Egg production, somatic growth and productivity of copepods in the Benguela Current system and Angola-Benguela Front

Copepods form an important link between phytoplankton and fish, so estimate s of their growth rates are essential for understanding their role in the m arine food web. To date, no empirical estimates of copepod growth rate in t he northern Benguela system off Namibia or the Angola-Benguela Front system off Angola have been published. To redress this situation, we used bottle incubation techniques to measure the daily growth rate of 13 copepod specie s from this region during two BENEFIT cruises in April/May 1997 and July/Au gust 1999, in terms of egg production by adult females and somatic growth o f copepodite stages. Mean growth rate was fast (0.13-0.24 d(-1)) for small copepods (< 1800 mum total length: Calanoides carinatus stages C3 and C4, a nd female Centropages brachiatus) and slow (<0.1 d(-1)) for larger copepods (females of Nannocalanus minor, Pleuromamma spp., Scolecithrix spp., Metri dia lucens, Candacia armata, Euchaeta spp., Undinula vulgaris, Calanoides c arinatus, Eucalanus spp., Rhincalanus nasutus, Pontellidae spp. and Eucalan us elongatus). A strong negative relationship between mean growth rate (g) and mean body mass (BM) was found for the northern Benguela system (g = 0.8 66 x 10(-0.075BM), r(2) = 0.81, n = 15). For comparison, an equation was al so derived for the southern Benguela system (g = 0.572 x 10(-0.042BM), r(2) = 0.89, n = 21) from previously published and unpublished data. These equa tions were used to calculate copepod production (growth rate x biomass). Th e estimate for the northern Benguela system of 39 g C m(-2) yr(-1) is less than previous indirect values of 52-69 g C m(-2) yr(-1). The estimate of an nual copepod production for the southern Benguela system of 99 g C m(-2) yr (-1) is at the upper end of previous estimates, which range from 11 to 120 g C m(-2) yr(-1). The considerably lower production calculated for the nort hern Benguela may reflect the inadequate estimates of size-differentiated b iomass available. The application of our growth rate-body size relationship to biomass estimates is a simple means of estimating copepod production in the study region.