Influences of native and non-native benthivorous fishes on aquatic ecosystem degradation

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1 Hydroiologi (213) 711: DOI 1.17/s z PRIMARY RESEARCH PAPER Influenes of ntive nd non-ntive enthivorous fishes on quti eosystem degrdtion Jesse R. Fisher Ree M. Krogmn Mihel C. Quist Reeived: 2 My 212 / Revised: 21 Ferury 213 / Aepted: 23 Ferury 213 / Pulished online: 14 Mrh 213 Ó Springer Siene+Business Medi Dordreht (outside the USA) 213 Astrt Invsive ommon rp Cyprinus rpio hs long een identified s ontriutor to wter qulity deteriortion, disrupted eosystem proesses, nd shifts in iologil ssemlge struture. In ontrst, little informtion is ville regrding the effets of ntive enthivorous speies on quti systems despite their funtionl similrity to ommon rp. Effets of ommon rp nd the ntive lk ullhed Ameiurus mels on sediment resuspension, nutrient onentrtions, mrophytes, nd ssemlge struture of zooplnkton nd mroinvertertes, were experimentlly evluted. We oserved deresed wter lrity, inresed nutrient onentrtions, deresed mrophyte iomss, nd deresed enthi mroinverterte undne nd iomss ssoited with ommon rp, regrdless of the presene of Hndling editor: Kty E. Kovlenko J. R. Fisher (&) Deprtment of Nturl Resoure Eology nd Mngement, Iow Stte University, Ames, IA 511, USA e-mil: fisher@istte.edu R. M. Krogmn Fisheries Division Srmento, Cliforni Deprtment of Fish nd Gme, Srmento, CA 95811, USA M. C. Quist U.S. Geologil Survey, Idho Coopertive Fish nd Wildlife Reserh Unit, Deprtment of Fish nd Wildlife Sienes, University of Idho, Mosow, ID 83844, USA lk ullhed. In ontrst, lk ullhed inresed totl phosphorus, nd hlorophyll onentrtions nd opepod undne, ut hd little or no effet on other mesured wter qulity nd iologil vriles when ompred to ontrol onditions. Overll, experimentl results suggest tht lthough lk ullhed tend to e tolernt of degrded eosystems, they re not soure of physil hnges to the environment known to e responsile for perpetuting degrded wter qulity (e.g., stle stte shifts). Therefore, inresed undne of ntive speies, suh s lk ullhed, following the invsion of ommon rp, my serve s n inditor of eologil onditions nd should not to e ssumed s ustive. Keywords Aquti mrophytes Benthi mroinvertertes Blk ullhed Common rp Wter qulity Introdution Common rp Cyprinus rpio is one of the most widely introdued quti speies worldwide nd hs long een ssoited with physil, hemil, nd iologil ltertions to quti systems (Chn, 1929; reviewed y Weer & Brown, 29; Kulhnek et l., 211; Whl et l., 211). Beuse of their feeding ehvior, high feundity, long lifespn, lk of nturlly ourring predtors, nd ility to exploit regulrly distured hitts (e.g., those experiening

2 188 Hydroiologi (213) 711: winter hypoxi), invsive ommon rp hve een linked to severe disruptions to shllow freshwter systems (Zmrno et l., 21; Bjer & Sorensen, 21; Jkson et l., 21). Speifilly, ommon rp resuspend sediments nd ssoited nutrients in the wter olumn y diretly feeding on or uprooting mrophytes while forging for enthi invertertes (King & Hunt, 1967; Miller & Crowl, 26; Mtsuzki et l., 29). These tivities my rete positive feedk s unonsolidted sediments re more suseptile to resuspension y nturl fores, suh s wind. Furthermore, nutrients ound to sediments often eome ville fter resuspension, stimulting lgl looms nd further deresing wter lrity nd the re-estlishment of mrophytes. Diret effets of ommon rp, suh s deresed wter lrity, inresed nutrients, redued mrophytes, nd destilized sustrte, olletively result in shifts of physiohemil sttes (i.e., ler, mrophyte-dominted vs. turid, plnkton-dominted: Sheffer et l., 1993) of shllow quti eosystems tht result in onditions tht re often diffiult or impossile to restore (Zmrno & Hinojos, 1999; Zmrno et l., 21). For instne, Shrge & Downing (24) reported rpid shift in wter lrity of Ventur Mrsh, Iow, USA fter 75% redution in ommon rp undne. However, fter the re-estlishment of juvenile ommon rp, the system quikly reverted to turid-wter stte. In ddition to hnges in physil hitt, invsion of ommon rp hs lso een ssoited with shifts in iologil ssemlge struture. Lkes with high iomss of ommon rp typilly ontin fewer sight-feeding fish speies, while enthi, non-sight feeding, omnivorous, nd tolernt speies generlly inrese in undne (Breukelr et l., 1994; Jkson et l., 21). As result, ntive speies tht persist in the presene of ommon rp often eome ssoited with degrded onditions nd re ssumed to ontriute to environmentl deteriortion (e.g., Egertson & Downing, 24; Shrge & Downing, 24). Common rp-indued shifts in fish ssemlges to enthivore-dominted ssemlges hve spurred reserh foused on evluting the reltive eosystem effets of ntive speies tht re funtionlly similr (e.g., trophi guild, hitt-use). In experimentl mesoosm studies ompring ntive speies to ommon rp, Cline et l. (1994) oserved tht rown ullhed Ameiurus neulosus did not inrese turidity nd Prkos et l. (23) reported tht hnnel tfish Itlurus punttus hd no effet on turidity, suspended solids, or mrophytes. A redution in hironomid densities in the presene of juvenile ommon rp (3 4 m) ws oserved y Btzer (1998), wheres dult nd juvenile rown ullhed hd no effet on mroinvertertes in ponds of western New York, USA. Similrly, ommon rp deresed nnelid, hironomid, nd odonte iomss in experimentl mesoosms, while Prkos et l. (23) did not oserve hnges in mroinverterte undne for hnnel tfish ompred to ontrol onditions. Although lk ullhed Ameiurus mels is txonomilly nd funtionlly similr to ommon rp, little reserh hs een onduted on its influene on onditions in quti eosystems. Unlike rown ullhed nd hnnel tfish whih re less tolernt, lk ullhed is generlly onsidered tolernt of wide rnge of environmentl onditions (Brown et l., 1999; Hnhin et l., 22). Blk ullhed is lso le to sustin high popultion iomsses (Crlnder & Moormn, 1956) nd is uiquitous ross North Ameri (Lee et l., 198). Consequently, lk ullhed is often onsidered n eologil equivlent to ommon rp (Egertson & Downing, 24; Shrge & Downing, 24). In ddition, high undne of lk ullhed is often ssoited with tht of ommon rp (Brown et l., 1999) when the ssemlge is not ompletely dominted y the invsive ommon rp (Egertson & Downing, 24). Beuse of this ssoition with deteriorted eologil onditions nd ommon rp, lk ullhed hs een trget of removl efforts in ttempts to improve qulity of lke eosystems (Shpiro & Wright, 1984; Shrge & Downing, 24). However, in the only study, we re wre of, tht hs evluted the influene of lk ullhed on quti eosystems, Brig nd Johnson (23) experimentlly tested the effets of dult nd juvenile lk ullhed density on turidity in shllow wetlnd of Ohio, USA. Although the uthors found tht lk ullhed signifintly inresed turidity over fishless ontrol onditions, turidity in lk ullhed enlosures t high iomss (i.e., up to 2,438 kg h -1 ) ws onsistently less thn mesurements otined from outside the enlosures where high turidity ws ttriuted to wind resuspension (Brig & Johnson, 23). Therefore, further reserh is neessry to determine whether mngement efforts

3 Hydroiologi (213) 711: tht trget ntive enthivores for removl re wrrnted or re simply the result of ssumed funtionl similrities with invsive ommon rp. The mngement nd restortion of quti eosystems is dependent on understnding how enthivorous fishes intert with wter qulity onditions. Although enthivorous fish speies my often our together t high undne, few studies hve experimentlly evluted the influene of multiple enthivorous speies ommonly found in North Ameri on wter qulity onditions. Moreover, most reserh on the effets of ommon rp (i.e., field oservtions, single-speies experiments) hs foused on smll suset of environmentl ftors (e.g., turidity) or ntive speies not ommonly ssoited with degrded onditions like lk ullhed (e.g., hnnel tfish: Prkos et l., 23). The ojetive of our study ws to identify nd quntify the reltive eologil impts of lk ullhed on quti eosystem hrteristis known to e ltered y ommon rp invsion. We designed mesoosm experiment to exmine the effets of oth ommon rp nd lk ullhed on wter lrity, nutrient onentrtions [totl phosphorus (TP), nitrte (NO 3 - ), nitrite (NO 2 - ), ionized mmoni (NH 4? )], sumerged mrophyte iomss, zooplnkton density, nd mroinverterte undne nd iomss. Bsed on the limited informtion ville of lk ullhed effets on turidity (Brig & Johnson, 23) nd those of speies with similr feeding morphology nd hits (Siluriformes: Cline et l., 1994; Btzer, 1998; Prkos et l., 23), we hypothesized tht lk ullhed would hve redued, if ny, impts on wter lrity nd ssoited nutrient onentrtions reltive to ommon rp. Methods Experimentl mesoosms During the summer of 29, 16 experimentl mesoosms were onstruted t the Iow Stte University Hortiulture Reserh Sttion ( N, W) loted in entrl Iow, USA. Mesoosm size nd dimensions (1.2-m height m dimeter) were seleted to eliminte the influene of wind resuspension on sediments nd ssoited nutrients. Eh mesoosm ws filled with pproximtely 2 m of littorl sediment, plnted with 2 stems of floting-lef pondweed Potmogeton ntns nd.5 m 2 of oontil Certophyllum demersum, nd filled with wter from nery 5-h lke on 19 June 29. Mesoosms were llowed to estlish for 28 dys nd rndomly ssigned to one of four tretments on 16 July 29. Tretments inluded stokings of no fish (i.e., ontrol) nd equl totl iomsses (i.e., pproximtely 1, g) of dult ommon rp, dult lk ullhed, nd the omintion of oth speies (i.e., pproximtely 5 g eh). Eh tretment ws replited four times. Common rp were olleted from Ventur Mrsh, Ventur, Iow, USA ( N, W) nd lk ullhed were olleted from sediment retention wetlnds of Ad Hyden Lke, Ames, Iow, USA ( N, W). Common rp nd lk ullhed used in this study were ± 5.6 (men ± SE) nd ± 3.5 mm in totl length (TL) nd ± 22.4 nd 76.8 ± 5.4 g in weight, respetively. Fishes were rndomly ssigned to tretments until the pproximte iomss (i.e., 5 or 1, g) ws otined for eh speies. Men totl fish iomss stoked in mesoosms ws 1,75.9 ± 19.8 g (4,98. ± 75.3 kg h -1 ). The experiment persisted for 35 dys fter stoking fish. The durtion of the experiment ws sed on the time tht effets of enthivorous fish were oserved in omprle study (Prkos et l., 23). Wter nd zooplnkton were smpled two to three times weekly from the week prior to fish stoking until the end of the experiment (2 August 29). Susurfe 1-L wter smples were olleted from eh mesoosm two to three times weekly to mesure turidity (nephelometri turidity units; NTUs) nd onentrtions (lg/l) of hlorophyll (hl-), TP, NO 3 -,NO 2 -, nd NH 4?. Wter smples were stored on ie in opque ontiners nd trnsported to the lortory for nlysis within 1 h of olletion. Anlyses of TP, NO 3 -,NO 2 -, nd, NH 4? onentrtions were onduted using HACH DR/3 spetrophotometer (HACH Compny, Lovelnd, CO, USA) nd stndrd wter nlysis methods (APHA, 25). Turidity ws mesured with HACH 21P turidimeter (HACH Compny, Lovelnd, CO, USA). A susmple of 2 ml ws filtered through.7-lm Whtmn GF/F filter (Whtmn Interntionl, Midstone, UK). Chlorophyll ws extrted with 9% etone solution nd sorne ws red using n Agilent 8453 spetrophotometer (Agilent Tehnologies, In. Snt Clr, CA, USA) to determine

4 19 Hydroiologi (213) 711: hl- onentrtions. Zooplnkton smples were olleted weekly using vertilly integrted PVC tue smpler (dimeter 5 m, length 8 m), filtered through 8-lm mesh, nd preserved in 95% ethnol. Zooplnkton were identified to fmily for Arthropod (i.e., Cruste, Dipter) nd to phylum for Rotifer. Benthi mroinvertertes were smpled with n Ekmn dredge (re 225 m 2 ) prior to fish stoking nd on the lst dy of the experiment. For oth smpling events, single enthi mroinverterte smple ws tken from eh mesoosm nd wshed through 5-lm mesh sieve. Smples were preserved in 1% formlin solution nd identified in the lortory to the lowest prtil txon whih ws typilly fmily or order. Terrestril invertertes were grouped seprtely from quti invertertes nd removed from further nlyses. Benthi inverterte iomss ws estimted using sh-free dry mss. Smples were dried for 24 h t 6 C nd shed for 4 h t 5 C. Individul tx nd mesoosms were proessed seprtely. After ompletion of the experiment, mrophytes were olleted from eh mesoosm. The wet weight of mrophytes ws determined for eh speies nd morphologil struture (i.e., stems nd leves, roots) for eh mesoosm y lipping stems nd lef iomss nd sieving root iomss from the sustrte. Sttistil nlysis Repeted mesures (RM) nlysis of vrine (ANOVA) ws used to test tretment effets of wter qulity vriles (i.e., turidity, TP, NO 3 -,NO 2 -, NH 4?, hl-) nd zooplnkton undne mesured from individul mesoosms repetedly (i.e., one to three times weekly) using PROC MIXED (SAS, 28). Akike s informtion riterion for smll smple size (AIC; Hurvih & Tsi, 1989; Burnhm & Anderson, 22) ws used to ompre RM ANOVA models with different ovrine strutures (Littel et l., 22) for eh wter qulity dt set (i.e., turidity, TP, NO 3 -,NO 2 -,NH 4?, hl-) nd zooplnkton tx (i.e., rotifers, opepods, ldoerns). In ddition to the RM ANOVA, one-wy ANOVA ws used to ompre tretment mens within weeks for wter qulity vriles nd zooplnkton undne using Tukey s honestly signifint differene test for multiple omprisons (Tukey, 1949). Tretment effets of vriles mesured pre- nd postexperiment (i.e., iomss of mrophytes nd enthi mroinvertertes nd undne of enthi mroinvertertes) were ompred individully with onewy ANOVA. Dt were nturl log-trnsformed when neessry to meet the ssumption of homogeneous vrines mong tretment groups. All nlyses were performed using SAS 9.2 (SAS, 28) with type I error rte of.5. Results Turidity Men turidity inresed in the presene of fish tretments nd ws onsistent throughout the ourse of the experiment (Fig. 1; Tle 1). Turidity of the ommon rp nd oth-speies tretments ws similr (RM ANOVA; F 1,12 = 2.3, P =.15), ut differed from tht of the ontrol tretment (RM ANOVA; F 1,12 = 341, P \.1; F 1,12 = 4, P \.1, respetively). Men turidity inresed in the ullhed tretment mesoosms reltive to the ontrol tretment (RM ANOVA; F 1,12 = 153, P \.1), ut ws signifintly less thn tht of the ommon rp tretment (RM ANOVA; F 1,12 = 37, P \.1) nd the oth speies-tretment (F 1,12 = 58, P \.1). Nutrient onentrtions Men TP onentrtions inresed in tretments ontining fish, nd no effet of tretment 9 dy intertion ws evident (Fig. 1; Tle 1; RM ANOVA F 21,84 =.71, P =.81). Men TP onentrtions were highest in the oth-speies tretment nd were similr to those of the ommon rp tretment (RM ANOVA; F 1,12 =.57, P =.47), ut were higher thn those of the lk ullhed (RM ANOVA; F 1,12 = 6.4, P =.27) nd ontrol (RM ANOVA; F 1,12 = 42, P \.1) tretments. Men onentrtion of TP for the lk ullhed tretment inresed reltive to the ontrol tretment (RM ANOVA; F 1,12 = 16, P =.19) nd did not differ from tht of the ommon rp tretment (RM ANOVA; F 1,12 = 3.1, P =.1). Tretment effets on men NO 3 - onentrtions vried with time (Tle 1; F 3,12 = 4.4, P \.1). Men NO 3 - onentrtions inresed in ommon rp nd oth-speies tretments ompred to the lk ullhed nd ontrol tretments (Fig. 1;

5 Hydroiologi (213) 711: Turidity (NTU) TP ( µ g L -1 ) Control A. mels C. rpio A. mels + C. rpio d 5 5 NO3 ( µg L -1 ) NO2 ( µ g L -1 ) e 25 f -1 ) NH4 ( µg L Week Chlorophyll ( µ g L -1 ) Week Fig. 1 Turidity (), TP (), NO 3 - (), NO 2 - (d), nd NH 4? (e), nd hl- (f) (men ± SE) from mesoosms over time with no fish (ontrol), nd 1, g of iomss of lk ullhed (A. mels), ommon rp (C. rpio), nd oth speies (A. mels? C. rpio). Week- vlues represent smples tken prior to fish stoking (dshed line). Eh tretment ws replited four times nd vlues with the sme letter were not signifintly different (P \.5; one-wy ANOVA of log trnsformed dt) for within week mens Tle 1). The men onentrtion of NO - 3 ws onsistently highest for the oth-speies tretment (Fig. 1) throughout the experiment, ut similr to tht of the ommon rp tretment (RM ANOVA; F 1,12 =.42, P =.53). The ontrol nd lk ullhed NO - 3 onentrtions were similr (RM ANOVA; F 1,12 = 1.9, P =.2) nd lower thn those of the ommon rp nd oth-speies tretments (RM ANOVA; F 1,12 = 18 39, P B.1). Tretment effets on men NO 2 - onentrtions vried with time (Tle 1; tretment 9 dy intertion; F 33,132 = 4., P \.1). Men NO 2 - onentrtions of the othspeies nd ommon rp tretments were similr (Fig. 1d; RM ANOVA; F 1,12 =.18, P =.68), while

6 192 Hydroiologi (213) 711: Tle 1 Summry results of RM ANOVA used to test tretment effets for limnologi vriles nd zooplnkton undne Vrile Tretment Dys Tretment 9 dy df (Num,Den) F P df (Num,Den) F P df (Num,Den) F P Limnologi Turidity 3, \.1 11, \.1 33, TP 3, ,84 2 \.1 21, Chl- 3,12 3 \.1 5, , NO 3 3,12 19 \.1 1,12 55 \.1 3, \.1 - NO 2 3,12 26 \.1 11, \.1 33, \.1? NH 4 3,12 38 \.1 1, \.1 3, \.1 Zooplnkton Rotifers 3, ,48 13 \.1 12, Copepods 3,12 38 \.1 4, , Cldoerns 3,12 6. \.1 4, \.1 12, Letters indite the ovrine model seleted using Akike s informtion riterion for smll smple size ( uto regressive, ompound symmetry, unstrutured) in the RM ANOVA TP totl phosphorus, Chl- hlorophyll greter thn those of the ontrol nd lk ullhed tretments (RM ANOVA; F 1,12 = 32 45, P B.1). The ontrol nd lk ullhed men NO 2 - onentrtions tretments were similr (RM ANOVA; F 1,12 =.42, P =.53). Tretment effets on men NH 4? onentrtions vried with time (Tle 1; F 3,12 = 3153, P \.1). Throughout the experiment, men NH 4? onentrtions of the oth-speies nd rp tretments were similr (Fig. 1e; RM ANOVA; F 1,12 =.25, P =.63) ut onsistently higher thn those of the lk ullhed nd ontrol tretments (RM ANOVA; F 1,12 = 34 77, P B.1). Chlorophyll Men hl- onentrtions inresed in the lk ullhed tretment (Fig. 1f; Tle 1) ompred to ll other tretments (RM ANOVA; F 1,12 = 39 77, P \.1) nd tretment effets were onsistent for the durtion of the study (Tle 1; tretment 9 dy intertion; F 15,6 = 1.8, P =.56). The men onentrtion of hl- for the oth-speies tretment ws greter thn tht of the ontrol tretment (RM ANOVA; F 1,12 = 6.3, P =.28) nd similr to tht of the ommon rp tretment (RM ANOVA; F 1,12 =.97, P =.35). Aquti mrophytes Below-sustrte mrophyte iomss (i.e., root) ws not influened y experimentl tretment (Fig. 2; ANOVA; F 3,12 = 2.2, P =.15). However, men totl mrophyte iomss (i.e., stems, leves, nd roots) differed mong tretments (ANOVA; F 3,12 = 3.6, P =.45). Men totl mrophyte iomss ws lower in the ommon rp (ANOVA; F 3,12 = 7.5, P =.18) nd oth-speies (ANOVA; F 3,12 = 5.7, P =.35) tretments reltive to the ontrol tretment. Men mrophyte iomss of the lk ullhed tretment ws similr to tht of the ontrol tretment (ANOVA; F 1,12 =.31, P =.59), ut greter thn tht of the ommon rp tretment (ANOVA; F 1,12 = 4.8, P =.49). Mrophyte iomss of the oth-speies tretment ws similr to tht of the ommon rp tretment (ANOVA; F 1,12 =.13, P =.73) nd mrginlly similr to tht of the lk ullhed tretment (ANOVA; F 1,12 = 3.3, P =.93). Zooplnkton omposition Throughout the experiment, zooplnkton omposition ws dominted ([75% of totl zooplnkton undne) y rotifers represented mostly y Brhinonus nd Kertell speies. Copepods were the next most undnt tx smpled (2.8% of totl zooplnkton

7 Hydroiologi (213) 711: Mrophyte iomss (g) 7 Totl; F 3,12 = 3.6, P = Below-sustrte; F 3,12 = 1.2, P =.34 Control A. mels C. rpio A. mels + C. rpio Fig. 2 Post-experiment mrophyte iomss (men ± SE) from mesoosms with no fish (ontrol), nd 1, g of iomss of lk ullhed, ommon rp, nd oth speies (n = 4 per tretment). Vlues with the sme letter were not signifintly different (P \.5; ANOVA of log trnsformed dt) undne) nd were predominntly nuplii (66.5% of totl opepod undne) followed y dult ylopoid nd lnoid opepods (25.7 nd 7.8% of totl opepod undne, respetively). Cldoerns omprised the smllest proportion of zooplnkton smpled (\1%), nd were represented y Bosminide, Chydoride, Dphniide, nd Sidide speies. Men undne of rotifers differed mong experimentl tretments, nd tretment effets were onsistent ross time (Fig. 3; Tle 1; RM ANOVA tretment 9 dy intertion; F 12,48 = 1.9, P =.61). Rotifer undne of the ontrol tretment ws similr to tht of the lk ullhed tretment (RM ANOVA; F 1,12 = 5.6, P =.35), ut mrginlly similr to tht of the oth-speies tretment (RM ANOVA; F 1,12 = 3.6, P =.82). The ommon rp tretment hd higher undne of rotifers thn the oth-speies tretment (RM ANOVA; F 1,12 = 4.8, P =.48) nd the ontrol tretment (RM ANOVA; F 1,12 = 17, P =.15), ut ws similr to tht of the lk ullhed tretment (RM ANOVA; F 1,12 = 3., P =.11). Tretment effets on men opepod undne were onsistent for the durtion of the experiment (Fig. 3; Tle 1; RM ANOVA; F 12,48 = 1.9, P =.52) nd men opepod undne ws higher in ll tretments ontining fish reltive to the ontrol tretment (RM ANOVA; F 1,12 = 56 75, P \.1). Copepod density in the oth-speies tretment ws similr to those in the ommon rp tretment (RM ANOVA; F 1,12 = 1.5, P =.24) nd the lk ullhed tretment (RM ANOVA; F 1,12 =.63, P =.44). Men ldoern undne vried with time for tretments (Fig. 3; Tle 1;RM ANOVA; F 12,48 = 2.5, P =.11). Cldoern undne ws lowest in the ommon rp tretment, whih ws similr to tht of the oth-speies tretment (RM ANOVA; F 1,12 =.6, P =.82). Cldoern density ws highest in the ontrol tretment nd differed from those of the ommon rp nd othspeies tretments (RM ANOVA; F 1,12 = 1 12, P B.78). Cldoern density of the lk ullhed tretment ws similr to tht of the ontrol (RM ANOVA; F 1,12 =.49, P =.5). Benthi mroinvertertes Benthi mroinverterte ssemlges were dominted y Chironomide nd Oligohet, whih omprised 6.6 nd 48.6% of the pre- nd postexperiment densities, respetively. Pre-experiment totl enthi mroinverterte undne did not differ mong tretments (Fig. 4; ANOVA; F 3,12 =.62, P =.61). However, post-experiment men density ws influened y experimentl tretment (ANOVA; F 3,12 = 6.2, P =.87) nd ws highest for the ontrol tretment, whih ws similr to tht of the lk ullhed tretment (ANOVA; F 1,12 =.2, P =.88). Densities of enthi mroinvertertes in the ommon rp nd oth-speies tretments were similr (ANOVA; F 1,12 = 1.7, P =.22) nd were sustntilly lower thn those of the ontrol nd lk ullhed tretments. Similrly, men iomss of mroinvertertes ws similr prior to the experiment (Fig. 4; ANOVA; F 3,12 = 1.3, P =.33), ut differed post-experiment (ANOVA; F 3,12 = 4.3, P =.28). Biomss of mroinvertertes ws highest in the lk ullhed tretment nd ws similr to tht of the ontrol tretment (ANOVA; F 1,12 =.59, P =.46), ut higher thn tht of the ommon rp (ANOVA; F 1,12 = 9.5, P =.94) nd those of the oth-speies (ANOVA; F 1,12 = 6.7, P =.23) tretments. Mroinverterte iomss of the ontrol tretment ws greter thn tht of the ommon rp tretment (ANOVA; F 1,12 = 5.4, P =.39). In ddition, the iomss of mroinvertertes ws similr (ANOVA; F 1,12 =.24, P =.63) for the ommon rp nd oth-speies tretments.

8 194 Hydroiologi (213) 711: Rotifers (no. L -1 ) Copepods (no. L -1 ) Cldoerns (no. L -1 ) Disussion Control A. mels C. rpio A. mels + C. rpio Week Deresed wter qulity (e.g., inresed turidity, inresed NO 3 -,NO 2 -,NH 4?, nd TP onentrtions), redued mrophyte iomss, nd redued enthi inverterte undne nd iomss were onsistently oserved in tretments ontining ommon rp. Additive effets of ommon rp nd lk Fig. 3 Weekly zooplnkton density (men ± SE) from mesoosms over time with no fish (ontrol), nd 1, g of iomss of lk ullhed, ommon rp, nd oth speies (n = 4 per tretment). Week- vlues represent smples tken prior to fish stoking (dshed line). The P vlue represents the signifine of the tretment effet from the RM ANOVA. Vlues with the sme letter were not signifintly different (P \.5; ANOVA of log trnsformed dt) for within week mens Benthi mroinvertertes (no. m -2 ) Benthi mroinverterte iomss (g m -2 ) Pre-experiment; F 3,12 =.62, P =.61 Post-experiment; F 3,12 = 6.2, P =.87 1 Pre-experiment; F 3,12 = 1.3, P =.33 Post-experiment; F 3,12 = 4.3, P =.28 ullhed were not oserved in tht results from the tretment with oth speies were onsistently similr to those of the ommon rp tretment for nerly ll of the ioti nd ioti responses mesured. However, intermedite inreses in turidity nd TP onentrtions ourred for the lk ullhed tretment reltive to ontrol onditions nd those ontining ommon rp nd likely resulted in elevted hl- onentrtions. Therefore, the eologil impts of lk ullhed reltive to ommon rp do not seem to wrrnt their trget for removl during the restortion nd mngement of quti eosystems. Furthermore, the results of our experimentl study orroorte other reserh tht hs evluted the effets of ntive fishes tht oupy similr eologil nihe to tht of ommon rp (e.g., rown ullhed, hnnel tfish: Cline et l., 1994; Btzer, 1998; Prkos et l., 23) nd re likely the result of differing mehnisms for Control A. mels C. rpio A. mels + C. rpio Fig. 4 Pre- nd post-experiment enthi mroinverterte density () nd iomss () (men ± SE) from mesoosms with no fish (ontrol), nd 1, g of iomss of lk ullhed, ommon rp, nd oth speies (n = 4 per tretment). Vlues with the sme letter were not signifintly different (P \.5; ANOVA of log trnsformed dt)

9 Hydroiologi (213) 711: disturne etween ommon rp nd lk ullhed. Like mny enthi fish speies, ommon rp nd lk ullhed possess dpttions tht re enefiil to loting prey in enthi hitts. However, differenes in the oserved responses of ioti nd ioti vriles for tretments ontining lk ullhed nd ommon rp were possily ttriuted to morphologi nd ehviorl differenes etween the speies ssoited with feeding. Speifilly, ommon rp rely on the sution of enthi sustrtes with protrusile mouth to filter prey from lrge volumes of wter nd inorgni prtiles with their gill rkers (Siing, 1988). In ontrst, lk ullhed hve terminl mouth struture, nd similr to mny tfish speies (Siluriformes), rely hevily on gusttory orgns (i.e., tste uds) tht re present on the epidermis of the ody nd rels to lote prey (Prker, 191; Hr, 1994). Therefore, ommon rp re less disriminte feeders thn lk ullhed nd hve greter potentil to physilly suspend enthi sediments, therey inresing ville nutrients nd ontriuting to ltered physil sttes of quti eosystems. The lrger dult size of ommon rp is lso ruil to the pility of uprooting quti mrophytes while tively forging for prey. Blk ullhed did not lter rooted mrophyte iomss in the experiment nd therefore should not e onsidered nuisne to lerwter, mrophyte-dominted sttes of shllow quti systems. Thus, our omprison of two enthi omnivores demonstrted dissimilr eosystem effets tht were likely the result of differenes in morphology nd feeding ehvior. Common rp n inrese nutrient onentrtions in the wter through exretion, resuspension of sediments into the wter olumn, or the relese of nutrients used y the destrution nd resulting dey of quti mrophytes (Crpenter & Lodge, 1986; Qin & Threlkeld, 199; Breukelr et l., 1994; Chumhl & Drenner, 24). As suh, numerous experimentl nd oservtionl studies hve demonstrted inresed nutrient onentrtions ssoited with inresed ommon rp iomss (e.g., Lougheed et l., 1998; Chumhl et l., 25; Mtsuzki et l., 27; Roozen et l., 27). In the present study, tretments ontining ommon rp onsistently inresed NO 3 -, NO 2 -, nd NH 4? onentrtions ompred to ontrol onditions. Blk ullhed, however, hd no effet on inresed NO 3 -,NO 2 -, nd NH 4? onentrtions intermedite to those of ontrol nd ommon rp tretments for the durtion of the experiment. The oserved ptterns of nutrient onentrtions in the ontrol tretment supported the effets used y ommon rp tivity in oth tretments ontining ommon rp. Speifilly, onentrtions of nitrogen omponents (i.e., NO 3 -, NO 2 -,NH 4? ) onsistently deresed over time in the ontrol tretment, suggesting uptke y quti utotrophs (i.e., mrophytes, phytoplnkton) nd denitrifition. Therefore, inresed nitrogen onentrtions in tretments ontining ommon rp my hve een ttriuted to limited mrophyte uptke resulting from uprooting nd eventul relese of sequestered nutrients y deying vegettion (Crpenter & Lodge, 1986). Despite dereses in NH 4? in weeks one through three, NH 4? onentrtions inresed in ll tretments ontining fish during weeks four nd five. This inrese ws likely the result of inresed NH 3 through exretion in losed mesoosms stoked with high iomss of fish. Pre-experiment TP onentrtions in mesoosms were eutrophi (pproximtely 9 lg l -1 ), whih ws similr to those reported y Prkos et l. (23). Prkos et l. (23) oserved intermedite inreses in TP onentrtions ssoited with hnnel tfish nd suggested tht enthi fishes tht distur the sediment less thn ommon rp my inrese phosphorus primrily through exretion. Similr to Prkos et l. (23), we oserved intermedite inreses in TP ssoited with lk ullhed ompred to the ontrol nd tretments ontining ommon rp (i.e., ommon rp nd oth-speies tretments). However, we do not know if inresed TP in lk ullhed tretments over ontrol onditions in our experiment ws the result of the physil disruption of sediments or exretion. Inresed hl- onentrtions were not oserved in tretments ontining ommon rp. This ws in ontrst to other studies tht hve found tht ommon rp n inrese phytoplnkton undne (using hl- onentrtions s surrogte for phytoplnkton densities; reviewed y Chumhl & Drenner, 24; Chumhl et l., 25; Mtsuzki et l., 29). Similr to our results, Lougheed et l. (1998) did not oserve signifint reltionship etween hl- nd ommon rp iomss despite inreses in TP nd NH 4. In our study, n inrese in men hl- onentrtion for the lk ullhed tretment ws oserved pproximtely 1 week fter stoking nd then persisted throughout

10 196 Hydroiologi (213) 711: the experiment. Low hl- onentrtions in tretments ontining ommon rp were possily used y light limittion resulting from inresed turidity; therey negting the potentil effets of inresed nutrients. Therefore, moderte inreses in TP oupled with light vilility in the lk ullhed tretment my hve resulted in inresed phytoplnkton prodution nd susequent hl- onentrtions, while lso sustining mrophyte ourrene. The indiret effets of enthivorous speies on zooplnkton re omplex nd not well understood. As suh, studies of dult ommon rp-indued effets on zooplnkton densities hve ommonly reported mixed results for vrious tx. For instne, ommon rp presene hs used derese or no hnge in the density of zooplnkton (Qin & Threlkeld, 199; Lougheed et l., 1998; Sidorkewij et l., 1998), wheres inresed density of opepods (Prkos et l., 23; Mtsuzki et l., 29) nd rotifers (Chumhl et l., 25; Mtsuzki et l., 27; Mtsuzki et l., 29) hve een reported. Despite differenes in the hl- onentrtions (i.e., phytoplnkton undne), inresed opepod density ws oserved in ll tretments ontining fish. Inreses in ville nutrients (e.g., TP) n often inrese phytoplnkton undne nd iomss, whih n indiretly inrese undne of zooplnkton grzers (e.g., lnoid opepods). In our study, inresed density of opepods in the lk ullhed tretments my hve resulted from inresed phytoplnkton undne. In ontrst, Prkos et l. (23) ttriuted deresed opepod undne in rp enlosures to redued inverterte predtors (e.g., odontes; Burks et l., 21). Inresed undne of rotifers hs ommonly een ssoited with inresed iomss of ommon rp (Chumhl et l., 25; Mtsuzki et l., 27; Mtsuzki et l., 29). We did not oserve onsistent ptterns of rotifer density mong experimentl tretments, whih ws omprle to previous studies (Lougheed et l., 1998; Roozen et l., 27); however, our smpling used 8 lm mesh nd my hve underrepresented the density of smller rotifers (Chik et l., 21). Despite potentil underrepresenttion of very smll rotifers, the reltive omprison of tretments using the sme methods should remin vlid for rotifers suseptile to smpling with 8 lm mesh. In ontrst to Roozen et l. (27), we oserved inresed ldoern undne in the sene of ommon rp. This my hve een ttriuted to deresed predtion y inverterte predtors (Burks et l., 21; Prkos et l., 23) nd inresed iomss of mrophytes (e.g., refugi; Burks et l., 21) in tretments not ontining ommon rp. Common rp n inhiit mrophyte growth diretly through physil uprooting nd onsumption (King & Hunt, 1967; Crivelli, 1983; Sidorkewij et l., 1996; Hs et l., 27) or indiretly through shding used y inresed turidity (Sidorkewij et l., 1996; Lougheed et l., 1998; Zmrno & Hinojos, 1999; Mtsuzki et l., 27). Chnges in quti mrophytes nd other wter qulity hrteristis due to invsive ommon rp hve een ssoited with deresed iodiversity (e.g., wter irds: Hs et l., 27; Bjer et l., 29). In ddition, lrger ommon rp n e more destrutive to mrophytes thn smller individuls (Crivelli, 1983; Sidorkewij et l., 1998; Kloskowski, 211). Therefore, results from our study my not e diretly omprle mong tretments (i.e., differenes in sizes of ommon rp nd lk ullhed) despite equl iomss stokings. However, the smller verge dult size of lk ullhed ( mm TL; Beker, 1983) would suggest limited effet on uprooting nd destrution of mrophytes reltive to ommon rp ( mm TL; Beker, 1983) in nturl systems. In ddition, indiret effets suh s sediment resuspension n e prtiulrly inhiitive to mrophyte growth. In study evluting the reltionship etween wter lrity nd mrophyte diversity of shllow wetlnds, Lougheed et l. (1998) oserved speiesrihness threshold of 2 NTU for mrophytes. Systems with turidity ove 2 NTU onsistently ontined fewer thn five sumerged mrophyte speies tht were tolernt of high turidity (e.g., sgo pond weed Potmogeton petintus), wheres less turid systems hrored diverse mrophyte ssemlge (up to 15 speies). Similr to results reported y Brig nd Johnson (23), we did not oserve inresed surfe turidity ove pproximtely 2 NTU in the lk ullhed tretment, despite greter iomss densities in our experiment (4, kg h -1 ) ompred to their study (2,438 kg h -1 ). In ddition, no differene in mrophyte iomss ws oserved etween ullhed nd ontrol tretments. It should e noted tht our experiment evluted the impts of oth speies on estlished mrophytes, nd further reserh is required to understnd how ntive enthi omnivorous fish speies impt the emergene of

11 Hydroiologi (213) 711: mrophytes. Therefore, our results suggest tht even t high density, the potentil indiret nd diret effets of lk ullhed tivity on estlished quti mrophytes do not pper to e eologilly signifint ompred to those oserved for ommon rp. Although the primry ojetive of our study ws to experimentlly ompre the reltive influene of two enthi fish speies, the high iomss of fish nd smll size of the mesoosms re potentil limittions of our study tht wrrnt further onsidertion efore mking inferenes to nturl systems. The iomss of fish used in our study ws limited y the size of ommon rp tht ould e olleted (i.e., pproximtely 5 g), the size of the mesoosms, nd the study design (i.e., equl fish iomss tretments). Wheres iomsses of ommon rp hve een reported s high s 3,144 kg h -1 (Driver et l., 1997) nd densities of 7,7 nd 3,616 no. h -1 for rp\1 nd[1 mm in Austrli, respetively (Reid & Hrris, 1997), iomsses of ommon rp in lenti eosystems of North Ameri re generlly less thn 5 kg h -1 (Crivelli, 1983; Bjer et l., 29). In ddition, our use of high iomss (4,98. ± 75.3 kg h -1 ) my not reflet nturl ggregtions of fishes during forging or spwning euse of the influene of smll mesoosms. However, ommon rp generlly inhit the littorl res of lenti systems (Swee & MCrimmon, 1966; Penne & Piere, 28; Bjer et l., 21) where mrophytes re present nd whole-lke extrpoltions of iomss my serve s onservtive estimte for speies strongly ssoited with littorl res. Although the onditions of our study (e.g., seline wter qulity, zooplnkton, nd mroinverterte ssemlge struture) re refletive of eutrophi onditions, they re likely representtive of the mjority of quti systems (i.e., shllow lkes, smll impoundments) in whih ommon rps indue tstrophi hnges (i.e., stle stte shifts; Jkson et l., 21; Weer & Brown, 211). In shllow quti eosystems where lk ullhed re ntive, the speies my provide prtil monitoring tool for environmentl ssessments. For exmple, high suseptily to smpling methods tht re ommonly used to monitor lenti fish ssemlges (Brown et l., 1999; Hnhin et l., 22; Cuherousset et l., 26) nd popultion hrteristi responses (i.e., inresed undne, deresed mortlity, inresed reruitment, inresed growth) to dereses in environmentl qulity (e.g., Brown et l., 1999; Phelps et l., 25; Mork et l., 29) re hrteristis tht mke lk ullhed potentilly useful inditor of eologil onditions of quti systems. In summry, results of the urrent study imply tht lk ullhed do not strongly ontriute to the deteriortion of wter qulity onditions nd my e viewed s n eologil inditor, rther thn trget of mngement mesures where the speies is ntive. Aknowledgments The uthors thnk S. Bisping, L. Brown, R. Clyton, M. Dzul, C. Hinz, N. Howell, N. Johnson, M. Mork, J. Morris, C. Smith, nd J. Spiegel for their ssistne with the projet. The uthors lso thnk M. Colvin, C. Pukert, S. Diehl, K. Kovlenko, nd five nonymous reviewers for providing useful omments nd dvie on previous mnusript versions. This projet ws supported, in prt, y Iow Stte University, Iow Deprtment of Nturl Resoures, nd Idho Coopertive Fish nd Wildlife Reserh Unit. The Unit is jointly sponsored y the University of Idho, U.S. Geologil Survey, Idho Deprtment of Fish nd Gme, nd Wildlife Mngement Institute. The use of trde, firm, or produt nmes is for desriptive purposes only nd does not imply endorsement y the U.S. Government. Referenes APHA, 25. Stndrd Methods for the Exmintion of Wter nd Wstewter, 21st ed. Amerin Puli Helth Assoition, Wshington, DC. Bjer, P. G. & P. W. Sorensen, 21. Reruitment nd undne of n invsive fish, the ommon rp, is driven y its propensity to invde nd reprodue in sins tht experiene winter-time hypoxi in interonneted lkes. Biologil Invsions 12: Bjer, P. G., G. Sullivn & P. W. Sorensen, 29. Effets of rpidly inresing popultion of ommon rp on vegettive over nd wterfowl in reently restored Midwestern shllow lke. Hydroiologi 632: Bjer, P. G., H. Lim, M. J. Trvline, B. D. Miller & P. W. Sorensen, 21. Cognitive spets of food serhing ehvior in free-rnging wild Common Crp. Environmentl Biology of Fishes 88: Btzer, D. P., Trophi intertions mong detritus, enthi midges, nd predtory fish in freshwter mrsh. Eology 79: Beker, G. C., Fishes of Wisonsin. The University of Wisonsin Press, Mdison. Brig, E. C. & D. L. Johnson, 23. Impt of lk ullhed (Ameiurus mels) on turidity in diked wetlnd. Hydroiologi 49: Breukelr, A. W., E. Lmmens, J. Breteler & I. Ttri, Effets of enthivorous rem (Armis rm) nd rp (Cyprinus rpio) on sediment resuspension nd onentrtions of nutrients nd hlorophyll-. Freshwter Biology 32:

12 198 Hydroiologi (213) 711: Brown, M. L., D. W. Willis & B. G. Blkwell, Physiohemil nd iologil influenes on lk ullhed popultions in estern South Dkot glil lkes. Journl of Freshwter Eology 14: Burks, R. L., E. Jeppesen & D. M. Lodge, 21. Pelgi prey nd enthi predtors: impt of odonte predtion on Dphni. Journl of the North Amerin Benthologil Soiety 2: Burnhm, K. P. & D. R. Anderson, 22. Model Seletion nd Multimodel Inferene: A Prtil Informtion-Theoreti Approh, 2nd ed. Springer, New York. Chn, A. R., The effet of rp on smll lke the rp s dominnt. Eology 1: Crlnder, K. D. & R. B. Moormn, Stnding rop of fish in Iow ponds. Proeedings of the Iow Ademy of Siene 63: Crpenter, S. R. & D. M. Lodge, Effets of sumersed mrophytes on eosystem proesses. Aquti Botny 26: Chik, J. H., A. P. Levhuk, K. A. Medley & J. H. Hvel, 21. Underestimtion of rotifer undne muh greter prolem thn previously ppreited. Limnology nd Oenogrphy-Methods 8: Chumhl, M. M. & R. W. Drenner, 24. Interreltionships etween phosphorus loding nd ommon rp in the regultion of phytoplnkton iomss. Arhiv Fur Hydroiologie 161: Chumhl, M. M., W. H. Nowlin & R. W. Drenner, 25. Biomss-dependent effets of ommon rp on wter qulity in shllow ponds. Hydroiologi 545: Cline, J. M., T. L. Est & S. T. Threlkeld, Fish intertions with the sediment wter interfe. Hydroiologi 275: Crivelli, A. J., The destrution of quti vegettion y rp omprison etween southern Frne nd the United Sttes. Hydroiologi 16: Cuherousset, J., J. M. Pillisson & A. Crpentier, 26. Is mss removl n effiient mesure to regulte the North Amerin tfish Ameiurus mels outside of its ntive rnge? Journl of Freshwter Eology 21: Driver, P. D., J. H. Hrris, R. H. Norris & G. P. Closs, The role of the nturl environment nd humn impts in determining iomss densities of ommon rp in New South Wles rivers. In Hrris, J. H. & P. C. Gehrke (eds), Fish nd Rivers in Stress: The NSW Rivers Survey. NSW Fisheries Offie of Conservtion nd the Coopertive Reserh Centre for Freshwter Eology, Cronull: 298. Egertson, C. J. & J. A. Downing, 24. Reltionship of fish th nd omposition to wter qulity in suite of griulturlly eutrophi lkes. Cndin Journl of Fisheries nd Aquti Sienes 61: Hs, K., U. Kohler, S. Diehl, P. Kohler, S. Dietrih, S. Holler, A. Jensh, M. Niedermier & J. Vilsmeier, 27. Influene of fish on hitt hoie of wter irds: whole system experiment. Eology 88: Hnhin, P. A., D. W. Willis & M. J. Huers, 22. Blk ullhed growth in South Dkot wters: limnologil nd ommunity influenes. Journl of Freshwter Eology 17: Hnhin, P. A., D. W. Willis & T. R. St Suver, 22. Comprison of onurrent trp-net nd gill-net smples for lk ullheds. Journl of Freshwter Eology 17: Hr, T. J., The diversity of hemil-stimultion in fish olftion nd gusttion. Reviews in Fish Biology nd Fisheries 4: Hurvih, C. M. & C. L. Tsi, Regression nd time-series model seletion in smll smples. Biometrik 76: Jkson, Z. J., M. C. Quist, J. A. Downing & J. G. Lrsheid, 21. Common rp (Cyprinus rpio), sport fishes, nd wter qulity: eologil thresholds in griulturlly eutrophi lkes. Lke nd Reservoir Mngement 26: King, D. R. & G. S. Hunt, Effet of rp on vegettion in Lke Erie Mrsh. Journl of Wildlife Mngement 31: Kloskowski, J., 211. Impt of ommon rp Cyprinus rpio on quti ommunities: diret trophi effets versus hitt deteriortion. Fundmentl nd Applied Limnology 178: Kulhnek, S. A., A. Riirdi & B. Leung, 211. Is invsion history useful tool for prediting the impts of the world s worst quti invsive speies? Eologil Applitions 21: Lee, D. S., C. R. Gilert, C. H. Houtt, R. E. Jenkins, D. E. MAllister & J. R. Stuffer, 198. Atls of North Amerin Freshwter Fishes. North Crolin Stte Museum of Nturl History, Rleigh. Littel, R. C., W. W. Stroup & R. J. Freund, 22. SAS for Liner Models. SAS Institute In., Cry. Lougheed, V. L., B. Crosie & P. Chow-Frser, Preditions on the effet of ommon rp (Cyprinus rpio) exlusion on wter qulity, zooplnkton, nd sumergent mrophytes in Gret Lkes wetlnd. Cndin Journl of Fisheries nd Aquti Sienes 55: Mtsuzki, S. S., N. Usio, N. Tkmur & I. Wshitni, 27. Effets of ommon rp on nutrient dynmis nd littorl ommunity omposition: roles of exretion nd ioturtion. Fundmentl nd Applied Limnology 168: Mtsuzki, S. S., N. Usio, N. Tkmur & I. Wshitni, 29. Contrsting impts of invsive engineers on freshwter eosystems: n experiment nd met-nlysis. Oeologi 158: Miller, S. A. & T. A. Crowl, 26. Effets of ommon rp (Cyprinus rpio) on mrophytes nd inverterte ommunities in shllow lke. Freshwter Biology 51: Mork, M. D., S. M. Bisping, J. R. Fisher & M. C. Quist, 29. Popultion hrteristis of lk ullhed (Ameiurus mels) in Iow nturl lkes. Journl of Freshwter Eology 24: Prker, G. H., 191. Olftory retions in fishes. Journl of Experimentl Zoology 8: Prkos, J. J., V. J. Sntui & D. H. Whl, 23. Effets of dult ommon rp (Cyprinus rpio) on multiple trophi levels in shllow mesoosms. Cndin Journl of Fisheries nd Aquti Sienes 6: Penne, C. R. & C. L. Piere, 28. Sesonl distriution, ggregtion, nd hitt seletion of ommon rp in Cler Lke, Iow. Trnstions of the Amerin Fisheries Soiety 137: Phelps, Q. E., M. J. Wrd, C. P. Pukert, S. R. Chipps & D. W. Willis, 25. Bioti nd ioti orreltes with lk

13 Hydroiologi (213) 711: ullhed popultion hrteristis in Nersk Sndhill Lkes. Journl of Freshwter Eology 2: Qin, J. G. & S. T. Threlkeld, 199. Experimentl omprison of the effets of enthivorous fish nd plnktivorous fish on plnkton ommunity struture. Arhiv Fur Hydroiologie 119: Reid, D. D. & J. H. Hrris, Estimtion of totl undne of fish popultions: the lirtion experiments. In Hrris, J. H. & P. C. Gehrke (eds), Fish nd Rivers in Stress: The NSW Rivers Survey. NSW Fisheries Offie of Conservtion nd the Coopertive Reserh Centre for Freshwter Eology, Cronull: 298. Roozen, F., M. Lurling, H. Vlek, E. Krn, B. W. Ielings & M. Sheffer, 27. Resuspension of lgl ells y enthivorous fish oosts phytoplnkton iomss nd lters ommunity struture in shllow lkes. Freshwter Biology 52: SAS, 28. Version 9.2, Cry, NC. Sheffer, M., S. H. Hosper, M. L. Meijer, B. Moss & E. Jeppesen, Alterntive equiliri in shllow lkes. Trends in Eology & Evolution 8: Shrge, L. J. & J. A. Downing, 24. Pthwys of inresed wter lrity fter fish removl from Ventur Mrsh; shllow, eutrophi wetlnd. Hydroiologi 511: Shpiro, J. & D. I. Wright, Lke restortion y iomnipultion: round Lke, Minnesot, the first two yers. Freshwter Biology 14: Siing, F., Speiliztions nd limittions in the utiliztion of food resoures y the rp, Cyprinus rpio: study of orl food proessing. Environmentl Biology of Fishes 22: Sidorkewij, N. S., A. C. L. Czorl & O. A. Fernndez, The intertion etween (Cyprinus rpio L.) nd (Potmogeton petintus L.) under qurium onditions. Hydroiologi 34: Sidorkewij, N. S., A. C. L. Czorl, K. J. Murphy, M. R. Stini, O. A. Fernndez & J. C. J. Domniewski, Intertion of ommon rp with quti weeds in Argentine dringe hnnels. Journl of Aquti Plnt Mngement 36: 5 1. Swee, U. B. & H. R. MCrimmon, Reprodutive iology of rp (Cyprinus rpio L.) in lke St. Lwrene, Ontrio. Trnstions of the Amerin Fisheries Soiety 95: Tukey, J. W., Compring individul mens in the nlysis of vrine. Biometris 5: Whl, D. H., M. D. Wolfe, V. J. Sntui & J. A. Freedmn, 211. Invsive rp nd prey ommunity omposition disrupt trophi sdes in eutrophi ponds. Hydroiologi 678: Weer, M. J. & M. L. Brown, 29. Effets of ommon rp on quti eosystems 8 yers fter rp s dominnt : eologil insights for fisheries mngement. Reviews in Fisheries Siene 17: Weer, M. J. & M. L. Brown, 211. Reltionships mong invsive ommon rp, ntive fishes nd physiohemil hrteristis in upper Midwest (USA) lkes. Eology of Freshwter Fish 2: Zmrno, L. & D. Hinojos, Diret nd indiret effets of rp (Cyprinus rpio L.) on mrophyte nd enthi ommunities in experimentl shllow ponds in entrl Mexio. Hydroiologi 48: Zmrno, L., M. Sheffer & M. Mrtinez-Rmos, 21. Ctstrophi response of lkes to enthivorous fish introdution. Oikos 94: