Pelagic food web configurations at different levels of nutrient richness and their implications for the ratio fish production: primary production

Sommer, Ulrich, Stibor, H., Katechakis, A., Sommer, Frank and Hansen, Thomas (2002) Pelagic food web configurations at different levels of nutrient richness and their implications for the ratio fish production: primary production Sustainable Increase of Marine Harvesting: Fundamental Mechanisms and New Concepts: Proceedings of the 1 st Maricult Conference held in Trondheim, Norway, 25-28 June 2000. Developments in Hydrobiology, 167 . Springer, Berlin, Germany, pp. 11-20. ISBN 978-90-481-6217-8 DOI 10.1007/978-94-017-3190-4_2.

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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. Up-welling systems are characterised by high levels of plant nutrients and high ratios of Si to N and R. Phytoplankton consists mainly of diatoms together with a subdominant 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, N and 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 (jellyfish) replace fish.

Document Type: Book chapter
Additional Information: Reprinted from Hydrobiologia, volume 484 (2002)
Keywords: plankton, food web, trophic level, ecological efficiency, copepods, fish production
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > GEOMAR > FB3 Marine Ecology
Refereed: Yes
DOI etc.: 10.1007/978-94-017-3190-4_2
ISSN: 0018-8158
Projects: MAST, COMWEB
Date Deposited: 18 Feb 2008 17:25
Last Modified: 30 Jan 2017 10:44

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