PolychaetecommunitystructureintheSouthEasternArabianSea continental margin(200–1000m)

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PolychaetecommunitystructureintheSouthEasternArabianSea continental margin(200–1000m)
K. U. Abdul Jaleel , P. R. Anil Kumar, Nousher Khan K, Correya N. S, Jacob Josia, Philip R, V. N. Sanjeevan, Damodaran R (Study are a ands ampling design- Jul 2014)
Abstract

Macrofaunal polychaetecommunities(4500 mm) intheSouthEasternArabianSea(SEAS)continental margin (200–1000m)aredescribed,basedonthreesystematicsurveyscarriedoutin9transects(at 200m,500mand1000m)between71000and 141300N latitudes.Atotalof7938polychaetesbelonging to 195specieswereobtainedin136grabsamplescollectedat27sites.Threedistinctassemblageswere identified inthenorthernpartoftheSEASmargin(10–141300N), occupyingthethreesampleddepth strata (shelfedge,upperandmid-slope)andtwoassemblages(shelfedgeandslope)inthesouth (7–101N). Highestdensityofpolychaetesanddominanceofafewspecieswereobservedintheshelf edge, wheretheArabianSeaoxygenminimumzone(OMZ)impingedontheseafloor,particularlyinthe northern transects.Theresidentfaunainthisregion(Cossuracoasta, Paraonisgracilis, Prionospio spp. and Tharyx spp.) werecharacteristicallyofsmallersize,andwellsuitedtothriveinthesandysedimentsin OMZ settings.Densitieswerelowestalongthemostnortherlytransect(T9),wheredissolvedoxygen (DO) concentrationswereextremelylow(o0.15mll1, i.e.o6.7 μmol l1). Beyondtherealmof influence oftheOMZ(i.e.mid-slope, 1000m),thefaunaldensitydecreasedwhilespeciesdiversity increased. Therelativeproportionofsiltincreasedwithdepth,andthedominanceoftheaforemen- tioned speciesdecreased,givingwaytoformssuchas Paraprionospiopinnata, Notomastus sp., Eunoe sp. and lumbrinerids.Relativelyhighspeciesrichnessanddiversitywereobservedinthesandysedimentsof the southernsector(7–91N), whereinfluence oftheOMZwaslessintense.Theareawasalso characterizedbycertainspecies(e.g. Aionidella cirrobranchiata, Isolda pulchella) thatwerenearlyabsent in thenorthernregion.ThegradientsinDOconcentrationacrossthecoreandlowerboundaryofthe OMZ, alongwithbathymetricandlatitudinalvariationinsedimenttexture,wereresponsiblefor differences inpolychaetesizeandcommunitystructureontheSEASmargin.Spatialandtemporal variationswereobservedinorganicmatter(OM)contentofthesediment,butthesewerenotreflected in the density,diversityordistributionpatternofthepolychaetes