in the eastern and western regions of the lake than 

 to any movement on the part of individual organisms. 

 The response in the Eastern Basin may be from 4 to 

 6 weeks later than In the southwestern area, so that 

 the community observed first in the Cleveland - 

 Lorain area in July may be expected west of Long 

 Point in August. This condition is shown both in the 

 quantitative and qualitative distribution reccffds. 



During the period of rising temperature, dif- 

 ferences in the relative propcxtion of members in the 

 plankton community occur not only from east to west 

 but also on the two sides of the lake. The latter con- 

 dition results from the fact that in the eastern area 

 the seasonal response is much more rapid on the 

 American side, and persists until the dominant cla - 

 doceran species become generally distributed through- 

 out the lake in late August. In July and early August 

 (1929) copepods still formed the bulk of the catch in 

 Canadian waters, while Cladocera dominated on the 

 American side. A few weeks later the expansion of 

 the cladoceran pulse was evidenced by a uniform 

 distribution over the whole area. 



The mean volume of macroplankton in Lake 

 Erie for the summer of 1929 was 495 cc. (combined sur- 

 face and bottom 5-minute hauls with a meter net), 

 that of the area east of Long Point being 508 cc. and 

 to the west 474 cc. When the investigations began in 

 June the influence of vernal production was just becom- 

 ing evident by an increase In the adult crustacean 

 population. At this time, however, only 2 stations 

 yielded over 300 cc. and only 11 out of 49 stations 

 reached 200 cc. Except for occasional local responses 

 in some alongshore outwash areas, widespread vernal 

 production centered first in the southwestern portion 

 of the Great Plains Basin, with a gradual trend toward 

 the northeastern part of the basin and the Deep Hole as 

 the summer progressed (figs. 64-65). 



By July the mean volume for the lake had risen 

 to 412 cc. , an Increase of 270 percent over the pre- 

 vious month. The western area had increased 227 

 percent, and the eastern 330 percent, the production 

 In the latter area being concentrated for the most part 

 along the American side except at the extreme eastern 

 end (Pt. Abino). 



The lake was restocked by some species such as 

 Diaptomus ashlandl twice during the season. Other 

 species, although widely distributed, never appeared 

 In numbers sufficient to be of economic significance. 

 Other species such as SIda and Diaphano soma, with 

 short breeding seasons, never appeared to flourish 

 in the eastern part of the lake although in the Central 

 Basin the former species comprised 94 percent of the 

 macroplankton community In restricted localities In 

 July. Probably the Ixeeding periods of such species 

 pass before the temperature in the Deep Hole region 

 reaches their minimum reproductive requirements. 



Volume of Plankton 



To those accustomed to quantitative values in 

 the sea, the volume of animal plankton in this lake 

 is amazing. It is more remarkable because the total 

 amount consists of organisms having high fish -food 

 value. Except for Insect larvae which, particularly 

 In the marginal zone, often appear in significant 

 quantities, the macroplankton is made up entirely 

 of Crustacea. In the ocean the plankton is usually 

 made up of several groups of animals. Often the 

 greater portion may consist of coelenterates, Sagittae , 

 and other forms which must contain relatively little 

 nourishment. 



There was a further Increase of approximately 7 

 percent for the lake as a whole In August, but this 

 was due to a steady rise of 35 percent at the eastern 

 end where conditions now more closely resembled 

 those of the previous month in the west. In the Great 

 Plains Basin there was actually a decline of 17 percent, 

 the mean volume dropping from 440 cc. in July to 

 364 cc. In August. During this period a rise from 

 399 cc. to 540 cc. took place In the eastem area. 



The mean volume In September rose 44 percent 

 over the lake as a whole. In the western area pro- 

 duction again rose 69 percent to reach the season's 

 peak of 633 cc. , exceeding July production in the 

 same area by 40 percent. In the eastern area a grad- 

 ual increase of 8. 5 percent took place yielding a mean 

 volume of 586 cc. Although tables 19 and 20 Indi- 

 cate that the western area in September was still 

 mcare productive than the eastern (fig. 65), this pro - 

 ductlon was centered In the northeastern portion of 

 the Central Basin although relatively high values 

 extended over the whole lake at this time. 



Unfcfftunately, figures for the whole lake are not 

 available for 1928 but a comparison of the eastern 

 area for the two years indicates that in 1928 the mean 

 volume averaged 584 cc. or 15 percent higher than 



179 



