MEPS 279:161-181 (2004)  -  doi:10.3354/meps279161

ABSTRACT: This paper explores the global rates and patterns of fecundity in marine epipelagic copepods as a function of temperature, body weight of the female and the concentration of chlorophyll a in the natural waters in which these copepods were incubated. We divided data into 3 groups, broadcast spawners, sac spawners (including calanoids, cyclopoids and harpacticoids) and poecilostomatoids (although these are sac spawners, they were treated entirely separately). We examined global fecundity patterns in the first 2 groups, but data were too sparse to examine patterns in the poecilostomatoids. Fecundity was revealed to be significantly and positively correlated with temperature and body weight in both broadcast and sac spawners. Michaelis-Menten relationships revealed that fecundity rates are significantly related to chlorophyll a (chl a) concentration for broadcasters, but not significantly so for sac spawners. Broadcasting copepods have a maximum fecundity (f_max) of 47 eggs female^-1 d^-1, with a half-saturation coefficient (K_m) was 2.4 µg chl a l^-1, when all data are adjusted to 15°C and a body weight of 10 µgC ind^-1. In comparison, fecundity rates in sac spawners are much lower, typically attaining a maximum rate of only ~5 eggs female^-1 d^-1. Of the broadcaster genera examined, Centropages spp. proved to have the highest maximum fecundity (f_max) at 71 eggs female^-1 d^-1 (data corrected to 15°C), and Paracalanus spp. the lowest (f_max) at 25 eggs female^-1 d^-1. While for the sac-spawning genera Pseudocalanus spp. we found a significant relationship between fecundity and chl a, with an f_max of only 7.8 eggs female^-1 d^-1, for Oithona spp. no significant relationship was evident. By comparing in situ with laboratory food-saturated rates we were able to assess the degree to which fecundity is food-limited in the natural environment. The degree of food limitation increases with increasing temperature in sac spawners; at low temperatures (~5°C) in situ rates are similar to laboratory food-saturated rates, but at 25°C rates are on average 23% of laboratory food-saturation values. In nature, increasing food limitation with increasing temperature may be the result of greater food requirements to balance respiration demands, i.e. decreasing net growth efficiency in warmer situations. It may also be due to lower availability of suitable food in terms of quality or quantity with increasing temperature, possibly partly as a result of increased dominance of smaller phytoplankton size fractions (e.g. picoplankton) in warm waters. The actual degree of food limitation in the environment may be more severe than these comparisons suggest, as we have demonstrated that laboratory food-saturated fecundity rates in broadcasters often underestimate true food-saturated rates in the environment, with laboratory food-saturated rates being as little as 36% of the real maximum rates (f_max rates) achievable in the natural environment.

KEY WORDS: Fecundity · Copepod · Chlorophyll a · Temperature · Body weight · Food · Food limitation