Life-history theory predicts that maturity and resource allocation patterns are highly sensitive to selective predation. Under reduced adult survival, selection will favour genotypes capable of reproducing earlier, at a smaller size and with a higher reproductive effort. When exposed to water that previously held fish, (size selective predators which prefer larger Daphnia), individuals of Daphnia hyalina reproduced earlier, at a smaller size and had a higher reproductive investment. Hence the prey was able to switch its life history pattern in order to become less susceptible to predation by a specific predator. The cue that evokes the prey response is a chemical released by the predator.

A recent meta-analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton (Shurin et al. 2002, Ecol. Lett., 5, 785-791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia-dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.

Based on existing knowledge about phytoplankton responses to nutrients and food size spectra of herbivorous zooplankton, three different configurations of pelagic food webs are proposed for three different types of marine nutrient regimes: (1) upwelling systems, (2) oligotrophic oceanic systems, (3) eutrophicated coastal systems. Upwelling systems are characterised by high levels of plant nutrients and high ratios of Si to Nand P. Phytoplankton consists mainly of diatoms together with a sub dominant contribution of flagellates. Most phytoplankton falls into the food spectrum of herbivorous, crustacean zooplankton. Therefore, herbivorous crustaceans occupy trophic level 2 and zooplanktivorous fish occupy trophic level 3. Phytoplankton in oligotrophic, oceanic systems is dominated by picoplankton, which are too small to be ingested by copepods. Most primary production is channelled through the 'microbial loop' (picoplankton -heterotrophic nanoflagellates -ciliates). Sporadically, pelagic tunicates also consume a substantial proportion of primary production. Herbivorous crustaceans feed on heterotrophic nanoflagellates and ciliates, thus occupying a food chain position between 3 and 4, which leads to a food chain position between 4 and 5 for zooplanktivorous fish. By cultural eutrophication, Nand P availability are elevated while Si remains unaffected or even declines. Diatoms decrease in relative importance while summer blooms of inedible algae (Phaeocystis, toxic dinoflagellates, toxic prymnesiophyceae, etc.) prevail. The spring bloom may still contain a substantial contribution of diatoms. The production of the inedible algae enters the pelagic energy flow via the detritus food chain: DOC release by cell lysis -bacteria -heterotrophic nanoflagellates -ciliates. Accordingly, crustacean zooplankton occupy food chain position 4 to 5 during the non-diatom seasons. Ecological efficiency considerations lead to the conclusion that fish production:primary production ratios should be highest in upwelling systems and substantially lower in oligotrophic and in culturally eutrophicated systems. Further losses of fish production may occur when carnivorous, gelatinous zooplankton Gellyfish) replace fish.

In the mid-20th century, the unicellular and genetically tractable green alga Chlamydomonas reinhardtii was first developed as a model organism to elucidate fundamental cellular processes such as photosynthesis, light perception and the structure, function and biogenesis of cilia. Various studies of C. reinhardtii have profoundly advanced plant and cell biology, and have also impacted algal biotechnology and our understanding of human disease. However, the 'real' life of C. reinhardtii in the natural environment has largely been neglected. To extend our understanding of the biology of C. reinhardtii, it will be rewarding to explore its behavior in its natural habitats, learning more about its abundance and life cycle, its genetic and physiological diversity, and its biotic and abiotic interactions.

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