MEPS 338:145-158 (2007)  -  doi:10.3354/meps338145

Life-cycle and population dynamics of Rhincalanus gigas (Copepoda: Calanoida) in the Scotia Sea

G. A. Tarling*, R. S. Shreeve, P. Ward

British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Rd, Cambridge CB3 0ET, UK

ABSTRACT: A stage- and age-structured model was constructed to simulate stage-abundance patterns of Rhincalanus gigas in a data set consisting of over 80 yr of net-catch observations in the Scotia Sea. The model was initialised with the observed annual abundances of the CI stage and the population developed according to pre-defined developmental stage durations, which varied according to life-cycle phenotype. Better fits to net-catch observations were achieved by models that allowed a number of different life-cycle phenotypes to co-exist in the population. In particular, a model in which 71% of individuals reached adulthood in 2 yr (2 yr phenotype) and 29% in 1 yr (1 yr phenotype) achieved the best fit. Of the 2 yr phenotypes, most individuals spent their 1st winter as a CIII, although a fraction passed this period as a CIV or CV. The 1 yr phenotypes entered their 1st winter as a CV but moulted through to adulthood before the following spring. During the productive period, the mortality rate of the early developmental stages was 0.1 d–1, but this fell to 0.007 d–1 as individuals developed beyond stage CIII. During the winter, the mortality rate fell further to 0.003 d–1. Such rates meant that around 1.5% of the copepodite population lived for 3 yr or more. Many of these spent 2 yr as an adult. Quantitative descriptions of development and mortality rates in the later stages of long-lived copepods are relatively few because of the difficulty in distinguishing the many generations in a typical population. As well as being the first to determine these rates in R. gigas, this study provides a methodological framework for determining such rates in other copepods with multi-year life cycles.

KEY WORDS: Copepod · Zooplankton · Southern Ocean · Phenotype · Diapause · Mortality · Development · Stage-structured model

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