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  • Title: [Non-predatory mortality of the crustacean zooplankton and its possible causes (a literature review)].
    Author: Dubovskaia OP.
    Journal: Zh Obshch Biol; 2009; 70(2):168-92. PubMed ID: 19425353.
    Abstract:
    General mortality (death rate, d) in natural populations of the crustacean zooplankton is calculated as difference between birth rate (b) and population growth rate (r). The mortality includes both predatory (consumptive) and non-predatory (non-consumptive), or "natural", deaths of individuals due to senescence, diseases and parasites, starvation, limiting physical and chemical factors of anthropogenic or natural origin. Modem methods of evaluation of non-predatory mortality of the plankton crustaceans, including direct method based on live/dead sorting by special staining of samples and measurements of sedimentation rate of dead individuals using a sedimentation trap are briefly characterized. Possible causes of non-predatory mortality of crustacean are examined based on different (mainly fresh) temperate water bodies. The possible causes are classified as: physical conditions including temperature, wind effects, ultraviolet radiation, water turbidity, current velocity; chemical conditions including concentration of dissolved oxygen, pH value, water toxicity of both anthropogenic (due to pollutant inflow) and natural (due to cyanobacterial bloom and ingestion of some toxic diatoms by copepods) origin; parasites and epibionts; bottom-up factors or food limitation including quantity and quality of food, the former as content of carbon (energy) and the latter as content of essential compounds in food. It is concluded that, for the populations of crustacean herbivorous zooplankton, the biotic factors appeared to be more important and more probable causes of non-predatory mortality than the abiotic ones, under conditions of non-acid water bodies of the temperate zone when the current speed is less than critical one (0.25 m/c) and in absence of the anthropogenic toxicants. These factors are primarily a food poor quality due to low content of phosphorus, nitrogen, polyunsaturated fatty acids of omega3 family and others, as well as microparasites causing infections and, to a lesser extent (just in blooming water bodies), natural toxicity of cyanobacteria. Non-optimal for the zooplankton physical and chemical factors, as causes of non-predatory mortality of plankton crustaceans, appeared to be less important because of their acting episodically in time locally in space, so the zooplankton is able to avoid their effects and to regenerate fast.
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