Partial in

Numerical, Growth and Secondary Production Responses of the Benthic Macroinvertebrate Conununity to Whole-Lake

Enrichment in Insular Newfoundland

by

Keith Clarke B.Sc (Hc ne }

Department of Biology Memorial unive."sityof Newfoundland

A thesis submitted to the School of Graduate Studies in Partial fulfilment of the requirements for the degree of

Master of Science

1995

St.John's Newfoundland

i i ABSTRAcr

A whole-lakeenrichment (N+P) experiment wasco nd uc t e d over a three-year period to evaluate the feasibility of boosting benthic productivityin insular Newfoundland lakes. Response of the benthicconenund tyto enrichmentwas monitored by a combinationof biomonitoring (artificial au bs t r a t e ) and quantitat ivedredge samplingin both the enriched lake and two contro l lakes.

Observationsof benthic abundance throughhi o mon i tori ng approaches revealed a co n t i n uum of positive numeri cal responses to enrichment. Responses were mostrapi din short- livedherbivores such as chironomids, gastropodsand sphaeriid clams whilelonger-lived detritivores (ma y f lie s , amphipodsl and predators (flal:wotms, leeches and dragonfliesI

demonstrateda slower, more modest numericalresponse, The benthicmacroinvertebrate communities of thest u d y lakee were composed of cosmopolitan speciesfromthe North American fauna in relatively lowde ns i tie s. Benthicbiomasswas dominated by gastropoda and theodonate~, Secondary pr od uc t i on estimates were relatively low when compared to main land sys t e ms. Short-lived herbivores (~ , ~) were observed to have increased secondary pr odu c t i on in the enriched pond. Secondary produ ctionestimates weresimilar in the thr e e study ponds fo r the other macroinvertebra tetaxa. Some of these taxa were observed to have increa s e d growth

i ii

(~, and/or recruitment (.EnAl..la9maJla t einthe study. 'rtd e pattern indicates that benthic macroi nv e r teb rate corrmunityprod uct ion was stil l increasing in the enri c hed pond.

iv ACKNOWLIIDGBMBNTS

I would like to thank my supervisor, Or.Roy Knoechel, fo r his guidance, supervision and patience throughout the course of this project. Financial auppozt; for this project was provided through Dr. xnoecner from a Long Range Transport of Air Pollutants (LRTAP) contract, a NSERC- DFO subvention grant and a NSERe research grant.

Appreciationis ex tendedto the members of my supervisory committee, Dr. M.H . Colbowho providedinvaluablehelpwith the identification of benthic organisms and Dr.D.Schnaider who introduced me to th e statistical procedure of randomization. In addition, they both constructivelyreviewed an earlier version of this thesis .

I would also like to thank Pat Ryan of D.F.O. who supplied several papers and his 20 years experience on the linmologyof the Bxpe.r imentia LPonds Area, Roy Ficken provided photographicservices for this thesis anda poster presen ted at AS!;"O 1994. Dr. J.J. Kerekes of the Canadian Wildlife Service supplied several pa pe r s on benthic organisms and pr imaryproduction.

I wouldalso like to thank ChrisBr own who stayed sane thr o ugh three ye a r s of livi ng in a traveltrailerfor4months of the year. Chriswas my fieldpartnerandaidedwithall facets of sample collections, which were of ten extremely difficult in thedamp andcoldconditionsof Newfoundland.

TABLBOFCONTBNTS

Abstract . ... ... ... ... . . ... . . . .. ..ii Acknow ledgements... ... .. ... .. . .. . . .... iv

Tableof conten ts .

Lis t of tables vi

Li s t of fi gures ix

Chapter1: General Int r od u c tion .

Chap t er2: The St udy Site .

Physical Characteristics .

Biol ogicalChara c teristics .

Expe r i ment a l Man ipulat i on . Chapt er 3: Nume r i cal Re s p on se sas Ind icated us ing

Biomoni t oringTe c hn i ques (Art if ici al

Substrates)... .... . . ... . ... 9 Int r od ucti on... .... . ... ... 9 Materi a l and Method s.. ... .. ... . . . .. 13

Re sults andDiscussion 16

Summary 29

Chapte r 4: Macroinvertebrate Respo ns e to Fer tilizat ion : Growt h, De ns i ty and Produ ct i on 30

Int rodu ct ion. ... . . . . .... .. .... .. ... 30 Material and Me thods.. .. . ... .. . ... 32

Re sults andDiscu s s ion 38

Summary 82

Chapter 5: General Summary. .. .. .... . .. ... ... .. ... . 85 Ref erenc es ... . ... ... ... . . . . ... ... .. . ... ... . . ... 89 App e ndix A: Length :Dry weightregressions use d in

Benthi cBiomas s Est imate s .. ... . . . . .. ... . .. 96 Appe nd i x B: Sec ondary Pro d ucti o nBst i mat e s for the Most

Abundant BenthicOrgan i s ms 100

Tabl e 2.1:

Table 3.1:

Table4.1:

Table4. 2:

Table4.3:

Table4.4:

Tab le 4.5:

Table4.6:

Tab le4. 7:

Tab le4.8:

Tabl e81:

vi LISTOF TABLBS

physical cha racte ristics of the studyponds in theEx pe r i men t al Ponds Area... . ... 5 Cha ra c t eri 2 ~\ti onof the most abundantbenthic organismsbylife spa nandtrophicxote. Ea c h ta x on is typically dominated by a singlegenus or fa mily asindi c ate din parenthesis. . ... 10 Listof the taxa collectedinthe three ponds over the course of the aeudy wi th the

quantitative dre dge sampler 39

Ta x a and me t hod s employed in secondary producti onestimates. . ... ... .... ... 66 Density,individualdry weight and produc t ion estimates for the gastropod~ 68 Size-freque ncy characte r istics uae d in the calculation of secondaryproduction ofth e odonate~in HeadwaterPond (est imates reported for an aquatic life-cycle of4and 5

years) 73

gLze-Er-equerrcycharacteristicsus e d in the calculation of secondary pr od u c tion of the odonate .cw.:d!.Il..i.a in Spruce Pond (e s t i mat e s reportedfo r anaquaticlife- c yc l e of4 and5

years) 74

Size-frequency characterist ics us e d in the ca l c ula t i on of secondaryprod u c t i o n of the odonatecm:s1l1l.1..ain Coles Pond (e s t i ma t e s repo rtedfor anaquatic life - cycle of4

and5years) 75

Pr od uc t i on estimates for the most abundant taxa fromJuly199 2- August1993. Estimates are given in mgdry wt .jm':.jyr 80 Benthic communi ty responses to wh ole - lake enrichment in ColesPond: SummaryTa b le.. . 83 Densi ty, average individua l dry weightand production estimates for the gastro pod Ya.l.Y:a..t..a •• • ••• •.•••• • •••••••••• •.• •. .•. .•• •101

Table 82:

Ta b le B3:

Tabl e84:

Table 85:

Table 86:

Table97:

Table98:

Table 99:

Tabl e BI0:

vii

Density, averageind i vidualdryweight and production es t i ma t e s for the ephemeropteran

~ 101 Density, average individual dry weight and produc tionest imatesforthe eph emeropteran

Leptopblebja, 102

De n s i t y, average indiv idualdryweight and pr od u cti on estimates for th e trichopteran

~ 103

Density, average individual dry weight and product i on es t imates for the tricho ptera n

~ 104 Size frequency charact eristic sused inthe calculation of secondary produc tion of the damselflyE.n..a.U.as:ma.inCol es Pond (e s t i ma t es reported for an aquat i c life-cycle of 18

months) 105

Size frequen cy cha rac t e r i st i c s used in the calculation of secondary product ion of the damselflyE.n..a.U.as:ma.in Spruce Pond (e s t i ma t e s reported for an aqua t i c li fe- cycle of 18

months) ,.1 06

Size frequency characteris tics used in the calculation of secondary production of the damselfly E.n..a.U.as:ma. in Headwater Pond (e s t i mates reported for an aquatic lif e - c yc le

of 18 months) 107

Size frequency Characteristics used in the calc ul a t i o n of secondary production of the gastropod Hel.i..a..oma.in coi .en Pond (e s t i ma t e s repo rted for an aquatic life-CyCle 18

months) 108

Size frequenc y characteri sti c s us ed in the calculation of secondary production of the gastropodHe.l..i...a.amain Spruce Pond (estimates reported for an aquatic life-cycle 18

months) 109

Table Bll:

TableB12:

Tabl eB13:

Ta bl e B14 :

viii

Size frequency characteristics used in the calculation of secondary pr od uc ti on of the gastropod He.lia.cma in Headwater Pond (es t imate sre po rtedfo r anaquatic lif e- cycle

18 months) 1~O

Size frequency characteristic s used in the calculation of secondary production of the arnphipod ~ in Coles Pond (e s t i mat es reported for an aqu at i c life-c yc l e of 9

months ) 111

Size frequency cha racteristics used in the calculation of secondary production of the amphipod ~el.l.a.in Spruce Pond (e sti ma t e s reported £or an aquatic life-cycle of 9

months) 111

Size frequency characte ristics used in the calcul ation of secondary production of the amp hi po d~inHe a dwa t er Pond (e s t i mate s re p o r t e d fo r an aquati c life -cycle of 9

months) , 111

Figure2.1:

Figu re 3.1:

Figure3.2:

Figure3.3:

Fi g u r e3.4:

Figure3.5 :

Figure3.6 :

Fi gu re 3.7:

ix LIST OF FIGURES

The Experi mental Ponds Area of centra l Newf oun d l an d highlighting the ponds used in this study. . ... . ... ... .... .. . 6 Exp erimental pond (Co le s Pond) and control pond (Sp ru c e Pond) withart ificial substrate

stationshi ghlighted. Arrows indicate

the dire c ti on offlowLnth est reams and

IF' denotes the site whe re ferti l i zer wa s added.. ... ....,..14 The abundanceof chironomidsinthe enh a n c e d pond (Col e s Pond) anda contro l po nd (Spruce Pond) duri ng the firs t three years of fertilization. Bara are 95\ confidence

intervalsof the mean 17

The abundanceof ga st r opod s in the enhanced pond (Coles Pond) and a control pond (Spruce Pond ) duri ng the fi r s t three years of fertilizat ion. Bars are 95\ co nf i d e n ce

intervals of themean 18

The abundance of sphaeriid calms in the enha nc e d pon d (Cole s Pond) anda control po nd (s p ruc e Pond)dur i ng the fir st threeye ars of fertilhation. Bar.s are 95\ con f i de nce

intervalsof the mea n 19

The abun danceof tric ho pt e ran~in enhanc e dpon d (Coles Po nd )and a control pond

(Sp ruce Po nd ) during the firs t thr e e yearsof fe r t il i za tio n. Bars ar e 95\ conf idence

intervalsof theme a n 21

The abundance of amphipoda in the enhanced pond (Coles Pond ) ann.a con t rol pond (spruce Pond) duri ng th e fir s t thre e ye a r s of fertilization. Bars are 95\ con fidence

int ervalsofthemean 23

TheabundanceofEphe mer optera in theenhance d pond (Coles Pond ) anda control pond (Sp ruce Pon d) dur i ng the fi r s t three years of fert il izat ion. Ba rs are 95\ confidence

int e rval s of the mea n 24

xi

Figu r e 3.8: The ab undance of flatworms in th e enhanced pond (Coles Pond) and acon t r ol pond (spruce Pond ) du r ing the firs t three years of fertili zation. Ba r s ar e 95\ confidence in te rvals of the mean. . 25 Figure 3.9: The abundance ot: leechesin theenha nc e d pond (Col e sPon d) and a con t r ol pond(Sp ru ce Pond) during thefi r s t threeyearsof fertilization.

Bars ar e 95\ con f i d enc e intervals of the mean•• ••••• •• •••• • .•••.•• .•••••••••• •••• ••.27 Figure 3.10: The abundanceofOdon a t a in the enhancedpond (ColesPond ) and acon t r ol pond (Sp ruce Pond ) duringthe firstthreeyearsof fertilizatio n . Bars are 95\ confidence in tervals of the mean ..•... . ... ... .. .•...•. ..•.28 Figure4.1: Dredge sampler used in quantitative samp ling regime. Theop e n i ng at the left is25em. 33 Figure 4. 2 : Stu d y pon ds highlighting the quantita tive sampling sites. Arrowsind i c at e th e direction of flowfor the majorscreams. Notethe pond a

arenot drawn to sca l e 35

lo'igure4.3: Benthic biomassestimatesfor the studyponds:

Showing the relative importance of themajor

taxonomi c gr oup s 42

Figur e 4.4: Averagein d ivi du a l weight ( )anddens i t y (---) ofth e dragonfly Conlulia, 44 Figu re4.5: Median lengths for th e dragonfly~ in the three studypondsthroughou tthecou r s e of

this study 46

Figure4.6 : comparison of individualweight gain of the odonate~ (J Uly 19 9 2 - August 19 9 3) amongthe three study ponds , illu s t rat i n g tha t the greatest increase was in the fertilized

pond 47

Figure 4. 7: Average individualweight ( ) and density (-- -) of theodonateEnal..l.asma .•• .... .. • ..49

Figure4.8 :

Figure4.9:

Figure 4.10:

Figure4.11:

Figure 4.12:

Figure 4.13

Figure4.14:

Figure4.15:

l"igure4.1 6:

Figure4.17:

Figu r e 4.18:

xii

Comparison of density increases (recruitment) for the odonateEnal.l.agma (Augus t 1992 - May 1993) among the threeponds, demonstratingthe highest level of increase in the fertilized

pond 50

Average individual weight ( ) and density (-- - ) of th e gastropod~. • indicates

the re.nge of replicate weight

determina t ions 52

Comparison of individual we i gh t ga inof the gastropod~ (July 199 2 - August 1993) among the three study ponds, ill u s t r ati ng that thegre ate s t inc r e a s e was in the fertilized

pond 53

Average individual weight ( ) and density (-- - ) of the gast ropod H.e~... • •. . .... 55 Average ind ividualweight ( ) and density

(---) of thetrichopter a n ~ 57 a):Average individual weight gai ns for August 19 9 2 - July 1993; indicating very similar values among all ponds and b) re c ru i t men t during Ju ly 1992 Ma y 19 9 3 fo r the trichopteran~ indicating much lowe r recruitment in Headwate r Po nd.. . . .. . ...58 Average ind ivi dua l weight ( ) and density

(---) of the tric hop t e r a n~ 60 Average individualweight ( ) and density

(_u) of the ephemeropteranI.eptQphlebia

sp 62

Density increasea (recruitment) of the domi nant I,ep t Qphl ebia sp.August199 2 - Jul y 1993. Illustrating the highes t recruitmentin Spruce Pond and the lowe s c in Headwacer

Pond , , ", 63

Average individual weight ( ) and density (- --} of the ephemeropteran.caenia.. .. .. ... ⁶⁵

~ produc t ion (Augu s t 1992 - August

1993 ) , 70

Figure4.1.9:

Figure4.20:

Fi gure4.21:

Fi gu r e4.22:

Figu r e AI:

Figure A2:

FigureA3:

xii!.

~ production (Augu s t 19 92 - Augu st 1993. illustrating the differences in the north (no ash) and south (a s h) basins of HeadwaterPond.... ... .... .•.. . ... .. .. . .. 71 Annual secondary production of ~: Produ ct i on wascalculatedusingboth a4and5 ye a r aquatic life-stage dur a t i o n 76 Producti on esti mat e s for three annual taxa compar ing the period July - August for both

1992and 1993 78

Ma cro inv ertebratesecondaryproduc tio n forthe thre e study pond s (production was corre c t ed

for an annual bas i s ) 79

The length : Dry we ight regres sion for the dragon f ly ~ 97 The length : Dry weight re gre s sion for the dar.ls elflyEna.ll.asma.•. ..•....•.•.•. .• .•..• 98 'l'heleng t h: Dry weight regression fo r the

gastropod~ 99

CHAPTER 1: GBNBRAL INTRODUCTION

Lakes were once considered isolated micr oc o s ms and the r e f o r e have long been used to test and develop hypotheses on the structureand functioning of ecosystems (Wetzel 1983). One of the more intensiveareas of investigationsince the 1970'Shas been the effect of nutrien t loa d i ng (S.: h i nd l e r 1977). Studiesof the effectsof nut ri e n t in c r e a s e s on lake ecosystems can be divided into two basic groups: thos e in which the nutrient increase resulted from land use and pollution (Ca tta ne o 1987, aarper and Stewart 1987, Hough et al.1989,Doughert yand Morgan1991,Stauffer 1991, Kumar et al. 1992) , and those where nutrient levels have been experimentallymanipulated to determine ecosystemresponses (St o c kne r and Short reed 1985, Schindler1990,Cowell and Dawes 1991, Niederhauser and Schanz 1993).

The basic premiseof any nutrientenrichment or fertilizationexperimentisthCl t the artificially induced increase innut rie nt s will result in an increase inec osys t e m productivity. Thi s is basically a "bottom-up" view of ecosystemstructure, whichhas beenverified inthe past by expe r-Imenta that have linked increases in phytoplankton (Reine rt s e n 198 2 , Henry -.t al198 5, Stockner and Shortreed 198 5 , Havens andDeCosta1986,Ni ederhauserand Scha n z1993) and benthic algae(Bj ork~Rambergand Anell1985,Carrick.. nd Lowe 1989, Bergm ann and Wel c h1990) to nutrientloading.

·'the -bottom-up-vie wofec o sys t e m structure statesthat corrmuni typrocesses (i.e. pr eda t i on ) will work to pass the increa sedprimary production thr oug h the food. ch a i n , thus cr e a t i n gamore productiveec o s y s t e m with higher bi omas s at all trophic levels. This has been verifiedbyst u dieswhich ha ve linkedincreased pr imaryproductionto re s pons e s inthe zoopl a nkt.on (Lange landan d Rei nertsen 1982 , BIser andMackay 1989, Fai rchildeta1. 1989 ) an dfish communities (Re i n e r tsen and Langeland1982, Hyattand Stockne r 1985, Mills198 5) .

Newfoundlan d la ke s differ from their count erparts in main l a nd North America and Europe in several ways, The major ity of the lakes, or ponds as they are known in Newfoun dland,are smallbod i e s of acidict.aca r surroundedby a mixtu reof coniferous for estand peatland. Theproduc t ivity of the s elakes is general lylow (Ke r e ke s 1975, Knoeche l and Ca mpbel l 1988) and observation s of stream and precipitation Chemis try (R. Knoechel, unpub. data) suggest: that the surroundi ng vegeta tionacts as a nutrinnt sink keeping the prccuc e .ton of these lakes low. 11le main Ushepeodeeare the st icklebackGasteroateuB~,the brooktro u t~.B

.f..c.nt..1na.U. and the Atla n tic salmonSAlmQ B.Al.u:. All the s e species appear to rely heavily onthet-ent h i c communityfor theirfood (Bro wn 1993 ;Baggs1989; K, Clar ke ,unpub.data), Thisbe nt hos -ba s ed foodweb is funda menta l l y different than thos e in eeosystems whe r e prevte ua fertiliza tion

experimentshave bee n conducted, where a more di r e c t pelagic fo od cha i nis thenorm. Thebenthic conmunityhas largely tee nov e rlooked in lak e fertilizati on studiesof the past, although Schindle r (19 87)hassugge sted tha tbenthicorga n iBlll8 may be more respons i ve to nutrient loa d ing because of 3ccumulation ofnutri e nts andorga nicmatter inthesed ime nts. The few fertil iza t i on studie swh ichha ve tried toinc o rporate benthos (Smi t h 1969 ,Milbrink and Holmgren1981,Aagaard 1982, Brylinsky1993) have reportedvaryi ng andambi guou sre s u l to.

The main object iveof this stud yiotocharac t eri ze the res pons e of the benth i c conununity tonutrien t enric hme n t in Newf ound l and lake s. Responses are evalua t ed in terms of nume rical increases, gr010lth rate inc re ments and ch a nge s in population productivity throug h a combinatio n of ar tifi cial subst rat e (Ch apte r 31 and quant it a tive dredge sampling (Chap te r 41. The influence oflif e· cycl e characte r i sticsand fe e ding mode <ie. herbivore,carni vore, detritivor elon the magnit ud eandspee d of reepcoee is also investigated.

CHAPTBR 2:THB STUDY SITB PHYSICALCHARACTERIS TICS

The stu d ywas car ried outin ColesPond (48~17.4'N 55°31' E) , Sp ruce Po nd (4 8~1.9'N55~28' E)and Hea d water Pond (4 8·16 ' N 55°29' E) at the Departme nt of Fishe ries and Oceans Ex pe rimental Ponds Are a (EPA)in central Ne wf oundl and (F igure 2.1). The BPAhasserved as thesi t eofseve ralbiornoni t o ring proje cts in the peu c. Mo s t recently it was a partof the Ca nad ian Long Ransre Tr a n s port of Air Pol lutan ts i~RTAP ) proj ec t whi c h involved samp l ing for wat er chemi s try, phy top l an kton , zoop l ankto n and macroinve rtehra te s pl u s the estimat i on of sa lmoni dpopulatio ns (Ryallet ai.1994) . Thi searlier work pr ovidedexten s i ve backg round inf ormat ion forthe present study.

The lakesin theBPAare small, shal lowand dystrophic (Ta ble 2. 1), typic al of lakes in the ar e a (Ryan andWakeham 1984 , Ry a net at.1.994 ) an dre mai n well mix e dthroughou t the Lce - reee season. The experiment al lake,Cole s Pond , hasa low rat i o of catc hmen t bas i n to sur f ace aree (Ta ble 2

.n ,

which result s ina loW'summerflushing rate that makes i t easier to menrpui eee chemically . He adwate r Pond is simi lar to Cole s Pond in thati t isa headwater lake witha lowsumme r flushing rate. It was used as one control while Spruce Pond , the second pond downst reamfromHea dwater Pon d, was used as a secondcontrolsystem . Spru ce Pondis more simi l a r to Col e s

Table 2.1: Phys icalchar ac t e r isti csof th e studypondsin the Experimental Ponds Area.

Me a n Sur:::ac e Catchment

Pond deoth (m)area {h al area(hal Areanarrc

Coles Pond 1.3 25.7 331 12. 88

scrccePon d 1.0 36.5 200 6 54.96

Hea dwa t er 1.1 76.1 596 7.8 3

Pond

Note:Arearatio..Catc hme n tto sur fac earea rat i o.

..

N

in surface area (Tab l e :2.1 ) and it has a low eff e c ti ve flushing ra t e in spite of its largeca t c hme ntar e a. This low flush ing ra t e is due to the adjacent loc a t i o n of bot h the major inle t andthe outl etin the southend ofthepond. The wate rshedof tneee lakeE' is made upof peatland andcon iferous forestwhich is dominatedby black spruce. The exce p t ionto this isHeadwate r Pondwhere a fore stfir ein1986left mo r e tha nhalfofthe weste r nshorelinecons ist ingof charred tr ee remains and low- lyingregroW'':h. The majo r substrateofthe s e pondsis a ge l ati nous brownsediment frequentlyreferred toas Idyl (Rutt ner 196 9J . Thislo os e or gan ic substrat e does not supportdense agg rega t ionsofma c r o phyt e s and creates a fairly uniformsu bstr a te type acr ossal l thr e e ponds . Nea r-s hore areassub j e ctto wave actionhavea cobb le-bou ldersubstrate, theseareas arerelativ e lylim i t ed , es pe c i a l l y in Col esPond.

BIOLOGICALCHARACTERI ST ICS

The st udy ponds are typical of insular Ne wfcund j.andin tha t they are ol igotrop hic (Knoechelan dCampbell198 8 ) aad have a depauperatefauna . Theresiden t" fishpopulat i ons in the Expe riment al Ponds Areainc l ud e ; brook trout (~

~) , juve nileAtlant icsal mon{s..aJ.mg.a..al..w:.J, and the three spi n ed sti Ckleback (Ga a t ematell A~J (Rya n and Knoechel ~994 J. Li mi ted prior be nthi c studies (Ryanee.al . 1985 , Rya n et.al.1990)ind i c ate thatthese po ndsaretypi cal

of Newfoundland systems in that th e benthic corrmunity is composed of the widespread ep eeree from mai nl a~d No rth American fauna (La rson and Co~bo ~9831 . These epec.cee generally occur in low densities and de t ailed characterizationat: the macroinvertebrate fauna for these pondsLn documentedinthis~heais(Ch a pt e r 4).

EXPERIMENTAL MANIPULATION

Coles Pond was fertili z ed during the summer (June- september)withnitrogenandphosphorusetdditions at a rateof 0.824 Kg Nper dayand 0.118 Kg P perday sta r t i ng in the Bunmer of 1991and continuing in the sunnerof 1992. The fertilizati on cont i nu ed in199 3 but at a three-fold greater ra t e. The nitrogenwas supplied aspe~1et sof either anmonium nitrate or sodiumnitrate whichwere addedto pailsina major inlet where they dissolved. The phosphorusvas added inthe fo rm of phosphori c acidwhi ch was drippeddirectlyinto the po nd at alocation adjacenttocne major in l et.

CIIAPTRR 3:NUMERICALRESPONSBS AS INDICATBD USING BIOMONITORING TBCHNI QUBS (ARTI FIC IAL SUBSTRATES)

INTRODUCTION

Past: fertilizationexperimentshave successfullylinked experimen tal in c r ea s e s of nutrients to anove r a l l increasein biomass torfreshwater lakes (Smith 1969, aemercee n 19 8 2, Henry et al 19 85, Stockner and Shortreed 1985, Elser and MacKay 19 89). This suggests that at least in the initial stages of fertilizat ion-bottom- up-controls are structuring the chang eswit hintheecosystem. Thus,my working hyp o the sis wag that an experimental increaseofli mitingnutrientswould increas e overal l benthicbiomass in ColesPond .

The speedand magnitudeofre s ponse to fertilization will di ffer among the vardoue spec ies populat ions wit hin the benthiccommuni tyand these differences shouldbe relatedto thelife span (St eins andWharf 19 87 ) andthetrophi c roleof theorgani sms. Itis ther efore us ef ul to sununarizeesti mates oflif e span andtrophic rolefor thepopUlationsusedin this analysis (Table3.1). Itisexpec-iedthatshort-live dspeci es such as chi ronomids should show fas t e r re s pons e s to fertili z a tion thanlonger-lived speciessuch asdra go nfli e s.

Organisms feeding ne a r thebaseofthe food websuchas filt er feeding clams andherb i vo r ou s gas t ro podssho u l d show qui cker res ponses tha n de tri tivo r o u s may f liesand preda tory le e che s.

Thecombinatio nof life spanand tr ophicroleshouldbe

Table3.1:

10

Life span and trophic role of the most abu ndan t ben thic organisms. Ea ch taxon is typically dominated by a single ge nus or family as indicated in pa renthesis.

Trophic Principle

Taxon life soan role food

Di p tera +/.1year mixed div e r se (Chironomidae)

Gastropoda <18months herbivore periphyton (A!nni=lill

(~~~:;~~:e )

<18 months her bivore phytoplankton

Tri chop t e r a_(~l +/. 1year herbivore ~t~::entous

(~~~~~~r

^{+/. 1year} detritivore coarse detritus Ephemeroptera <2ye ars detritivore fine

detritus

( 1

Tur be l l a ri a .1-I year predator small in v e r t s Hirudinea >3years predator snails,

(Gl Qs ai phq o i a) (except- chironomids

tH~l ~l

Odona ta >3years predator ch ironomids.

(l:lmlll.I.ial mayflies etc.

additive,therefore short-livedherbivoresshoulddisplay the quicke s t response while long -l i ved predators sh o ul d display the slowest.

The benthosof freshwater,.laked have been found to be an effectiveindicator of ecosystemchange because theyprovide a cumul at l v e indication of condi t ions over time, unlike cnemi.cer data which provide a snapshot of ambie nt conditions (Re i c e and Wohlenberg 1993) . An increa se of limiting nutrients from fertilization should pr oduce an Lnc r eane in product i onand,subsequently,abundanceof benthic or g a n i sms . The relationShip between benthicbiomass and nutrient level has beenstudied in thepast. Forexample, Schel l and Ke r eke s

(198 9 ) reported thatphosphorouswas significantly re l a t edto

the abundance of benthicmacroinvertebrates in eight Nova Scot i a la ke s. Fertili za tion experiments, however, have displayedvar iable results withrespect tothe response of benthic taxa. Smith (1 9 61,19 6 9)reportedthat fertilization of a lake increased the biomass of sma ll, fast-growing organisms such as chironomids , amphipodS, ga s t r opod s and sphaeriid clams. Peterson et a1. (1 9 93) reported tha t phos phorusadditionstoatund r a riverinc r e as ed insect growth rate but that abundance was held in check by community interactions such as predation. Brylinsky (1993), in contrast, did not find any significant differences in abundance of benthic organisms in four ferti1i~~dand four

12

co nt r ol wetlands in the Tobeatic Wildlife Management Area of xc va Scotia Canada.

A possible expla n a t i o n forth e differing results in these fertilizat ion experiments may be the varying le vels of sampling effort. Benthicsampling isexpensive because of the large amountof time re qu i r e d for sorting and iden tification.

Therefore most whol e ecos y s t e m studies ha ve had a limited benthic compon e nt (Reice and Wohlenberg 1993). Various strategies were employed in the above studies toreduce the time ne e d e d to sample the benthos. Smith (1961) reduced sampl e processingti me byus i ng a Imm meshto sieve his Ekman grabs. This size mesh would pass many of the smaller organisms suchasch iro nomi d s andflatworms. Brylinsky(1993) employed sweep net samplingto follow the response of the benthiccommunities. Sweep netting is a qualitativemethodof sampling which makes quantitative comparisons among sites diff icul t. Peterson et ej,.(1993) collectedsmall "1·tmbersof samplesthusreducing the powerof thest a t i s t i c s which could be employed. The net result of any of the s e strategies is reductionof th e sensitivi tyfor detecting differences. An efficient method of quantitative samplingwith well-defined statisticalprecisionisre qu i r e d to efficient ly quant ify the response of the bentho s to a pertur bat ion such as fertilization.

Arti ficia lsubst ra tes ar e inexpensiveand have been shown

13

to have low va ria b ilit y(Ros e nb e r g andae s n 1982 ) . This makes them ideal for following the abundance of benthic macr-o- inv e r teb r ates through time to highlight dif f e r encesbr o ug h t aboutbeca use of artificialperturbation .

MATERIALSAND MBTHODS

Artificial substratesampling was used to evalua te the numerical responseof thebenthic invertebrate commun i t y to fertiliz ation in the pre sent study . Sixty art if i cial substrates (r o ck -ba gs)wereplacedinbothth e fertilizedand co ntrol ponds in the Bummer of 1991. These rock - b a g s cons ist e d of approx i mately 11309 of coarse (2.5 em) road gravel encased by pla sti c ve x a r mesh (1. 5 em, stre t c h measure ) . Rock-bagswere placedat3 st at ions perpond, each st ation cons is t i ng of 4 lines with 5 roc k- ba gs per line extendingperpendicular fromthe eoore andthus providinga varietyof depths (Fi gu r e 3.1). The rock-bagswerecoll ec t e d in the spring andfall of each year(19 91-93) beginn i ng in the fall 1991, shak.en vigorously in a bucket of water for 40 seconds to re move organisms and then visually inspect e d to in s u r e complete remo val . The only item not removedwi th100\

efficiencywasleech egg cases and these wereusually empty.

The rock-bagswere thenreplaced in the pond until the next sampling.The water was fi l t ere dthro ug h a 300urn Nitex screen and allorganisms retainedwere preserved in 95\ ethanol.

14

i r

o ^l000m

Figure 3.1:Bxperimentalpond (C,)lesPond) and control pond (Spru c e Pond) with artiUcial substrate stations highlighted. Arrowsindicate the direction of flowin the streams andIpidenotesthe site where fertilizerwas added.

IS

A sub-sample"f 15 rock-bags con s isting of fivebagsfromeach st a t i on andone bagfrom ea c h of the ne a r- shor e tooff-shore pos ition s was sele c t ed for each pond and sampling da te.

Initial analysis revealed no statist ically significant differencesamong sta tions and depths therefore all samples have been pool e d. Thespecimen sof the s e samp l eswe r e sorted and identified using the following keys: aquatic insects (e x cep t Trichoptera) Merritt and CUrrmins (l984) :Trichoptera, Wiggins (1977)jallot h e r macro-invertebrates , Pennak (1978) . Graphical technique swere used to show the temporal patternof abundance of each taxonomic group through time. or gan i s m/rock- b ag data was no t no rmall y dis t ri bu t e d therefore 95\ confidenc e int e rva ls of the mean were estimated by randomizationtechniques. The 15 es ti mat e s of abundancewere replicated 200times toproduce a popu l a t ionof 3000values whichwerethe nrandomly sampled inset sof 1.5. one thousand time s. The 95' conf idence inte rval s of the mean were then determined from thi s set of one thousand means. Lack of ove r l a p of the 95\ confidenceintervalaround the mean ofone se t of sampleswith the mean of a secondset thus indicates a greater than 2 standard errordifference between the means defininga statistically significanceof p< 0.05.

16 RESULTS.ANDDISCUSSION

Artificial fertilization has been repe a t e dl y shown to in cre a s e primaryproductivityinfreshwaters (Smi t h19 69, Hall et al. 1970, Petersonee al. 1993, Brylinsky 199 3). It i.a expected that th i s in c r e a s e in primary productivity sh o u l d also lead to an increasein abundance of or gani s ms in the be n thic co mmun i t y.

Itwa s expected that the speed and scale of response wouldbe related to the life span and tr ophic roleof the indiv idual taxa as summaz-Lae d in Table 3.1. The most pronouncedre s p on s e to;';ertil izati on observed in the benthic commu ni ty was bythe sma l l, short·lived, herbivoressuch as chironomids (Figure 3.2 ) , gastropods (Fi gu r e 3.3) and sphaeriid clams (Fi gure 3.4). These organisms have the ability to reproduce morethanoncea yearand have relatively short life cycles (l e s a than 18 months) making themideal rapidindicatorsofcha ng e inthe abiot i cenvironment. Th e se findings aresimilarto those ofSmit h (1961 , 1969) who noted in c r e a s e s in clams and gastropodsduringthesecond and third yearsafter fert il izat i on. Thechironomids (Fi gu r e 3.2) had the largest inc r e a se in abundance, showing almost a 6-fold in c r e a s e in 1992 over 1991. The numbersdroppeddrastically during the winter of 1992 butro s e toan evenhigher level by the fall of 1993. Thelarge re ductionover the winterof 1992 suggests thata large amount of chironomidbiomass wasshunted

o

It) N

g

N

17

: 2 .,

8 a-

DD

o

g

~

~ )~

:>NIIONnSII (6eq·~ooJ/# 3

o

3, r--- - - - - - -- - - - - - - -

2.5

~

~

o

^Coles

[JS p ru ce

o

911 92s 921 93s

SAMPLING DATE

Agure 3.10:Theabundance of Odonata In the enhanced pond (Coles Pond) and a control pond (Spruce Pond) duringthefirst three yearsof fertilization Barsare 95%confidence Intervals of the mean.

g;

²

.a.;, oo

~

1.5 w

o z s

z ill

0.5

«

...

~

D Coles

o

Spruce

928 921 938 931

SAMPLING DATE

~ . >

/ -:

; [>< ^-: N

~ A"

1.5

0 911

2

Ci ..

~ "

! w o ~

CO.5

z

:::>

III..:

Figure 3.9:Theabundanc eofleech" Intheenhanced pond(Col••Pond)and

• co ntrol (SprucePond )during the firstthreeyearaoffQrt ilizat lo n.

Barsare95%co nfi de nceInterval.01themean.

20

up the food chain (p r eda tion) or le f t the systemthrough a mass emergence late in the fall or early inthe spring.

Gastropod abundanc e (Fi gu re 3.3 ) increa s e d in the fertilized pond,ex c e pt for the springof 1993 when abundances declined in both ponds sugges ting either harsh winter condi tions or hi gh winterpredation rates. Sphaeriidcl a ms (P:tgure 3.4) whichare similar tothe gastropodsin life span and trophicrole (Ta b l e 3.1), increasedsignif icantlyin Col es Pond after the firs t ye a r of fertilization (1 99 1) an d have sUbsequently re ma i ne d at consistent, elevated levels . The clams may have been held from increasingfurther eithe r by increased pre da t i onorby a re d uc t ionin the i r food supply . Chlorophyll levels remain elevated in Coles Pond (R.Knoe c he l unpub.data) however and stomach content analysisof benthic- feeding salmonids (unpub.data)and sticklebacks (Br o wn 1993) revealed that clams were no t an important diet item. Thusthe mechanism maintai ning the apparent steady state abundance level is unclear.

The response ofthe trichopteran~ (Figu r e 3.5 ) is anexception to the general trend seen in the herl:.ivores. There was a slight divergence between the two populations ove r thewinter in both 1991and 1992 suggesti veof enhanced wi nter survival in Coles Pond . The abundance level in Coles Pond was not significantlyhigher until fall 1993,however . This migh t be attributableto a delay inthein c r eas e of filamentous

III

21

.,

" u

., 2 '0

Q.

U Ul

D O

'It .., <'I

(6eq·~~oJ/#)3:lN'IONnS'l

22

benthic algae that these organismsfeed on. Large 'clo ud s 'of filamentous benthical ga e were observed inCol es Pond inthe summer of1993 but were no t obvious in 1991or 1992.

The larger,longer-lived or g a ni sms with mainly detritus- based diets responded moreslowl ytofertilization. Arnphipod levels(Fi gu r e 3.6)we r esigni f i c a n t ly higherin ColesPond in thefallof 1992 butthe populationswere at similarlevelsat all other sampling times. This is in contrast to the observations of Smith (1961) where amphipods showed significant, quick increases after fertilization. Ephemeropteran abundances (Figure 3.7) remainedsimilar in bothpo nds th r ou gh the fall of 199 2followedby adiverg e nc e overthe winterof 1992-93 with decreased abundanceinspruce Pond. Thus bythespringof 1993 the abundance in Coles Pond was signific an tl yhigher than that observed inSpruce Pond.

This trendcontinued through the fallof 1993 and is expected tobe maintaineduntil the mayfly

popUlationinColesPondstabilizesat ane wequil i br i um with theirfood supply and their predators.

The final group of organisms considered were the predatorsof the benthic community. The flatworms (Fi gu r e 3.8 )are the smallest and have the shortest life cycle (Table 3.1) of the predators considered in this analysis. They showed significantlyhi g he r abundance inColes Pond in the spring of 1992 but their levels were not significantlygreater

16rl- - -- - - -- -- - - - -- ----,

14

j12

,,;,u

fO

w 8 o z j§ 6 z

::>

lD<0:

o

911 928 921 93.

SAMPLING DATE

⁹³¹

D e a lBa

O Sp rucB ^~_w

Figure 3.7:Theabundance ofEph.m.ropl....In theltnhanced pond (Col ••Pond) and

• controlpond (Spruce Pond) durIngthe flrat three years of fertilization.

Bars .r.95% confidence Inlerv" tof the mean.

10r,- - - - - -- - - - -- -- - - - - - - - ,

-;; 8

j 2

⁶

w

~ o

~ 4

z

c ::>

CD

"" 2

o

^Coles

[J Spruce

~

o

----gjf 920 921 930

SAMPLING DATE ⁹³¹ Figure3.6:Theabundance of amphlpods inV.leenhanced pond (Coles Pond) and

and a control pond(SprucePond)duringthe first threeyearsof fertilization.

Barsare 95% confidence Intervals of the mean.

to

25

= _~

'0 [

U III

D O

CD lI) "lit C"') N (68q-~OOJ/#)30N'IONnB'I

26 again until the fall of 1993.

The leeches (Figure 3.9 )have shown steady increases in abundance in Coles Pond since the spring of 1992 although the level was only significantly higher than Spruce Pond in the spring or 1993. Withcontinued fertilizationi tis expected that the abundance of leeches will continue to climb and eventue:lly maintain a level significantly higher than that observed in spruce Pond.

The Odonata (Fi gu r e 3.1Q ) were always significantly higher in abundance in Coles Pond than Spruce Pond. There were no significant differences in Spruce Pond abundances over time while there was a significant increase in Coles Pond by ::,pring1993. The subsequent sharp decline in Coles Pond was correlated with an increase in salmonid abundance that summer (Knoechel unpub. data). Odonata ccnscituce a major portion of salmonid diets in these ponds (Clarke unpub. data).

27

'"

.. "

'" ::>

'0 a-

u

til

DO

CD q- e"J

(6.q-~O OJ/#)3:lN'<faNna'<f

.. B .. 2

'0

Q.

o

Ul

D O

28

'"

^o

29 SUMMARY

Artificial fertilizat i o n of Coles Pondhasinc reased the abunda nceofseve ra l benthic mac roinve rte br ate taxa. Thelife history and feeding charac teristicsof the organismstudLed was rel at ed to both the speed and the magni tude of the re s pons e tofertiliz a t i on. For example, smal l, short- l ived herbivores(ga stropods)demonstrated a quicke r re spons e than did large r, long-lived detritus feede rs (mayflies) which in turn ha d a quicke r respo nse than did larger pre da tors (lee che s ). The wi d e n ingabun da ncediff erent ialobserved fo r most taxasuggest that continued fe rti lizationwil l incr ease the abun da nc e of benth i cor gani s ma in Coles Pond until the communi t yse ttlesintoane wequ ilibrium at an overa llhigher leve l of abund a nceand pr od uction.

30

CHAPTBR 4: MACROINVBRTKBRATB RBSPQNSB TO PRRTILIZATION:

GROH'11I, DBNSITY AND PRODUCTION.

INTRODUCTION

Most studies of experimental perturbation of the benthic community employsimple estimates of numerical abundance when making comparisons among treatments (Benke 1994. Rosenberg and Resh 1993). However, numerical abundance is influenced by the balance between reproduction and death, each of which may respond independently to the perturbation. Simple numerical estimatesalsocannot reflect differences in individual size that may result from growth rate enhancement. Secondary production estimates may be more powerful indicators of ecosystem change because they take reproduction, growthand death all into account (Be n k e 1994). Obtaining accurate secondary production estimates requires large sample sizes and labour-intenaive weight determinations,consequentlyth e y are infrequently reported in the literature.

Benthic community prOduction has been shown to be affected by stresses inclUding insecticides (Lugthart and Wallace 1992), nutrient increases from agriculture (Sallenave and Day 1991) and organic enrichment (Flossner 1982, Lazin and Learner19 B6,Losos 1984).

Benthic communityproduction has usually beenne g l e c t e d in mesocosmfertilization experiments and benthic production estimatesare almost non-existent in whole lake fertilization

31

experiments. Acomputer-basedsearch of Biological Abstracts from January1985to June1994and a subsequent review of the literature cited in the eeaectee references obtained,revealed only two papers dealing with eeoondary production of the benthic community following fertilization. One of these articles (Pe t e :.:s on et al. 1993) dealt with a tundra river system and the other (Aaga a r d 19821 was a whole lake enrichment experiment but only reported production estimates for two ch d.rono mi .d species. Both articles (Pe t e r s on et al. 1993, Aagaard 1982) however, report conflictlng results relating fertilization to benthic community production.

Peterson et al. (1 9 93) reported in i t i a l growth rate increases but total secondary production did not increase due to 'top- down' processes (predation) in the community. Aagaard (1982) reported density increases but these increases and the production estimates were reported as being within theli mi t s expected hy annual variation alone and thus the effect due to the fertili2ation was not clear.

The present study aims to hetter quantify the relationship between whole lake fertilization and its effect on benthic secondary production. Coles Pond experimentally fertilized with inorganic nitrogen and phosphorus beginning in eunmer- 1991 (s e e Chap.2) while Spruce and Headwater ponds served as control ecosystems. The working hypothesis was that the increase in nutrient load to the

32

enriched ecc eyee ee (Co~e s Pond) would incr e a s e primary product.i vity whichIn turnwouldinc r e a sethe pr oductivityof th e be nt hos. Benthic re spon s e s could be manifested as numerical increa ses and/or growt h ra t e incr eases (larger size). both of wh ich shoul d be reflected in population produc t i on estimates.

MATERI ALSANDMETHO DS

Densit y, bi omas sand production es t imatesfor the ma j or macro invertebrate taxa wer e obtain edus ing a quantita t i ve sampli n g re g ime ini t i a ted in the secondyear of the study.

Sampl i n gstartedin JUly 1992andwas repeatedfou r add i t ional ti mes thr oughout the stu dy(Augus t1992,May 1993 ,July 1993 andAugus t 19931. sampl es vez-ecollected using ahand-held dredge sampleraffixed with a2flIDNitexmeshbag des ignedto re tainthe macroinverteb r ates while passing thesedimentand microinver tebrates (Pigure4.1). It thUB enabled saI1'lPling of the large are as ne c es sary for quan t itativedesc r ipt io n of la rge . low-de nsit y organisms. The la rg e r mesh size ot the dredgesampler meanstha t theres ul t s of th issampling me t hod are not directlycomparableto thos e in Chap ter 3 in which the arti ficia l substratecollectionswere si e v e d using a 300um mesh screen.

The samp l e r wasdep loyed bysno r kel ling out and back alonga15mtra nsec t. Thesamp l e r had a 0.25mwide apert ure

33

34

andtnus eachsamplecoveredanarea of 7.5m". Sa mp l es were collected in triplicate at 3st a t i ons perpond (Figu r e 4,2) and two depths (0. 5 and 1. a m) per station . This sampling re gime produced18samples per pondper samplingdate which were preserved in 95 \ ethanol. A Bub-set of 12 samp l e s per pond per sampling date, representing 90 m^l of benthic sUbstrate . were so r ted and the sp ecime n s cou nted and ide ntifi e dusin g thekeyscited in the materials andmethods sectionofChap t e r 3. Conf i d enc e intervals(95\ )of the mean densitywereesti matedusingrand o mizat i ontec hniques. The12 estimates were replicated toproduce a population of 2400 value swhichwerethenrandomly sampled in sets of 12, one tho u s and times. The 95\ con fi de nce limits ofthe mean were then empirically determi ned from thi s set of one thousand These 95\ confidence intervals are shown in all figures and sample means which lie outside the confidence interval for a gi v e n si te and date were jUdged to be significantlydifferent at the 5\ level .

Standing stock biomass (drywt./ma) was ca lcu l a t e d for use in secondary production estimates . Dry weight was ob t a i ned after drying the specimens at60 "C for 24 hours , bothclamsandsnails were weighted wholewithshel lsdue to the small size « 3 rom) o:f the dominant epecfee. Biomass es timates were then calculated by mul tiplying the average weight bythe average density for taxa that disp layedlittle

Pigure 4.2:St udy pondshi ghlig hti ng the quant i ta.tivesampling sites. Arrows iDdicate thedirectionot flowtor th e maj o r streams. Note:The pondsare notdra wn to sc ale

w

~

36

ran ge in size such as ~. The averagedry weigh t was estima t e d by weig hing group:. of 20-25 rand omly selected specimens in dupl i ca t e where number s permit t e d (de ns ity

>0.25/~). For taxarep r e s en t e d byfewe r than 20 spec i men s the numbe r of indiv iduals we i gh ed can be estimat ed by multiplyingthedens ity , graphed inthefigu r es,by the 90m' sample size. Log le ngth : log dryweight regressions were used to estimate the biomass of taxa that variedwidely in size suc h as~. The re gress i ons are pr e s ent e d in Appendix A.

Bvaluation of the genera l lif e· hlst o ry pattern for several of th eeceeabund a nttaxawas in ves t iga tedbypl ott i ng theiravera ge densityandaveragewei ght though ti me. The patterns observedin thesepl ots were interp reted usinga set of si mpl e rules. A large incr e a s ein dens ity and/ordecrease inaverage weightwasinterpr ete d as evidenc e forrecruitment while a sha rp dec line in density indicated a period of emergence (aqua ticinse cts )or high mor tality (predation, mass die off ). Growthresponses ofindi vi dualtaxawere evaluated by comparingweigh t gains inthe three ponds over important growing perious. Likewi s e , re spon s e in rec rui tmen t was evaluat.e d by comparingthe cha n ge in density in the three ponds du ring important recruitmentperiods. Theseanalyses were onlycar riedouti f the taxon's lite cycle was foundto bein phasein all three ponds.

37

Productionestimateswere then calcul a t e dus i ngone of two methods. secondary producti on of populat ions with dis ti nct univoltine cohorts was calculated using the increment -summationmethod as described by Rigler and Downing (1 9 84) us ingthe equation:

Eq.1. P",r:liHm,. -

m..,»

where N is the average #/m^l at time k and k·l, rn,is the averageweight (mg) at timek andm,..tisthe average weightat the previous sampling date. When sampling datesspanned an emergence (us u a lly denoted by a sha rp decl ine in ave r a ge indi vidu al weight) the numberat k-l for the new cohort was set at 0 and th e number at k for the oldcohortwas set at0 giving an estimate of production for the twocohorts (See exampleAppendix B) . Annual produc tionwas calculaterlus ing a correctionfactor whichwas36 5 dividedby theda y s elapsed during the study . Daily secondary production for specimens wherecohortswere not readilyidentifiedwas calculatedusing the size-frequencymethod.of Hamil ton (1969) with a correction foractual cohortproduction int erval(CPI) (Be nke197 9 ) using the equation:

Eg. 2.

whereP1 is the daily productionof an arbitrarysizecl a s s i,

&1is theaverage#/m^l in thesi z e class,m,••te the maximum weight (rog)in the size class an dm.••is the miniurn we i g h t in thesi z e class. 01is the averagedurat ionof each sizeclass

38

which iaest ima tedbydi viding 365days bythenumber of size cla sses. Size clas ses were as signed arbit rarily by the his togr a m funct ionin MINTASwith onlyonere quirement,eac h siz e cl a s s had to ha v e both a minimum and maximum obs e rved weigh t (ie .th erehad tobemor e t.hanoneindividua l in the cl a s san d they hadto vary in weight). It this requirement was not me t then twoormor esize classeswe r ecombined to ensurea range inwe ig ht s within ene si z ecl a s s.

The estimate is then multipliedby the CPI whic h is a correction for act ual duration of the aquati c life-cycl e. Thiscor r ectionis neces sarybecau s ethe sbe- f r equen cymethod wa s formulat ed for or g anismswith a 365dayaqu atic life-st age durati on. The resulting production esti mate was the n mul ti plie dby365day s togive annu al product ionin mg.m-'yr·' .

RESULTS ANDDISCUSSION BENTHICc:c:wMUNITYCCHPOS IT I ON

Be n thi c commmity taxonomi c composition wa s si mil ar amongthe threestudyponds (Table4.11. Therewer e five taxa unique to Col e s Pond colle ctions and four unique to Spruce Pon d but all taxa clas s i fi e d asabundantin anyonepo ndwere present in each of the others with the exception of the trichopteranPo] YGe ntrQPuB. which wasabsentfrom SprucePond co l l ec tions. Most of the taxa listed are holarct ic in distributio n andare typical of Newfoundland' s benthic ta una

Table 4.1:

39

Li st of thetaxa identifiedfromcollections in the thr e e ponds over the course of the st udywi ththe quan titativ e dredgesampler(* indi ca t e s presence, .. indicates abundan t taxa)

oP..,,_ = ..

...

^{~ ,...,.}

. ....

....

""

...,<'O~.

. .

^oo

..

••JIO"""" ^oo oo

..

"", ...

^oo

.ulu.

"'

...

Ily"•••

orJ. .

. . .. ..

'"

-'pod'

" d J o oo oo

..

:.: . . ^{, .}

O••n'.

. . . .

.. - ,"",. . . . . ..

" ". ,.

. .

^~.

. . . .

..

⁰⁰

^{, ..}

, ..

to. . ...U<'<>

,-,r•• ,••

,,-

.,,,

~

. . . .

u. 1....

Oono. .. oo oo

. _=

" " '01010 oo

. .

-- ^{. .}

^oo

plo,

oo.

~ "'

. .

l~ ,_

".

",1""".

40

"

."...".

. . ..

"

... ....

....II

.. .

. "

.. ....

0.,,,,,,•••,,...

. . .. . .

Co,.,

, .. ^{.. ..}

^"

...

,

. .. . .

...1l~

."

."

.. .. ..

~,

....

,

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. .

C)•• •,

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....'_H.

. . . . ..

...

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....

ro"""

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..

^'0"

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. ^{. _1I...}

-

"""",,,^'"

_.1. .. . . _"

41

(Larson and ccrbc1983). and have been previouslycatalogued in theExperimental Ponds Area (Ry a n et al .19901. The one exception isth e clam shrimplEub r a n ch i o pod a )~

~whichwasonly collectedinCol es Po n dand has not been previously reported in Newfoundland . The distributionof th i s species is thoug ht to be holarctic (Penna k1978) but it ha s onl y be e n reported in th e litera t u r e th r e etimes for all ofCa na d a, the most eas terly po i n t bei ngin Quebec (Mart i nand Belk 1988 ). Its dis c overyin insularNe wf oundlandsupport s it s hav ing a cosmopolitan di s t ribu t i on ; its infrequ e n t re po rti ngmaybedu e todifficul tie s in identificat ion,as i t is easily mistakenfor an ostracod.at first glance,or due to its very low abundance .

MACROINVERTEBRATEBICMASS

Totalbenthicmacroinvertebratebiomasswas comparablein Coles Pond and HeadwaterPond throughout the study (Fi gu r e 4.3). Biomas s was initia lly highest in Spruce Pond but declinedbyAugust1993 tole v e ls similar tothe othe r ponds.

Biomass wasgenerally domin a t e d by gastropoda in all three po nds (Fi gu re 4.3 ) wi t h odonata, dominated by the ge l,u s

~. the ne xt most important grou p. Total biomas s declined from JulythroughAugust 199 2 , rec overed ov er the win t e r and the ndeclin e d from Ma y thr o ug h July1993 inall t.h r e e pond s. Thebiomas sde c lin e co n t i nue dthrou ghAu gu s t

42

.. --

t J

I I '

0o",."

.Tlle""''''

111..",,-

eM.." ...

•r,h"I\II"I"~

OAM,".

eaOlIIl.tl Doutt",ll', oNY Allfl'tt "IT

I .1 I ,IS

SAMPLING DAft

Pigure 4.]:Benthic bloma81 estimateJ for the Itudypond.: Showing the relative importanceot the major tAXonomic group"

43

1993in Spruce Po nd while an increa se was ob s e rved inboth Co l e s and He adwa te r ponds. These pat t ernssuggestanover all decli ne in bent hic biomass ove r the BUtlIIIer. while aquati c inse ct s are emerging and bent hic - fe ed ing salmo nlds are most active, and a fall in c r e a se correspond ingtothe recruitment per iodof aquatic in s e cts andthe brook trout spawningperiod .

DENS I TY AND GROWTHPATTERNS

Secondaryproduction is much easierto calculat ei fthe orga nism in question ca n be followed thro ugh ti me as a distinctcohort (Ri gle r andDowning19 84,Ben ke 1994 ). It is therefo re important to have an understanding of the general biol ogy of the orga n i smbe for e calculationsare attempted.

~

~filn1tt.1&ill (Co rd u l i dae: Odo n a t a )is the dominant benthic predacor li n terms of bi omas!'1 in these systems.

~ has been observed to have 10- 14 instars in Ne wfoundlan dsy st ems (Pa r r e ll198 5 , Cl a r ke 1992 , Larson and House 1990). Laborato ry experiments (Cl a r ke 1992) and ob s e rvatio ns in the field (Cl arke unpub.) sugges t that it would re qu i r e4-5years to completethisnumberofin s t a r s in Newfound land. Thi s est imateis similar tothat of ~

~ilIIIU.UiB. of No r the a stAs ia (Ubukata1981 ).

Densities ot~increased significl'.nt ly in Coles andHea dwaterponds fromAugust 199 2 toMa y19 93 (Figure4.41. Density increased in Spruce Pond over the sametime period but

..

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t •

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Figure" .4:Averageindividual veigbt ( - ) and. densityl- ••J ot the dragonflyQm1u.1J..I.

45

difference s were nee signi fic an t (Fi gure 4.4) . 'ruee e in c r e a s e s corre s pondtoaperiod of re cruit ment inall three pond s. This re crui t ment wa s followedbya periodof emergenc-e and / or hi g h pre dati onpressurefromMay1993to August1993as indicated by th e sign ifica nt decline in densities (Figure 4.41 . The average ind ivi d u a l weight of c.::w1l.ll.i..i increased th r o u g hou t the study in all ponds (Fi gu re 4,4). The increasing average weight despite recruitment suggests the influenceof a strong. ol dercohort. This is illustrated in Fi gur e 4.5 which shows the median length continual ly in c r e a s i n g in the three ponds overthecourse of the study. There wa s anabsence of smaller indi viduale inth e August sa mpl e s (Cl a r ke unpub . datal ~ugge8ting that recruitment to cat c h a bl e size is fa irly synchronous and thu s ~ may ha v e a synchron ou s emergence intheseponds. Thisob s e rvatio n agr e e swit hobs erva tio nsin Quebec wherethe sa mespe cieswe re ob s e rved toemerge synchronously over a oneweek period in 1982 anda two we e k period in19 8 3 (Ca ronand Pilo n 1990 ). The average ind i v idual weight gai nove r th e studyperiod (J u l y 1992 to August19 9 3)in ColesPond was morethan double that in Spruceand Headwater pond s (Figure 4.6). Th e weight gain was pa r t i c u l a r ly la r g e inColesPond overthe July to August 1993 interval (Fi gu r e 4. 4), suggesting th a t growth rates werestillin an accelerationphaseand th a t recruitment rates shouldthu s inc r eas e in fu t u r e years. Analter native

20,--,- -- - - ,

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··- Sp ru ce -.Headwater --.~

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Pond Aug 92

0' I

July92

Figure 4.5:Median lengths for the dragonflyCorduliain the threestudy ponds throughout thecourse of this study

10

8

Ci .s

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OJ

c:

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E

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0 Cole s Spruce Headwater

POND

Figure 4.6:Compari son01Individual weightgain oftheodonateCordull.(July1992 · AugU111993) among thethree study ponds.Notethai thegreal.,tIncre..e was In the fertilized pond.

~

48

mechanismbehindthelargerweight gain inCol es Po n d co u l d be higher rates of size-sele ctive predation on the smaller individuals relati ve to the oth er ponds. This hypothesis however. was not supportedby a salmonid stomach analysis conducted inthe s e ponds in 1993 whichrevealed a preferance towards larger ~ in salmonid die t s (Cl a r ke unpub. data)•

~ is the most abu n d a n t zyg opteran (d a ms e l fl y ) odonate in the study sys tems. It is a preda t or of small benthic invertebratesandgenerallyhas anaqu a t i c life stage duration of 18-24months (Me r r i t t and Cummins1984).

Densityincreasedsign if ica n tly from August 1992to May 1993inall ponds. indicating aperiod of recruitment(Fi gu r e 4.7 ) the magnitudeof which was highestin ColesPond(Figur e 4.8 ). This was followed by a periodof emerge n cebetween May and July 1993 indicated by the significantdecline in densi ty.

The average individual weight did not dropat the same time whichsuggests both a lack of recruitment from JUly toAugust 1993 and that emergence wasno t totally syn c h ron o u s in the population (Figure 4.7 ).

Amni.<:<ll.a

Aml1.kQl.a was the most common gastropod in the study ponds. It feeds main lyon periphyton algae and generallyha s a life-history duq.tionof 12 months(Pe n n a k 1978) although

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Pigure 4. 1:Ave rageindivid ualweigbt (- ) and denB1ty(•••J oftheooonate1nAl1.Isml.

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(~w/#)

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51

the life-history of Newfoundland populations has not been determined .

Densitydeclined significantly in Spruce Pond fr omAugu s t 1992 to August 1993 (Figure 4.9) and significant density declinesfor Headwater Po ndwereob s e rve d from August 1992to JUly 19 93 with the me an for August 1992 not being significantlydifferent from that of Ju l y 1993 (Figure 4.9). The density in ColesPond declined significantlyfromMay1993 to Au gu s t 1993 and the estimate for August 1992 was not significantlydifferent fromthatof May1993. These trends suggest that there is only one coho rt represented in the samples fromAu gus t 1992 to Augus t 1993 . This is th e time period used forcalcu l a t i o ns of secondary productionfor this species . Small me mbe r s of a new cohort would not be repreeeneed , dueto the 2 rom meshsizeof th e sampler. The averageweight of~in c re a s e d throughou t the course of the studyin Colesand Headwater ponds as wouldbe expectedof a single coh ort (Fi gu r e 4.9). Theav e r a g e weight in Spruce Pond declined ove r the first sampling int e rva l but then followed the same pattern as in the other ponds. The annual weight gain fromAugust 1992 toAu gus t 19 93 was highest in Coles Pond (Figure 4.10) . This observationwasla r g ely due to a muchla r g e r weight increasein ColesPo n d from July 19 9 3 to Augu s t 1993 ascompa r e d to the other two ponds (Fi gu r e 4.10) . These observationssuggest that~had enhanced growth

i 1 ..

52

-

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pigure4.9:Aver ageIDd.lvldual weight ( -) and density I•••) ofthogalttopod~ .

I,.

indicatesthe range ot.replicateweight dete rminatione .

S3

III

to

~

0

(6w)

u!e~

11I61aM

5.

rates in the enriched pond especially duringthe latterpart of the study.

He.l..i.a.Qma. was the second most abundant gastropod in the study ponds. I t feeds on periphyton bu t i t is much larger than~and is generally thoughttohave a longer life cycle (Pe nna k 1978).

Densitiesdeclinedsignificantlyfr om July 1992to July 1993inall ponds followedbya significant increasefromJ~l'y

1993to August 1993 in Spruce and Coles ponds (Fi gur e 4.11).

A density increase was alsoobserved in HeadwaterPond for the same time period but it was not signif i c a nt. The average weight also showed a generaldecl ine over the course of the study. weight-densi typatterns were consist entthroughout the study in that wheneverthe densitydeclinedthe averageweight increasedanddeeversa . This suggests thatth e population ....as going through periods where recruitment was higher than mortality followed byperiods where the opposite is true.

Coles Pond had the most rapid density decline and thelowe s t averageweight whichsugg e s t s that it has the highest rate of mortali ty (preda tion ) and the youujest; population age structure. There were no clear recruitment or growth differencesamong the pondsduring the course of the study.

55

"

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eou'

pigure 4.11:Averageindividualweight (-) and density(....) ot the gastropod.~·