File:The crustacea of the plankton, July, 1894-Dec., 1896 (1897) (14774417072).jpg

Identifier: crustaceaofplank00birg (find matches)
Title: The crustacea of the plankton, July, 1894-Dec., 1896
Year: 1897 (1890s)
Authors: Birge, E. A. (Edward Asahel), 1851-1950
Subjects: Plankton
Publisher: (Madison : s.n.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ringthe half-month. These figures show that Diaptomus begins to decline towardits winter condition early in the autumn. There is no markedreproductive period in the fall which supplies the individualswhich are to live over winter, but the numbers steadily andrather rapidly decline after the time when the lake has decid-edly cooled from its summer temperature. The table also showsthat the mortality must be very small in winter. In spite ofthe fact that there is no reproduction, the numbers show verylittle decline after the winter conditions are fairly established,and only a slow decrease in the late autumn. Indeed from themiddle of October until the first or middle of May, the semi-monthly averages show no more variation than might easilyappear in two catches made on the same day at the same place.This persistence of the numbers of the species must be attributedto the absence of competition and of enemies during this season.The food supply is ample for the winter stock of Crustacea and
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> o > s H o. X d Oo►a ►d Diaptomus. > 321 the reproduction of the Crustacea in winter is slower than thatof the algae. It is not impossible that the slight decline innumbers noticeable in 1895-6 may be attributable to the multi-plication of Cyclops in that winter. The decline in Diaptomusis too small to allow of certainty in the inference, but the adultCyclops fell off rapidly in March of that year as they did not inthe preceding winter when little reproduction took place. Foodalso became much more scanty in the spring of 1896 than in thepreceding year. The amount of food material in the spring of1895 was estimated as at least four times as great relatively tothe number of Crustacea present. The chief enemies of the Crustacea are the larvae of insects andthe young fish, both of which are absent or few during the winter.Leptodora also, though living chiefly on Cyclops and Daphnia,must devour some Diaptomi during the summer; while it iswholly absent in winter. At this seaso

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