F1SHFR\ BULLETIN: VOL 72, NO. 2 



relatively large size of postlarvae (e.g., over 10 mg 

 organic weight). 



The 11% overall mean in the equal transfer 

 efficiency is surprisingly close to the values of 

 ecological efficiency measured in the laboratory 

 (Silliman, 1968; Slobodkin, 1968); food chain 

 efficiency is the same as ecological efficiency if all 

 food available to a consumer level is ingested (the 

 range for ecological efficiency is generally ac- 

 cepted to be 5-20%). The stability and con- 

 vergence characteristics of these efficiencies must 

 be set by two boundary conditions: 1) the 

 minimum net production and food required to just 

 replace the component species within a trophic 

 level and 2) the age-structure weighted max- 

 imum gross growth efficiency of the component 

 species within a trophic level. The upper limit is 

 set by the physiological maximum gross growth 

 efficiency of each developmental stage weighted 

 over all stages and species in proportion to their 

 relative abundance. In this regard the adults of P. 

 bachei are very efficient (60% ) at converting food 

 ingested into somatic tissues, and this is probably 

 near the upper limit of gross growth efficiency. 

 Low ecological efficiency is found in species popula- 

 tions dominated by older, slowly growing indi- 

 viduals with low growth efficiency and low rates of 

 mortality (Mann, 1965). In nature it would seem 

 unlikely that food chain efficiency through several 

 successive trophic levels could vary widely. For 

 example, a low efficiency through producers to 

 herbivores means that less net herbivore produc- 

 tion would be available to first-order carnivores, 

 all else being equal. Under these circumstances 

 the efficiency through herbivores to first-order 

 carnivores should also be low, because the carni- 

 vores must search a larger volume or area to feed 

 and this decreases growth efficiency. Conversely, 

 a high efficiency through producers to herbivores 

 should perpetuate a high efficiency through her- 

 bivores to carnivores, unless the age or size dis- 

 tributions of herbivores which yields high net pro- 

 duction from producers is not conducive to max- 

 imize the efficiency through herbivores to 

 first-order carnivores (i.e., the herbivores are 

 predominantly younger stages which are not avail- 

 able to those stages of carnivores which possess 

 the highest growth efficiency). 



There is some evidence from lakes and from 

 theoretical considerations of growth patterns that 

 food chain efficiency is at least in some cases de- 

 termined by growth efficiency of component 

 species in a food chain and their metabolic 



flexibility in response to size and abundance of 

 prey (Kerr and Martin, 1970; Kerr, 1971). In com- 

 plex marine systems considerable effort must be 

 expended before the predator-prey interactions 

 are described and the metabolic rates and 

 efficiencies are measured. Meanwhile, an expla- 

 nation based on sound theoretical grounds is 

 needed to show why the food chain and ecological 

 efficiencies tend to converge on 10% and have a 

 relatively small range from about 5 to 20%. 



SIGNIFICANCE OF P. BACHEI IN 

 THE PLANKTON 



The coastal waters of southern California rep- 

 resent an ecotone which includes the boundary of 

 land and sea. It is influenced strongly by physical 

 processes and the biota in the water from several 

 sources. The relatively shallow depths within the 

 first 2-3 km from shore emphasize the inter- 

 dependence and coupling of the benthic and 

 planktonic communities. The benthic community 

 depends on the planktonic community for some of 

 its food supply and for removal of the least fit 

 individuals of those meroplanktonic larvae re- 

 leased by benthic animals. The plankton commun- 

 ity receives some of its food in the form of mero- 

 planktonic larvae, and the benthic community re- 

 turns the materials removed from the water in the 

 form of regenerated nutrients, detritus, and de- 

 composing tissues. It is not surprising, therefore, 

 that Euterpina andOithona are the prey of young 

 stages of newly settled juvenile garibaldi, Hyp- 

 sypops rubicunda (Clarke, 1970) and also of P. 

 bachei. 



The pattern of high standing stocks of different 

 trophic levels and intense biological activity 

 within the first 5-10 km from shore is probably 

 associated with the high regeneration rates of 

 nutrients and high productivity in shallow water 

 (Anderson and Banse, 1961) and life history adap- 

 tations of coastal water species to exploit highly 

 productive zones. The short generation times of 

 microcopepods, parthenogenesis in cladocerans 

 and spined eggs o^Acartia are some adaptations to 

 enable rapid exploitation of favorable conditions 

 in the plankton. The coastal waters may be com- 

 pared to a chemostat. The rates of dilution by 

 physical forces vary in time and space, but the 

 specific growth rates of the organisms plus their 

 refugial seed stocks and immigrants enable them 

 to persist over time. The quasi-continuous change 



332 



