The potential role of microzooplankton in a northwestern Australian pelagic food web

Abstract

The role of microzooplankton in waters adjacent to Australia's North West Cape (21°49′S 114°14′E) was studied during the austral summers 1997/1998 and 1998/1999. We estimated microzooplankton abundance and biomass at a shallow (∼20 m) shelf station and at a shelf break station (∼80 m). Microzooplankton were placed into six categories: four ciliate groups (strombidiids, strobilidiids, tintinnids, “other ciliates”), dinoflagellates, and sarcodines. Total microzooplankton abundances ranged between 0.14×10³ l⁻¹ and 3.4×10³ l⁻¹. The most abundant groups were the dinoflagellates (mean 459±73 standard error l⁻¹) and strombidiids (mean 334±42 standard error l⁻¹). Total microzooplankton biomass ranged between 0.03 and 1.70 µg C l⁻¹ (mean 0.33±0.05 standard error l⁻¹). Redundancy analysis indicated differences in microzooplankton community composition between stations and sampling years but no differences with sampling depth. The microzooplankton community showed considerable variability between adjacent sampling dates, reinforcing the conclusion of earlier studies that this area is a dynamic environment. Ciliate production on the shelf was estimated to be 1.05 µg C l⁻¹day⁻¹ (∼20 mg C m⁻²day⁻¹) and 0.79 µg C l⁻¹day⁻¹(∼70 mg C m⁻²day⁻¹) at the shelf break. Ciliate production near North West Cape was two- to six-fold higher than the rate of secondary production by juvenile copepods. Despite this, ciliate grazing appears to account for only ∼5% of primary production and ciliates do not appear to be a major conduit between primary producers and higher trophic levels in these waters.

Keywords:

• Abundance
• biomass
• community composition
• gazing impact
• production

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

We thank Miles Furnas (AIMS) for access to his primary production data and for help and advice throughout the study. In addition, we wish to thank all involved in the North West Cape study, especially the crew of the RV Lady Basten for their help at sea, and Samantha Duggan (AIMS) for help both at sea and in the laboratory.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark