TOWARDS A GLOBAL-MODEL OF IN-SITU WEIGHT-SPECIFIC GROWTH IN MARINE PLANKTONIC COPEPODS

The dependency of in situ weight-specific fecundity of adult females l as egg production) and growth of juveniles las somatic production) upo n individual body weight in marine planktonic copepods was examined. A compilation was made of results where wild-caught individuals were in cubated in natural seawater (often pre-screened to remove large organi sms), at near in situ temperatures, over short periods of the order of 24 h. The results demonstrate that for the adult broadcast-spawning g roup weight-specific fecundity rates are dependent upon body weight, b ut independent of temperature. We postulate this may be the result of global patterns in available phytoplankton. Weight-specific growth rat es are dependent upon individual temperature and body weight in juveni le 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 ape temperat ure-dependent. Globally applicable equations are derived which may be used to predict growth and production of marine copepods using easily quantifiable parameters, namely size-distributed biomass and temperatu re. Some of the variability in growth which remained unaccounted for i s the result of variations in food quantity and quality in the natural environment. Comparisons of the rates compiled here over the temperat ure range 10 to 20 degrees C with previously compiled food-saturated r ates over the same temperature interval, revealed that in situ rates a re typically suboptimal. Adults appear to be more food-limited than ju veniles, adult rates in situ being 32 and 40% of those under food satu ration in broadcasters and sac-spawners, respectively, while juvenile in situ rates are on average similar to 70% of those at food saturatio n in both broadcasters and sac-spawners.