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Distribution, biomass and production of Ceratonereis erythraeensis (Fauvel) and Ceratonereis keiskama (Day) at the Berg River Estuary, South Africa

Keywords: Ceratonereis erythraeensis , Ceratonereis keiskama , Reproduction , Distribution , biomass

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ENGLISH ABSTRACT: Population dynamics of the polychaetes Ceratonereis keiskama and C. erythraeensis were studied at the Berg River estuary, South Africa, from December 1987 to April 1989. There was marked size-related depth stratification of both species, with small worms being concentrated in the upper layer of the substratum and larger ones deeper down. Reproduction of both species occurred in summer. Three cohorts were distinguished in both populations. Recruitment of C. keiskama peaked in December whereas that of C. erythraeensis varied between years and sites (December-April). The population biomass of C. keiskama peaked in midsummer and was lowest during the spring and winter. C. erythraeensis maintained a high population biomass during winter and reached its lowest biomass during January-February. The total annual production of C. keiskama in the restricted area of the estuary where it occurred was 7,58 9 m-2 y-l, with a mean annual biomass of 4,11 9 m-2 making PIB = 1,84. Total annual production of C. erythra88nsis for the whole estuary was 14,42 9 m-2 y-l, mean annual biomass was 7,59 9 m'"2, and P/B = 1,90. ******* AFRIKAANSE OPSOMMING: Die populasie-dinamika van die polychaete Ceratonereis keiskama en C. erythraeensis by die Bergrivier strandmeer, Suid Afrika, is van Desember 1987 tot April 1989 bestudeer. 'n Opvallende grootteverwante diepte-stratifikasie is vir beide spesies waargeneem, met kleiner wurms gekonsentreer in die boonste laag van die substraat en met die grater wurms dieper a1. Reproduksie vind by albei spesies in die somer plaas. Drie kohorte is in beide populasies onderskei. Rekrutering van C. keiskama het 'n piek in Desember getoon terwyl dit in C. erythraeensis van jaar tot jaar en tussen lokaliteite gevarieer het (Desember-April). Die bevolkingsbiomassa van C. keiskama het in die middel van die somer 'n maksimum bereik en was die laagste in die winter. Die biomassa van C. erythraeensis het 'n hoe vlak in die winter gehandhaaf en was die laagste gedurende Januarie-Februarie. Die totale jaarlikse produksie van C. keiskama, in die beperkte gebied van die strandmeer waar dit voorgekom het, was 7,58 9 m-2 r1 , met 'n gemiddelde jaarlikse biomassa van 4,11 9 m-2, en 'n PIB van 1,84. Die totale jaarlikse produksie van C. erythraeensis vir die hele strandmeer was 14,42 9 m-2 r die gemiddelde jaarlikse biomassa was 7,59 9 m-2 , en P/B 1,90.

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