File:The crustacea of the plankton, July, 1894-Dec., 1896 (1897) (14751749706).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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ee maxima and minima which are of un-equal value. The spring maximum is by far the greatest, theCrustacea reaching a maximum number of 3,000,000 per sq. m.of surface, and in 1896 reaching an average of nearly 2,500,000for the first half of May. This maximum is due almost entirelyto the rapid development of Cyclops brevispinosus. After themaximum has passed, this species rapidly declines in number,and the total number of Crustacea sinks with it, so that by themiddle or last of June the number is reduced to less than halfthe maximum. This is the early summer depression, which maybe greatest at any time from the middle of June to the firstweek in July. A rapid, but slight, recovery follows, due chieflyto renewed reproductive activity on the part of the species al-ready present in the lake, leading to the mid-summer maximum,in July, Then follows a decline, usually somewhat slow, reach- M 9 o <T+- &5 CO QOCO GO Q £0 <5 o e-f-O* a CO to oo ooo q 02<r+- POCDSO COCO COCO *p CO o
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The Annual Distribution of the Crustacea. £03 ing a point of greatest depression about the last of August.During this period of decline, most of the periodic species areintroduced, but their numbers do not usually compensate for thefalling off in the number of the permanent species. In 1896, how-ever, Chydorus increased so rapidly during this time as to morethan counterbalance the decline in other species. In September a rise in the number of Crustacea begins, causedchiefly by increase in Daphnia of all species and in Cyclops.This increase culminates in the last of September or in October.This is the fall maximum, which, in general, is decidedly greaterthan the early summer maximum, the Crustacea at this timereaching a number perhaps two-thirds as great as that of thespring maximum. During the later part of the fall and theearly winter, the number declines very rapidly at first, and thenmore or less slowly, until the winter conditions are establishedwith the freezing of the lake in D

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