Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 417992
Title Did the loss of phytoplanktivorous fish contribute to algal blooms in the Mwanza Gulf of Lake Victoria?
Author(s) Witte, F.; Silsbe, G.M.; Hecky, R.E.; Goudswaard, P.C.; Guildford, S.J.; Kishe-Machumu, M.A.; Wanink, J.H.
Source Hydrobiologia 679 (2012). - ISSN 0018-8158 - p. 283 - 296.
Department(s) IMARES Delta
Publication type Refereed Article in a scientific journal
Publication year 2012
Keyword(s) sardine rastrineobola-argentea - perch lates-niloticus - introduced nile perch - east-africa - haplochromine cichlids - oreochromis-niloticus - nutrient enrichment - chlorophyll-a - waters - kenya
Abstract Possible causes of the increased algal blooms in Lake Victoria in the 1980s have been disputed by several authors; some suggested a top-down effect by the introduced Nile perch, whereas others suggested a bottom-up effect due to eutrophication. In this article the potential impact is established of grazing by fish on phytoplankton densities, before the Nile perch upsurge and the concomitant algal blooms in the Mwanza Gulf. The biomass and trophic composition of fish in the sublittoral area of the Mwanza Gulf were calculated based on catch data from bottom trawls, and from gill nets covering the whole water column. Estimates of phytoplankton production in the same area were made from Secchi values and chlorophyll concentrations. The total phytoplankton intake by fish was estimated at 230 mg DW m 2 day 1 . The daily gross production ranged from 6,200 to 7,100 mg DW m 2 day 1 and the net production from 1,900 to 2,200 mg DW m 2 day 1 . Thus, losses of phytoplankton through grazing by fish were about 34% of daily gross and 1012% of daily net phytoplankton production. As a consequence it is unlikely that the phytoplankton blooms in the second half of the 1980s were due to a top-down effect caused by a strong decline in phytoplankton grazing by fish.
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