Zooplankton efficiency

One example for a chemically defended zooplankton species is the Antarctic pteropod Clione antarctica. This shell-less pelagic mollusk offers a potentially rich source of nutrients to planktivorous predators. Nonetheless fish do not prey on this organism, due to its efficient chemical defense. In a bioassay-guided structure elucidation, pteroenone 37 could be isolated and characterized as the main defensive principle of C. antarctica [82,83]. If embedded in alginate, this compound is a feeding-deterrent in nanomolar concentrations. This unusual metabolite is likely to be produced by C. antarctica itself and not accumulated from its food, since its major food sources did not contain any detectable quantities of 37. 

Redfield (1934), who analyzed the major elemental content of many samples of mixed plankton (phytoplankton and zooplankton) caught in nets towed through the surface ocean. They compared the carbon, nitrogen, and phosphorus composition of these collections to concentration profiles of dissolved inorganic carbon (DIC), NOs, and P04 throughout the water column. This pioneering research demonstrated that these three elements are continually redistributed in the ocean by selective removal into plankton cells and their remains (i.e., fecal pellets), which are then efficiently respired as they sink through the marine water column. 

The predominance of phytoplankton-derived carbon in diets of many fish species, despite its small contribution to floodplain production, can be explained by the selective consumption of algae. However, Bayley (1989) argued that phytoplankton production was too low to contribute significantly to regional fish production. He based his argument on a food chain with three trophic levels (phytoplankton—zooplankton— fish), and assumed a 10% transfer efficiency between trophic levels. This model is inappropriate for detritivorous and herbivorous fish which consume plant materials directly. A model with two trophic levels would be more appropriate and would indicate a higher potential contribution to... 

Le Borgne, R. (1982a). Zooplankton production in the eastern tropical Atlantic Ocean Net growth efficiency and P B in terms of carbon, nitrogen and phosphorus. Limnol. Oceanogr. 11, 681-698. 

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