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DIURNAL RHYTHM OF BIODIVERSITY IN A ZOOPLANKTON COMMUNITY OF A MACROSCALE ANTICYCLONIC GYRE

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Zooplankton sampling in the upper 200 m layer (at two hour intervals throughout the day) was carried out at a long-term drift station (11° S 22° W; December 1985) within the macroscale convergence zone in the southern tropical Atlantic Ocean. The distinct diurnal changes of total copepod abundance and single species-abundances are compared to less pronounced species- and genus-diversity changes in the upper 200 m. The coefficient of variance for the diurnal changes of the total abundance is 33%, while it is 26% for species-diversity, and 22% for genus-diversity. The increase of the total abundance of copepods is associated with an increase of the slope of the size spectrum. Peaks of species-diversity and genus-diversity do not coincide. They shift in time, with a lag of four hours approximately. The diurnal patterns of individual copepod species-abundance are quite diverse. Some species exhibit well pronounced uni-modal rhythms, others show bi-modal and multi-modal diurnal rhythms of abundance. The abundant species have bimodal diurnal rhythms as a rule. The diurnal rhythm of total copepod abundance corresponds, in general, to the fluctuation of the phytoplankton pico-fraction (less than 2.5 mu m) abundance, sampled at the same stations. From copepod population structure it is obvious that within the convergence zone of the macroscale anticyclonic gyre a mature zooplankton community, typical for the final phase of the spatio-temporal succession in epipelagic planktonic ecosystems is found. Species-diversity is high, and abundance values are low (4000-16000 ind m-3). In general, 11 species compose 75% of total copepod abundance, and only three species contribute for slightly more than 10% each. The population structure of the species is also quite different. In 92 species, females dominate the population by forming more than 50% of it. In five species copepodite stages I to III form more than 50% of the population. Male dominance has not been found.

Zooplankton sampling in the upper 200 m layer (at two hour intervals throughout was carried out at a long-term drift station (11 S 22 W; December 1985) within the convergence zone in the southern tropical Atlantic Ocean. The distinct diurnal changes copepod abundance and single species-abundances are compared to less pronounced genus-diversity changes in the upper 200 m. The coefficient of variance for the diurnal of the total abundance is 33%, while it is 26% for species-diversity, and 22% for genus-diversity. The increase of the total abundance of copepods is associated with an increase of the size spectrum. Peaks of species-diversity and genus-diversity do not coincide. time, with a lag of four hours approximately. The diurnal patterns of individual copepod are quite diverse. Some species exhibit well pronounced uni-modal rhythms, show bi-modal and multi-modal diurnal rhythms of abundance. The abundant species diurnal rhythms as a rule. The diurnal rhythm of total copepod abundance Un echantillonnage de zooplancton dans la couche sup erieure des 200 m (a intervalles de deux heures tout le long du jour) a ete effectue a une station flottante a long terme (11° S 22° W, decembre 1985) dans la zone de convergence a grande echelle dans l'ocean Atlantique sud tropical. Les changements diurnes distincts de l'abondance totale des cop epodes et des abondances d'une seule espece ont ete compares aux changement moins prononces des diversites specifique et generique dans les 200 m superieurs. Le coefficient de variance pour les changements diurne de l'abondance totale est de 33%, alors qu'il est de 26% pour la diversit e specifique et de 22% pour la diversit e generique. L'accroissement de l'abondance totale des copepodes est associe a un accroissement du seuil du spectre de taille. Les pics de diversite specifique et de diversite generique ne coincident pas. Ils sont d ecales dans le temps de quatre heures environ. Les mod eles diurnes de l'abondance specifique individuelle sont tout a fait divers. Certaines especes montrent des rythmes uni-modaux bien prononc es, d'autres des rythmes diurnes bi- ou multi-modaux. Les esp eces abondantes ont, en regle generale, des rythmes diurnes bi-modaux. Le rythme diurne de l'abondance totale des copepodes correspond en general a la fluctuation de l'abondance de la picofraction du phytoplancton (mois de 2,5 mu m) echantillonn e aux memes stations. D'apr es la structure de la population de copepodes il est manifeste que, a l'interieur du tourbillon anticyclonique, on trouve une communaute zooplanctonique a maturite, typique de la phase finale de la succession spatio-temporelle dans les ecosystemes planctoniques epipelagiques. La diversit e specifique est haute, et les valeurs d'abondance sont basses (4 000-16 000 ind m-3). En general, 11 especes composent 75% de l'abondance totale des copepodes, et trois especes seulement contribuent pour un peu plus de 10% chacune. La structure de population des esp eces est aussi tout a fait differente. Chez 92 esp eces, les especes dominent la population en en formant plus de 50%. Chez cinq esp eces, les cop epodites I a III forment plus de 50% de la population. La dominance des males n'a pas ete trouvee.

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/content/journals/10.1163/156854099502772
1999-01-01
2016-12-05

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