The distribution curves for diatoms (fig. 46) 

 show graphically the fluctuations in the quantity from 

 one station to another on each cruise during the 4 

 months. The "peaks" and "valleys" indicate remark- 

 able variations in diatom production throughout the 

 lake. August shows the least lateral variation and 

 September the most. In general, production was 

 greatest in the western area, least in the Long Point 

 region, and moderate in the Buffalo end of the lake. 



The horizontal variations in the abundance of 

 green algae (fig. 47) were less striking than those of 

 the diatoms, but differences were apparent. In June 

 and July the Buffalo area, the Long Point region, and 

 those stations between Rondeau and Fairport, all 

 showed larger numbers than the numerous weaker sta- 

 tions marked with an "X" or small circle on the map. 

 In August and September greater abundance occurred 

 in the shallow areas. Decided infertility was appar- 

 ent in the central western area in September. The 

 map may, however, give an exaggerated impression 

 of abundance in the eastern area because of the lar- 

 ger number of observations made in that region. 



The blue-green algae (fig. 48) of the central 

 western region outnumbered the entire eastern portion 

 and most of the along-shore stations in June. These 

 sharp differences were reduced in July, and a ten- 

 dency toward uniform distribution was apparent. There 

 was an abundance of blue -green algae in the eastern 

 area in August while the western area was weak in 

 this group. In September a slump occurred in the 

 east, but the extreme western stations indicated 

 strong increases in blue -green algae. 



Rotifers (fig. 49) were abundant throughout the 

 summer in the Long Point Bay region and also in the 

 waters off Port Maitland and south of Port Colborne. 

 Gatherings with the tow -net along shore (fig. 50) 

 showed this same remarkable rotiferan fauna in Long 

 Point Bay, Port Rowan, and Port Maitland. Long 

 Point Bay was found to be very favorable for rotifers 

 in 1928. Conditions in these parts must be peculiar- 

 ly favorable for the development of a rotiferan fauna 

 just as other regions in the west favor the growth of 

 diatoms or blue -green algae. 



These variations are not surprising when we con- 

 sider that tributary creeks, cities, factories, etc. , 

 are continually emptying mineral matter and organic 

 materials into the lake, thus altering the chemical 

 environment. Some of these inflowing materials 



may be harmful (see chemical report in this bulle- 

 tin), others beneficial to the natural fauna and flora 

 as suggested for the English lakes by Pearsall (1923). 

 The vernal and autumnal overturning, as well as the 

 irregular upwelling of bottom materials due to wind 

 and wave action, probably make available varying 

 amounts of nutrients at different times and places. 



It is an interesting fact that Reighard (1894) 

 reported similar inequalities in the distribution of the 

 total plankton in Lake St. Clair which empties its 

 waters into Lake Erie at the extreme western end. 

 Many other investigators (Apstein 1896, Bigelow 1924, 

 Muenscher 1928) have likewise reported horizontal 

 variations and swarms of plankton in different bodies 

 of water, but very little definite correlation has been 

 made with the causal factors. 



Seasonal Variation 



The earliest observations on the seasonal perio- 

 dicity of plankton in Lake Erie are those made by 

 C. M. Vorce (1880) who studied the species which he 

 filtered from the city water supply in Cleveland, Ohio. 

 He divided the annual cycle into three parts as fol- 

 lows: (1) the period from February to May, during 

 which Stephanodiscus niagarae and Rhizosolenia 

 eriensis are very abundant; (2) May to November, the 

 period of greatest abundance of the prevalent forms 

 Melosira , Tabellaria, etc. ; (3) November to Feb- 

 ruary, when the warm weather species decline and 

 are replaced by the winter species. 



This author also emphasizes the "marine relict" 

 character of Amphiprora ornata, Rhizosolenia erien - 

 sis, and Stephanodiscus niagarae , whose relatives are 

 marine species. The query raised by H. M.Smith 

 (1878) as to whether the presence of the Rhizosolenia, 

 just newly discovered, should be taken as an indica- 

 tion of saline bottom waters in the Great Lakes was 

 discredited, but an interesting suggestion was at the 

 same time offered to account for the observed facts. 

 These "relicts" seemed to thrive best in cold winter 

 waters, and this was taken as a further indication of 

 their marine origin, for is not the sea cold? 



The observations begun in June were perhaps a 

 little too late to detect the maximum vernal pulse. 

 In June diatoms occurred in large numbers at many 

 shallow water stations near shore (fig. 44). Espe- 

 cially large catches were made off Cleveland, Fair- 

 port, Ashtabula, Erie, Port Stanley, etc. In July 



131 



