Research Article Occurrence and Distribution of a Diatom

Hindawi Publishing CorporationInternational Journal of OceanographyVolume 2013 Article ID 350594 6 pageshttpdxdoiorg1011552013350594

Research ArticleOccurrence and Distribution of a Diatom-DiazotrophicCyanobacteria Association during a Trichodesmium Bloom inthe Southeastern Arabian Sea

T Jabir1 V Dhanya2 Y Jesmi1 M P Prabhakaran1 N Saravanane2

G V M Gupta2 and A A M Hatha1

1 Department of Marine Biology Microbiology and Biochemistry School of Marine SciencesCochin University of Science and Technology Fine Arts Avenue Kochi 682016 Kerala India

2 Centre for Marine Living Resources and Ecology Kendriya Bhavan Kakkanad CSEZ PO Kochi 682037 Kerala India

Correspondence should be addressed to A A M Hatha mohamedhathagmailcom

Received 4 May 2013 Accepted 12 July 2013

Academic Editor Renzo Perissinotto

Copyright copy 2013 T Jabir et al This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Symbiotic diatom-diazotrophic cyanobacteria association (DDA) of Rhizosolenia hebetata and Rhizosolenia formosa withendosymbiotic cyanobacteria Richelia intracellularis was noticed and documented for the first time during a bloom of thecyanobacterium Trichodesmium erythraeum in the oligotrophic shelf waters along Kochi and Mangalore transects southeasternArabian Sea (SEAS) during spring intermonsoon (April 2012) Although the host is frequently seen the symbiont is rarely reportedin the Indian EEZ The presence of nitrogen-fixing symbiotic association of Rhizosolenia-Richelia along with Trichodesmiumerythraeum highlights the significance of DDAs on the nutrient and energy budgets of phytoplankton in the oligotrophicenvironments of the Arabian Sea during spring intermonsoon

1 Introduction

Planktonic organisms that fix atmospheric nitrogen (dia-zotrophs) have a critical role in oceanic production andin the marine nitrogen cycle [1] Abundance and growthrates of such organisms depend on their ability to assimilatevarious sources of nitrogen [2] The availability of fixednitrogen (such as nitrate and ammonium) can limit theproductivity of the sea [3] Diatom-diazotroph associations(DDAs) are widely reported in oligotrophic waters and havethe capacity to form episodic largely monospecific bloomsthat exhibit very high rates of carbon and nitrogen fixationworldwide [4ndash7] Annually Trichodesmium contributes 1ndash5mmolNmminus2 dminus1 while diazotrophic diatoms contribute04ndash24mmolNmminus2 dminus1 which forms one quarter of thetotal input of nitrogen to the sea [8] Globally DDAs fix479 TgN yminus1 [9] which forms almost 25 of total input ofnitrogen to the sea [8]

One of the most conspicuous free-living diazotrophicspecies is the colony-forming cyanobacteria a species ofthe Trichodesmium that is found throughout tropical and

subtropical oceans and forms large-scale surface blooms[10] A unique group of open ocean diazotrophs is theheterocystous cyanobacteria that live symbiotically withother members of phytoplankton primarily diatoms Suchendosymbiotic associations help most of the diatoms to fixatmospheric nitrogen in oligotrophic waters with the helpof such endosymbiotic associations [11ndash13] The cyanobacte-ria Richelia intracellularis and Calothrix rhizosoleniae werefound in associationwith diatom genera such asRhizosoleniaHemiaulus Bacteriastrum and Chaetoceros They are alsoseen as epiphyte or endosymbiont in Guinardia cylindrusin warm tropical and subtropical oligotrophic waters [612 14] Only a few workers have reported Rhizosolenia-Richelia associations from the Indian Exclusive EconomicZone (EEZ) [15ndash18] Several reports [15ndash17] described theoccurrence of this species from the southeast coast of Indiawhile there is only one report [18] from the northeasternArabian Sea (NEAS)There are no reports on this aspect fromthe southeastern Arabian Sea (SEAS) This report forms thefirst in this regard

2 International Journal of Oceanography

Mangalore

KochiIndia

Arabian Sea

135∘N

13∘N

125∘N

12∘N

115∘N

11∘N

105∘N

10∘N

95∘N

9∘N

735∘E

74∘E

745∘E

75∘E

755∘E

76∘E

765∘E

77∘E

Figure 1 Study area showing sampling locations

Figure 2Trichodesmium erythraeum bloom observed in the coastalwaters along Kochi transect during April 2012

2 Materials and Methods

The study was a part of monthly observations made in thesoutheastern Arabian Sea (SEAS) and observations madealong the Kochi and Mangalore transects during April 2012(spring intermonsoon) are reported in this paper (Figure 1)Surface water samples were collected from both of thesetransects onboard Fisheries and Oceanographic ResearchVessel (FORV) Sagar Sampada Surface samples were col-lected from six stations based on depth (13 20 30 40 50and 100m) A surface sample was also collected from a bloomof Trichodesmium erythraeum located between the 50 and100m stations along Kochi transect (9∘ 571015840 5210158401015840N 75∘5010158403810158401015840EFigure 2)

Temperature and salinity data were obtained using a CTDrosette system (Sea-Bird SBE 911 plus) Dissolved oxygen(Winklerrsquos method) and nutrients in the sea water weredetermined using standard procedures [19] Surface sea watersamples were collected using a bucket sampling methodTwenty-five liters of sample were filtered through 20 120583mbolting silk net and preserved in 3 formalin and Lugolrsquos

Table 1 Hydrographical variables observed along the Kochi andMangalore transects during April 2012

Variables Range of observed valuesKochi Mangalore

Temperature (∘C) 3010ndash3070 3006ndash3144Salinity (psu) 3389ndash3501 3460ndash3519Wind speed (msminus1) 241ndash1398 244ndash997DO (mlLminus1) 402ndash494 405ndash469Ammonia (120583M) 041ndash194 037ndash169Nitrate (120583M) 006ndash196 004ndash024Silicate (120583M) 049ndash158 170ndash530Phosphate (120583M) 011ndash052 003ndash056

iodine Live and preserved samples were analysed using aNikon Eclipse microscope with a Nikon DN 100 series digitalcamera and photomicrographs of the samples were takenIdentification of species was done using standard references[20 21]

3 Results and Discussion

The endophytic cyanobacteria were identified as Richeliaintracellularis J Schmidt 1901 The systematic position of Rintracellularis is given below

class Cyanophyceaeorder Nostocalesfamily Nostocaceaesubfamily Anabaenoideae

Trichomes of Richelia intracellularis are solitary short 13ndash20 celled straight or slightly arcuated more or less cylin-drical along the whole length without sheaths or gelatinousenvelopes isopolar and slightly constricted at cross-wallsHeterocytes are more or less spherical and develop termi-nally on one or (later) on both ends they are sphericalwider than vegetative cells Akinetes are lacking They aremarine in nature and generally seen as endophytic withincells (intracellular) of oceanic planktonic diatoms mainlyin species of Rhizosolenia and sometimes in species ofHemiaulus and as epiphytic on species of Chaetoceros [6 1214] However in the present studyR intracellulariswas foundto be symbiotic in Rhizosolenia hebetata and R formosaThe occurrence of this diatom-diazotroph association is thefirst record from the coastal waters of SEAS Examinationof slide preparations of the collected samples using epifluo-rescence microscopy revealed the presence of Rhizosolenia-Richelia symbioses Two trichomes ofR intracellularis havingunequal length were observed within the cells of Rhizosoleniahebetata (Figure 3(a)) and four trichomes within R formosa(Figure 3(b)) The prevailing hydrographic conditions aregiven in Table 1 which depicts the tropical and oligotrophiccharacteristics of these coastal waters

Examination of preserved samples using bright fieldinverted microscopy revealed the presence of Rhizosolenia-Richelia symbiosis Cells of Rhizosolenia hebetata containing

International Journal of Oceanography 3

(a) (b)

Figure 3 (a) Rhizosolenia hebetata with trichomes of Richelia intracellularis (times400) (b) Rhizosolenia formosa (times400) with trichomes ofRichelia intracellularis

Richelia intracellularis in general had two trichomes withheterocyst located at the ends of the filaments (Figure 3(a))Free living trichomes were not observed during the entirestudy Rhizosolenia hebetata was the only host diatomobserved from the Kochi transect It was also the dominanthost along the Mangalore transect except at station 2 whereRhizosolenia formosa was dominant with four trichomesin each diatom cell (Figure 3(b)) Although Rhizosoleniahebetata was found at all the stations the DDAs were seenonly at deeper stations (40ndash100m) along the Kochi transect(Figure 4(a)) and beyond 20m along the Mangalore transect(Figure 4(b))

Distribution of major groups in the phytoplanktonshowed that diatoms were dominant along both the Kochiand Mangalore transects constituting 83 and 58 respec-tively of the total phytoplankton population (Figures 5(a)and 5(b)) followed by cyanobacteria and dinoflagellatesTrichodesmium erythraeum constituted 45ndash85 and 40ndash60of the total cyanobacteria from the Kochi and Mangaloretransects respectively Rhizosolenia constituted 04 and06 of the total diatoms at the two transects respectivelyNumerical abundance of cells containing diazotrophs wasless than 5 cells Lminus1 at both of the transects The occurrencewas more widespread along the Mangalore transect where itwas observed at all stations except at 13m depth station Thebloom sample taken from deeper stations along the Kochitransect farther waters was dominated by Trichodesmiumerythraeum (over 85) while diatoms constituted only 64Rhizosolenia hebetata with endosymbiotic Richelia intracel-lularis abundance in the bloom sample was found to be 6cells Lminus1

The blooming of the cyanobacterium Trichodesmiumerythraeum is commonly seen in the SEAS during peak SIM(April-May) when favourable conditions like very warmcalm and nitrogen depleted conditions prevail [18] Duringthe present observation period there were near nitrate

depleted conditions at most of the stations (Table 1) whichis sufficient enough for Trichodesmium erythraeum to pro-liferate and bloom Interestingly the Rhizosolenia-Richeliaassociation was seen only with Trichodesmium erythraeumwhich means that the environmental requirements for theseto occur are the same The diazotrophs release fixed nitrogenas ammonium or dissolved organic nitrogen which is thenavailable to the nutrient starved nondiazotrophic community[8] Nitrate and phosphate concentrations were compara-tively low in the study area (Table 1)

Richelia intracellularis has been reported to be among themost important and widespread nitrogen-fixing endosymbi-otic cyanobacteria in marine pelagic tropical and subtropicalwaters [22 23] However reports of such studies in theArabian Sea are scant and not previously documented fromthe SEAS The heterocystous R intracellularis is an extracel-lular endosymbiont which locates itself in the periplasmicspace between the plasmalemma and silica cell wall in thediatoms [22] It was found as an endosymbiont in five speciesof Rhizosolenia Hemiaulus membranaceus H hauckii andGuinardia cylindrus and rarely as an epiphyte on Chaetocerosspecies or exists freely in water [22] It is assumed that theabundance of endosymbiotic cyanobacteria was due to theircapacity to fix atmospheric nitrogen in oligotrophic waters

This is the first reported observation on the occurrence ofthe nitrogen-fixing endosymbiotic cyanobacterium Richeliaintracellularis in Rhizosolenia hebetata and R formosa in theSEAS along with Trichodesmium erythraeum blooms whichoccurred offmost parts of Kochi andMangalore transects andappeared like a saw-dust mat in the surface waters (Figure 2)These waters were characterised by stratification during thespring intermonsoon (SIM) and strong upwelling during thesummer monsoon [24] The Arabian Sea during the SIM(MarchndashMay) is renowned for its stratified condition whichresults in nutrient poor oligotrophic surface waters (Table 1)Such conditions favour high abundance of nitrogen-fixing


02468

101214161820

13 20 30 40 50 100Station depth (m)

Cel

ls Lminus

1

Rhizosolenia without RicheliaRhizosolenia with Richelia

(a)

0

2

4

6

8

10

12

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)

Figure 4 Cell density of Rhizosolenia with and without Richeliaintracellularis along (a) Kochi and (b) Mangalore transects

cyanobacteria in both coastal and open ocean waters It wasobserved that the occurrence of Rhizosolenia species withRichelia intracellularis was coincided with Trichodesmiumerythraeumwhere nitrate levels were very low (004ndash196 120583M)and ammonium concentrations were sufficiently high (037ndash194 120583M) This indicates that the diazotrophs along withcyanophyceans not only support the production of a nondi-azotrophic phytoplankton community through regeneratedammoniumproduced from these nitrogen fixers [17] but alsoplay a significant role in nitrogen cycling and the budget ofoligotrophic SEAS during the SIM

Observations on diatom-diazotroph symbioses are lack-ing in the eastern Arabian Sea as the importance of DDAs inthe nutrient budget of these oligotrophic waters is unknownThe nutrient profile of the study area reflects the oligotrophicconditions which may have resulted in the Rhizosolenia-Richelia symbiosis Forming a symbiotic association mightthen be considered as an ecological adaptation to life in theoligotrophic ocean Compared to their terrestrial counter-parts [25] marine symbiotic systems are greatly understud-ied and thus many intricacies of these relationships remainlargely unresolved This paper reports the first observationof occurrence of DDAs and is evidence for the presenceof symbiotic association of nitrogen-fixing organisms inSEAS This study is based on the visual examination of

0500

1000150020002500300035004000

13 20 30 40 50 100Station depth (m)

DiatomDinoflagellateCyanobacteria

Cel

ls Lminus

1

(a)

0

500

1000

1500

2000

2500

3000

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)

Figure 5 Distribution of major groups in the phytoplankton along(a) Kochi and (b) Mangalore transects

diatom assemblages using light microscopy It highlightsthe presence of potentially significant DDAs in the highlyproductive SEAS which directly affect the oceanic nutrientinventory through the addition of new nitrogen to the oceanecosystemAlthough there have been observations on bloomsof Trichodesmium species in the Arabian Sea there havebeen relatively few reports on the contribution of nitrogenfixation by cyanobacteria to the marine nitrogen budget[26] According to Gandhi et al [27] nitrogen fixation byTrichodesmium species occurs mainly in the upper 10m ofthe ocean surface and their fluxes to the Arabian Sea wereestimated to be at 154 plusmn 15TgN yminus1 which is equivalentto sim92 of total ldquonewrdquo nitrogen supply to the Arabian Seaand sim11 of the global nitrogen fixation DDAs althoughfound less in number in the SEAS during the present studysymbiotically support noncyanophyceans (diatoms) in fixingnitrogen for their metabolic activity thereby their role in thenitrogen cycling of the region is very important

4 Conclusion

The present study highlights the presence of diatom-diazotroph symbiotic associations which along with Tri-chodesmium erythraeum influence the nutrient and energy


budgets of phytoplankton in the oligotrophic environment ofthe SEAS

Abbreviations

SEAS Southeastern Arabian SeaNEAS Northeastern Arabian SeaDDA Diatom-diazotrophic associationSIM Spring intermonsoonEEZ Exclusive Economic Zone

Acknowledgments

This work was supported by the Ministry of Earth Sciences(MoES) Government of India under the Sustained IndianOcean Biogeochemical Cycle and Ecological Research (SIBER)programme The authors are thankful to the Centre forMarine Living Resources and Ecology (CMLRE) KochiIndia and the researchers and staff members of FORV SagarSampada for providing the facilities for sampling and also tothe Head Department of Marine Biology Microbiology andBiochemistry School of Marine Sciences Cochin Universityof Science and Technology (CUSAT) Kochi for providingnecessary facilities for carrying out this work

References

[1] J E Dore R M Letelier M J Church R Lukas and DM Karl ldquoSummer phytoplankton blooms in the oligotrophicNorth Pacific Subtropical Gyre historical perspective andrecent observationsrdquo Progress in Oceanography vol 76 no 1pp 2ndash38 2008

[2] BD Jenkins J P Zehr AGibson and L Campbell ldquoCyanobac-terial assimilatory nitrate reductase gene diversity in coastal andoligotrophic marine environmentsrdquo Environmental Microbiol-ogy vol 8 no 12 pp 2083ndash2095 2006

[3] A White ldquoThe trouble with the bubblerdquo Nature vol 488 pp290ndash291 2012

[4] R A Foster A Subramaniam C Mahaffey E J Carpenter DGCapone and J P Zehr ldquoInfluence of theAmazonRiver plumeon distributions of free-living and symbiotic cyanobacteria inthe western tropical north Atlantic Oceanrdquo Limnology andOceanography vol 52 no 2 pp 517ndash532 2007

[5] L Martınez M W Silver J M King and A L AlldredgeldquoNitrogen fixation by floating diatom mats a source of newnitrogen to oligotrophic ocean watersrdquo Science vol 221 no4606 pp 152ndash154 1983

[6] A L Alldredge and M W Silver ldquoAbundance and productionrates of floating diatom mats (Rhizosolenia castracanei and Rimbricata var shrubsolei) in the Eastern Pacific OceanrdquoMarineBiology vol 66 no 1 pp 83ndash88 1982

[7] T H Mague N M Weare and O Holm-Hansen ldquoNitrogenfixation in the North Pacific OceanrdquoMarine Biology vol 24 no2 pp 109ndash119 1974

[8] A J Poulton M C Stinchcombe and G D Quartly ldquoHighnumbers of Trichodesmium and diazotrophic diatoms in thesouthwest Indian Oceanrdquo Geophysical Research Letters vol 36no 15 Article ID L15610 2009

[9] E J Carpenter J P Montoya J Burns M R Mulholland ASubramaniam and D G Capone ldquoExtensive bloom of a N

2

-fixing diatomcyanobacterial association in the tropical AtlanticOceanrdquo Marine Ecology Progress Series vol 185 pp 273ndash2831999

[10] D G Capone J A Burns J PMontoya et al ldquoNitrogen fixationby Trichodesmium spp an important source of new nitrogento the tropical and subtropical North Atlantic Oceanrdquo GlobalBiogeochemical Cycles vol 19 no 2 Article ID GB2024 pp 1ndash17 2005

[11] R A Foster A Subramaniam and J P Zehr ldquoDistributionand activity of diazotrophs in the Eastern Equatorial AtlanticrdquoEnvironmental Microbiology vol 11 no 4 pp 741ndash750 2009

[12] M E Ferrario V Villafane W Helbling and O Holm-HansenldquoThe occurrence of the symbiont Richelia in Rhizosolenia andHemiaulus in the North Pacificrdquo Revista Brasileira de Biologiavol 55 no 3 pp 439ndash443 1995

[13] T A Villareal ldquoMarine nitrogen-fixing diatom-cyanobacteriasymbiosesrdquo in Marine Pelagic Cyanobacteria Trichodesmiumand Other Diazotrophs E J Carpenter D G Capone andJ G Rueter Eds pp 163ndash175 Kluwer Academic PublishersAmsterdam The Netherlands 1992

[14] F Gomez K Furuya and S Takeda ldquoDistribution of thecyanobacterium Richelia intracellularis as an epiphyte of thediatom Chaetoceros compressus in the western Pacific OceanrdquoJournal of Plankton Research vol 27 no 4 pp 323ndash330 2005

[15] M O P Iyengar and T V Desikachary ldquoA systematic account ofsome marine Myxophyceae of the South Indian coastrdquo Journalof Madras University vol 16 pp 37ndash63 1944

[16] R Subrahmanyan ldquoA systematic account of the marine plank-ton diatoms of the Madras coastrdquo Proceedings of the IndianAcademy of Sciences B vol 24 no 4 pp 85ndash197 1946

[17] V V Kulkarni R R Chitari D D Narale J S Patil andA C Anil ldquoOccurrence of cyanobacteria-diatom symbiosis inthe Bay of Bengal implications in biogeochemistryrdquo CurrentScience vol 99 no 6 pp 736ndash737 2010

[18] K B Padmakumar B R Smitha L C Thomas et al ldquoBloomsof Trichodesmium erythraeum in the South Eastern Arabian Seaduring the onset of 2009 summer monsoonrdquo Ocean ScienceJournal vol 45 no 3 pp 151ndash157 2010

[19] K Grasshoff M Erhardt and K Kremling Eds Methods ofSeawater Analysis Chemie Weinheim Germany 2nd edition1983

[20] C R Tomas IdentifyingMarine Phytoplankton Academic pressNew York NY USA 1997

[21] R Santhanam N Ramanathan K Venkataramanujam and GJegatheesan ldquoPhytoplankton of the Indian seasrdquo in An Aspectsof Marine Botany Daya Delhi India 1987

[22] T J Lyimo ldquoDistribution and abundance of the cyanobacteriumRichelia intracellularis in the coastal waters of Tanzaniardquo Journalof Ecology and the Natural Environment vol 3 no 3 pp 85ndash942011

[23] S Janson J Wouters B Bergman and E J Carpenter ldquoHostspecificity in the Richelia-diatom symbiosis revealed by hetRgene sequence analysisrdquo Environmental microbiology vol 1 no5 pp 431ndash438 1999

[24] HHabeebrehmanM P Prabhakaran J Jacob et al ldquoVariabilityin biological responses influenced by upwelling events in theEastern Arabian Seardquo Journal of Marine Systems vol 74 no 1-2pp 545ndash560 2008


[25] A N Rai E Soderback and B Bergman ldquoCyanobacteriumndashplant symbiosesrdquo New Phytologist vol 147 no 3 pp 449ndash4812000

[26] T K Westberry and D A Siegel ldquoSpatial and temporaldistribution of Trichodesmium blooms in the worldrsquos oceansrdquoGlobal Biogeochemical Cycles vol 20 no 4 Article ID GB40162006

[27] N Gandhi A Singh S Prakash et al ldquoFirst direct measure-ments of N

2

fixation during a Trichodesmium bloom in theeastern Arabian Seardquo Global Biogeochemical Cycles vol 25 no4 Article ID GB4014 2011

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Mining


Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal of

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OceanographyInternational Journal of


Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering


GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of


OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in


MineralogyInternational Journal of


MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Geological ResearchJournal of


Geology Advances in


Mangalore

KochiIndia

Arabian Sea

135∘N

13∘N

125∘N

12∘N

115∘N

11∘N

105∘N

10∘N

95∘N

9∘N

735∘E

74∘E

745∘E

75∘E

755∘E

76∘E

765∘E

77∘E

Figure 1 Study area showing sampling locations

Figure 2Trichodesmium erythraeum bloom observed in the coastalwaters along Kochi transect during April 2012

2 Materials and Methods

The study was a part of monthly observations made in thesoutheastern Arabian Sea (SEAS) and observations madealong the Kochi and Mangalore transects during April 2012(spring intermonsoon) are reported in this paper (Figure 1)Surface water samples were collected from both of thesetransects onboard Fisheries and Oceanographic ResearchVessel (FORV) Sagar Sampada Surface samples were col-lected from six stations based on depth (13 20 30 40 50and 100m) A surface sample was also collected from a bloomof Trichodesmium erythraeum located between the 50 and100m stations along Kochi transect (9∘ 571015840 5210158401015840N 75∘5010158403810158401015840EFigure 2)

Temperature and salinity data were obtained using a CTDrosette system (Sea-Bird SBE 911 plus) Dissolved oxygen(Winklerrsquos method) and nutrients in the sea water weredetermined using standard procedures [19] Surface sea watersamples were collected using a bucket sampling methodTwenty-five liters of sample were filtered through 20 120583mbolting silk net and preserved in 3 formalin and Lugolrsquos

Table 1 Hydrographical variables observed along the Kochi andMangalore transects during April 2012

Variables Range of observed valuesKochi Mangalore

Temperature (∘C) 3010ndash3070 3006ndash3144Salinity (psu) 3389ndash3501 3460ndash3519Wind speed (msminus1) 241ndash1398 244ndash997DO (mlLminus1) 402ndash494 405ndash469Ammonia (120583M) 041ndash194 037ndash169Nitrate (120583M) 006ndash196 004ndash024Silicate (120583M) 049ndash158 170ndash530Phosphate (120583M) 011ndash052 003ndash056

iodine Live and preserved samples were analysed using aNikon Eclipse microscope with a Nikon DN 100 series digitalcamera and photomicrographs of the samples were takenIdentification of species was done using standard references[20 21]

3 Results and Discussion

The endophytic cyanobacteria were identified as Richeliaintracellularis J Schmidt 1901 The systematic position of Rintracellularis is given below

class Cyanophyceaeorder Nostocalesfamily Nostocaceaesubfamily Anabaenoideae

Trichomes of Richelia intracellularis are solitary short 13ndash20 celled straight or slightly arcuated more or less cylin-drical along the whole length without sheaths or gelatinousenvelopes isopolar and slightly constricted at cross-wallsHeterocytes are more or less spherical and develop termi-nally on one or (later) on both ends they are sphericalwider than vegetative cells Akinetes are lacking They aremarine in nature and generally seen as endophytic withincells (intracellular) of oceanic planktonic diatoms mainlyin species of Rhizosolenia and sometimes in species ofHemiaulus and as epiphytic on species of Chaetoceros [6 1214] However in the present studyR intracellulariswas foundto be symbiotic in Rhizosolenia hebetata and R formosaThe occurrence of this diatom-diazotroph association is thefirst record from the coastal waters of SEAS Examinationof slide preparations of the collected samples using epifluo-rescence microscopy revealed the presence of Rhizosolenia-Richelia symbioses Two trichomes ofR intracellularis havingunequal length were observed within the cells of Rhizosoleniahebetata (Figure 3(a)) and four trichomes within R formosa(Figure 3(b)) The prevailing hydrographic conditions aregiven in Table 1 which depicts the tropical and oligotrophiccharacteristics of these coastal waters

Examination of preserved samples using bright fieldinverted microscopy revealed the presence of Rhizosolenia-Richelia symbiosis Cells of Rhizosolenia hebetata containing


(a) (b)









02468

101214161820

13 20 30 40 50 100Station depth (m)

Cel

ls Lminus

1


(a)

0

2

4

6

8

10

12

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)




0500

1000150020002500300035004000

13 20 30 40 50 100Station depth (m)


Cel

ls Lminus

1

(a)

0

500

1000

1500

2000

2500

3000

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)



4 Conclusion




Abbreviations


Acknowledgments


References










2





















2











Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


(a) (b)









02468

101214161820

13 20 30 40 50 100Station depth (m)

Cel

ls Lminus

1


(a)

0

2

4

6

8

10

12

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)




0500

1000150020002500300035004000

13 20 30 40 50 100Station depth (m)


Cel

ls Lminus

1

(a)

0

500

1000

1500

2000

2500

3000

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)



4 Conclusion




Abbreviations


Acknowledgments


References










2





















2











Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in


02468

101214161820

13 20 30 40 50 100Station depth (m)

Cel

ls Lminus

1


(a)

0

2

4

6

8

10

12

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)




0500

1000150020002500300035004000

13 20 30 40 50 100Station depth (m)


Cel

ls Lminus

1

(a)

0

500

1000

1500

2000

2500

3000

13 20 30 40 50 100Station depth (m)


Cell

s Lminus1

(b)



4 Conclusion




Abbreviations


Acknowledgments


References










2





















2











Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in



Abbreviations


Acknowledgments


References










2





















2











Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in





2











Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in










Volume 2014

Mining


Journal of



Geophysics







Journal of




Advances in











Geology Advances in

Documents

Research Article Occurrence and Distribution of a Diatom