Comparative ecology of the copepods Calanoides carinatus and Calanus agulhensis — the influence of temperature and food

  • JA Huggett Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2, Rogge Bay 8012, South Africa; Marine Research (MA-RE) Institute and Zoology Department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
  • AJ Richardson Department of Mathematics, University of Queensland, St Lucia 4072, Australia; Wealth from Oceans Flagship, CSIRO Marine and Atmospheric Research, Cleveland 4163, Australia
  • JG Field Marine Research (MA-RE) Institute and Zoology Department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa

Abstract

Hypotheses regarding temperature, food abundance and food size were tested to explore niche separation between Calanoides carinatus, an abundant copepod in the cool and food-rich southern Benguela upwelling system, and Calanus agulhensis, the dominant copepod on the warmer, relatively food-poor Agulhas Bank off the south coast of South Africa. Under non-limiting food conditions, egg production by both species increased linearly with temperatures between 9°C and 18°C. Egg production by C. carinatus was relatively faster at 21°C, but was offset by greater mortality. Both species showed similar functional responses to food concentration in the field, reaching satiation at ~15mg Chl a m–3, or ~3–4ppm. Food abundance was the most important predictor of egg production, whether measured as Chl a or as particle volume. Both species preferred larger particles that dominated the biomass peak, but particle size appeared more important for C. carinatus, with increasingly faster rates of egg production as the proportion of large cells (>10μm) exceeded 50%, and slower ingestion of small (<10μm) cells. Omnivory may be more important to C. agulhensis. Niche separation between the two species appears unrelated to temperature, food abundance or diel vertical migratory behaviour, and is more likely a function of variability in food availability, although food size may also play a role.

Keywords: Agulhas Bank, Calanoides carinatus, Calanus agulhensis, cell size, copepods, egg production, food concentration, southern Benguela, temperature

African Journal of Marine Science 2007, 29(3): 473–490
Published
2008-02-07
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X