Moulting and growth of the early stages of two species of Antarctic calanoid copepod in relation to differences in food supply

Abstract

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 175:109-119 (1998) - doi:10.3354/meps175109 Moulting and growth of the early stages of two species of Antarctic calanoid copepod in relation to differences in food supply Rachael S. Shreeve*, Peter Ward British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge CB3 OET, United Kingdom *E-mail: rssh@pcmail.nerc-bas.ac.uk ABSTRACT: Instantaneous measurements of moulting and growth of the early copepodite stages of 2 species of Antarctic copepod, Rhincalanus gigas and Calanoides acutus, were made at 4 regions around South Georgia during austral summer 1996/1997. Sea surface temperature was ~3°C across the study area whereas chlorophyll a concentrations were considerably higher towards the western end of the island. Despite this, moulting rate experiments showed that stage durations of both species were invariably short with no significant regional differences. Stage durations of R. gigas CI, CII and CIII averaged 9, 28 and 15 d respectively, and those of CII, CIII and CIV C. acutus were 4, 7, and 16 d respectively. Daily mass-specific growth rates were lower and less variable in R. gigas (mean 0.05 d-1) than in C. acutus (mean 0.14 d-1), and showed no measurable regional differences. Those for C. acutus however, were higher off-shelf at the western end of the island where the copepodites were heavier than elsewhere. In addition to variations in concentration of chlorophyll a, qualitative differences in the microplankton food supply may also have influenced growth rates. Large diatoms were far more abundant off-shelf at the western end of the island compared to elsewhere, where micro-flagellates and small diatoms dominated. It is suggested that the more opportunistic feeding mode of R. gigas gave stability to its growth rate, whereas C. acutus, which is predominantly herbivorous, was affected by the fluctuations in phytoplankton concentrations and species composition. Moulting occurred within a narrow range of carbon and dry mass for both species, although this range varied between stations. KEY WORDS: Rhincalanus gigas · Calanoides acutus · Moulting rates · Growth · Production · Southern Ocean · South Georgia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 175. Publication date: December 17, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.