High rate of prey consumption in a small predatory fish on coral reefs

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1 Corl Reefs (1) 31: DOI 1.17/s z High rte of prey consumption in smll predtory fish on corl reefs W. E. Feeney O. M. Lönnstedt Y. Bosiger J. Mrtin G. P. Jones R. J. Rowe M. I. McCormick Received: June 11 / Accepted: 14 Ferury 1 / Pulished online: 11 Mrch 1 Ó Springer-Verlg 1 Astrct Smll piscivores re regrded s importnt regultors of the composition of corl reef fish communities, ut few studies hve investigted their predtory ecology or impct on ssemlges of juvenile fishes. This study investigted the forging ecology of common corl reef predtor, the dottyck Pseudochromis fuscus, using underwter focl niml oservtions. Oservtions were conducted t two times of yer: the summer, when recruit fishes were n ville food item nd winter, when remining juveniles hd outgrown vulnerility to P. fuscus. During the summer, P. fuscus directed 76% of its strikes t invertertes nd 4% t recruiting juvenile Communicted y Biology Editor Dr. Stephen Swerer Electronic supplementry mteril The online version of this rticle (doi:1.17/s z) contins supplementry mteril, which is ville to uthorized users. W. E. Feeney Evolution, Ecology nd Genetics, Reserch School of Biology, Austrlin Ntionl University, Cnerr, ACT, Austrli W. E. Feeney O. M. Lönnstedt Y. Bosiger G. P. Jones R. J. Rowe M. I. McCormick School of Mrine nd Tropicl Biology, Jmes Cook University, Townsville, QLD 4811, Austrli W. E. Feeney O. M. Lönnstedt Y. Bosiger G. P. Jones M. I. McCormick (&) ARC Centre of Excellence for Corl Reef Studies, Jmes Cook University, Townsville, QLD 4811, Austrli e-mil: mrk.mccormick@jcu.edu.u J. Mrtin Deprtment of Resources Fisheries, Berrimh, NT 88, Austrli fishes. When striking t fishes, P. fuscus exhiited two distinct feeding modes: n mush (6% successful) nd pursuit mode (5% successful). Predtor ctivity in the field peked t middy, verging.5 cptures h -1 of juvenile fishes. Monitoring of ctivity nd forging in the lortory over 4-h periods found tht P. fuscus ws diurnl predtor nd ws ctive for 13 h d -1 during the summer. The numer of hours during which forging ws recorded differed gretly mong individuls (n = 1), rnging from 4 to 13 h. The numer of predtory strikes did not increse with stndrd length, ut the success rte nd consumption rte of juvenile fishes did increse with size. Estimted hourly mortlity on juvenile fish rnged from.49 fish h -1 in smll P. fuscus individuls (3 39 mm stndrd length, SL; equting to 6.3 per 13 h dy) to.4 fish h -1 in lrge P. fuscus individuls (55 65 mm SL; 3.6 per 13 h dy). During the winter, P. fuscus struck t invertertes with similr rte to the summer period. These oservtions of the predtory ecology of P. fuscus support the hypothesis tht in corl reef systems, smll piscivores, ecuse of their high metolism nd ctivity, re proly importnt regultors of corl reef fish community composition. Keywords Predtion Corl reef fishes Mesopredtor Recruitment Piscivore Digestion rte Introduction Predtion is fundmentl driver of mny ptterns in ecologicl nd evolutionry time (Lim nd Dill 199; Verdolin 6; Johnson nd Hixon 11). The ctivity of predtors influences mny spects of the ecology of prey popultions including undnce ptterns (e.g. Almny 4; Berger nd Gese 7; McCormick nd Meekn

2 91 Corl Reefs (1) 31: ; White et l. 1), ctivity schedules (e.g. Mukherjee et l. 9; Stroe et l. 11), species composition (e.g. Almny et l. 7; Stllings 9) nd the distriution of phenotypic chrcters (e.g. O Steen et l. ; Fuimn et l. 6; Gglino et l. 7; Holmes nd McCormick 9; Johnson nd Hixon 1). The drmtic reduction in the numers of pex predtors in most systems glolly hs encourged reserchers to investigte the role of predtors in determining nd regulting the composition nd function of communities (Frnk et l. 5; Myers et l. 7; Estes et l. 11). It is well estlished tht pex predtors re importnt components of stle topdown ecologicl systems (Myers et l. 7; Estes et l. 11). However, not ll predtors re pex predtors, nd in most systems, there is lck of informtion on the direct nd indirect roles tht smller predtors ply in influencing ecosystem processes necessry to prmeterise ecosystem models. Recent studies hve found tht these smller, more undnt predtors re importnt elements of stle nd diverse ecologicl systems (Finke nd Denno 4; Nvrrete nd Berlow 6; Elmhgen nd Rushton 7). In corl reef systems, the importnce of smll predtors of juvenile fishes is universlly cknowledged (Crr nd Hixon 1995; Holrook nd Schmitt ; Holmes nd McCormick 1; Beukers-Stewrt et l. 11). Predtordriven mortlity in nïve post-settlement fishes produces n exponentil mortlity schedule, which cn result in over 6% loss of cohort within 48 h of settlement (Doherty et l. 4; McCormick nd Hoey 4; Almny nd Wester 6). These high mortlity rtes re lrgely ttriuted to smll predtory fishes, mking these fishes primry influence over community composition (Connell 1998; Holrook nd Schmitt ; Holmes nd McCormick 1). Despite the ecologicl significnce, few studies hve exmined the feeding ecologies of non-pex predtors (ut see Swetmn 1984; Beukers-Stewrt nd Jones 4; Stllings 9; Côté nd Mljković 1), mking their potentil impct on corl reef fish ssemlges difficult to ssess. A common nd importnt predtor of juvenile corl reef fishes is the dottyck, Pseudochromis fuscus (Beukers nd Jones 1997; Holmes nd McCormick 1). P. fuscus is widely distriuted throughout the Indo-Pcific, extending from Jpn in the north, Sri Lnk to the west, Vnutu to the est nd the southern Gret Brrier Reef to the south (Gill 4). It is gpe limited, moile nd ctive (Mundy et l. 3; Holmes nd McCormick 1), with two geneticlly identicl colour morphs whose function hs een ttriuted to predtory mimicry towrds similrly coloured juvenile dmselfishes (Pomcentride) (Mundy et l. 3; Messmer et l. 5). On some tropicl reefs, P. fuscus cn comprise up to 1% of the totl numer of piscivorous fishes in the corl reef ssemlge (Stewrt nd Jones 1). The present study investigted the predtory ecology of P. fuscus, including diet, forging ehviour nd success in order to determine the potentil impct tht this common smll predtor hs on juvenile reef fish ssemlges. The specific gols were (1) to determine the diet of P. fuscus of different sizes; () to exmine the extent to which P. fuscus ws piscivore, nd how forging chnged through the yer; (3) to document the reltive deployment nd strike success rte of the different feeding modes used y P. fuscus to cpture juvenile fishes; (4) to ssess whether strike rte nd success rte vried with size in P. fuscus; (5) to investigte whether P. fuscus displyed diurnl vrition in predtory ctivity; (6) to determine the digestion rte of juvenile fishes y P. fuscus; nd finlly, (7) to estimte the potentil dily consumption of juvenile fish y P. fuscus using informtion from ims 3 to 5. Mterils nd methods Study site nd smpling for stomch contents All dt were otined t Lizrd Islnd (14 4 S, E), northern Gret Brrier Reef, Austrli. Fishes typiclly recruit t this loction during the summer (Octoer through to Ferury). Fifty-six P. fuscus (39 8 mm totl length, TL) were collected from the shllow fringing reef round Lizrd Islnd in Decemer 1994 using solution of the nesthetic quinldine nd ethnol nd hnd net. Fish were euthnized y pithing, nd their gut cvities were injected with 1% formlin. In the lortory, the gut ws removed from the preserved limentry trcts nd contents identified to rod txonomic level. Field ehviourl oservtions Behviourl oservtions were conducted on the shllow reef ( 4 m) surrounding Lizrd Islnd in Decemer 9 (fish recruitment seson; C) nd August 1 (non-recruitment seson; C). During the recruitment period, individul P. fuscus (1 yellow nd 1 rown colour morphs) were oserved for periods rnging from 55 to 75 min (men ± SE = ± 1.6 min, totl 1,33 min). Due to logisticl constrints, oservtions were performed etween 8 nd 17 hours. During the smpling episode in the non-recruitment period, 3-min oservtions were undertken on 6 P. fuscus (13 of ech colour morph). On entering study site, detiled serch of the hitt ws undertken, nd the first P. fuscus locted ws oserved t minimum distnce of m (similrly to Côté nd Mljković 1). This distnce cused no pprent

3 Corl Reefs (1) 31: distress to the fish, nd fish ppered to ehve normlly (s per Swetmn 1984). As these fish re territoril, the sme site ws not visited more thn once to mintin replicte independence. The totl length nd stndrd length (TL nd SL) of ech fish were estimted y noting the position of the tip of the snout, end of the hyurl plte nd the end of the cudl fin reltive to points on the sustrtum nd then mesuring these to the nerest 5 mm. For ech focl individul, oservers noted the ehviour nd predtory ecology of P. fuscus. All strikes nd their success were recorded together with the prey type they were directed towrds. Strikes directed t sustrtum were clssed s eing directed towrds invertertes. Alge ws never oserved in gut smples, ut rther smll crustcens, molluscs nd fishes (see gut dt elow). Preliminry oservtions found tht two distinct feeding modes were used when striking t juvenile fishes: mush nd pursuit feeding modes. Amush feeding strikes were defined s feeding strikes directed towrds recruit fish where it ws ovious to the oserver tht the recruit ws not wre of the ttcker s loction prior to the feeding strike. Pursuit feeding strikes were defined s feeding strikes directed towrds recruit fish where it ws ovious to the oserver tht the recruit ws wre of the loction of the predtor prior to the feeding strike. If the P. fuscus hd juvenile fish in its mouth, or if the juvenile fish ws chsed into rock crevice nd it did not emerge within 3 min, the ttck ws considered successful (s per Swetmn 1984). The ltter represented out 5% of strikes tht were recorded s successful. To enle the exmintion of the diurnl vrition of strike rte t fish nd success for P. fuscus, the field oservtions were undertken over three time periods during the recruitment smpling period: morning (8 11 hours; n = 6), middy (11 14 hours; n = 6) nd fternoon (14 17 hours; n = 8). To exmine whether size influenced strike success, individuls were seprted into 3 size clsses: smll (3 39 mm SL; n = 6), medium (4 54 mm SL; n = 6) nd lrge (55 65 mm SL; n = 8). Lortory oservtions of diel ctivity ptterns Ten P. fuscus were cptured using n nesthetic clove oil/ lcohol/sltwter solution nd hnd net on SCUBA round Lizrd Islnd during Mrch 11. Following cpture, individuls were trnsported to the reserch sttion nd plced into 16-L quri to cclimte for minimum of 4 h. While cclimting, fish were fed it squid once dily t rndom time. Oservtion filming ws conducted in purpose-designed 18-L PVC predtor prey tnks ( cm), with 7.5-L ( cm) predtor comprtment nd 6-, 1.5-L ( cm) prey comprtments (Pomcentride). Comprtments were seprted y Perspex to llow predtors nd prey to oserve ech other without physicl interction nd hd -cm lyer of snd on the ottom. Ech predtor comprtment hd one plstic tue (*1 cm long 9 4 cm dimeter) plced in the centre of the comprtment to provide shelter. A smll Pocillopor hrd corl (pproximtely cm) ws plced t the ck of ech prey comprtment to crete shelter for prey. To ensure tht predtors received oth visul nd olfctory cues of prey, 3-L heder tnk contining prey fish (Pomcentride) delivered erted sewter into the predtor prey tnk. Predtor prey tnks were situted outside to insure tht predtors could ccess ll potentilly necessry temporl cues (e.g. sun position, temperture). Sunrise nd sunset were t pproximtely 6 nd 183 hours, respectively. Wter temperture within the quri verged 8. C over the study period. One P. fuscus ws trnsferred to the predtor chmer, nd prey (recruit dmselfish) were trnsferred to ech prey chmer 4 h prior to the strt of filming. Ech P. fuscus ws filmed for 4 h using digitl colour infrred cmer. P. fuscus were fed prior to trnsfer to the predtor prey tnk ut not during experimenttion (48 h) to control for feeding ssocited vritions in ehviour. Predtors were relesed into predtor prey tnks t one of two different times of the dy (13 hours or 16 hours). Predtors were thus t their mximum hunger level t one of two different times. Prey fish in prey comprtments nd in the heder tnk were fed Artemi twice dily, nd cre ws tken to rndomise feeding times to ensure tht incresed predtor ctivity ws not due to the feeding of prey. The ctivity schedule of P. fuscus over 4-h period ws mesured from the videos y ssessing ctivity in 1-min lock per hour. Preliminry investigtion suggested tht 1 min gve n ccurte representtion of ctivity rtes in 1-h period. Activity rtes were then extrpolted to estimte totl ctivity during ech 1-h period. Forging rte nd ctivity level were recorded for P. fuscus throughout the 4-h period. Forging rte ws recorded s the totl numer of strikes t prey comprtments per time period. A predtory strike ws distinguished from norml motion y speed (movement greter thn.5 ody lengths per second) together with noticele C- or S-strt (Domenici nd Blke 1997). Activity ws recorded s the time spent swimming. Digestion rte Eleven P. fuscus were cptured using quinldine/lcohol nesthetic solution nd hnd net off the reef flt surrounding Lizrd Islnd during Decemer 1994 (men length = 51.4, rnge mm SL). Individuls were trnsferred to seprte quri with flow-through sewter

4 91 Corl Reefs (1) 31: Tle 1 Description of index used to ctegorise levels of digestion for Pseudochromis fuscus Digestion ctegory (t 8 C) nd shelter nd llowed to cclimte nd evcute their guts for 1 h. Fish were then given live or recently euthnized recruit dmselfish (Dischistodus perspicilltus, Pomcentrus coelestis or Pomcentrus wrdi; men size 13 mm SL) s their only prey. The time of feeding ws recorded, nd the P. fuscus were killed t vrious time intervls fter feeding (.5 h n = 3, 1 h n = 3, h n = 3, 4 h n = ). The stomch contents were dissected out, nd fish prey ssigned to one of 6 digestion ctegories, rnging from fresh remins (ctegory 1) to n empty stomch (ctegory 6) (Tle 1). Sttisticl nlysis Description 1. Fresh Little or no digestion, pprently recently ingested. Minor digestion 3. Moderte digestion 4. Mjor digestion 5. Advnced digestion 6. Stomch empty Superficil surfces digested. Length mesurements of prey possile Body mostly digested, flesh showing myomeres. Length mesurement possile only s estimte Body roken down into pieces of one nd flesh Some hrd structures nd smll frgments of flesh only Stomch lining clen or contining mucus only To test whether the strike rte (per hour) t invertertes nd totl numer of strikes were similr etween recruitment nd non-recruitment smpling periods, two one-fctor ANOVAs were conducted. One fish during the recruitment seson tht hd ite rte t invertertes much higher thn the rest (143 strikes h -1 ) ws excluded from these nlyses s sttisticl outlier (Gru s test, p \.5). This fish ws not excluded from other nlyses tht did not involve this vrile ecuse of the smll dtset. To investigte whether strike rte nd cpture rte differed etween mush nd pursuit feeding modes, pired t-tests were used. Unequl vrinces etween the feeding modes for cpture rte necessitted the use of Sign test. We used one-fctor ANOVA to test whether strike nd success rtes of P. fuscus for juvenile fish were influenced y time of dy (morning, middy nd fternoon) or predtor size (smll, medium nd lrge). The nture of significnt differences found for time of dy nd size were further exmined with Tukey s HSD mens comprison tests. To investigte whether hourly cpture, strike rtes nd cpture rte differed etween the two colour morphs of P. fuscus onefctor ANOVA ws lso employed. Digestion rte ws nlysed using regression nlysis. The ssumptions of homogeneity of vrince nd normlity were exmined y residul nlysis. Hourly consumption of juvenile fishes y P. fuscus ws clculted s the men of the hourly rtes of successful strikes of the oserved individuls during the recruitment smpling period. Strike success rte ws clculted for individul P. fuscus s the numer of successful strikes divided y the totl numer of strikes within the oservtion period stndrdised to 1 h. Men strike success rte ws the rithmetic verge of the individul strike success rtes. To clculte n estimted dily consumption on juvenile fishes, differences in strike success with time of dy were tken into ccount. Overll, dily cpture estimtes were clculted for three forging dy lengths: 13 h (representing totl dylight hours in Decemer 9: sunrise 545 hours, sunset 1845 hours; the three time intervls used for clcultion eing hours; hours; hours); 4 h (representing the minimum numer of hours one lortory fish ws found to strike; llocted for clcultion s 3-h middy nd 1-h fternoon); 9.7 h (the men numer of hours lortory fish ws found to strike; llocted for clcultion s 3.35-h morning, 3-h middy nd 3.35-h fternoon). For dily consumption estimtes, 95% confidence limits (CL) were determined y summing the vrinces of the three time periods (morning, middy nd evening), clculting stndrd error nd multiplying this with Student s t vlue t n - 1 degrees of freedom. Results Diet of Pseudochromis fuscus Of the 5 fish tht contined food items (4 were empty), 5.% contined fish tissue, 3.7% fish scles, 84.6% contined crustcen remins (including 9.6% tht contined crs) nd 7.7% contined molluscs. This confirmed tht P. fuscus primrily feeds crustcens nd smll fishes. The smllest P. fuscus found to hve remnnts of fish (scles) in its guts ws 36 mm SL, though only 3 fish were smpled tht were smller thn this fish. Sesonl ptterns of forging During the recruitment period, n verge of 3.7% of strikes (rnge, 19.4 h -1 ; men, 1.5 h -1 ) ws directed to juvenile fishes (16 of 91 strikes in.5 h of oservtion). During the non-recruitment period, 99.4% of strikes were mde t invertertes on the sustrtum. The remining strikes out of 364 strikes over 13-h totl oservtion period were mde t recruit dmselfish. P. fuscus mde significntly more totl strikes per hour in the recruitment periods thn in nonrecruitment periods (F 1,43 = 7.96, p =.7), ut there ws

5 C pture rte e Success rt Strike rte Corl Reefs (1) 31: no difference in the numer of strikes directed to invertertes etween periods (F 1,43 =.6, p =.873; men, 7.85 nd 8.5 h -1 for non-recruitment nd recruitment periods, respectively). During the recruitment period, cpture rte nd strike rte per hour nd success rte per strike did not differ etween the colour morphs (F 1,18 =.114, p =.739; F 1,18 =.44, p =.837; F 1,18 =.13, p =.971. n = 1 yellow nd 1 rown, respectively). Feeding modes During ll oservtion periods, ech individul P. fuscus continuously ptrolled the re within its home rnge. In the recruitment period, P. fuscus regulrly moved etween, nd spent time round, res of high juvenile fish undnce (primrily dmselfishes). Upon rrivl in n re of high recruit fish undnce, P. fuscus oserved the locl recruit popultion with miniml disturnce. When possile, it mde strike t fish tht ppered unwre of its loction (mush strike). When the locl juvenile fish popultion ws wre of its loction, either predtory pursuit ensued (pursuit strike) or no strike ws mde, fter which the P. fuscus resumed ptrolling its home rnge. Periodiclly, the fish stopped ptrolling nd mde severl feeding strikes towrds the sustrtum (presumly invertertes on snd, live corl, corl rule or in the wter column) nd then resumed its ptrolling ehviour. Pursuit feeding strikes occurred more often thn mush feeding ttempts (t 1, 19 =-5.18, p \.1; Fig. 1). Amush feeding strikes were found to hve significntly higher success rtes per ttempt thn pursuit feeding ttempts (6 vs 5%; sign test, Z =.7, p =.3; Fig. 1), ut no significnt difference ws found in the overll cptures per hour on juvenile reef fishes etween the two feeding modes (t 1, 19 =., p =.6; Fig. 1c). Field oservtions of diurnl ctivity ptterns Strike rte nd the numer of successful strikes on juvenile fishes differed with time of dy. Strike rte per hour ws highest in the middy period nd lower in morning nd fternoon periods (F, 17 = 4.7, p =.4; Fig. ). This trend ws emphsised in the cptures per hour, with the highest numers of successful strikes per hour occurring round middy (.5 h -1 ; F, 17 = 3.91, p =.4; Fig. c). The proportion of successful strikes per hour did not differ significntly with time of dy (F, 17 =.363, p =.7; Fig. ), lthough mirrored similr trend to the other vriles. Lortory oservtions of diel ctivity ptterns Lortory oservtions over 4-h periods indicted tht P. fuscus ws diurnlly ctive predtor. The distriution of the proportion of the oservtion hour spent moving ws c Amush pltykurtic with n verge of 7% of the time spent moving during dylight hours (Fig. 3). Eight P. fuscus out of 1 showed some swimming ctivity for 13 h, with the remining two were ctive for 15 nd h. Men strike rte showed little pttern within dylight hours given the high levels of vriility mong individuls (Fig. 3). Individul fish showed mrkedly different periodicities in strike rte throughout dylight hours (Fig. 4), rnging from imodl signture of eing most ctively striking in the erly morning nd evening (Fig. 4), through to eing ctive for very restricted period of time round middy (Fig. 4). Four fish struck t prey in 1 of the 13 h of dylight, fish struck in 4 of the dylight hours, while one fish struck over ech of 13, 11, 1 nd 7 h of dylight (men numer hours over 4-h period in which strikes occurred = 9.7 h). Influence of size on strike rte Pursuit Fig. 1 Comprison of two feeding strtegies displyed y Pseudochromis fuscus towrds juvenile reef fishes (per hour; n = ). Numer of strikes; success per strike; c totl numer of juvenile fishes cptured per hour. Mens with stndrd errors re shown Predtor size clss did not significntly ffect P. fuscus strike rte on smll fishes (F, 17 =.96, p =.4; Fig. 5), with

6 Strike rte Cpture rte 914 Corl Reefs (1) 31: Success rte c fish striking t smll prey fish during the recruitment period on verge 1.5 times h -1 (±1.4 SE). There ws no difference in strike success mong size clsses, with success verging 13.1% (F, 17 = 3.41, p =.6; Fig. 5). Lrge individuls hd significntly higher consumption of juvenile fish thn smll individuls (.36 fish h -1,.49 fish h -1, respectively), with medium individuls eing non-significnt nd intermedite etween the two (1.18 fish h -1 ; F, 17 = 6.35, p =.1; Fig. 5c). Digestion rte Time of dy (hrs) Fig. The effect of diurnl time period (8 159 hours, n = 6; hours, n = 6; hours, n = 8) on Pseudochromis fuscus: strike rte success per strike c totl numer of juvenile fishes cptured per hour. Error rs re stndrd error. Letters denote Tukey s HSD grouping (p \.5) Regression nlysis reveled significnt reltionship etween time (h) nd digestion stte of consumed recruit dmselfishes (digestion stte = 1.56?.69 time, r =.5, p \.5), with complete digestion in *6.4 h. Recruit fishes were in the sttes of mjor nd dvnced digestion fter only 4 h. Proportion of time moving Strikes per hour Time of dy Fig. 3 Men diel ctivity ptterns for Pseudochromis fuscus housed in quri with visul nd olfctory ccess to prey cues. Proportion of time per hour spent moving; numer of strikes per hour. Error rs re stndrd errors Dily consumption of juvenile fish popultions The P. fuscus oserved during the recruitment period mde totl of 16 strikes t fishes of which 3 were successful, giving n overll 13.9% strike success rte (13.1% ±. SE clculted s men of individul success rtes). The informtion from the field nd lortory studies of strike rtes fcilittes the clcultion of preliminry estimtes of overll dily consumption rtes. Lortory studies showed tht while ll individuls were ctively swimming during dylight hours (13 h), they struck t prey in the lortory for etween 4 nd 13 h in 4-h period (men 9.7 h, n = 1 fish). Also, oservtions in the field showed tht strike success ws highest round middy. If 13 h of forging is ssumed, then the overll cpture of fish is estimted to e 16.4 juveniles/p. fuscus/ dy (±3.4 CL). Of this, the mush feeding mode ccounted for 11. fishes (±.8 CL, n = ), nd the pursuit mode ccounted for 5. fishes (±1.8 CL, n = ). If minimum of 4 h of forging is ssumed per dy, then consumption is estimted s 8.5 juveniles/p. fuscus/dy (±1.9 CL), while if we ssume men forging ctivity of 9.7 h, then overll cpture rte per dy is 14.4 juveniles P. fuscus -1 dy -1 (±.7 CL).

7 Proportion strikes Corl Reefs (1) 31: Strike rte dy per Success rte of c c Cpture rte Smll Medium Lrge Fig. 5 The effect of Pseudochromis fuscus size (smll, n = 6; medium, n = 6; lrge, n = 8) on: strike rte success per strike c totl numer of juvenile fishes cptured per hour. Error rs re stndrd error. Letters denote Tukey s HSD grouping (p \.5) A significnt reltionship ws found etween hourly consumption of juveniles nd size clss. Lrge individuls hd higher consumption of juveniles per hour thn their smll counterprts (Fig. ). This resulted in n hourly consumption of.49 juveniles ±. SE for smll P. fuscus (6.33 juveniles dy -1 ± 7.3 CL, n = 6), 1.18 ±.49 SE for medium individuls (15.39 dy -1 ± 16.4 CL, n = 6) nd.36 ±.38 SE for lrge individuls (3.6 dy -1 ± 13.6 CL, n = 8). Discussion Time of dy Fig. 4 Diel ctivity ptterns of three (,, c) Pseudochromis fuscus housed in quri illustrting individul vriility in the distriution of strikes t prey over 4-h period While mny studies stte tht mortlity is high for reef fishes immeditely fter settlement (e.g. Hixon 1991; Crr nd Hixon 1995; Cley 1998; Almny nd Wester 6), reltively few studies hve quntified predtion rtes from the point of view of the predtors involved (for some exceptions, see Swetmn 1984; Connell 1998; Holrook nd Schmitt ; Beukers-Stewrt nd Jones 4; Côté nd Mljković 1; Green et l. 11). Estimtes of recruit mortlity within the first 48 h on the reef vry widely, from totl loss to no loss, with one study estimting the verge loss t 56% (Almny nd Wester 6). The present study shows tht Pseudochromis fuscus is smll ctive predtor tht consumes high numer of juvenile fishes when they re ville nd my e responsile for much of the mortlity in the erly juvenile life phse where it occurs. Field oservtions reveled very high cpture rtes, which indicte tht this species my hve mjor influence on the composition of the fish ssemlge tht develops within its hitt. The rtes of prey removl y P. fuscus exceed previous estimte of prey removl rtes y other corl reef predtors tht consume smll nd juvenile fishes. Most informtion

8 916 Corl Reefs (1) 31: on the potentil impct of vrious predtor species comes from gut content nlyses (e.g. Connell 1998; St John 1999, 1). Some studies couple this informtion with gut evcution rtes to otin estimtes of potentil cpture nd consumption rtes (e.g. Mrtin 1994; Beukers-Stewrt nd Jones 4). This method ws used on two rock cod species, known to e common predtors of smll nd juvenile reef fishes, Cephlopholis oenk (.41 fish d -1 ) nd C. cynostigm (.63 fish d -1 ) (Beukers-Stewrt nd Jones 4). Few studies hve used focl niml oservtions in the field to investigte the predtory ecology of smll predtors on corl reefs. Swetmn (1984) followed the lizrdfish, Synodus vriegtus, t the sme loction s the present study. This mush predtor struck t prey on verge 1.7 times h -1, with.14 fish h -1 cpture rte. Overll 11% of feeding strikes were successful with its mush feeding mode. This equted to n verge consumption of 1.8 fish d -1. Côté nd Mljković (1) nd Green et l. (11) followed n invsive popultion of Indo-Pcific lionfish, minly Pterois volitns, in the Bhms in unmnipulted field conditions. This predtor ws oserved to strike t 1.98 juvenile or dult prey fishes per hour nd hd very high success rte of 7%. This resulted in predtion rtes of 1.44 cptures h -1 nd n estimted dily consumption of pproximtely 13 fishes over 1-h dy. The cpture rtes found for P. fuscus in the present study re mong the highest recorded to dte nd re similr to the stonishingly high rtes found for lionfish in the Bhms (Côté nd Mljković 1). P. fuscus employed two distinct feeding modes tht hd very different success rtes: n mush feeding strtegy tht ws successful 7.8% of the time, nd pursuit mode tht yielded 6.9% success rte. Overll, the success rte ws 13.9%. The reltively high feeding success nd high strike rte comined to n verge dily consumption of 16.4 juvenile fishes per P. fuscus over 13-h dy, or conservtively, 8.5 juveniles per P. fuscus over 4-h dy. This is considerly higher estimted impct thn other nturlly occurring predtors of juvenile fishes, with n individul P. fuscus eing potentilly responsile for 5 9 times greter juvenile mortlity thn lizrdfish, nd over 13 times greter mortlity thn individuls of the two rock cods. The high consumption rte in P. fuscus my e fcilitted y high rtes of digestion, high strike rte nd the smll size of prey consumed. Estimtes of digestion times of smll recruits y P. fuscus (6.4 h) re twice tht of Cephlopholis oenk, whose digestion rte ws ssessed using similr methods (*1 h, Beukers-Stewrt nd Jones 4). While the overll strike success rte for P. fuscus ws not much higher thn the lizrdfish (13.9 vs 11%), the strike rte (successful or otherwise) ws 6 times higher (1.5 vs 1.7). Lizrdfish were lso found to consume prey tht were 36% s lrge s themselves, with ech smll fish cptured representing 6% of their ody weight (Swetmn 1984). In comprison, P. fuscus selects for smll recruits (*1.7 mm SL; Holmes nd McCormick 1), which represent only *1.3% of the predtor s ody mss, nd this my fcilitte their higher prey intke. The extremely high consumption rtes for P. fuscus compred to other predtors for which estimtes re ville re surprising nd my e due to the reltively high energy intke tht is necessry to fuel fst metolism. Physiologicl rtes (metolism) scle with power to ody weight (Kleier s lw, Willmer et l. ), so P. fuscus should hve much higher metolism thn the lizrdfish or the two rock cods due to its smller ody mss. Compring lrge individuls cross species, ut limiting them to size tht my still et recruits, would men tht P. fuscus (t 8 mm TL) would hve pproximtely 5 times the metolism of S. vriegtus (t mm TL), 9 times tht of C. oenk (t mm TL) nd 1 times tht of C. cynostigm (t mm TL). Preliminry estimtes of metolism suggest tht they do indeed hve fst metolic rtes (4.3 g fish t 9 C minimum metolic rte 17 mgo kg -1 h -1, mximum 66 mgo kg -1 h -1 ), which is fr higher thn the estimte of 84 mgo kg -1 h -1 for 34 g lionfish (Côté nd Mljković 1). Applying similr clcultions to those used y Côté nd Mljković (1) yields consumption estimtes necessry meet metolic demnds in keeping with our field oservtions:.6 recruits d -1 (when resting) to 1 recruits d -1 (when ctive) (Electronic Supplementl Mteril, ESM Appendix 1). These estimtes reinforce the potentil influence of smll predtors, such s P. fuscus, on the recruit ssemlge. Estimting the direct effect of predtors on prey popultion is difficult due to the rpid nd spordic nture of predtion events. All methods of collecting informtion out the influence of predtors on their prey re inherently ised to vrying degrees. Estimtes sed on the comintions of vriles such s gut contents, digestive rtes, predtor nd prey densities often do not ccount for the error estimtes ssocited with ech component, mking the confidence round estimtes of consumption uncler. Moreover, fishes re often collected for gut contents in non-rndom wy (e.g. sperfishing nd linefishing), hmpering interprettion. Direct oservtions of predtion minimise the need to comine vrinces; however, they ssume tht individuls oserved re representtive of the trget popultion; n ssumption common to ll methods. While ttempts were mde in the present study to rndomly choose focl P. fuscus y undertking intensive serches, the smple my hve een ised towrds hungry individuls if gut fullness ws negtively relted to ctivity levels. This my skew oservtionl dt to individuls tht

9 Corl Reefs (1) 31: re older nd more ctive (e.g. Wilson et l. 1993), who tend to hve higher ite rtes (McCormick nd Meekn 1). Côté nd Mljković (1) found tht feeding ttempts were n order of mgnitude lower for sttionry lionfish thn ctive individuls, emphsising this potentil prolem. Our estimtes of mortlity were somewht improved y exmining individul vriility in ctivity nd strike rte over the diel cycle, ut this cn only e undertken in the controlled nd rtificil environment of lortory. In concert, despite the potentil ises in smpling, our most conservtive estimtes sed on the most inctive fish (who struck t prey in only 4 out of 4 h) still suggest tht P. fuscus my hve sustntil impct on its prey ssemlge (8.5 juveniles d -1 ). P. fuscus is n importnt predtor with strong influence on the community of settling fishes in the hitt it occupies. Not only is it responsile for n extremely high level of juvenile mortlity ut it is lso highly selective. Lortory nd field experiments hve shown tht P. fuscus selects the lrgest recruits immeditely fter settlement, when juveniles re lrgely nive to reef-sed predtors (McCormick nd Meekn 7; Holmes nd McCormick 1). This strong nd selective filter on recruit phenotypes differentilly removes individuls tht hve grown fstest in cohort ecuse in tropicl fishes, these fish tend to e the ones tht settle lrgest (e.g. McCormick 1994). Phenotypic selection y predtors cn drmticlly lter the reltionships etween pre- nd post-settlement growth histories nd the costs nd enefits tht erly life history imposes on post-settlement life (McCormick nd Hoey 4; Hmilton et l. 8; McCormick nd Gglino 9; Grorud-Colvert nd Sponugle 11). Given the gpe limit nd size preference of P. fuscus, smll fish with typicl dmselfish growth trjectory re only susceptile to this importnt mortlity gent for *14 dys. While this is short time in the life of smll fish tht my hve longevity greter thn 15 yers (Chot nd Roertson ), the intensity of mortlity nd selection mens tht ctive mesopredtors hve the ility to drmticlly lter the size of cohorts mong loctions nd through time depending upon their densities nd feeding ctivity. At this life stge, smll chnges in the proportion of individuls surviving cn led to mjor ltertions to the numers reching lter life stges (Houde 1989). In conclusion, the high consumption rte of juveniles fishes during the ustrl summer suggests tht P. fuscus hs the potentil to e n importnt influence on the composition of fishes in corl reef sites it inhits through trgeted predtion on recruit fishes. It is uncler how this potentil influence on the development of the juvenile fish ssemlge is ffected y other predtors tht my compete with P. fuscus. Stllings (8) hs recently shown tht intermedite predtors cn hve strong effects on smll prey through the ehviourl modifiction of smll predtors. Most studies tht exmine predtors focus on lrger, more commercilly importnt species, such s corl trouts (Serrnide) nd snppers (Lutjnide). While these re no dout importnt predtors, the current study highlights tht smller predtors, such s P. fuscus, should not e overlooked. Climte chnge is predicted to reduce reef topogrphy (Mundy et l. 8) nd therefore likely to not just influence shelter sites for prey, ut lso for smller predtors, ltering the fundmentl interctions etween predtors nd prey t crucil life stge. The more we understnd out these smll, highly undnt predtors nd their role in determining species composition of communities nd energy flow, the etter we will e le to predict their response to the environmentl chnges forecst. Acknowledgments We thnk Susnnh Lehy for field ssistnce nd the stff t the Lizrd Islnd Reserch Sttion for logistic support. 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