Ecology of Dictyosphaerium pulchellum Wood (Chlorophyta, Chlorococcales) in a shallow, acid, forest lake |
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Authors: | Haseeb Md Irfanullah Brian Moss |
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Institution: | (1) School of Biological Sciences, The University of Liverpool, Jones Building, Liverpool, L69 3GS, UK;(2) Present address: IUCN – The World Conservation Union, Bangladesh Country Office, House 11, Road 138, Gulshan 1, Dhaka, 1212, Bangladesh |
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Abstract: | This study relates to the ecology of Dictyosphaerium pulchellum Wood in Delamere Lake in Cheshire, UK. Dictyosphaerium pulchellum is a cosmopolitan, green colonial phytoplankton species that occasionally forms dense, monospecific populations in lakes.
Delamere Lake is a small, shallow, acid lake (mean pH, 4.5) with very high phytoplankton biomass (annual mean chlorophyll
a, 290 μg l−1) and devoid of any significant cladoceran population, the efficient grazers of phytoplankton. A predominantly unicellular
form of D. pulchellum was the dominant species in Lake Delamere, and it comprised on average ca. 80% (maximum >99%) of the lake phytoplankton biovolume.
Laboratory and lake experiments were conducted on this species showed that its pH tolerance varied between 2.4 and 10.7, and
its optimum tolerance range between 3.3 and 8.5 depending on other environmental variables. Low pH was not responsible for
the unicellular habit of this alga, but a very high nutrient regime could be an important factor. Bioassays revealed that
in Delamere Lake this species was limited by nitrogen, but nitrogen did not hamper high growth in the lake. Dictyosphaerium pulchellum can persist at low light levels, tolerate CO2-deficiency and can grow in polyhumic water with water colour around 300 mg Pt l−1, but probably not in darker waters. The dominance of D. pulchellum in Delamere Lake is apparently due to a combination of several factors: its ability to tolerate both low pH and high turbidity,
exploit high nutrient conditions, absence of effective grazing pressure by zooplankton and being a superior competitor. |
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Keywords: | Acid lakes Bioassays Eutrophication Humic compounds Monospecific growth Phytoplankton |
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