A. G. Hirst á R. S. Lampitt Towards a global model of in situ weight-speci®c growth in marine planktonic copepods Received: 18 September 1997 / Accepted: 13 May 1998 Abstract The dependency of in situ weight-speci®c fe- cundity of adult females (as egg production) and growth of juveniles (as somatic production) upon individual body weight in marine planktonic copepods was exam- ined. A compilation was made of results where wild- caught individuals were incubated in natural seawater (often pre-screened to remove large organisms), at near in situ temperatures, over short periods of the order of 24 h. The results demonstrate that for the adult broad- cast-spawning group weight-speci®c fecundity rates are dependent upon body weight, but independent of tem- perature. We postulate this may be the result of global patterns in available phytoplankton. Weight-speci®c growth rates are dependent upon individual temperature and body weight in juvenile broadcast-spawners, with rates declining as body weight increases. Sac-spawners have growth/fecundity rates that are independent of body weight in adults, juveniles, and both combined, but which are temperature-dependent. Globally applicable equations are derived which may be used to predict growth and production of marine copepods using easily quanti®able parameters, namely size-distributed bio- mass and temperature. Some of the variability in growth which remained unaccounted for is the result of varia- tions in food quantity and quality in the natural envi- ronment. Comparisons of the rates compiled here over the temperature range 10 to 20 °C with previously compiled food-saturated rates over the same tempera- ture interval, revealed that in situ rates are typically sub- optimal. Adults appear to be more food-limited than juveniles, adult rates in situ being 32 and 40% of those under food saturation in broadcasters and sac-spawners, respectively, while juvenile in situ rates are on average 70% of those at food saturation in both broadcasters and sac-spawners. Introduction In order to appreciate the role of zooplankton in ma- terial ¯ow and transformation in the sea, it is essential that their rates of growth and production can be deter- mined, and the factors of control understood. Deter- mining natural rates of growth in marine zooplankton is costly in time and eort, and a number of globally ap- plicable models which allow prediction from a few easily measurable parameters such as temperature (Huntley and Lopez 1992) or temperature and body weight (Ikeda and Motoda 1978; Hirst and Sheader 1997) have been developed. There has been much dispute over whether models of in situ weight-speci®c growth and fecundity need to be body-weight sensitive in copepods, but most recently Hirst and Sheader (1997) showed that juvenile weight- speci®c growth is body-weight dependent, while for adult female weight-speci®c fecundity this question was left unresolved. Kiùrboe and Sabatini (1995) reported important dierences between the growth rates of broadcast-spawners, i.e. those which shed eggs freely, and sac-spawners, i.e. those which carry their eggs ex- ternally on the body. The two spawning types were not distinguished by Hirst and Sheader, their aims being to compare the prediction abilities of previous global models and to produce a broadly applicable empirical equation without the need for separation of copepod taxa. These divisions were made in the present investi- gation, and the adult and juvenile distinction was also included. The principal aims of the present study were (1) to determine whether both weight-speci®c growth of adult females (fecundity) and juveniles (somatic) are body size and temperature-dependent in marine Marine Biology (1998) 132: 247±257 Ó Springer-Verlag 1998 Communicated by J.P. Thorpe, Port Erin A.G. Hirst (&) á R.S. Lampitt George Deacon Division, Southampton Oceanography Centre, Empress Dock, Southampton SO14 3HZ, Hants, England Fax: +44 (0)1703 596247 E-mail: a.hirst@soc.soton.ac.uk