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Spatial and temporal distribution of invertebrate organisms inhabiting the Chara zone Humphreys, Robert David 1964

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SPATIAL AND TEMPORAL DISTRIBUTION OF INVERTEBRATE ORGANISMS INHABITING THE CHARA ZONE  by Robert David Humphreys B.Sc., University of B r i t i s h Columbia* 1961.  A Thesis Submitted I n P a r t i a l Fulfilment Of The Requirements For The Degree Of Master of Science  i n the Department of Zoology  Ve accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October, I964.  In the  requirements  British  mission  for  Columbia, I  available  for  for  an  cation  of  this  w i t h o u t ; my  written  Department  of  and  by  It  thesis  that  Wwg,  the  Library I  this  Head  for  financial  permission*  °  ^ ° ,  C^T Columbia,  1 ^ 4  the  thesis  fulfilment  University  shall  further  o f my  i s understood  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, C a n a d a Date  the  of  in partial  degree at  study.  copying  granted  representatives.  thesis  advanced  reference  be  this  agree  extensive  p u r p o s e s may his  presenting  make i t  agree for  that  Department  shall  not  of freely per-  scholarly or  that, c o p y i n g or  gain  of  be  by publi-  allowed  ABSTRACT Two methods o f c o l l e c t i o n were employed i n the i n v e s t i gation of the density, d i s t r i b u t i o n , and movements of invertebrates inhabiting the Chara zone of lakes: (1) Chara samples were obtained at regular depth i n t e r v a l s over the Chara shoals with the aid of Scuba gear, p a r t i t i o n i n g the Chara stand Into  two  approximately equal v e r t i c a l halves - top h a l f and bottom h a l f ; (2)  a long-handled dipnet was used to sample the surface of the  Chara stand and the waters above the standi  Sampling with the  dipnet on a 24-hour basis provided data on the d i e l movements of organisms i n the Chara zone. The density of the invertebrate populations was  lowest  i n June due to the reduction of stocks over the winter months by predatidn and other causes of death.  The high numbers i n  September were attributed to the r e s u l t s of early summer reproduction 0  Fluctuations i n density over the summer months were  traced to the changing i n t e r p l a y between hatching and emergence of various invertebrate groups.  Eradication of f i s h from one of  the lakes resulted i n an increase i n numbers of the major f i s h food organisms, i n d i c a t i n g predation by f i s h as an important factor controlling density of invertebrate stocks. The d i s t r i b u t i o n of invertebrate organisms over the Chara shoal from shore to the l i m i t of the vegetation offshore and v e r t i c a l l y within the Chara bed i t s e l f was ii  remarkably  iii homogeneous.  Minor differences i n d i s t r i b u t i o n o f several  invertebrate groups were demonstrated by s t a t i s t i c a l means. Daily v e r t i c a l and horizontal movements of many of the organisms were shown to produce large density fluctuations on the Chara surface.  ACKNOWLEDGEMENTS  The author would l i k e to express h i s sincere gratitude to Dr. T. G. Northcote f o r h i s supervision, guidance, and c r i t i cism throughout t h i s study. S t a t i s t i c a l procedures were developed with the advice of Dr. Di P. Ormrod, Department of Agriculture, and programmed for the computer by Mr. Hugh Dempster, Department o f Mathematics. The writer i s indebted to both these gentlemen f o r t h e i r time and invaluable assistance. F i e l d work was made possible by the F i s h e r i e s Research D i v i s i o n o f the B r i t i s h Columbia F i s h and Game Branch.  Collec-  t i o n of data was accomplished with the assistance of Mr. M. Teraguchi and Mr. E. Zyblut, both of whom deserve the writer's sincerest appreciation.  !  F i n a l l y , the writer wishes to express thanks to those who assisted i n the sorting o f samples and to Beverley C. Humphreys f o r her encouragement and aid i n preparing script.  viii  the manu-  TABLE OF CONTENTS Page LIST OF FIGURES .......  .  ..  .  ...  ..  LIST OF TABLES .  v vii  ACKNOWLEDGEMENTS  ..  ..  viii  INTRODUCTION ..........................................  1  DESCRIPTION OF THE STUDY AREAS  3  ..  Ai  Location and morphometry ..........•..,.  3  B.  Physi c a l and chemical condi tions ..............  4  C»  Th6 Chara hahi t a t „  7  METHODS  o * « « * * « a » « « « e o o « « e i i » o a e « « « * o o « o « * o * * * * » * « * » » o o e  ZLX  A.  Description of the diving method  11  B*  Description of the dipnet method  12  Co  S"b&*tis"fcXcstl .proc@cLiii*6S  REtSUTjTS  *•  • • • •  o  & • ee«o e*o©  o«o«•  • •»o • •  »ft© © © « e o * • © s o  • « « • » • « * • » o  Density and composition of the invertebrate populations of Chara shoals  B.  E f f e c t of f i s h removal on invertebrate l i f e xxi C3n&i*5t sho SOL S © C O © © © © © © © © © * © © » • • • © © • • • © © © •  D. E.  13  oft* o * •ft• • © © o • © © © ©  A.  C.  •o  15  © © O  26  V e r t i c a l d i s t r i b u t i o n of invertebrates within * t l X © Ctlclffcl S t / H X l C l o o e o © © © * © o ©©••;•> a o © e • • • •oo»©o«oo Horizontal d i s t r i b u t i o n of invertebrates within the Chara zone  37  D i e l movements of Invertebrates of the Chara 20X10 • « o o « e f t « e « f t ' « e o o o o f t e o f t « « o B « « « « * o « « * f t a « « « « « o o  DX S C U S S X O U  © e » © » ©:« • • • o e © « e o e o © o o o o o o e © • a «ft« • • • • « • • oftft© ©  XiX T E R A T U R E  CX T E D  «•  • © © © « « o « ©  o «> o » ©  iv  1>  © * * • © © © • • • • © » • • • • •«*> © ©  73  8^  3^  LIST OF FIGURES Figure 1. 2.  Page T y p i c a l midsummer thermal conditions i n Paul, Corbett and Courtney lakes ...  5  Typical midsummer oxygen conditions i n Paul, Corbett and Courtney lakes  6  3.  Lakes showing sampling l o c a t i o n s  9  4.  Number and volume of invertebrates inhabiting Chara shoals. ....', ........................... Percent composition of invertebrate populations of the Chara shoals of Corbett and Courtney lakes  19  6.  Number and volume of H y a l e l l a i n the Chara shoals of Corbett and Courtney lakes  24  7.  Seasonal changes i n the length-frequency di s t r i b u t i o n of H y a l e l l a azteca  25  Numerical density of invertebrates i n the Chara shoals of Paul Lake - September 1962 and September 1963  28  Seasonal changes i n v e r t i c a l p o s i t i o n of organisms w i t h i n the Chara stand  32  10.  Seasonal changes i n h o r i z o n t a l d i s t r i b u t i o n of organisms inhabiting Chara shoals ...............  38  11.  Seasonal changes i n h o r i z o n t a l d i s t r i b u t i o n of H y a l e l l a azteca  41  12.  Seasonal changes i n h o r i z o n t a l d i s t r i b u t i o n of chironomid larvae  43  13.  Seasonal changes i n horizontal d i s t r i b u t i o n of Gyraulus spi  45  14i  Seasonal changes i n h o r i z o n t a l d i s t r i b u t i o n of SympG"tn^iii .X13.3. S.CLS & * © © & o © © o ©««•««•« -o o a • • » • o • • • • • • •  J^f  D i e l changes i n density o f Diaptomus on the Chara Jf cLC3 © • « © • • » o • • « o o o o o o o « « e o • » » © « o o • » * o • » o e©a«o  51  5.  8.  9.  15.  v  22  vi Figure 16.  Page D i e l changes i n density of Diaptomus i n the open water above the Chara shoal and on the Chara surface  52  17.  D i e l changes i n density of Daphhia on the Chara surface  54-  18.  D i e l changes i n density of Daphnia i n the open water above, the Chara shoal on the Chara surface..  55  19.  D i e l changes i n density of Chaoborus on the Chara surface .... ..  57  20.  D i e l changes i n density of Chaoborus i n the open water above the Chara shoal and on the Chara surface  58  D i e l changes i n density of Eurvcercus on the Chara surface  60  21. 22.  D i e l changes i n density of Sympetrum on the Chara SIXntTclCO  23.  25.  o s e o o o © * * ©  6*2  © © • • • » © © © • • • © © ©  D i e l changes i n density of Baetis on the Chara SUrfcLC©  24.0  © • • • © • • • • • • • © © © ©  •  O  O  9  « ft O  O  0«  O  • ft «  O  «  •  • ft « ft • - © ft 0 ft ft ft O ft «  •  O ft • ft ft ft • ft ©  0  &Jfy  D i e l changes i n density of H y a l e l l a on the Chara surface  65  D i e l changes i n density of Ceriodaphnia on the Chara surface  67  26.  Comparison of density of chironomid larvae on the Chara surface at each station . . . o o . . . 68  27.  D i e l changes i n density of chironomid larvae on Cli3.r3. surf3.c© © * o o o f t o « o o o © f t » « f t « » © o f t » o « f t © o t > < > o © o  V0  LIST OF TABLES Table I. II.  Page Total dissolved solids by evaporation i n Paul, Corbett, and Courtney lakes .,...........  .  8  Average number and volume of invertebrate organisms per 300 gms of Chara i n Corbett Lake ...  16  I I I . . Average number and volume of invertebrate organisms per 300 gms of Chara i n Courtney Lake ..  17  IV. V. VI.  Average number of invertebrate organisms per 300 gms of Chara i n Paul Lake  27  Organisms found i n the substrate underlying the Chara stand - Paul Lake. September 7, 1962 .......  31  Organisms found o n t h e surface of the Chara bed and i n the waters above the shoal - Corbett Lake, J u l y to October, 1963...  48  vii  INTRODUCTION  Much work has been done i n the past to ascertain the importance of aquatic vegetation i n the general b i o l o g i c a l productivity of lakes.  I t i s usually held that the most con-  spicuous importance of aquatic vegetation consists i n i t s habitat r e l a t i o n s with various invertebrate, fish-food organisms. 1926,  The studies of Baker (1918), Muttkowski (1918), Lundbeck Rawson (1930), Juday (1942), and B a l l (1948) stress the  importance of vegetation-^covered  bottoms f o r the existence of  a r i c h fauna. Apart from t h i s knowledge of the a b i l i t y of plants to harbour large numbers of animals, l i t t l e has yet been done on the ecology of plant fauna. was,  The purpose of the present  study  therefore, to estimate the density of organisms inhabiting  Chara shoals and to discover how  these organisms are d i s t r i b u t e d  h o r i z o n t a l l y and v e r t i c a l l y within the Chara stand.  Seasonal  and d i e l changes i n density and d i s t r i b u t i o n were observed. The study began i n September, 1962 when samples of the Chara shoals of Paul Lake were obtained with the aid of Scuba gear.  Sampling was  programme designed  carried out i n conjunction with a poisoningto r i d the lake of i t s f i s h stocks, as the  redside shiner Richardsonius  balteatus had become over-abundant. 1  2 Only two other sampling series were undertaken on Paul Lake one i n June and the other i n September of 1963.  —  The data from  these series were used i n an attempt to determine the e f f e c t s of toxaphene treatment and f i s h removal on the invertebrates of the Chara zone. Throughout the summer of 1963, however, the emphasis was placed much more heavily on the sampling of two smaller lakes, Corbett and Courtney*  The abundance of invertebrate or-  ganisms i n the Chara shoals of Corbett and Courtney Lakes f a c i l i t a t e d the i n v e s t i g a t i o n of the organisms' d i s t r i b u t i o n a l patterns and d i u r n a l migratory behaviour.  Also, since the red-  side shiner i s present i n Courtney Lake but absent i n Corbett, e f f e c t s of predation by the shiner on the Invertebrates of the Chara zone was  facilitated.  DESCRIPTION OF THE STUDY AREAS  A,  Location and Morphometry Paul Lake i s by f a r the l a r g e s t of the three lakes  studied* having a surface area of approximately 271 hectares (680 acres), a maximum depth of 28,4 metres (93 f t . ) .  Rawson  (1934) concluded that Paul was t y p i c a l l y oligotrophic but with r e l a t i v e l y high productivity because of the extensive shoal areas and Chara beds.  The lake l i e s i n a narrow rocky  v a l l e y at an a l t i t u d e of 777 metres (2,542 f e e t ) , 19.2 metres (12 miles) north-east of Kamloops, B. C.  I t has  kiloone  major i n l e t , Upper Paul Creek, which drains Pinantan Lake, and there are a few mountain streams entering the lake which become dry i n the summer months.  There i s only one outlet,  Lower Paul Creek. The greater p o r t i o n of the shore of Paul Lake slopes o f f at an angle of from 20 to 25 degrees. sampling  But, at the Chara  station, the slope was much more gradual (10 to 15  degrees) and the Chara shoal extended to a depth of 7.6 metres (25 f e e t ) . The other two lakes, Corbett and Courtney, are small, highly productive eutrophic lakes l y i n g adjacent to one  an-  other approximately 19 or 20 kilometres south of Merri t t , B. C» 3  4 Corbett Lake l i e s at an a l t i t u d e of 1,068 metres (3,500 feet) and Courtney Lake, at an a l t i t u d e o f 1,052 metres (3,450 f e e t ) *  Corbett has a surface area of 2 4 . 2 hectares  (60.5 acres) and a maximum depth of 19 metres (62 f e e t ) . Courtney Lake has an area of 71.6 hectares (179 acres) and a maximum depth o f 17 metres (56 f e e t ) . I n both Corbett and Courtney Lakes the basins slope o f f from shore at an angle of 15 to 20 degrees.  But, at a  depth o f between 4«0 and 4.5 metres, a sharp drop-off occurs, thus, l i m i t i n g the extent o f the Chara shoals from shore to 4.0 metres i n Corbett and from shore to 4 . 5 metres i n Courtney. Bt,  Physical and Chemical Conditions Temperature V e r t i c a l temperature series were recorded at the  deepest parts of Paul, Corbett, arid Courtney Lakes during the summers of 1962 and 1963.  Typical midsummer temperature curves  (Figure l ) were selected from the 1963 data f o r Paul and Corbett Lakes and from the 1962 data f o r Courtney Lake as no comparable series was taken i n midsummer o f 1963 on Courtney. T h e r m a l . s t r a t i f i c a t i o n i s apparent i n the curves f o r both Paul and Corbett lakes, but i s weak or absent i n Courtney Lake. .. Oxygen Oxygen determinations, using the Winkler method, were made at i n t e r v a l s throughout the summers of 1962 and 1963.  :  5  T E  0  °1  5  M  P  10  E  R  A  T  U  R  E ( ° C )  15  25  246or hUJ  I h-  8-  IO1214-  Q_ 16UJ Q 1820-  2 4042-  PAUL •  LAKE  COURTNEY  -X COR B E T T  LAKE LAKE  44F i g , 1,  T y p i c a l midsummer thermal conditions i n Paul, Corbett and Courtney lakes.  6  O X O  2  Y G E 4  N  (MGS./ 6  L.)  8  10  OC hLd  I »-  CL bJ Q  Figo 2b  o_o  PAUL  L A K E  • — •  COU RTNEY  X — x  C O R B E T T  LAKE LAKE  Typical midsummer oxygen conditions Paul, Corbett and Courtney lakes.  7  T y p i c a l midsummer oxygen conditions at the deepest part o f the lakes are shown i n Figure 2. Oxygen-supply i s abundant even i n the very deep waters of Paul Lake but i s present only above the thermocline i n Corbett.  Although there i s l i t t l e evidence o f a thermocline i n  Courtney Lake, oxygen i s depleted below 8.0 metres. Records show that on August 30, 1962, strong winds caused a turnover o f the waters o f Courtney Lake carrying an abundance of oxygen to a l l depths,  Corbett Lake, however,  being much more sheltered from the wind and thermally s t r a t i f i e d , was not affected.  S t r a t i f i c a t i o n remained i n t a c t i n Corbett  Lake and oxygen absent below the thermocline u n t i l l a t e Septembero Total P i ssolved S o l i d s Water samples obtained at the surface o f Corbett and Courtney lakes on various dates during 1961 and 1962 were used i n determining average t o t a l dissolved s o l i d s f o r the two lakes (Table I ) .  The figure f o r Paul Lake i s from Johannes and L a r k i n  (1961). Larkin, e t a l . , 194-9 give more complete information on the limnology of Paul Lake. C.  The Chara Habitat The stonewort Chara i s found i n the l i t t o r a l zones o f  each of the three lakes investigated, i n a dense shoal.  This  "Chara Zone" extends around the entire shoreline i n Corbett and  8  : / : . o ^ ^ V . ; : .  v  : .  TABLE I  TOTAL DISSOLVED SOLIDS BY EVAPORATION IN PAUL, CORBETT* AND COURTNEY LAKES  Lake  T.D.S.  Paul  216  Corbett  336  Courtney  387  ,  10  Courtney lakes and around 95% of the shoreline of Paul Lake and includes the lake bottom to a depth offshore determined by the slope of the basin and the penetration of l i g h t *  Figure 3  indicates the extent of the Chara zone i n the three lakes and the sampling l o c a t i o n s . The plants undergo a period of rapid growth early i n spring and maintain a luxuriant " f o l i a g e " throughout the summer months.  I t i s the abundant branching of the Chara  t h a l l u s which provides the necessary  surface area f o r harbour-  ing the large numbers of invertebrate organisms found i n a Chara stand (Rosine, 1955)» A d e s c r i p t i o n of the l i f e h i s t o r y of the Chareae i s found i n Robinson (1906) „  METHODS  A.  Description of the Diving Method With the a i d of Scuba gear, t r i p l i c a t e Chara samples  were taken at regular depth i n t e r v a l s from 1.0 metre to the l i m i t of the Chara shoal at a depth of A.O to 4.5 metres. P a r t i t i o n i n g of the Chara stand into two approximately equal v e r t i c a l halves was attempted by clipping the Chara with shears midway between the t i p s of the t h a l l i and the substrate.  Each  sample was c a r e f u l l y placed i n a net bag (mesh aperture 0.6  mm)  which was held i n close proximity to the sampling s i t e i n order to avoid l o s s of organisms.  An attempt was made to r e s t r i c t  the size of the samples to an area of 527 sq em (9 sq i n ) . On September 7, 1962 i n Paul Lake, substrate samples were taken with a 527 sq cm Ekman dredge a f t e r removal of the overlying Chara mat.  :  This practice was discontinued as the  number of organisms present i n the s o i l underlying a Chara stand proved to be n e g l i g i b l e . Upon removal of the samples from the lake they were washed through a bucket sieve having a mesh aperture of 1.00  mm  i n order to remove extraneous material, placed i n p l a s t i c bags, labelled,' and preserved i n a 5 percent solution of formalin.  11  12 In the laboratory the contents of each p l a s t i c bag were again washed through a 1,00 mm aperture sieve so that the formalin was washed away.  The material retained by the sieve  was then transferred to a white enamel pan and the organisms were c a r e f u l l y removed.  As i t was d i f f i c u l t to maintain a  uniform size of sample, the Chara was washed and drained a f t e r removal of the organisms and the weight used to determine the numbers and volumes of each organism present i n a standard 300 gm Chara sample. The organisms were i d e n t i f i e d , placed into taxonomic groups, and  enumerated.  Volumes of organisms were estimated by choosing a sample .of each group, representative of i t s range i n size on each sampling date.  These values were then used to calculate the  volumes of organisms present i n each sample. Length-frequency diagrams of H y a l e l l a from Corbett and Courtney lakes were plotted, following procedure of Anderson and Hooper (1956). B.  Description of the Dipnet Method The dipnet method was used to investigate d l e l  movements of organisms inhabiting the Chara shoals.  Sampling  stations were established on a l i n e roughly perpendicular to the lake shore at depths of 0.5, 1.0, 1.5 and 2.0 metres, measuring from lake surface to substrate.  These have been  13 subsequently referred to as Station No s 1 to 4 , respectively« 1  The sampling apparatus consisted of a net bag (mesh aperture 0.6 mm)  with a 23 cm square steel band sewn into  i t s open end and equipped with a 2.5 metre wooden handleo The net was lowered to the top of the Chara stand at each sampling s t a t i o n and moved over the tops of the plants f o r a distance of 1.5 metres.  The net was never allowed to sample  more t h a n t h e tbp 5.0 cm of Chara stems.  This procedure was  repeated at four-hour i n t e r v a l s over a period of twenty-four hours. In July; when t h i s type of sampling was started, four i d e n t i c a l sweeps were combined to constitute one sample» r e p l i c a t e s were taken.  No  The samples proved to be much too large  f o r convenient analysis. On a l l subsequent sampling dates, only one, I.5-metre sweep was taken f o r each sample and two r e p l i cates were obtained at each station at each sampling time. Samples were washed d i r e c t l y from the net bag i n order to avoid l o s s of the smaller organisms. CV  S t a t i s t i c a l Procedures Data obtained by diving was subjected to an analysis  of variance after transformation of the o r i g i n a l counts to the square root.  The transformation was made i n order to s t a b i l i z e  the v a r i a t i o n present i n data of t h i s kind ( B a r t l e t t , 194?) °  When numerous counts l e s s than ten were present \Jcount + 0.5 was used. Wherever the analyses of variance indicated  sig-  n i f i c a n t differences between depth means, Duncan's new multiplerange test was applied to determine the significance of the differences and the means (Steel and Torrie, I960).  RESULTS  A  0  The Density and Composition of the Invertebrate Populations of Chara Shoals A wide v a r i e t y of invertebrate l i f e i s encountered i n  an i n v e s t i g a t i o n of the Chara habitat.  By f a r the greatest  percentage of the species present at any one time i n the Chara are species which l i v e only a part of t h e i r l i v e s i n the aquatic environment.  These are the immature stages of i n s e c t s  0  Small numbers of the c u l i c i d dipteran, Chaoborus. which cons t i t u t e s a l a r g e percentage of the limnetic plankton of Corbett Lake, make frequent excursions into the Chara zone and occasiona l l y appear i n f a i r l y high concentrations (Table II) i n the samples.;  Other members of the limnetic plankton such as  Daphnia sp. and Diaptomus sp. also occur i r r e g u l a r l y .  Since  the samples obtained by the diving method were washed through a wire mesh sieve of 1 . 0 0 mm  aperture, cladocerans and other  planktonic forms were not enumerated. In addition to the organisms presented i n Tables II and I I I , hirudineans and planarians also occurred i r r e g u l a r l y i n the samples but i n such small numbers that they were not recorded q u a n t i t a t i v e l y i n the data.  15  •>  <D  cl" H  O  ro  0  g  P 5  t  *<!  H  JO  H  VA)  ro 00  00  H  H  HO' Oct  No. o f samples  O  CT<  H y a l e l l a azteca-*  O  So  s ro  ro  Chltonomids  Co  O  M O H  H  CO  O •!>-  H ro -a  o  O  o  o  o •  •  •  •  *-  o  H  00  H  H  o  CO  H  •  b  O u>  ro-  H  b  .  Gyraulus sp. o <* o O  o  <5 o o H  o  Physa sp.  -3  P i s l d i u m sp. •  b o  O  O  ro  b H  b H  2° o l_i  H  H  •  o o o ro  •  o o ro  • o o  CO  Chaoborus sp. O  O  o ro H H  •  Syrup etrum sp.  #  ro -4  CO  H  vO  H  H  H  Aeshna S T J .  •  •  fe fe fe fe IO  ro  Ic  H C  1  .  ro  ro o  H -3  T r i chop tera  •  o O  VI  CO  H c  c oo  C  c  c ro  OC  o  -j c o  ro -a  ?o  E n a l l a m a sp. O O H  ro  H  .  .  O O  Ephemeroptera.  -3 VjJ ro  >•  ro  ro  H  —-  o ro  • OC  CO  \C  Average No. o f a l l . organisms per 300 gms Chara Average V o l . o f a l l organises g e r 300 gins  91  w  >  c+  •  p p(0  H  H >Jl  H oa  M  •Ot-  H OS  JO  00  •  ,  •  •  <  TO  03  <>  -t>-  o ?o  bCI  Ul  b  -3  O  o ~3 JO  .  VJ  o o  a o JO  H  H  •  0»  o  <J1  6  o  JO  H  H  •  O Ut  O  H  o  •  o O  H  .  .  o o o ro  o o o to  H  •  o •  o  o  Ci  o  n H •  a o  n a  •  o  *-  H  o H  •  o o o  ?o  o  Ci  a o  JO  •  vO  o  H 00  o  o  o  H  o  o  •  a o  < o  •  fe  H  Ci  <  o Ul  O Ut  O U, t  H #  H ~3  < o  #  H  H  H  H ~3  • H -J  •  H  H  H ~3  Aeshna sp.  H •  •  o  Sympetrum sp.  o  a o  H  Chaoborus sp.  •  a o o  P l s l d l u m sp.  < o H •  • a <! o o H •  . o  Physa sp.  •  o o ro  o  Gvratilus sp.  «=)  o •  JO  H  o  •  .''.  H O  Chlronomlds  < r> o  o o .  azteca*  O O o H  a o •  .  Ilyalella  ol  •  No. of samples  JO  -J  o  Ul  H O VJ S"  Enallagma sp.  o o H •  a o • Ci Ci  Trichoptera  <  o •  O  c  #  C c  JO  H fO • M  to  C C H. H 1  c  •  C  •  <*  o' •  •  C  c fo H  C •  a  Ci Ci  Ephemerop t e r a  o H  Average Ho. o f a l l organisms per 300 gms Chara Average V o l . of a l l organisms per 300 gms Chara  i  18  In general; the organisms making up the hulk o f the Ghara fauna both numerically and volumetrically are the amphipod H y a l e l l a azteca (Saussure), chironomid larvae, and the gastropod Gvraulus sp. The Odonata are represented i n the Chara by two genera o f anisopteran —  Aeshna sp. (family Aeshnidae)  and Svmpetrum sp. (family L i b e l l u l i d a e ) , and one zygopteran genus —  Enallagma sp. (family Agrionidae).  These animals occur  i n r e l a t i v e l y small numbers but their bulk adds considerably to the t o t a l volume of organisms present i n Corbett Lake (Table I I ) . The gastropod Physa sp. and the pelecypod Pisidium sp. are everpresent, minor constituents of the Chara shoals. . The amphipod Gammarus l a c u s t r i s was encountered i n small numbers i n the Chara samples.  For example, i n Paul Lake  on September 7, 1962 there were 7 Gammarus per 100 H y a l e l l a i n the samples.  This was the l a r g e s t number ever taken — the  species u s u a l l y occurring i n much smaller numbers at a l l times i n Corbett and Courtney lakes (e.g. 2 Gammarus/iOOO H y a l e l l a i n Courtney Lake on June 1 1 , 1963).  I t s numbers have, therefore,  been included with those of H y a l e l l a .  The l i n e depicting the  seasonal trend i n numbers of organisms i n Corbett Lake (Figure 4) indicates a s t r i k i n g increase i n numbers of i n d i v i d u als between June 10 and September 1 4 . however, does not correspond  The increase i n volume,  to the increase i n numbers as a  very s l i g h t decrease i n numbers between J u l y 10 and August 15  19  ° •  O «  VOLUME NUMBER Loco  < cc <  <  CORBETT  x-  oc c  cc < I  •aoo°  CO  2  O O 3-0o  r - 6 o o  o o  to 2  •400to 2 to z - < •200 g  c/> 2 0 •  z < z < CC L - O H O  AO A  hBOO  I COURTNEY  3  a. HI  3Q-  •600  O  >  z •400  20H  LU  LU  <  <  or  |  §! i-o<  cc  #-  o-  LU  •o •  -200 > <  5  Ltl  <  _3_  FIG. 4 . N U M B E R A N D VOLUME OF INHABITING C H A R A S H O A L S , STANDARD  ERROR  OF  MEAN  FOR  <2_  INVERTEBRATES VERTICAL  NUMBERS.  LINES  REPRESENT  20 r e s u l t s i n a much l a r g e r decrease i n volume due to the bulk of the organisms l o s t .  Table II shows that a l o s s of a few  Odonata naiads and Trichoptera larvae constitute over 80 percent of the l o s s i n volume. The Chara shoals of Courtney Lake were covered throughout the summer months by a dense growth of a filamentous alga to a depth of 1.5  metres.  Unfortunately, an i d e n t i f i c a t i o n of this  alga was neglected and samples of i t have not been retained. Chara growth from shore to 1.5  metres was greatly i n h i b i t e d and  much of the stand.was i n a state of decomposition.  I t was not  possible to divide the Chara into top and bottom halves i n the area affected by the filamentous alga, thus l i m i t i n g the study of d i s t r i b u t i o n within the Chara to the stations between 2.0 and 4 . 5 metres.  Total Chara samples were obtained, however, i n the  affected area and the numbers of organisms per 300 grams of Chara were recorded. These counts were included i n the data f o r average numbers of organisms found i n the Chara zone (Table III) . Data presented i n Figure 4 f o r Courtney Lake indicate the same general, numeri cal trend as was observed i n Corbett Lake ( i ..e.- from small numbers i n June to larger numbers i n September). The rapid increase i n Corbett Lake between June and J u l y appears to occur i n Courtney Lake between J u l y and August. ence w i l l be explained l a t e r .  This d i f f e r -  21 The.most s t r i k i n g difference i n the densities of invertebrate fauna between the two lakes l i e s i n the curves f o r volume.  The volume of organisms i s much lower per 300 gins of  Chara i n Courtney than i t i s i n Corbett and the curve i n d i c a t e s a uniform but s l i g h t increase throughout  the summer months,  Whereas, i n Corbett Lake the volumes are much greater and undergo a marked f l u c t u a t i o n during the course of the summer. I t i s necessary>  therefore, to compare the  percentage  compositions of invertebrate populations of the two lakes (Figure 5 ) v  I t i s obvious from t h i s figure that although the  Chara shoals of Corbett and Courtney lakes harbour the same kinds of organisms, quantitatively t h e i r compositions are very much different.  In p a r t i c u l a r , H y a l e l l a azteca completely dominates  a l l other invertebrate groups present i n the Chara of Courtney Lake, both numerically and volumetrically.  I t represents 88.8  percent of the t o t a l number of organisms present and 60,<4 percent of the t o t a l volume.  A l l other organisms, therefore, may  be  considered as minor constituents of the Chara invertebrate popul a t i o n of Courtney Lake. On the other hand, although H y a l e l l a i s numerically dominant i n the Chara of Corbett Lake, i t takes a  secondary  p o s i t i o n volumetrically due to the presence of small numbers of 0donata naiads and Tricoptera larvae which, as mentioned previously, add a considerable amount to the total, volume.  22  PER CENT NUMBER PERCENT VOLUME  60Ui  2 J  O  60-  >  2  40  CORBETT  ul  ffi  FIG. 5. PERCENT COMPOSITION OF THE CHARA SHOALS  OF OF  INVERTEBRATE POPULATIONS CORBETT AND COURTNEY LAKES.  23 Since H y a l e l l a plays such an important r o l e i n the seasonal changes i n Invertebrate density, i t s numbers and volume have been p l o t t e d separately f o r Corbett and Courtney lakes i n Figure 6.  I t w i l l be noted that a large increase i n numbers of  H y a l e l l a occurred between the June and J u l y sampling dates i n Corbett Lake,  But> i n Courtney Lake an increase i n numbers d i d  not take place u n t i l August 15.  The curves f o r volume of  H y a l e l l a i n the two lakes remain remarkably constant over the entire period under consideration. Length-frequency diagrams f o r the two H y a l e l l a populations help to explain the above observations (Figure 7).  On  June 10 and 11 the H y a l e l l a populations of both Corbett and Courtney lakes were composed of mature i n d i v i d u a l s ranging i n t o t a l length from 3.0 mm  to 6,5 mm.  Corbett Lake tended to have  a higher percentage of l a r g e r i n d i v i d u a l s than d i d Courtney Lake. Examination of the brood pouches of the females collected i n June indicated that most of the Corbett Lake population were carrying, eggs or young animals, but, very few of the Courtney Lake females bore eggs or young.  By J u l y 10, newly-hatched young  made up the bulk of the population i n Corbett Lake and most of the mature i n d i v i d u a l s had disappeared.  H y a l e l l a collected i n  Courtney Lake on J u l y I I were* however* a l l mature i n d i v i d u a l s except f o r one or two specimens 2;0 mm  i n length.  Females were  examined and found to be carrying eggs and young animals.  2A  H Y A L E L L A  A Z T E C A  NO.S o - o V O L .  CC  NO. C O R  B E T T  1  <  T J.  ./1  2.O0-  CC  QL < IE U  T 1 - i - o  <  -0-5  u  o  o- o  U) fe>00i  C O U R T N E Y  UJ  o o  Z> _i  ro O  o  A  4-ob-  > Lul  LU T  <  or  2.0O-  •1  _ 1-0  L  Ld -0-5 > <  > <  z ~3  >-  3  < DC  T/  LU  6.  C/)  CP  ra in  Number and volume of H y a l e l l a i n the Chara shoals of Corbett and Courtney lakes.  25  C 0 R B ETT  COURT  NEY  J U  Fig.  7.  " L E N G T H  ( M M )  S e a s o n a l changes i n the l e n g t h - f r e q u e n c y of Hyalella azteca.  distribution  26 In August, no sexually mature i n d i v i d u a l s were found i n either population; H y a l e l l a ranged i n size from 2 . 0 to 4 - . 0 mm i n Corbett and from 1.5 mm  to 3.5 mm i n Courtney.  The  September c o l l e c t i o n s indicated continuing growth; of i n d i v i d uals i n both lakes but ho further reproduction. " B.  E f f e c t s of F i s h Removal on Invertebrate L i f e i n the Chara Shoals Samples were taken of the Chara zone of Paul Lake on  September 7, 1 9 6 2 ,  seven days before the lake was treated with  toxaphene ( . 0 0 4 p.p.m.) f o r the elimination of the redside shiner, Rlchardsonius balteatus.  For the purpose of comparison,  the sampling was. carried out on June 8, 1963 and again on September 6, 1963 —  a year after toxaphene treatment.  Results  are recorded i n Table IV and presented graphically f o r September, 1962 and September, 1963 i n Figure 8. A low point i n numbers of organisms i s observed i n June.  This, however, i s a t y p i c a l occurrence as evidenced by  the data f o r Corbett and Courtney lakes and recorded numerous times i n the l i t e r a t u r e by various writers ( B a l l and Hayne, 1952; Eggleton, 1931; Lindeman, 1942)*  I t can i n no way  be  construed to indicate an e f f e c t of toxaphene on the abundance of invertebrate organisms.  TABLE IV AVERAGE NUMBER OF ORGANISMS PER 300 GRAMS OF CHARA - PAUL LAKE  o  Q> •P N CO  cd  0}  to  CO  Date  H H  <D  >  CO  § o o  CO  1  CO fn  o  CO CO  cd  >j  A  •H CO •H  a,  •p a) p  CO  3  CO  I  a> -p ft o CD  •H  P.  •H  ct?  H  CO  No. of sampies  Average no. o f a l l organisms per 3uugms. o f Chara  -J  1962 Sept. 7 1 4  0.00  26  0.06  0.6  0.3  0.06  0.9  0.6  12  77.52  1963 June 8  1  0.07  39  9  0.00  6.0  0.0  0.00  0.0  0  0.5  10  55.57  Sept. 6  5  5.00  31  7  8.00  1.0  3.0  0.4  0.2  3  4.0  15  67.60  * H y a l e l l a azteca plus small numbers of Gammarus l a o u s t r i s at 0.5 and 1.0 metres.  28  1  CD tJ>  o> 0~>  0_  CL  Ld  Ld  (/>  CO  J [  I  1VN3  HS3V  cnsid  HdV»V  o  to V d V H D  o  o rO  Q-Oe  O / ' O N  I  O  O  3 9VH3AV  F i g . 8, Numerical density of invertebrates i n the Chara shoals of Paul Lake - September 1962 and September 1963 •  29 The removal of f i s h from the lake resulted, i n September 1963, chironomids,  i n a s i g n i f i c a n t increase i n the numbers of  l i b e l l u l i n e and aeschhine Odonata> Ephemeroptera  and Hirudinea.  An increase also occurred i n numbers of  Mollusca. The t o t a l numbers of organisms per 300 gms of Chara i n September* 1963> d i d not reach the density recorded f o r September, 1962 due to the decrease i n numbers of amphipods. Presumedly the amphipods were d r a s t i c a l l y reduced i n numbers by the poisoning and had hot as yet f u l l y re-established themselves a year l a t e r * Stomachs of shiners collected i n 1959 Pinantan lakes (Johannes and Larkin, 1961)  i n Paul  and  indicate a diet  l a r g e l y composed of zooplankton organisms but other food i n cluded H ^ l ^ l l a , various aquatic and t e r r e s t r i a l insects* and molluscs*  In the summer during the day* shiners are concen-  trated d i r e c t l y over the shoals.  Trout tend also to be near  the shoals, but farther offshore and i n deeper water. Thus, the great increase i n numbers of aquatic i n s e c t s , molluscs, and perhaps also leeches after removal of the f i s h may  i n d i c a t e the effectiveness of the redside shiner  i n reducing; or holding at a lower l e v e l , those organisms upon which i t feeds.  30 C,  The V e r t i c a l D i s t r i b u t i o n of Invertebrates within the Chara Stand I t was o r i g i n a l l y intended that the v e r t i c a l p o s i t i o n  of organisms within the Chara habitat should be investigated by dividing the Chara stand into two approximately equal v e r t i c a l halves and then sampling the underlying substrate with an Ekman dredge.  Upon examination of the Paul Lake samples taken  on September 7, 1962, I t was discovered that macroscopic incertebrate organisms were confined to the Chara i t s e l f and that the s o i l underlying the bed d i d not harbour a macrofaunal population of i t s own (Table V),  Only organisms obviously  belonging to the overlying Chara were found i n the substrate samples and these only i n very small numbers.  None of the  organisms which are t y p i c a l l y associated with lake  bottom,de-  p o s i t s / such as oligochaetes, were taken i n the samples. The v e r t i c a l p o s i t i o n of organisms within the Chara bed was plotted f o r each sampling date (Figure 9 ) .  An analysis  of variance determined whether or not there were s i g n i f i c a n t differences between mean numbers of organisms i n the top h a l f and bottom h a l f samples on each date. treated as a whole.  Organisms were f i r s t  Then, each group present i n s u f f i c i e n t l y  large numbers to allow s t a t i s t i c a l analysis was considered separately and i n order of t h e i r numerical abundance i n the Corbett Lake samples..  31 TABLE V ORGANISMS FOUND IN THE SUBSTRATE UNDERLYING THE CHARA STAND - PAUL LAKE, SEPTEMBER 7, 1962 Organism  ^Average No. i n 527 sq cm of substrate  H y a l e l l a azteca  8  Chironomids  0  Gyraulus  1  Physa  2  Lymnaea  <1  Pisidium  <1  Sympetrum  < 1  Aeshna Enallagna Ephemeroptera Hirudinea  0 •>  <1 0 <1  * Average number of organisms based on 12 samples taken at various depths over the Chara zone.  32  COURTNEY  CORBETT  40-  <  o 20-  (A  2 «z oo  Or  <  </><*  2 —•° ti in _«t /) zz << o ft ctio  o«  20  o<  20  U.O  oo  1 lU y, CD  2  O  20  Z  UJ  O  <  uJ  >  <  O  SEPT  14  6 4  • o  A : ALL ORGANISMS B •- H Y A L E L L A C : CHI RONOMI-D • LARVAE D:GYRAULUS E : SYMPETRUM NAIADS  ]  2 2  J. U4 NE Q IO  F I G . 9.  TOP HALF o BOTT. HALF  SEASONAL OF  CHANGES  ORGANISMS  IN  WITHIN  VERTICAL THE  CHARA  POSITION STAND.  33  a) A l l Organisms In general, s t a t i s t i c a l and graphical analyses indicated only minor differences i n v e r t i c a l p o s i t i o n of organisms within the Chara bed,  A seasonal trend was  apparent, however, toward  greater numbers i n the lower h a l f of the Chara. considering a l l organisms c o l l e c t i v e l y (Figure 9 A ) ,  In Corbett Lake, highly  s i g n i f i c a n t differences (p = 0 . 9 9 ) were demonstrated between average numbers of organisms i n the top and bottom halves of the Chara stand on September 14,  there being many more organisms  present i n the bottom h a l f than i n the top.  The same trend  occurred i n Courtney Lake although i t was possibly not quite as obvious due to the difference i n hatching between the two lakes.  time of H y a l e l l a  This point w i l l be made clearer when  considering H y a l e l l a separately.  On J u l y 11,  sampling showed  the presence of larger numbers of organisms i n the top h a l f of Courtney Lake Chara than i n the bottom h a l f .  From that date on,  numbers i n the bottom h a l f increased more r a p i d l y than d i d numbers i n the top h a l f (Figure 9 A ) . b) H y a l e l l a azteca The v e r t i c a l p o s i t i o n of H y a l e l l a azteca within the Chara stand changed seasonally and was  apparently correlated  with the age of the i n d i v i d u a l s within the population. of new  Hatching  i n d i v i d u a l s occurred several weeks l a t e r i n Courtney than  i t d i d i n Corbett (Figure 7) .  Differences i n d i s t r i b u t i o n of  H y a l e l l a between the two lakes are the r e s u l t of the difference  34 i n hatching time of the two populations.  In Corbett Lake,  large numbers of young H y a l e l l a were taken on J u l y 10 and  they  were present i n s i g n i f i c a n t l y greater numbers i n the top h a l f than i n the bottom h a l f of the Chara (Figure 9B) „ were not present i n Courtney Lake on July 11,  Young animals  however, and  although there were s i g n i f i c a n t l y greater numbers of organisms present i n the top h a l f than i n the bottom h a l f of the Chara stand, the difference was  due  to a l o s s of numbers i n the bottom  h a l f than to an increase i n the top h a l f .  No  appreciable  increase occurred i n numbers of H y a l e l l a i n Corbett Lake a f t e r the i n i t i a l Increase i n J u l y (Table I I ) . p o s i t i o n of the organisms was 11  and September 14*  However, the v e r t i c a l  altered considerably between July  Numbers of organisms i n the top h a l f Of  the Chara continued to diminish whereas numbers i n the bottom h a l f increased — (p = 0 . 9 9 )  r e s u l t i n g i n highly s i g n i f i c a n t differences  between the two l e v e l s of Chara on September 14«•  Courtney Lake the trend was  In  also toward increasingly greater  numbers of H y a l e l l a i n the bottom h a l f of the Chara bed, differences were not s t a t i s t i c a l l y demonstrable.,  but  This was  due,  presumedly, to the entrance of young H y a l e l l a into the populat i o n at a l a t e r date i n Courtney Lake than was  the case i n  Corbett. c) Chironomid larvae Chironomid larvae as a whole tend to be d i s t r i b u t e d with greater density i n the deeper layers of the Chara bed  (Figure 9C)  0  35 Numbers of chironomid larvae were very much lower i n Courtney Lake than they were i n Corbett,  This was possibly due to heavy  predation by the redside shiner, which i s present i n Courtney Lake but not i n Corbett,  In spite of t h i s difference i n t o t a l  numbers, the two populations were d i s t r i b u t e d v e r t i c a l l y i n the same general manner.  S i g n i f i c a n t differences (p = 0,95)  between numbers i n the top h a l f and bottom h a l f of the Chara bed were demonstrated f o r a l l but the August samples on Corbett Lake and i n the June and September samples on Courtney Lake, I n a l l cases where there were s i g n i f i c a n t differences, the greater numbers of larvae were i n the bottom h a l f of the Chara, d) Gvraulus sp. The planorbid Gvraulus appeared i n the Corbett Lake samples i n more or l e s s equal numbers i n top and bottom halves of the Chara on June 10, J u l y 10 and August 15 (Figure 9D), However, a difference between the number of Gvraulus i n the two l e v e l s of Chara was demonstrated s t a t i s t i c a l l y (p = 0.95) September 14 —  on  there being more Gvraulus i n the top h a l f than  i n the bottom h a l f on that date.  The differences between  numbers i n each l e v e l was accompanied by an increase i n t o t a l number of Gyraulus i n the Chara samples (Table I I ) , thus, i n d i c a t i n g an addition of new i n d i v i d u a l s to the population as the cause of the difference between l e v e l s .  36 The v e r t i c a l p o s i t i o n of Gvraulus i n the Chara o f Courtney Lake appears to be quite d i f f e r e n t from that o f Corbett Lake (Figure 9 D ) .  S i g n i f i c a n t differences'(p = 0 . 9 5 ) between  the two l e v e l s o f Chara were detected on June 1 2 , J u l y 1 1 , and September 14«  I n each case the bottom h a l f of the Chara con-  tained the larger number of animals.  There were also many l e s s  Gyraulus i n the Courtney Lake population again suggesting predation by the redside shiner as the possible cause of the d i f f e r ence i n d i s t r i b u t i o n within the Chara beds of the two lakes. e) Sympetrum sp. Sympetrum was not present i n s u f f i c i e n t l y great numbers i n Courtney Lake to allow s t a t i s t i c a l treatment*  Therefore, the  i n v e s t i g a t i o n of i t s v e r t i c a l d i s t r i b u t i o n within the Chara was l i m i t e d to Corbett Lake.  The numerical density of Sympetrum  within the Chara dropped from 11 per 300 gms o f Chara on June 10 to 4 per 300 gms of Chara on September 14- (Table I I ) .  It is  apparent from Figure 9 E that most of the l o s s was of i n d i v i d u a l s which had been situated i n the upper part of the Chara stand. Numbers i n the bottom h a l f remained r e l a t i v e l y constant throughout the summer months. difference (p - 0 . 9 5 )  Thus, on September 14, a s i g n i f i c a n t between numbers indicates that the remain-  ing members of the Sympetrum population were located mainly i n the lower h a l f of the Chara stand.  I t was found that the naiads  present i n the top h a l f samples i n August had a mean body length of 11.0 mm and ranged i n length from 10.0 to 14.0 mm.  Whereas,  37  the naiads remaining i n the Chara i n September had a mean body length of 8 . 7 mm and ranged from 6 . 0 to 1 1 . 0 mm. D.  The Horizontal D i s t r i b u t i o n of Invertebrates within the Chara Zone  a) A l l Organisms A d i r e c t comparison of h o r i z o n t a l d i s t r i b u t i o n o f the t o t a l invertebrate populations o f Corbett and Courtney lakes i s , •  i  perhaps, not very meaningful  as the d i s t r i b u t i o n s of the entire !  populations are determined by the d i s t r i b u t i o n s o f the i n d i v i d u a l components and t h e i r numerical densities*  A l s o / the e f f e c t s o f  the filamentous a l g a l cover i n Courtney Lake altered the d i s t r i butional pattern considerably during the early summer months.' As a r e s u l t few s i m i l a r i t i e s were apparent i n the d i s t r i b u t i o n a l patterns of the two populations. The most s t r i k i n g c h a r a c t e r i s t i c of the h o r i z o n t a l d i s t r i b u t i o n of the invertebrate population as a whole i n Corbett Lake i s i t s uniformity.  On June 10 the 4.0-metre s t a t i o n had a  s i g n i f i c a n t l y higher numerical density of organisms (p = 0 . 9 5 ) i than the 2.0-metre s t a t i o n and remained i n that relationship on ; J u l y 10 (Figure .10)..  The 1.5-metre s t a t i o n showed much greater '  numbers of organisms than the other stations on J u l y 10 due to the hatch of H y a l e l l a azteca as previously described.  Other than  these few minor differences, numerical d e n s i t i e s o f organisms at a l l stations over the Chara shoal of Corbett Lake were found to be equivalent to each other.  38  COURTNEY  C O R B E T T  <  oc < I u  20-  2  IO-  30-  o  J  u N E  o o m  (A  2  <3o^  //%  *-  S 2 0 V  O u.  O  tz UJ CD  cc »-  u  \  to • z < z icH o < oc  J  L Y  O  530-|  A U  O OC  •  °>  IOH  , 2 0 - ,  „ • — •  z ui O < ut  > <  30-  s;  _  E P T  20 IO-  I.O FIG.  2  IO.  T  —1—  1  T  T  3-D 4.O JDE P T H (.METRES) SEASONAL CHANGES IN H O R I Z O N T A L OF O R G A N I S M S INHABITING CHARA 0  3.O  1  1  4.O D 1 S T R| B U T I O N S H-O-A-L S .  39 The density of the invertebrate population of the Chara shoals of Courtney Lake at each s t a t i o n sampled on four sampling dates i s also i l l u s t r a t e d i n Figure 10,  No s t a t i s t i c a l d i f f e r -  ences (p =0,95) could be demonstrated between stations on June 11 or J u l y 12.  However, t o t a l counts made at the 1.0-metre  s t a t i o n i n the area covered by filamentous alga were not treated s t a t i s t i c a l l y as the analysis was set up to handle only data broken down i n t o top and bottom h a l f samples.  I t i s apparent  graphically (Figure 10) that there was a marked s c a r c i t y of organisms i n the affected area on both the.June and J u l y sampling dates.  By August the filamentous a l g a l cover began to disappear  and patches of healthy Chara were present among the decayed material.  Samples taken at the 1.0-metre station i n August i n -  dicated a large increase i n numbers of organisms present at that depth*  The analysis of variance carried out on the August date  indicated significant, differences (p = 0.95)  between stations,  but, Duncan's t e s t f a i l e d to reveal which o f the means were s i g n i f i c a n t and which were not.  I t i s obvious (Figure 10), how-  ever, that there were more organisms present at the deep stations (4.0 and 4.5 metres) than at the shallower ones. Analys i s of the September samples showed that the 2.0-metre s t a t i o n had a s i g n i f i c a n t l y lower density than the other stations on that date and that the 4.0-metre station had s i g n i f i c a n t l y greater numbers of organisms present than d i d the two shallower stations included i n the analysis.  1  40 The organisms are presented separately i n the pages i n order of t h e i r numerical abundance as  following  previously  described. b) H y a l e l l a azteca The  analysis of the horizontal d i s t r i b u t i o n of H y a l e l l a  over the Chara shoals of Corbett Lake on four sampling dates over the summer months indicated minor s h i f t s i n the concentration of the population.  These changes i n d i s t r i b u t i o n are  strongly  correlated with the l i f e h i s t o r y of the i n d i v i d u a l s as stated i n the previous section.  I t may  be noted that the mature animals  which make up the population on June 10 occur i n greater numbers at the deepest station whereas on J u l y 10, when the population i s composed l a r g e l y of newly-hatched i n d i v i d u a l s , by f a r the greater density occurs at the 1.5-metre s t a t i o n .  The  animals  then apparently r e d i s t r i b u t e themselves over the Chara shoal so that by August 15 no s t a t i s t i c a l differences stations can be detected.  (p - 0.95)  between  In the September samples* however,  s t a t i s t i c a l tests indicate the presence of minimum numbers of H y a l e l l a at the 2.0-metre s t a t i o n (p = 0.95).  Looking back over  the d i s t r i b u t i o n s plotted on the three previous sampling dates (Figure 11), i t i s apparent that a 2.0-metre minimum i s at l e a s t suggested i n each p l o t . In Courtney Lake. H y a l e l l a azteca constitutes percent of the t o t a l invertebrate and,  almost 90  population of the Chara shoals  thus, the d i s t r i b u t i o n a l patterns described above for  the  41  C O R B E T T  COURTNEY  -  <  cc < I  --•  u m  J U N  2  »  <  Z  o o o  » 5"  -  A  J U  < oc* O  L  J  -J  u.  -J  Z  <  <  *•  Y  1U (A  >  ------  E  4  X  A  o o cc  U  cc  G *  us I CD 6 Z Ul  <  a ui > <  >  x  IO  T  •r 20  •  S E < P T  30 40 IO 20 D E P T H CMETRES) FIG II. S E A S O N A L CHANGES IN HORIZONTAL OF HYALELLA AZTECA. 30  40 DISTRIBUTION  42 invertebrate population i s e s s e n t i a l l y the d i s t r i b u t i o n of. Hyalella.  Low density of organisms at the 1.0-metre s t a t i o n i s  again noted oh June 11 and J u l y 12 due to the presence of the filamentous alga.  Highest numerical d e n s i t i e s occurred at the  3.0-metre station on August 17 and September 14«  I t i s observed  that no large concentration of H y a l e l l a was discovered a f t e r hatching of the new i n d i v i d u a l s as was the case i n Corbett Lake. I t i s presumed that the hatch occurred i n Courtney Lake shortly after the J u l y samples were taken and, thus* the animals had r e d i s t r i b u t e d themselves over the Chara shoal by August 17 when the next sampling was done. c) Chironomid larvae The d i s t r i b u t i o n of chironomid larvae over the Chara shoals i s complicated by the f a c t that the populations of chironomids  are composed of many species each of which, taken  i n d i v i d u a l l y , may d i s p l a y a d i f f e r e n t d i s t r i b u t i o n a l pattern. Only intensive studies on the biology of the i n d i v i d u a l species w i l l reveal what factors are most important i n the control o f the d i s t r i b u t i o n .  Also* as the species composition of the t o t a l  chironomid population of the Chara shoals a l t e r s seasonally as a r e s u l t o f emergence of some species and the addition of others, so must the pattern of d i s t r i b u t i o n a l t e r . Comparing the h o r i z o n t a l d i s t r i b u t i o n s of chironomid larvae i n Corbett and Courtney lakes (Figure 12), i t I s obvious that the two populations are d i s t r i b u t e d over the Chara shoals  C O R B E T T <  COURTNEY  30-  a. < x u  J U  20-  </i  N E  IO-  2  *  30-  J  1 20-  U  Q ^ -  CC  2 o O u. z co 0 Z EE  1  u  •  IO-i  Y  V  o  A U  a io-|  S E P T  UJ  20-  cc UJ  > <  4-  \  *  o30-  <  A  G  Z  O  • 8  uj in  2  4-  o-i—  «  >- 3 0 -  i  CO  8  L  •'  o £ o 20o a  oc  4-  •o-»  oCO  8-  I O - T  IO  20  30  F I G . 12. S E A S O N A L  40  8-  IO 20 DEPTH CMETRES) CHANGES IN HORIZONTAL CHIRONOMID LARVAE  •  • -• 30  40  DISTRIBUTION  OF  i n widely d i f f e r e n t manners. In Corbett Lake, the numerical densities of chironomid larvae at each s t a t i o n were not s t a t i s t i c a l l y d i f f e r e n t (p = 0.95)  from each other on August 15 or September 14.  In  June, the 1,5-metre station had a s u f f i c i e n t l y high number of larvae to make i t s i g n i f i c a n t l y d i f f e r e n t (p = 0.95) other three stations sampled,  from the  A minimum i n numerical density  occurred at the 2.0-metre s t a t i o n i n J u l y which was demonstrated to be s t a t i s t i c a l l y d i f f e r e n t (p = 0,95)  from a l l other stations  sampled. In Courtney Lake, the chironomid population of the Chara shoals i s almost non-existenti  S t a t i s t i c a l tests f a i l e d  to show any differences between density at each s t a t i o n on any one sampling date (p = 0.95) •  Because of the small numbers of  larvae present i n Courtney Lake, the counts were plotted on the v e r t i c a l axis using a much larger scale than was used f o r the Corbett Lake data (Figure 12).  As a r e s u l t , although no s t a t i s -  t i c a l differences could be detected, the organisms appeared to be concentrated at the 1.0-metre and 4«0-metre stations on August 17 and at the 1,0-metre s t a t i o n on September 14. d) Gyraulus sp. Here, as with the chironomid data, i t was necessary to place the Courtney Lake counts on a much l a r g e r scale than those of Corbett Lake due to the small numbers of Gyraulus  AVERAGE to O  o im •  i « i •  Tt  O  u  I  u> O I  N U M B E R OF S Q . - R O O T  i •  o  to  O  O  _1_  \  C H A R A IO  o  O  _L_  _L_  O _i_  O _1_  i i •  i  6"  m  IO  O  lo  v»  GYRAULS / 300 CMS. TRANSFORMATION  O  >  O  z >  x > z o  o p  t  CD  i i i i  m  H i  i  06"  mm  •o  <  H  3D _ X  r> r c wx m  H  o rn m —° Ki  TJ  m  in co  CD C  >  < rc < _  m z  co _l_  O  • I—  i  6"  \  CD C H  z  OB I  o o c p  6"  (A H  o  c_  W  O Z H >  r  c  H Z  m 6"  £7  46  CORBETT  < CE <  u  J  6H  U  4  N  2-d  E  O J  U L Y  A  U G  S Ld  6  E  <  P  Ld > <  T _L_  O -  1-5  F i g , 14..-  20  2-5  DEPTH  4 0  (METRES)  Seasonal changes i n horizontal d i s t r i b u t i o n of Sympetrum naiads.  47 present i n the former lake (Figure 13).  A graphical comparison  of the d i s t r i b u t i o n s of the two populations i s , therefore, perhaps not desirable. apparent s t a t i s t i c a l l y ; .  Certain s i m i l a r i t i e s are, however, I t was  found that i n Corbett Lake  Gyraulus was d i s t r i b u t e d over the Chara shoal with lowest density at the shallow stations and l a r g e s t density at the deeper stations on each sampling date.  In Courtney Lake, density was  s i m i l a r l y high at the deep station (4.5 2.0-  metres) and low at the  and 3.0-metre stations, but, at the 1.0-metre station, the  numerical density of Gyraulus increased from J u l y 12 to September 14.  The species d i d , i n f a c t , become more numerous at the  1.0-  metre s t a t i o n than at any other station on September 14. e) Sympetrum sp. The analysis of variance on the Corbett Lake Sympetrum counts indicated s i g n i f i c a n t differences (p = 0.95) stations only on J u l y 10 (Figure 14)»  On that date the 1.0-metre  station had s i g n i f i c a n t l y more larvae (p = 0.95) deeper stations (3.0  between  and 4»0 metres).  than d i d the  No other s t a t i s t i c a l  differences between stations could be shown. E.  D i e l Movements of Invertebrates of the Chara Zone Samples obtained by the dipnet method revealed a wide  v a r i e t y of organisms associated either d i r e c t l y or i n d i r e c t l y with the surface of the Chara shoal and with the waters immediately above the Chara (Table VI) . :  Of these organisms, the  T u r b e l l a r i a , Hirudinea* Corixidae and Trichoptera were found  48 TABLE VI ORGANISMS FOUND ON THE SURFACE OF THE CHARA BED AND IN THE WATERS ABOVE THE SHOAL - CORBETT LAKE, JULY TO OCTOBER, 1963 Turbellaria Order T r i c l a d i d a Planar!a sp. Hirudinea Cladocera Family Chydodoridae Eurycercus lamellatus Family Daphnidae Ceriodaphnia auadranaula (?) Daphnia S P P * Copepoda Suborder Calanoida Family Diaptomidae Diaptomus sp. Malacostraca Order Amphipoda Family T a l i t r i d a e H y a l e l l a azteca (Saussure) Family Gammaridae Gammarus l a c u s t r l s (Sars) Mollusca Class Gastropoda Family Planorbidae Gyraulus sp* Family Physidae Physa sp. Class Pelecypoda Family Sphaeridae Plsidium sp.  Insecta Ephemeroptera Family Caenidae Family Baetidae Odonata Suborder Zygoptera Family Agrlonidae En^Uftfima, sp. Suborder Amisoptera Family Aeshnidae Aeshna, sp. Family L i b e l l u l i d a e Sympetrum sp* Hemiptera Family Corixidae Trichoptera Diptera Family Culicldae Subfamily Chaoborinae Chaobbrus spp. Family Tendipedidae (= Chironomidae)  49 o n l y s p o r a d i c a l l y and i n v e r y s m a l l numbers*  They were, t h e r e -  f o r e , e x c l u d e d from t h e counts o f organisms made on each sample. A l l o t h e r organisms were enumerated  i n an.attempt t o  d e t e r m i n e t h e i r movements o v e r a p e r i o d o f 24 h o u r s .  The  amphipod Gammarus l a c u s t r i s and n a i a d s o f t h e a u i s o p t e r a n Aeshna, a l t h o u g h counted, p r o v e d t o be p r e s e n t i n i n s u f f i c i e n t numbers f o r purposes o f t h i s i n v e s t i g a t i o n .  The m o l l u s c s G y r a u l u s .  P h v s a . and P i s i d i urn e x h i b i t e d no d i e l movements —  t h e i r numbers  r e m a i n i n g c o n s t a n t on t h e Chara s u r f a c e o v e r t h e e n t i r e period.  24-hour  The z y g o p t e r a n E n a l l a g m a f l u c t u a t e d i n number on t h e  s u r f a c e o f t h e Chara. b u t no c l e a r p a t t e r n o f movement c o u l d be demonstrated f o r i t on any o f t h e f o u r s a m p l i n g d a t e s . S e v e r a l members o f t h e l i m n e t i c p l a n k t o n o f C o r b e t t L a k e were found from time t o time o v e r t h e C h a r a s h o a l and on the  s u r f a c e o f t h e Chara.  An a t t e m p t was, t h e r e f o r e , made t o  i n c l u d e t h e l i m n e t i c p l a n k t e r s Daphnia spp., Chaoborus Diaptomus the  spp., and  sp. i n t h e s t u d y o f d i e l movements o f i n v e r t e b r a t e s o f  Chara zone. On t h e J u l y , August, and September s a m p l i n g d a t e s t h e  s u r f a c e o f t h e Chara s t a n d was sampled w i t h a d i p n e t .  Sampling  s t a t i o n s were chosen o v e r t h e Chara s h o a l a t d e p t h s o f 0.5, 1.5, and 2.0 m e t r e s , measured from l a k e s u r f a c e t h r o u g h t h e Chara bed t o t h e s u b s t r a t e * s t a t i o n s 1,  These d e p t h s a r e s u b s e q u e n t l y named  t o 4, r e s p e c t i v e l y *  No samples were t a k e n i n t h e  50 waters above the Chara on these dates.  On October 19 and 20,  however, sampling was l i m i t e d to Station 4 and samples were obtained i n the open water above the Chara stand at that depth. L i g h t readings taken at the lake surface with an electronic photometer on J u l y 20-21, August 18-19, and September 21-22 were included i n the graphs of d i e l movements.  No l i g h t  readings were taken on October 19-20, but; the approximate hours o f darkness and, daylight were plotted on the f i g u r e s . a) Diaptomus sp, Diaptomus d i d not appear i n the sweep samples on J u l y 22 but was present i n considerable numbers on August 21.  By  September 21, Diaptomus was very numerous on the Chara surface and remained.numerous i n the samples taken on October 19 and 20. Counts made of Diaptomus on the Chara surface on September 21-22 at Stations 1 to 4 are p l o t t e d against time i n Figure 15.  Increased density of Diaptomus was observed on the  surface of the Chara during the hours of highest l i g h t i n t e n s i t y (12 noon to 4*00 P.M.)  and a much lower density a f t e r sunset and  before sunrise. The movements of Diaptomus i n the open water above the Chara shoal were investigated i n the October sampling series (Figure 16).  I t i s apparent that Diaptomus leaves the surface  of the lake at sunrise, undergoing a downward; v e r t i c a l migration.  By 4s00 P.M.  only a small f r a c t i o n of the Diaptomus  51  DIAPTOMUS 4  A M  12  8  NOON  >  4  10  h80oo  Z  LU  4000  -160 -120 -80  if)  0LU LU  -40  0-  CO  -160 C\J  CO D  -120  -8Q  to  o rCL <  m_  4Q  oH  Q  -160 LL_  -120  ro  o  -80  10  or  •40  /  LU  •0-\  CD  80  ICO Figo 15o  D H40  0 — D i e l changes i n density of Diaptomus on the Chara surface.  1  52  D IAPTOMUS  •_ Ld UJ  CO  CO D  o  o_ < b  o  u CD  D Z  < or  Ld  > <  F i g . l6o D i e l changes' i n d e n s i t y o f D i a p t o m u s i n t h e o p e n w a t e r above t h e C h a r a s h o a l and o n t h e C h a r a s u r f a c e .  53 population remained i n the open water above the Chara shoal at Station 4 and numbers at the Chara surface were also much reduced. Since the sieve used to wash.Chara samples by the diving method d i d not r e t a i n Diaptomus. i t i s not known whether the organism enters the Chara bed i t s e l f during the hours of high l i g h t intensity* A f t e r sunset; samples taken i n the open water above the Chara shoal and on the Chara surface at 8:00 P.M. numbers of Diaptomug —  yielded large  the greatest density concentration  occurring 0.5 metre below the lake surf ace.  At midnight, con-  siderable numbers of Diaptomus had l e f t the top 0.5 metre of water suggesting, perhaps; a secondary downward migration. b) Daphnia spp. D i e l changes i n l i g h t i n t e n s i t y at the lake surface and i n numerical density of Daphnia on the surface of the Chara bed are plotted i n Figure 17 f o r three sampling dates.  Two points  must be emphasized i n the figure: ( l ) numerical density of Daphnia i s high on the Chara surface only during hours of darkness or decreasing l i g h t Intensity; (2) on J u l y 20-21 only Station 4 shows appreciable changes i n number o f Daphnia.on the Chara surface but by September 21-22, a l l stations including the shallow Station 1 show marked changes i n numerical density*  These r e s u l t s  are strongly suggestive of a h o r i z o n t a l movement carrying the organisms i n t o the l i t t o r a l zone over the Chara shoal during the hours of darkness and returning them to the deeper waters of the  54 D A P H NIA  A  A|U  ST. NO.I  2 0 - 21 4 S 12  J|U NOON PM  PM  M|BN  AUGUST 4 8 12 AM  4  18-19 8 12  SEPTEMBER. 4  8  PM M|DN AM  A U NOON PM  12  AM NOON  21-22  4  8  PM  PM  12 LUX M^BN  INTENSITY  JULY 8 12  -i<>* £  LIGHT  4  \j \  -eo  \ \  -40  <  —o ~ -280 •  2  •  -240  SWEEP  NO.  -2CO  i  -40 _ Kj  3 NO.  # i  STATION  •  t  •— .  -20C 1-5  •  i i i t  ~  -160 -120  i  i  0 0 0 0  »  i i i >  0  .'  •  "BO -40 - d  -  -360 -320  4  -280  STATION  NO.  • •  -240  1  (  -20C  1 1 1  -160  f • • »  \ % \ % %  1 1 ' | 1 , •  -120  1  i  1  "80 -40 ........  F I G . 17. D I E L THE  DAPHNIA /  0  METRE  -80  i i i i  0  OF  *  SAMPLED  •0  -120  r  0  NUMBER  NOT  0  0  CHANGES IN DENSITY CHARA SURFACE.  OF  DAPHNIA  -O ON  AVERAGE  STATION  -160  55  DA P H N IA  a. Ill LU  * If)  LU CC I11)  2 m  <  z x  <  CO  2  z LU  o  '< cc LU  > <  DARKNESS  DARKNESS  FIG. 18. DIEL CHANGES IN DENSITY OF DAPHNIA IN THE OPEN WATER ABOVE THE CHARA SHOAL AND ON THE CHARA SURFACE.  56  I  limnetic zone as l i g h t i n t e n s i t y increases at sunrise.  Also,  the movement i s apparently more extensive i n August and September as evidenced by the changes i n numerical density of Daphnia on the Chara surface at Stations 1 arid 2 on both the August and September sampling  dates.  Samples taken i n the open water above the Chara shoal at Station 4 on October 19-20  (Figure 18) are also suggestive of a  h o r i z o n t a l movement of Daphnia.  However* the data could be con-  strued to i n d i c a t e a v e r t i c a l migration instead, as could the data of Figure 17,  Numbers o f Daphnia over the Chara shoal drop  sharply at dawn and are completely absent at S t a t i o n 4 by noon* Then, as l i g h t i n t e n s i t y decreases between the hours of 4?00 and 8:00  P.M.,  P.M.  large numbers of Daphnia are again discovered over  the Chara shoal at Station 4*  These observations are considered  more f u l l y under the heading ^'Discussion.  11  c) Chaoborus spp. Chaoborus was  common i n the l i t t o r a l zone only during  the month of J u l y (see Table I I ) . Samples taken by the diving method on J u l y 10 showed that Chaoborus penetrated to the bottom of the Chara stand and was present i n more or l e s s equal numbers i n both top and bottom halves of the Chara bed during daylight hours* Counts made of Chaoborus obtained i n August arid September by the sweep method are not included i n the r e s u l t s  57  C H A O  B O R U S  40-1  40-I  20H  20H 4 A.M.  8 A.M.  UI  «A  O-  I : L 3  JL  4  STATION  ui OC ui 2  J I 1 2  _L 2  I  NO.  STATION  •4 I  JL 3 . 4 NO.  40H  40-  in t/>  2CH  \ 4  P.M.  20H  ,'12  NOON  cc  o CD  O <  1 2  J  L  STAT ION I  X  _L  3  1 2  4  NO.  J  L  3  S TATIO N  4 N O .  u. 80H  40u.  O I I  XL  60H  20-  UJ  a  co 2  *  o-  j  1 2 S T A T I O N  P.M.  i_  3  4  -40H I I  NO.  ui  O < OC UI  20H  /  12  MIDNIGHT  > < J  1 2  3  S T A T I O N  F I G . 19. D I E L CHANGES CHAOBORUS ON  IN THE  L 4 NO.  DENSITY CHARA  OF SURFACE.  58  C HAOBORUS  F i g . 2 0 . D i e l changes i n density of Chaoborus i n the open water above the Chara shoal and on the Chara surface.  59 as the samples d i d not contain s u f f i c i e n t numbers of i n d i v i d u a l s to i n d i c a t e d i e l density changes.  The October series was, how-  ever, included i n spite of the small numbers of i n d i v i d u a l s because of i t s value i n assessing movements i n the open water above the Chara shoal. There were marked f l u c t u a t i o n s i n the numerical  density  of Chaoborus on the surface of the Chara over a period of 24 hours on J u l y 20-21 (Figure 19).  These f l u c t u a t i o n s are appar-  ently due to a precise movement of some sort rather than to random wanderings (Figure 20).  Moreover, i t i s apparent i n  Figure 20 that the movements are correlated with changes i n l i g h t i n t e n s i t y : Chaoborus being much reduced i n number or absent from the waters above the Chara and from the Chara surface during dayl i g h t hours but present i n considerable numbers a f t e r dark. I t i s d i f f i c u l t to account f o r the changes i n density apparent i n Figure 19 s o l e l y on the basis of a v e r t i c a l migration. I f , indeed, i t were a v e r t i c a l migration taking place, one would expect to f i n d a s i m i l a r pattern of density change at a l l three sampling: stations.  The only other hypothesis  (since the hypoth-  esis of random movement i s d i s c r e d i t e d by Figure 20) I f that of a horizontal migration.  Such an hypothesis  can explain the f l u c -  tuations observed i f one considers concentrations or "schools" ofChaoborus moving h o r i z o n t a l l y offshore as l i g h t i n t e n s i t y increases.  Thus, the density concentrations would appear at  successively deeper stations at successively l a t e r hours of the  60  EURYCERCUS 4 -AijJ  JULY 20-2I 8 12 4 8 A ^ i MOOM PU  PJrf  12 M |DN  AUGUST 4 8 12  AM  AJri  18-19 4 8 12  NOON J»M PJrt MljPN  SEPTEMBER 4 8 12 4  AM  A M MOOM  21-22 8 12  P M P M M IjPN  LUX  >" I01 z tz  z o  / o z  o— -180 -|40 -IOO  V  z  o  -60  < oi  -20 O— ISO  z  -140  o" z  o  »Ul  2 in  -IOO  I<  NOT  S A M P L E  D  V  a  -20  u >-  O z  -180  z  •I40  o  U  -60  o—  Ul a  Ul lA.  O  IOO  <  •60  •  20  ID  2  •OH D  O  Z  z  ISO  z  -140  o  »«t z  a.  -IOO  •  -60 -20  o  o—  -Jt-  ISO z Ul-  •o-—O  «a  -140 IOO  ></!  F I G . 21. D I E L CHANGES IN DENSITY THE CHARA S U R F A C E.  OF  EURYCERCUS  60 20  o —'  ON  Ul o < a  > <  61 day and the return movement a f t e r dark would f i r s t r e s u l t i n greatly increased numbers on the Chara surface at the deepest s t a t i o n Sampled (Station 4) « d) Eurycercus lamellatus Although changes which took place i n numerical density of Eurycercus on the Chara surface were subject to considerable v a r i a t i o n between stations and between dates, i t was  apparent 21).  that a t y p i c a l pattern of movement was present (Figure  Variations observed were presumedly due p a r t i a l l y to sampling error and p a r t i a l l y to random movements of the species* By p l o t t i n g the average of counts made at each sampling s t a t i o n at each sampling time, a pattern of migration emerged which was was  s i m i l a r on each sampling date (Figure 2 1 ) .  Eurycercus  found to occur i n greater numbers on the Chara surface  shortly a f t e r sunrise and j u s t before sunset.  A minimum i n  numbers on the Chara surface occurred consistently at noon on a l l three sampling- dates.  Numbers declined again .on the Chara surface  a f t e r dark reaching a low at midnight or between midnight and  4:00 A.M. e) Symnetrum sp. No pattern of d i e l movement could be discovered of Svmpetrum naiads on J u l y 20-21.  The nymphs appeared to be moving  about at random throughout the Chara zone.  Samples taken by the  diving method indicated a trend towards greater numbers of  STiTIOH  S T A T JO N  S T A T ION  to to  i-  STATION  I  I I z  O O z PI  o—  QfO z  I*  \  X m o X  \  \  •  / /  •I  >  ON) z  >° Z. m » OD  if* z  Z  c  l8ro  •  I I !0>  V  - J  CD  z  - 0 0  -<  Z  I P  m c "T  -  -r 03  O  -I  -  T"  -T-  00  -r oo  IO  _L AVERAGE  NUMBER  OF  S Y M P E T R U M / SWEEP  LIGHT  I N T E NS I T Y  63 Sympetrum being found i n the lower h a l f of the Chara bed during daylight hours as the summer progressed (see Figure 9 ) . In the sweep samples taken on August 18-19 and September 21-22, although numbers of Sympetrum were not large, a d e f i n i t e v e r t i c a l movement was apparent.  Naiads o f Sympetrum  were obtained from the Chara surface only during the hours of darkness and were e n t i r e l y absent from the Chara surface during the day (Figure 22). No horizontal movement was apparent — pattern of movement was similar at each station  the  sampled.  •f) Baetis sp. Ephemeroptera  of the families Caenidae and Baetidae were  encountered i n the sweep samples i n J u l y and August but d i d not become numerous enough to allow analysis of t h e i r movements. Only larvae of the genus Baetis were taken i n the September sampl i n g series*  The horizontal and v e r t i c a l d i s t r i b u t i o n of t h i s  genus was not treated i n the foregoing sections* but counts of Baetis made on the Chara samples taken by the diving method i n d i c a t e a numerical density similar at a l l stations over the Chara during daylight hours. From the September sweep samples i t i s apparent that; apart from minor v a r i a t i o n , Baetis naiads undergo a well-defined v e r t i c a l movement which i s very s i m i l a r at each sampling s t a t i o n (Figure 23)'. Minimum numbers occur on the Chara surface at 4:00 A.M.; a peak i s reached at 8:00 A.M., and a second minimum  64  BAETIS SEPTEMBER 4 A M  8  4  12.  AW\  ?M  NOON  21-22 8 PM  1  ~ i — r — r — r  VAIbM  r  /  LUX  r-  .0 7 mo  3-2. X 10  O  -  •40 h20 10 • O H  :40  cvj  -20 L0  to i—  < b_ O  • O H  \  •  V CO  -40  \  —•  -20  -o— -40  r-  CO  V  O  z Ld  < CC  -20  Ld  >  -0 — <  F i g * 23. D i e l changes i n d e n s i t y o f B a e t i s on t h e Chara s u r f a c e .  65  HYALELLA J U LY '  200i  o  o  -  AUGUST  20-2I  »  —  -  AZTECA 18-19  SEPTEMBER  21-22  •  •  - O a tu LU 100-T to  —o\  ui a 200 1-  J  Ul  2 in  100—o200-  ui _l <  IOO-  X  — o300200-  co IOO5 2  —O  UI  200-  O < UI  > <  IOO-  —o *  A •  — '  • — — •  J  I  NOT  2*  I  L  3  4  I STATION  /  J  2  3 4 NUMBER  1  2  I  L  3  4  SAMPLED  FIG. 24.  DIEL CHANGES ON THE CHARA  IN  DENSITY SURFACE.  OF  HYALELLA  66 occurs at noom  A second peak at 4:00 P.M.  gradual l o s s of numbers between 4:00  P.M.  i s followed by a and 4*00  A.M.  g) H y a l e l l a azteca P l o t t i n g the counts of H y a l e l l a at each station on a single l i n e and using, separate graphs f o r each sampling (Figure 24),  time  i t became apparent that a h o r i z o n t a l component was  involved i n the movements of the organism.  Following the peaks  i n numerical density on the Chara surface, i t was observed  that  the H y a l e l l a population appeared i n greatest numbers at successively deeper stations ( i . e . farther offshore) as l i g h t i n t e n s i t y increased.  The reverse trend was observed as l i g h t  i n t e n s i t y decreased i n the l a t e afternoon r e s u l t i n g i n the maxima occurring at successively shallower stations as darkness, approached.  I t was not possible to include changes of l i g h t  i n t e n s i t y i n Figure 24 but, as they are recorded i n previous figures, they should be referred to at this time. h) Ceriodaphnia  sp.  Ceriodaphnia sp. occurred i n considerable numbers on the Chara surface during J u l y and August but had almost d i s appeared by September 21.  For t h i s reason, graphs were p l o t t e d  f o r J u l y and August data only. On J u l y 20-21, changes i n numerical density of Ceriodaphnia on the Chara surface occurred uniformly over the Chara shoal (Figure 25).  At a l l stations, numbers of Ceriodaphnia  67 C E Rl ODA JULY I60I208040i  20-21  PHNIA  AUGUST  18-19  •  ,A  y\, / <  *  \  / V  <->  •  160-  ' \  / •  40u 160-  *  •  /  t  40-  /  /  •  < 00  1 1 1 1 1 1 1  12080-  /  NOON  80-  2  •  12  SWEEP  120-  CE R I O D A P H N I A / 1 5 M E T R E  2  CJ  I6C-  2  120-  a  8040-  160-  A  /  NUMBER  1208040-  2  \  a  •  03  /N  \J  AVERAGE  160I208040-  t'' 1  *  NOT  ,  .  .  2* 3 4 S T A T ION  1  1  1 2 NUMBER  1  1  3  4  12 M I D N I G H T  OF  o  SAMPLED  FIG. 25. D I E L C H A N G E S IN D E N S I T Y OF C E R I O DA PHNIA ON THE CHARA SURFACE.  68  CHI R O N O M I D JULY  LARVAE 20-21  FIG. 26. A C O M P A R I S O N O F D E N S I T Y OF CHIRONOMID LARVAE ON THE CHARA SURFACE AT EACH STATION  69 were lowest at noon and highest during  the hours of darkness*  A secondary l o s s i n numbers from the Chara surface took place at midnight at a l l three stations sampled; On August 18-19, however, changes i n density were not similar at each s t a t i o n (Figure 25).  An horizontal component  had been added to the d i e l movements of the organism.  Numbers  of Ceriodaphnia grew progressively greater at the deeper stations and smaller at the shallower stations as l i g h t i n t e n s i t y increased  (see previous figures for l i g h t Intensity diagrams).  At noon, by f a r the greatest number of Ceriodaphnia were located at Station 4-»  The reverse movement then took place as l i g h t  i n t e n s i t y dropped and by midnight the highest concentration the population was  of  situated at Station 1.  i ) Chironomid larvae Chironomid larvae taken i n the July 20-21  samples on  the  surface of the Chara shoal appeared i n maximum numbers at successively l a t e r hours at successively deeper stations (Figure 26).  Thus, as with H y a l e l l a azteca and Ceriodaphnia sp.,  an horizontal, movement i s indicated*  The  same data used i n  Figure 26 i s plotted d i f f e r e n t l y i n Figure 27 and data obtained on August 18-19  and September 21-22  has been included to complete  the investigation* On J u l y 20-21, numbers of larvae on the surface of the Chara at Station 1 increased  consistently between 4:00  A.M.  and  70  CHIRONOMID JULY 2 4  0  -  2  0  -  0  -  0  -  2  1  A  U  G  U  LARVAE S  T  1  8  -  1  S  9  E  P  T  E  M  B  E  R  2 1 - 2 2  a Ui Hi  •  $• 4  2  2 Ui  0  -  ho 6  A  0  UJ  < >  <  4  0  -  1 «  •  2 0 H  h-o6  2 O z O  4  0  -  0  -  m  2  0  -  6  0  -  4  0  -  .  1  OC  X  u  /  o  7\  Z 6  0  -  4  0  -  0  -  UJ  O <  OC Ui  2  > h-o<  \  I  •  i 2  3  1  1  4 S  FIG.  1  1 T  A  T  I O  1  1  2  3 N  1  4 N  U  1 M  B  E  1  -r  1 2  3  4  R  27. D I E L CHANGES IN DENSITY OF CHIRONOMID LARVAE ON THE CHARA SURFACE.  71 12:00  noon.  Since, during t h i s i n t e r v a l , the increase took  place only at Station 1, i t i s assumed that i t was  the r e s u l t  of a movement offshore of larvae present at depths  shallower  than Station 1,  V i r t u a l l y no chironomids were present beyond  Station 1 u n t i l 4:00  P.M. when the population moving offshore  reached S t a t i o n 3v  However, the bulk of the population never  reached S t a t i o n 4.  Numbers of larvae increased once more at  Station 1 at 8:00  1  P . M . as the organisms moved inshore with  decreasing l i g h t i n t e n s i t y * The August 18-19  samples indicated that chironomid  larvae apparently moved f r e e l y over the entire Chara shoal  and  were not r e s t r i c t e d i n t h e i r movement as they were on J u l y 2021.  The bulk of the population was  at 4:00  AoMo (Figure 27).  observed to be at S t a t i o n 2  As l i g h t i n t e n s i t y increased; a  decrease i n numbers on the Chara surface occurred at Stations 1 and 2 and an increase at Stations 3 and 4« bulk of the chironomid population was sampling area. hours of 4:00  By 4*00 P.Mb  the  absent e n t i r e l y from the  Then, as l i g h t i n t e n s i t y dropped between the P . M . and 8:00  observed at Station 3.; chironomid larvae was  P . M . ' , an increase i n numbers was  By midnight,- the major concentration of once more located at S t a t i o n 2.  D i e l movement of chironomid larvae on September  21-22  as i l l u s t r a t e d i n Figure 27 i s perhaps* a l i t t l e more d i f f i c u l t to understando  The greatest number of larvae on the Chara  surface at 4:00  A . M . was  found at Station 3«  This may  be taken  72 to indicate an offshore movement already well advanced.  At  8:00 A.M. there was a drop i n numbers at Station 3 and an increase at Station 4 .  At noon, a very great increase i n numbers  of larvae occurred at the Ghara surface at Station 2 which, at f i r s t glance, may appear to be inconsistent with the assumption of an offshore movement.  However, i t w i l l be observed that the  increase i n numbers at Station 2 was coupled with a great decrease at Station 1 and can, therefore* be considered i n d i c a t i v e of a further offshore movement* By 8:00 P.M. the bulk of the chironomids has moved back into the shallow zone —  appearing  i n greatest concentration at  Station 2 and remaining i n t h i s l o c a t i o n u n t i l daybreak the following day.  DISCUSSION  The numerical  and volumetric densities of invertebrate  organisms inhabiting Chara shoals change markedly over the summer months.  The lowest number of i n d i v i d u a l s was demonstrated  i n June and the highest number i n September on both Corbett and Courtney lakes.  As Berg (1938) has stated, i t i s reasonable  to  expect a low number of organisms i n spring as a r e s u l t of the reduction of the population during the course of the winter by predatibn and other causes of death.  Fluctuations i n density i n  the course of the summer occur i n Corbett Lake but are absent i n Courtney.  This i s a r e f l e c t i o n of the difference i n  of the two populations*  composition  The Chara shoals of Corbett Lake harbour  comparatively large numbers of aquatic insects and the v a r i a b l e density i s due to the changing i n t e r p l a y between hatching emergence of these forms.  and  On the other hand, the Chara shoals  of Courtney Lake are characterized by an invertebrate population composed almost e n t i r e l y of H y a l e l l a azteca.  Thus, the density  of invertebrate organisms i n Courtney Lake i s determined by the size of the H y a l e l l a population and the timing of i t s reproduct i v e period.  The high numbers observed i n September i n both  lakes can be attributed to the reproduction of the d i f f e r e n t species i n spring and during the course of the summer,  73  I t was noted that H y a l e l l a produced one new generation during the course of the summer and that the hatch occurred several weeks l a t e r i n Courtney than i t did i n Corbetto  Mature  i n d i v i d u a l s which gave r i s e to the hatch were not found i n the samples after reproduction had taken place.  The animals grew  rapidly during the summer months but did not a t t a i n f u l l adult size by September 14-°  Anderson and Hooper (1956) report evidence  indicating that H y a l e l l a continue to grow u n t i l November but cease to grow during the period of ice-cover.  Their data also  suggest a probable turnover of at l e a s t 90 percent between May 22 and J u l y 10 —= r e s u l t s comparable to those found i n the present investigation,. In contrast to the above r e s u l t s , Gaylor (1922) describes a population of H y a l e l l a knickerbokeri Bate (=Ho azteca Saussure) which produced two generations during the warmer months. He found that H y a l e l l a produced during l a t e summer gave r i s e to an early summer brood the following year  0  Then, the early summer  brood matured s u f f i c i e n t l y to give r i s e to another generation during the l a t t e r part of the warm season.  These r e s u l t s suggest  that i t i s the duration of the warm season which controls the reproductive capacity of a population of H y a l e l l a . In comparing  the data compiled on H y a l e l l a populations  of Corbett and Courtney lakes, i t was found that the organism i s approximately twice as numerous i n Courtney Lake but the volumes of the two populations remain remarkably s i m i l a r .  This would  75  seem to i n d i c a t e some factor, present i n the environment of both populations, which l i m i t s the t o t a l biomass produced per given area at; any one time.  The volume of the i n d i v i d u a l i s small  where the number of i n d i v i d u a l s i n the population i s large and conversely, the volume of the i n d i v i d u a l i s large where the number of i n d i v i d u a l s i s small.  The evidence thus points to  available food as the factor l i m i t i n g growth of the i n d i v i d u a l . I f we can assume a comparable food source i n the two lakes, where there are fewer H y a l e l l a present more food i s a v a i l a b l e per i n d i v i d u a l / r e s u l t i n g i n increased growth of the i n d i v i d u a l .  Where  there are more H y a l e l l a there i s l e s s food a v a i l a b l e per i n d i v i d ual  "thus, a corresponding decrease i n growth of the i n d i v i d u a l . Working .with d i f f e r e n t population d e n s i t i e s of H y a l e l l a  azteca i n the laboratory, Wilder (1940) found that an i n i t i a l l y maximal s u r v i v a l i n a high density tended to drop to a lower density with advancing  age.  That i s , as the i n d i v i d u a l s grew, an  increased rate of mortality occurred i n the high density populations.  Wilder was  also able to demonstrate a d i r e c t proportion-  a l i t y between density and carbon dioxide tension, and an inverse r e l a t i o n between oxygen tension, food and space.  She  concluded  that the above stated r e l a t i o n between density and carbon dioxide, presumedly other excretory products, food and space might well be responsible f o r i n h i b i t i o n of growth and fecundity and, at very high d e n s i t i e s , of the a b i l i t y to survive.  76 Concerning the e f f e c t of predation by f i s h on the invertebrate organisms of the Chara shoals, i t was  discovered  that organisms such as the chironomid larvae, Odonata naiads, and Ephemeroptera naiads were either t o t a l l y absent or present i n very small numbers i n Paul Lake before f i s h were removed by toxaphene treatment. A year a f t e r treatment;  considerable  numbers of these organisms were found i n the Chara shoals. Except for-the s c a r c i t y of H y a l e l l a . which was  apparently  ad-  versely affected by the toxaphene treatment, the percentage composition of the invertebrate population i n the Chara shoals of Paul Lake, a year a f t e r treatment, approached that, of Corbett Lake f o r the summer of 1963.  Previously, the composition of the  Paul Lake Chara invertebrate population was Courtney Lake.  s i m i l a r to that of  Since Courtney Lake harbours a large population  of redside shiners, as did Paul Lake before treatment, and  since  Corbett Lake i s free of shiners, i t i s reasonable to suggest that the differences observed i n invertebrate population composit i o n may  be due to the presence, on the one hand, and the absence  on the other> of the redside shiner. Differences i n horizontal and v e r t i c a l d i s t r i b u t i o n of invertebrate organisms within a Chara shoal are not large and seasonal changes i n d i s t r i b u t i o n are of minor importance. Changes which do occur are correlated with recruitment of  new  i n d i v i d u a l s into the population as hatches occur and with l o s s of others by natural mortality, predation and emergence of  77 semi-aquatic forms. The v e r t i c a l p o s i t i o n of H y a l e l l a within the Chara stand was observed to change over the course of the summer. Rather than being a change brought about by changes i n the animal!s environment, the s h i f t appears more l i k e l y to be associated with the age of the i n d i v i d u a l within the population. The population i s composed almost exclusively of newly-hatched animals i n early summer, which tend to remain i n greatest abundance i n the.upper h a l f of the Chara bed.  By September 14,  however, these same organisms having attained near adult proportions, are found i n much greater abundance (at l e a s t i n Corbett Lake where the hatch of H y a l e l l a i s several weeks earlier) i n the lower part of the Chara stand.  A change i n horizontal  d i s t r i b u t i o n of H y a l e l l a was also observed i n Corbett Lake, which corresponds markedly with the age of the i n d i v i d u a l s within the population*  The young animals occurred i n remarkably high con-  centration at the shallow 1.5-metre station i n J u l y and had become more or l e s s equally d i s t r i b u t e d over the Chara shoal. Why H y a l e l l a should seek the deeper layers of the Chara bed as i t grows older i s not clear.  Since a l l samples taken by  the diving method were obtained during hours of high l i g h t i n t e n s i t y on each sampling date, the observed trend may be thought to i n d i c a t e a more pronounced negative phototropism with age.  However; sweep samples of the Chara surface reveal d i e l  changes i n density of the population which are just as extensive  78 i n July as at any other time during the course of the i n v e s t i gation. Although the chironomid populations investigated i n Corbett and Courtney lakes were obviously composed of numerous species, several generalizations can be made concerning the populations as a whole.  F i r s t , chironomid larvae i n general are  to be found i n greater abundance i n the deeper layers of the Chara bed.  Secondly, chironomids, as a whole are not r e s t r i c t e d  i n their d i s t r i b u t i o n over the Chara shoal to any p a r t i c u l a r depth.  But, variations which occur i n density at p a r t i c u l a r  stations during the summer months due, presumedly,  to hatching  of one or more species and the l o s s by emergence of others, suggest a l i m i t a t i o n i n d i s t r i b u t i o n on the s p e c i f i c l e v e l , Gyraulus. a pulmonate s n a i l of the family Planorbidae, was found i n greatest abundance i n the Chara of Corbett Lake, No changes were observed i n the horizontal d i s t r i b u t i o n of this animal during the course of the summer,  Gyraulus was d i s t r i b u t e d  on a l l sampling dates with lowest numbers at the shallower stations and the highest numbers at the deeper stations,  Cheatum  (1934-), on the other hand, found regular seasonal migrations manifested i n a l l of the seven species of pulmonate s n a i l s which he studied.  He was able to show that most of the i n d i v i d u a l s  migrate from the shallow, l i t t o r a l zone to the deeper waters during the f a l l months when the temperature of the water declines. When the water warms up i n the l a t e spring and early summer,  79 these same, s n a i l s were observed to move from the deeper water shoreward, D i e l fluctuations i n density of organisms on the surface of the Chara shoal of Corbett Lake and i n the open water above the shoal suggests the existence of an horizontal movement of some organisms i n addition to a v e r t i c a l migration*  The  greatest concentrations of Chaoborus spp*, H y a l e l l a azteca. Cerlodaphnia sp., and chironomid larvae were found at stations progressively farther offshore during daylight hours reappearing at the deepest station f i r s t as l i g h t i n t e n s i t y decreased  at  sunset and occurring at progressively shallower stations during the night. The changes i n density of Daphnia spp.- i n the waters above the Chara shoal and on the surface of the Chara i t s e l f also i n d i c a t e a movement offshore during the day i n i t i a t e d by an increase i n l i g h t i n t e n s i t y at sunrise.  However, since i t i s  not known to what extent t h i s organism i s able to penetrate into the depths of the Chara bed, one cannot completely eliminate the p o s s i b i l i t y of a v e r t i c a l migration as an explanation of the absence of Daphnia from the open water and from the Chara surface during daylight hours.  But, as Siebeck (1964) points  out, i f indeed i t was a v e r t i c a l movement, one would expect to f i n d i n i t i a l l y large concentrations of the organism on the Chara surface just after the i n i t i a t i o n of the migration i n the early morning.  This,;,however, i s not the case.  80 Working with plankton!c crustaceans, Siebeck used an experimental procedure which eliminated the influence of d r i f t upon, the organisms.  He found that the orientation of the swimming  reaction i n response to l i g h t changes was i t was decreasing  always offshore, whether  l i g h t i n t e n s i t y or increasing l i g h t i n t e n s i t y  that i n i t i a t e d the a c t i v i t y .  On t h i s basis, he postulates  planktonic organisms which are i n highest concentration low the, water surface i n the pelagic zone at night due  that  j u s t beto t h e i r  v e r t i c a l u p r i s i n g , are transported passively into the l i t t o r a l zone by water currents.  Then, changes i n l i g h t i n t e n s i t y Which  occur at sunrise i n i t i a t e swimming a c t i v i t y and the animals actively move offshore "under the influence of l i g h t , -  according  to an. o p t i c a l l y orientated reaction, the character of which i s s t i l l unknown."  •  The mechanism of a passive d r i f t coupled with active swimming may,  perhaps, explain the d i e l movements of plank tonic  Crustacea i n and out of the l i t t o r a l zone, but i t c e r t a i n l y cannot be applied to the behaviour of such organisms as H y a l e l l a azteca and chironomid larvae.  Movement of these organisms can-  not be attributed to a passive d r i f t , and i n i t i a t i o n of the i n shore movement as well as the offshore movement i s strongly correlated with rapid changes i n l i g h t i n t e n s i t y . The negative response of aquatic amphipods to l i g h t i n t e n s i t y has been recorded early i n the l i t e r a t u r e (Holmes, 1902;  Phipps, 1915).  Phipps also recognized  an o r i e n t a t i o n to  81 d i r e c t i o n o f l i g h t rays i n H y a l e l l a knickerbokeri Bate (=H. azteca Saussure).  Since, as Siebeck has pointed out, the  l i g h t received by an organism below the water surface i s always at i t s maximal i n t e n s i t y v e r t i c a l l y from above or, within an inverted cone, i t should follow that an animal responding  nega-  t i v e l y to l i g h t would undergo a more or l e s s v e r t i c a l movement away from the strongest l i g h t source.  But, i t has been observed  that although the movements may be p a r t l y v e r t i c a l , causing the organisms to penetrate deeper into the Chara bed as l i g h t i n t e n s i t y increases, there i s also a strong horizontal component of movement which carries the animals offshore during the day and back onto the Chara shoal at night.  Thus, Siebeck  postu-  l a t e s h i s " o p t i c a l l y orientated reaction" of unknown character which enables planktonic crustaceans to leave the l i t t o r a l zone during the day. He found no i n d i c a t i o n of the occurrence o f a v e r t i c a l migration of plankters i n the l i t t o r a l zone. Siebeck  Both  (1964) .and Ruttner (1914) are strongly opposed to the  opinion of Burckhardt (1910) who maintained  that "Uferflucht"  (avoidance of the shore) was a d i r e c t r e s u l t of the v e r t i c a l migration.  Burckhardt supposed that, even i n the l i t t o r a l , a  v e r t i c a l downward movement takes place, and that the animals, once they had reached the bottom, followed the slope of the Shore out into deeper water. A number of instances have been brought to l i g h t i n the present, i n v e s t i g a t i o n which, perhaps,, strengthen  82 Burckhardt's suggestion.  F i r s t l y * i t has heen observed that at  l e a s t one planktonic crustacean does undergo a v e r t i c a l migrat i o n i n the l i t t o r a l zone ( i . e . Diaptomus sp.). Secondly, the larvae of the c u l i c i d dipteran Chaoborus. which i s normally a member of the pelagic plankton assemblage and which has been shown to respond negatively to l i g h t , apparently undergoes both a v e r t i c a l and a h o r i z o n t a l movement i n the l i t t o r a l zone*  The  I n i t i a l response of Chaoborus In the l i t t o r a l zone to the increase i n l i g h t i n t e n s i t y at sunrise i s a v e r t i c a l downward movement. This movement r e s u l t s i n the absence of Chaoborus from the open water above the Chara shoal during the day and a concentration of numbers on. the surface of the Chara shoal which moves progressively further offshore during the daylight hours* Thus, i t i s apparent that a wide v a r i e t y of organisms present i n the l i t t o r a l zone undergo an active, horizontal movement i n response to changes i n l i g h t i n t e n s i t y *  Organisms which  are normally found i n the limnetic zone where they display a d i e l v e r t i c a l migration i n response to changing l i g h t i n t e n s i t y , may f i r s t undergo a similar downward v e r t i c a l migration i n the l i t t o r a l , followed by a movement offshore along the surface of the Chara shoal.  The f a c t that many invertebrate organisms  undergo a downward migration i n i t i a t e d by an increase i n l i g h t i n t e n s i t y and a corresponding upward migration as l i g h t intens i t y decreases suggests not only an avoidance of strong l i g h t i n t e n s i t y but also a preference f o r l i g h t of a p a r t i c u l a r degree  83 o f i n t e n s i t y . This observation, may be equally as w e l l applied to the observed horizontal movement i n the l i t t o r a l zone and could possibly explain the o r i e n t a t i o n o f the movement.  Since  the animals apparently show a preference f o r l i g h t of a p a r t i c u l a r degree or range i n i n t e n s i t y I t follows that they.would be able to detect a gradient i n l i g h t i n t e n s i t y which would cause them to move offshore during the day and back i n t o the shallow area at night*  LITERATURE CITED  Anderson, R. 0. and F. F. Hooper, 1956. Seasonal abundance and production of l i t t o r a l bottom fauna i n a southern Michigan lake. Trans. Amer. Micros. Soc. 75:259-270. Baker* F* C , 1918'. The productivity on the bottom of Oneida Lake with mollusks. Tech. Pub. No* 9, N.Y. Syracuse University. V o l . XVIII,  of invertebrate f i s h food s p e c i a l reference to State College of Forestry, No. 2.  B a l l ; B.C., 1948. Relationship between available f i s h food, reeding habits of f i s h and t o t a l f i s h production i n a Michigan lake. Tech. B u l l . Mich. Agric. Exp. Sta. 206:1-59. and-Hayne, D. W., 1952. E f f e c t s of the removal of the f i s h population on the fish-food organisms of a lake. Ecology _ : 4 1 - 4 8 . B a r t l e t t , M. S., 1947. The use of transformation. Biometrics _:39-52. Berg> K., 1938. Studies on the bottom animals of Esrom Lake. Mem. Acad. Roy. S c i . et L e t t . Danemark, Copenhagen, Sect* Sci* Ser* 9, 8:1-255* Burckhardt, G., 1910. Hypothesen und Beobachtungen uber die Bedeutung der v e r t i k a l e n Planktonwanderungen. Internat. Rev. ges. Hydrobiol* _:156-172. Cheatum, E. P., 1934* Limnological Investigations on respiration, annual migratory cycle, and other related phenomena i n fresh-water pulmonate s n a i l s . Trans. Amer. Micros* Soc. _:348-407. Eggleton, F. E.> 1931. A limnological study of the profundal bottom fauna of certain freshwater lakes. E c o l . Monogr. 1:231-332. Gaylor, D., 1922* A study of the l i f e history and productivity of H y a l e l l a knickerbokeri (Bate). Proc. Ind. Acad. S c i * (1921):239-250. Holmes, S. J . , 1902. Observations on the habits of H y a l e l l a dentata Smith Science (n.s.), 15: 529-530.  84  85 Johannes* R* E. and P. A. Larkin, 1961. Competition f o r food between redside shiners (Richardsonius balteatus) and rainbow trout (Salmo gairdneri) i n two B.C. lakes. J . F i s h . Res. Bd. Canada, 18(2), 1961. Juday, C , 1942* The summer standing crop of plants and animals i n four Wisconsin l a k e s . Trans. Wisc. Acad. Sci* _4:103-135. L a r k i n , P. A., et a l . . 1949. The production of Kamloops trout (Salmo g a i r d n e r i i kamloops. Jordan) i n Paul Lake, B r i t i s h Columbia. S c i . Publ. B.C. Game Dept. No. _:1-37. Lindeman, R. L., 1942. Seasonal d i s t r i b u t i o n of midge larvae i n a senescent lake. Amer. Mid. Nat. 27(2):428-444. Lundbeck> J * , 1926. Die Bodentierwelt norddeutscher Seen. Arch. Hydrobibl. Suppl. _:1-473. Muttkowski, R. A., 1918. The fauna of Lake Mendota. Trans. Wise. Acad. Sci* Arts, L e t t * , v o l . XI, part 1:374-454* Phipps> C. G., 1915. An experimental study of the behaviour of amphipods with respect to l i g h t i n t e n s i t y , d i r e c t i o n of rays, and metabolism. B i o l . B u l l . _:210-223. Rawson, D. S., 1930. The bottom fauna of Lake Simcoe and i t s role i n the ecology of the lake. Univ. Toronto Stud. B i o l . , Pub. Orit. Fish* Res. Lab. 40;1-183. 1934. Productivity studies i n lakes of the Kamloops region, B r i t i s h Columbia. B u l l . B i o l . Bd. Can. _2:1-31. Robinson, C. B., 1906. The Chareae of North America. B u l l . N*X. Bot. Garden _:244-308. Rosine, W., 1955. The d i s t r i b u t i o n of invertebrates on submerged aquatic plant surfaces i n Muskee Lake, Colorado. Ecology %6 (2): 308-314. Ruttner, F., 1914. Die Verteilung des Planktons im Subwasser. Fortschr* naturu. Forsch. 10, Aberderhalden, 273-336. Siebeck, 0*, 1964. Researches on the behaviour of planktonic crustaceans i n the l i t t o r a l . Verh. Internat. Verein. Limnol. XV:746-751. S t e e l , R. G. D. and J . H. T o r r i e , I960. P r i n c i p l e s and procedures of s t a t i s t i c s . McGraw-Hill Book Co., Inc., N. Y. Wilder, Janet, 1940. The e f f e c t s of population densi ty upon growth, reproduction and s u r v i v a l of H y a l e l l a azteca. P h y s i o l . Zool. Chicago _:439-461.  

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