudata formed 23 % of thephytoplankton community at Vizhinjam in December2001, but no casualties were reported.A massive bloom of Chattonella marina with highdensity of 4.68 x 10 5 cells l-1 was recorded for thefirst time from Narakkal region along Vypin island,central Kerala. Bloom of Noctiluca scintillans (98,000cells l-1) and associated mortality, especially ofbivalves was recorded at Thankassery bay, a5semienclosed man made bay along south Kerala inOctober 2002. At both the stations, it was noticed thatthe dominant members of the phytoplanktoncommunity of the region, the diatoms, bloomed firstutilizing the favourable conditions. The diatomCoscinodiscus asteromphalus blooms at lowertemperatures, <310C and salinity, <33 ppt. Rather thana definite range, the bloom was found to be stimulatedby a sudden lowering of both the parametersassociated with rainfall. Cell densities were highestwhen the temperatures was the lowest, 270 C. Nitrateand phosphate were higher, with dissolved inorganicphosphate between 0.4 to 3 µmol l-1 and dissolvedinorganic nitrate between 2.8 and 23.02 µmol l-1.Associated with the bloom, an increase in TSS levels(10.4- 50.2mg l-1) and a decrease in dissolved oxygenlevels (3.26- 4.83 mg l-1) were observed.Pennate diatoms Thalassiothrix frauenfeldii,Asterionella japonoica, Thalassionema  nitzschoides,Pleurosigma normanii were found to bloom at lowertemperatures (<300C), but at higher salinities (30 to36 ppt) and had an absolute requirement forphosphate (>1.25 µmol l-1) as indicated by thetriggering of the bloom when there was an additionof phosphate to the system. An increase in nitrogensource was not found essential. Fragilaria oceanicabloomed when phosphate was higher than. 2.5 andnitrate between 10.16 to 19 µmol l-1 respectively.Chaetoceros, the most frequent bloomer atVizhinjam was found to prefer lower temperatures(27-28oC), but higher salinities (34-35 ppt), had alower requirement for nutrients but bloomed wheneverthere was a slight increase in nutrients, in either nitrateor phosphate. At Vizhinjam, the species bloomedwhen the dissolved inorganic nitrogen was between0.06 to 11.68 µmol l-1 and dissolved inorganicphosphate between 0 to 1.41 µmol l-1. Decrease insurface temperature, increase in surface salinity andan increase in nutrients especially that of phosphatefollowing monsoon and upwelling led to the bloomingof Chaetoceros curvisetus. A lesser temperature ledto the replacement of this species and blooming ofanother, C.eibinii. A further increase in nutrientconcentration was followed by the bloom of the diatomFragilaria oceanica succeeded by Coscinodiscus andthen when the nutrient levels were low, C. curvisetusbloomed. Noctiluca scintillans was recorded atChombala, Vizhinjam and Thankassery bay. It waspresent in low densities at Chombala (100 to 142cells l-1) but reached bloom densities at Vizhinjam andThankassery bay (1,02,000 and 98,000 cells l-1).Abundance of diatoms, its main food and stableweather with high temperatures led to its bloom. AtVizhinjam and Thankassery, the species bloomedwhen the concentration of nitrate was high>15µmol l-1. Along the Calicut coast, the bloom ofChattonella marina was observed in the transitionperiod between SW and NE monsoon indicating awell-defined periodicity and annual rhythm inappearance. The annual cycle of occurrence of thealga is controlled by the formation of cyst and itsgermination. The excystement of cysts showed astrong correlation with temperatures and thevegetative cells remained in bloom condition as longas a higher temperature was maintained, perishingwith the lowering of temperature associated with theonset of NE monsoon.The phytoplankton blooms in the study sites werefound to have two definite pattern, a restrictedseasonal occurrence as exemplified by marinediatoms that dominate spring blooms and a nonseasonal increase in densities of dinoflagellates inresponse to short term events such as sunny calmweather that establishes thin upper layer within whichmotile species accumulate. Noctiluca blooms alwaysfollowed diatom maxima and stable weather.Chattonella marina illustrated a different seasonalpattern similar to that of dinoflagellates but the bloomoccurs by the excystment of cysts which is triggeredby an increase in water temperature and is known tobe genetically controlled.Mass mortality of fishes was observed in theregion between Puthiyappa and Kappad during thebloom of Chattonella marina in September 2002.Major fishes which were killed include Epinephelusspp, Otolithes sp, Cynoglossus sp and Johnius sp.Subsequent to this, mass mortality of green musselsof the region was also observed. Besides fishes andmussels, the mole crab Emerita spp  and the bivalveMactra violacea also suffered severe mortality. Lowdissolved oxygen (0.22 mg/l), low pH (7.05) and theproduction of a lipid soluble toxin were the majorreasons for the large scale mortality during theChattonella marina blooms.Prevalence of non toxic and harmful algal blooms along Kerala coast

Prevalence of non toxic and harmful algal blooms along Kerala coast

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