Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean

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dc.contributor.advisorMoloney, Coleen Len_ZA
dc.contributor.advisorMenard, Fredericen_ZA
dc.contributor.advisorTernon Jean-Francoisen_ZA
dc.contributor.advisorPotier, Michelen_ZA
dc.contributor.authorAnnasawmy, Pavaneeen_ZA
dc.date.accessioned2016-06-09T11:19:19Z
dc.date.available2016-06-09T11:19:19Z
dc.date.issued2015en_ZA
dc.descriptionInlcudes bibliographical referencesen_ZA
dc.description.abstractMicronekton fauna was investigated as part of a multi-disciplinary research project carried out in two different bioregions of the South West Indian Ocean: the East African Coastal Province (EAFR) and the Indian South Subtropical Gyre (ISSG). Food web structure was addressed using stable isotopes. Since particulate organic matter had high δ 15 N values in the ISSG province, copepods were chosen as baseline in trophic level estimations. Feeding regime and size were shown to influence the trophic position of micronekon. In the ISSG, carnivores (fishes and squids) and omnivores (crustaceans) had higher δ 15 N values and trophic positions than filter feeder s (gelatinous organisms such as salps and pyrosomes) and detritivores (leptocephali larvae). Fishes and squids encompassed a wide range of overlapping isotopic niches suggesting that organisms across different trophic levels feed on the same resources. Estimated trophic levels ranged from 1.67 to 4.73, showing that micronekton in the ISSG can be tertiary consumers. An average enrichment value of 6.7 ‰ was recorded between the sampled micronekton specimens and swordfish Xiphias gladius in the ISSG. Trawls, being selective in nature, were shown to sa mple smaller - sized micronekton with a lower trophic position than the micronekton being eaten by swordfish. In the EAFR, mean δ 15 N values of micronekton were higher than in the ISSG, exhibiting slightly higher trophic levels. Mesoscale dynamics in the EAFR provide mechanisms that enrich surface layers in nutrients and chlorophyll - a, therefore contributing to a higher abundance and micronekton species richness. In the ISSG, the large - scale wind - driven anticyclonic gyre pushes the nitracline, thermocline and deep chlorophyll maximum deeper in the water column , influencing the diel migration patterns of micronekton , with a significant proportion of micronekton staying in deep layers or slightly above the thermocline at dusk . Regardless of the differences in the ISSG and EAFR in δ 15 N values and trophic positions of micronekton, larger - sized swordfish sampled from these two provinces had similar mean δ 15 N values since swordfish are highly migratory and forage in different p arts of the Indian Ocean. However, smaller - sized swordfish specimens had lower mean δ 15 N values. With a combination of trawl surveys, stable isotope estimates, stomach content and acoustic analyses, this study shed new light on trophic interactions in the oligotrophic ISSG province.en_ZA
dc.identifier.apacitationAnnasawmy, P. (2015). <i>Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/19970en_ZA
dc.identifier.chicagocitationAnnasawmy, Pavanee. <i>"Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2015. http://hdl.handle.net/11427/19970en_ZA
dc.identifier.citationAnnasawmy, P. 2015. Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Annasawmy, Pavanee AB - Micronekton fauna was investigated as part of a multi-disciplinary research project carried out in two different bioregions of the South West Indian Ocean: the East African Coastal Province (EAFR) and the Indian South Subtropical Gyre (ISSG). Food web structure was addressed using stable isotopes. Since particulate organic matter had high δ 15 N values in the ISSG province, copepods were chosen as baseline in trophic level estimations. Feeding regime and size were shown to influence the trophic position of micronekon. In the ISSG, carnivores (fishes and squids) and omnivores (crustaceans) had higher δ 15 N values and trophic positions than filter feeder s (gelatinous organisms such as salps and pyrosomes) and detritivores (leptocephali larvae). Fishes and squids encompassed a wide range of overlapping isotopic niches suggesting that organisms across different trophic levels feed on the same resources. Estimated trophic levels ranged from 1.67 to 4.73, showing that micronekton in the ISSG can be tertiary consumers. An average enrichment value of 6.7 ‰ was recorded between the sampled micronekton specimens and swordfish Xiphias gladius in the ISSG. Trawls, being selective in nature, were shown to sa mple smaller - sized micronekton with a lower trophic position than the micronekton being eaten by swordfish. In the EAFR, mean δ 15 N values of micronekton were higher than in the ISSG, exhibiting slightly higher trophic levels. Mesoscale dynamics in the EAFR provide mechanisms that enrich surface layers in nutrients and chlorophyll - a, therefore contributing to a higher abundance and micronekton species richness. In the ISSG, the large - scale wind - driven anticyclonic gyre pushes the nitracline, thermocline and deep chlorophyll maximum deeper in the water column , influencing the diel migration patterns of micronekton , with a significant proportion of micronekton staying in deep layers or slightly above the thermocline at dusk . Regardless of the differences in the ISSG and EAFR in δ 15 N values and trophic positions of micronekton, larger - sized swordfish sampled from these two provinces had similar mean δ 15 N values since swordfish are highly migratory and forage in different p arts of the Indian Ocean. However, smaller - sized swordfish specimens had lower mean δ 15 N values. With a combination of trawl surveys, stable isotope estimates, stomach content and acoustic analyses, this study shed new light on trophic interactions in the oligotrophic ISSG province. DA - 2015 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2015 T1 - Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean TI - Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean UR - http://hdl.handle.net/11427/19970 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/19970
dc.identifier.vancouvercitationAnnasawmy P. Community composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Ocean. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2015 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/19970en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherApplied Marine Scienceen_ZA
dc.titleCommunity composition, migration and trophic positions of micronekton in two biogeochemical provinces of the South West Indian Oceanen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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