International Council forthe Exploration ofthe Sea

C.M.1994/L:17, Ref. M~iological Oceanography Committee

- .SALINITY AND TEMPERATURE TOLERANCE LIMITS FOR LARVAL'

SPOTTED SEATROUT, CYNOSCIONNEBULOSUS C.(PISCES: SCIAENIDAE)

by

Sabine AIShiJ.th and R. Gran.t GiJ.J:D.oreHarbor Branch Oceanographic Institution

5600 U.S. 1 North .Fort Pierce, Florida 34946

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Abstract

Salinity and temperature tolerance limits for the estuarine spawning spottedseatrout,. Cyrioscion nebülosus, from the Indian River Lagoon, east Florida,were evaluated by examining egg hatching rates, 24-hour and 2-week larvalsurvival. Laboratory-reared larvae from eggs collected'at known spawning sitesduring 1992 and 1993, spawned at salinities ranging from 24 to 27.5 ppt, wereused for mir experiments. Eggs were exposed to various tcmpcratures (20°, 25°and 30°C) and saliriities (0-50 ppt), covering 33 combinations. At 0-15 ppt cggssank to thc bottom, above 20 ppt eggs floated·to the surface at all temperatures.Tcmperature-salinity influence on hatching success and larval survival sho\vedpoor hatchirig rates at salinitics <10 ppt over all temperatures. Best conditionsfor hatching and 24-hour larval survival were 25 ppt and 30°C. Survival to 24 hwas influenced by both temperature and salinity. Poorest surnval was at 20°Cand 5 Ppt. Temperature was associated with significant differences in 2-weeklarval survival. The lowest temperature (20°C) rcsultcd in reduced survivalrates. Over all conditions highest survival was at 25 ppt and 30 ppt.

Temperature and salinity effect on larval growth rates was significant;growth at 20°C was much slowcr than at 25° or.30°C and vades inversely ,Vithsalinity. At 30°C high cannibillism occurred during postflcxion, rcsulting inincreased growth rates.

INTRODUCTION

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Temperature and salinity are iinport~mt_physical factors controlling the

distributiori of teieosts CHolliday Ül69). Toler~lIice of a broad range of saliriities is, ,I

important for estuarine spawners such a~ spotted seatrout (Cyn~sCion

nebulosus), which are likely to expenence large salinity flucttiations. Spottedseatrout are' distributed throughout the Indian River Lagoon of Fioridal Theyare abundant iri the estuarine environmerit which they use for feeding,spawning aneI as nursery grotind. These flshes seldom move great distancesarid remain within their natal estuary (Moffett 1961; Iversen and Tabb 1962).Planktonic larvae settle to the bottom from the plankton, and groWth thereafteroccurs in shallow \vater over seagrass }jeds (e.g. Pearson 1929; Springer and

Woodbtirn 1960; Tabb 1961; Gilmore 197.7; Brown 1981; Rutherford et al. 1989;

Ches~r and Thayer 1990).Spötted seatrout spawn from early spring to late fall (Mok rind Gilmore i983).

In the Gulf of Mexico, most spawning occurs from early April until late Gctaberwith two seasonal spawriing peaks in spring and summer CMcMichael and

. ., '.'

Peters 1989), whereas in southwest Florida earlier spawning in rriid-March hasileeri reported (Peebles and ToiIey 1988); although Jarinke (1971) suggested thatspawning occurs throughout the year in Everglades Nationai Park. The

seasonal variation in spawning is caused by several as yet undefined biodc and, .' .

abiotic factors which mayaIso influence egg hatching, larval stirvival and" ,. .

growth and consequently juvenile recruitment, the survivors of the larvalperiod.

Spotted seatrout are euryhaline rind occiir in water salinities ranging frorrias low as 0.2 ppt to as high as 75 ppt (HeraId and Strickland 1949; Simmons1957), with highest abundances usually occurririg at intermediate salinities (5­20 ppt, Gunter 1945; 15-35 pp!;; Tabb 1966). Spawnfng salinities, however, areprobably less variable than salinities tolerated by non-spawning adults. Spotted

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seatrotit spa~n iri intermediate to' high salinity waters within the estuary, but

not in brackish waters (PoweIl et al. 1989; Gilmore 1992).Variatioris in environmental factors such as temperatiire and salinity could

affect egg incubation and larvai surnval, and ultimately recrtiitment and year­class strength. For most larval fish, basic biology, including thc cffccts of

environmental factors on survival rind growth, is poorly understood and little is

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kriown about the tipper and lower liniits of terriperature and salinity imd theireffects on survival of eggs and early larVal stages, or on early development and

. growth. Few studies on spotted seatrout, however, have demoristrated optimalsalinity conditions for egg arid yolk sae larval survival to be 28.1 ppt at 28°C(TanigUchi 1981) anei both upper and iower salinity tolerance limits showed anage-linked pattern, decreasing to a miriimum tolerance range (6.4 to 42.5 ppt) atage 3 days after hatching at 28°C (Banks et aL :1."991).

The present study ori temperatllre and salinity effeets on spottrid seatroutlarval sUrVivai and growth was carried out to increase our know1E:~dge ofenvironmental tolerances arid habitat needs of recruits in their naturalenvironment. The impact of temperature and salinity changes in estuarine. ,

systems upon flsh populations reeruitment is complcx. In order to quantifysome of the parameters irivolved in response to such environmentai fluxes, ihisinvestigatfon had the following objectives: (1) to deterrriine egg and larval·mortality levels under various coritrolled salinity and temperature regimes; and(2) tb 'determine temperature and salinity effects on larval groWth. The rangesof temperature (20° - 30°C) and saiinity (0 - 50 ppt) selected for our experimentsare representative of condftions occurring in coastal waters during thespawning period.

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MATERIAL AND METHODS

Spotted seatrout eggs were coIiected dtiring the spawning seasons 1992 and1993 with a1 meter diameter ring plankton riet (335 Jlm) from surface waters attwo of the most productfve spawriing sites in the indiari River Lagoon,

e Iritracoastal Waterway Marker # 80 in Wabasso and # 168 in Vero Beach (seeFig.1).

Hydrophones were used to record vocalization of adult male spotted seatroutand to isohite estuadne spawning sites ",hieh then allO\ved eharacterization ofestuarine spawning areas. Adult males produce distfnctive vocalization,starting at Bunset and iasting two to three hours, which are known to beassoeiated with spawning.

Physical oceanographic parameters at the piincipal spawning site weremoriitored continuotisly with a submerged hydrolab unit and currerit meters..Furthermore, oceanographie parameters such as surface temperature, salinity

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and dissolvcd oxygen were studied at each hydroacoustic and planktonic ~tiition, t

With portable field gear. ILaboratory-reared larvae from spotted seatrout eggs sIniwned at salinities

ranging froin 24 ppt tO 27.5 ppt imd tempcratures from 27° to 29°d ware ulsed forour experiments. On arrival in the laboratory, the livhig ichthyoplknktonsampIes were inimediately sörted under th,~ microscöpe and thc fe~tilizeci

planktonic eggs transferred by pipette to thc' experimental tanks. Eggs wereirieu.bäted at'three different temperattircs (20°, 25° arid 30°C) in 20 liter tanks (45

ein diameter,' 20 cm height), each contairiing 100 to 150 eggs, filled With fiiteredseawater of different saJiriities (0 ppt, 5 ppt, 10 ppt, 15 ppt, 20 ppt, 25 ppt, 30 ppt,35 ppt, 40 ppt, 45 ppt and 50 PPt). .Test salinities ware made With fiiteredseawater, dihited with distilled water for hyposaliIiity coriditions. Hypersalineseawater was prcparöd by irictibating tanks for 48 hoürs at 30°C;' thus

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. evaporation resulted iri concentration tri ,approxirriately 550/00. Treatment waterfor t~lerance tests' salinity was adjusted by niixing thc filtered seawater,hypersaÜne water and desÜlled water. Our experimental set-np covered 33different teinperaturc-saliriity conditions, stUcÜöd in duplicates arid. tripliciltes.

Larvae were raised ui> to the secorid week in a separate holding chamber (22. , ,

cni diameter, 10 cm lieight) inside the 20 I tanks. The holding chambers weremade from 300 ~m Nitex net glued to a PVC pipe cylinder; the Nitex netforming thc bottom and the pipe the sides of the container. Aeration wasprovided öutside the holding chamber tri avoici producing turbulence rind bubbleswithiii the chamber but allowing for oxygen diffusiori into the chamber. Duririgthe first week, the water was not ch~mged, except for the addition of smallamoimts of water With tbc food orgariisms.' Duririg the subseqnent weeks, about50% of the water was chariged orice a week. Additiorially, temperatures werechecked claily and maintained within 0.5°;1°C. Salinity ,vas measured dailyusing a iefractometer and adjusted by ad.ding distilled water to theexperimental tanks. Ät 30°C, salinities were adjusted twice a daY.Illumination from fluoicscent room iarrips with a photopenod regime of 12hoürs light and 12 hours darkness was useci.

First feeding hlrvae were fed with cultured algae arid cultnred rotifers(Brachionus plicatilis). After five to seven dayä lai-vae fed on bririe shrimp

Arteinia saliiui~, . ,

LarVal survival at all tcniperature-salinity conditions was estimatcd daily.

Percentage hateh, percentage surVival of the lar-vae to 24 honrs and two week

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survival was calculated to determinc thc irifluencc of tcmpcrature arid salinity.Larvae were samplcd every day for growth measurements during the firstweek, later at irregular intervals, at the foiIowing temperature-salinitycoriditions: 20 0b with 10 ppt, 20 ppt, 30 ppt, 25°C with 10 ppt, 20 ppt, 25 ppt, 30ppt, and 30°C with 10 ppt; 20 ppt and 30 pPt. On each sanipÜng day t()tallerigthsof seven to twelve live larvae were measured.

RESULTS

L influence ofSalinity aoo Temperature on EgglLarval Deveiopment uliderLClbOititoiy Co1ülitioiJs

A. Femlizea eggs :. 0 ·20 hrs. alter ferliüzation: Spotted seatrout eggs enter thcwater "column two to threc h()urs after suriset and spawning activity wasobsen;~d to 2400 hr at tempcratures of 25°C t() 33°C and salinities öf 18 ppt to 33Ppt.Salinity inf7,uence: ·At salinities 0-15 ppt eggs sank to thc bottom; above 20 pptcggs floated to the surface at all tcmpcratures.Temperature. inf7,uence: .Watcr temperaturc affccted hatching time of seati-outeggs: At 25°C hatchirig occurred 18 h()urs after fertilization; whereas at 30°Chatching took place i3 hours after fcrtilization.

B. Hatchiitg jolk scic larvae ·13 ·24 hrs. after fertiliiidion: Spotted seatiOlit yolk.sac hirvae hatch at a mean lcngth of 1.65 rrim TL with unpigmcnted eyes and aciear primordial marginal fin.Salinity intluence on survival: The best concÜtions for hatchirig were salinitiesrariging from 25 ppt to 30 ppt which resuited in 100% hritching (Fig.2). Highersalinities above 45 ppt resulted in relativciyhigh niean liatchfrig ratesof 85-93%liatching, whereas lower saliriities belo\v 10 ppt showcd paor mean hatchingsuccess with 50 to 88.3% (Tab.1). No hatching was obscrvcd at salinity 0 ppt; allcggs dicd ('rrib.1; Fig.2).Temperature influence on survival: Hatching success was affected bytemperature with a lower mEmn hatching rate of 78.6% at 20°C, whereas at 30°Cmeiui hatching success was 85.6% over aii salinity conditions (Tab.i>.

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ITemperature-salinity combination - general impacts: Highar salinities above 45

" , ,ppt resulted' in relatively high maan hatching rates at 25° und 30°C with 90 to97%; whereas at 20°C, eggs seemad to be more sensitive to extreme skIiriity

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conditioris: high hatchirig rates were only observed at salinitif:is rängirig from 10'" .. . !.

ppt to 35 ppt; above 45 ppt mean hatchirig success was only 70%, below ,10 ppt, ,. " I

only 50% hatching was observed (Tab.l). Temperature-salinity influence on, ' I

hatching success and larval survival showed poor hatching rates at salinities<10 ppt over all temperatures and poor hatching rates associated with lowertemperatures (20° to 25°C), (Fig.2).

C. Post-hatch yolk säe larvae - 1 ;'5 days after hcitchiitg: Thc yolk sac stage wascompleted at a tritallerigth of 2.6 mm.

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Salinity influence on survival: Salinity influence on 24-hour larval survivalresulted in highest survival with 100% ä~25 ppt (Tab.l). Salinities ranging from15 to 35 ppt showed relativeiy high maan survival ubove 90%.' IncreasedmoiüiHty was observed at salinitics below 10 ppt with 86.6 to 48.3%. .Above 40 pptmean larval survival decreased from 84.7 tri 71.7% (Tab.l).Temperature influence on survival: Temperature also affected 24-hour larValsuivival:· At low temperature oe 20°C only 73.4% mean survival was observed;whereas liigher. temperatures resulted in higher mean survival rates with 79%at 30°C (Tab.l).Temperature-salinity combination - general impacts: 24-hour larval sUrVivalwas influenced significantly by both temperature and salinity. Lowertemperatures (20° and 25°C) and low salinities (below 10 ppt) were associatcdWith poor survival of thc yolk sae hirvae resultirig in only 50% mean survival.Poorest surVival was at 20°C and 5 ppt with 48.3% maan surviväL The bestconditiöns for 24-h larVal survival ware 25 ppt arid 30°C With up to 100% stirVival .(Tab.l).

D. First-feeding pre-flexion larvae ~ 4 :. 8 days after hatching: First feedingoccurs at 2.6 mm total length. This develolmiental stage is associa.ted with

highast mortality.Salinity influence on survival: Salinity influence on surviväl of first-feeding

larvae showed no significant differences (Figs.3 a-c). Lower saliIiity of 10 pptresulted in lowest survival rates of less than 5% at day five (Fig.3), whereas athigher salinities of 30 ppt iarval survival was higher at day five with 75 tQ'90%

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mean sUrVival and high rnortliÜty took place iater at eight to ten days afterhatching (Figs. 3a-c). .Temperature in[lw!nce on survival: Temperature affected larval survival atfirst feeding: At 20°C rnean larval suivival was low Witii less than 5% (Fig.3a).At 25°C mean sumval at first-feeding was higher with 28.3% (Fig.3b), whereasat 30°C a rnean surnval rate of 78.3% was observed (Fig.3c).Temperature-salinity combination - generai impacts: . Temperature-salinityinfluence OIi survival of first-feeding hirvae shawed poarest survival of first­feeding larvae at low saÜnities (10 ppt) over all ternperatures and higherrnortaÜties associated with lower ternperatures. Highest mean rnortalities of uptO 93% occiIrred at flve days after hatching at 20°C (Figs. 3a-c).

E. Fiexion iarvae. 15.20 days after hatching: Notochord flexion in spottedseatrout larvae was observed at 6.8 rnrn totallength.SciÜ'!-Üy influence on survival: Salinity influence on 2-week larval survivalresrilted in highest mean survival rates of 14% at 25 ppt, followed by highsurvival of 5.6% at 30 ppt (Tab.1). At lower salinities (20 to 5 ppt) mean larvaisurvival deereased from 8 to 0%. At higher saliriities above 35 ppt only 5.6 to0.3% ofspotted seatrout larvae srimved. No sumval was,observed after 2 wecksat 50 ppt (Tab.l).Temperature in[luence on survival: Temperaturewas assoCiated withsignificarit differences in 2-week larval survivai (Fig.4). The lowest ternperature(20°C) resulted . in lower niean survival rates of only 0.2% at 13 days afterhatching (Tab.1) With no larVal srirvival after 2 weeks (Fig.3a). Highest meansurvival rates were observed at 30°C With 8.3% and at 25°C with 4.5% (Tab.1).

F. LOte larvae aiuljuveniles 22 .25 days after hafching: Metamorphosis to thejuvenile stage occurred in spotted seatrout larvae at 16.3 mm totallength.Salinity in[luence on survival: . Salinity infhierice on postflexional and juvenilespotted seatrout survival at 25 days after hätching showed relatively high rneansurvival rates at 25 and 30 ppt viith up to 9.5%. No major differences wereobserv-ed at 16wer salinities (20 - 10 ppt) with low mean sumval of 0.2% (Figs. 3a­c). No sui'Vival at rnetarnorphosis was observed at salinitics above 35 pPt.Temperature in[luence on survival: At 300 d highest survival rates wereobscrvcd at 20 ppt and 30 ppt which resulted in high rnortality after 25 days

(Fig.3c). No larvae raise<! at 20°C survived over a 30-day penod (Fig.3b). At 25°C

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highest stirnval rates with 20% were obserVed after metamorphosis at 30 ppt(Fig.3b), whereas less than 1% ofthe larvae survived at io and 20 pPt. ITemperature-saliriity combiriätion - general impacts: At 25°C, 30 ppt s'älinity

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resulted in distiilC:t low larval mortality rates with 20% survival over a30-day-, ". I

period. Survival was relatively low at 10 ppt arid 20 ppt, With highest meansurvival rates of 0.5% at 10 ppt, however, lo\y larval sumval wäs obsei-ved atthese salinity conditions.

Ho iii/luenee öfSidinity aiid Temperature onLarväi GroWth umIerLaOO,riltoryCo1ulitions

c. Post-luitch yoik sac liIiVäe -1 :.5eJays fitte.,. hatchl"g:Salinity in/luence on growth: Salinfty influerice on groWth duririg the yolk sacstag~ was not obserVed CFigs. 5a-d). LarVal iEmgths are very ahort at hatching(1.65" "cini' TL) compared to one-day old larVae with 2.52 inm TL at a meangroWth rate of 0.875 mni day-1, correlated with high yolk absorption. However,groWth decreases from day two to daY-five oid larvae from 0.051 to 0.007 mmday.. l and is verY slow untillarvae stärt feeding at a11 saÜriities (Figs. 5a-d).Temperature influence on" growth: Tempcrature was resporisible for theduration of thc yolk sac stage: At 25°C larvae absorbed their yolk Within fivedays after hatChing, their eyes became pigmerited arid the mouth was developed,whereas at 30°C completion of the yolk sac stage takes place after three days.

D. FÜ'st-feeaiiigpre-/leXion ltiTVcie -4 -8days after hatehinij:Salinity in/luence on growth: No salinity fnfluerice on larval groWth rates atfirst feeding was observed (Figs. 5a;.d). •

" .Temperature influence on growth: First feedirig occurs withiri four days after. . .. ,

hatching ät 30°C and up tri eight days after hatching at 20°C.

E. FleXion liiivtie -15 ~ 20 days afterhatchiilg:. , . .

Salinity in/luence ön growth: Salinity influence on growth in flexion Iarvae wassignlticant at higher temperatures of 25° and 30°0' wlth higher growthassociatcd with lower sil1iriities (Tab.2; Figs. 5a-d). At 25°C maan totallerigthsof 5.85 mm ware observed at 10 ppt, whereas at 30 ppt larVae measured only 4.26mm. Lengths mcasurements at 30°C arid 10 ppt have shown mean lrirvai

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lerigths With 12.68 mrn compared to shorter lengths at 30 ppt with only 5.98 mrn, "

(Tab.2).Temperature ilifluence on groUJth: Notochord flexion occurs at 18 days afterhatchirig at 25°C. At 30°C flexion stages were observed at 15 days afterhatching, ",hereas at 20°C flexion occurred after 20 daYs. At this stage highergrowth was correlated significantly with higher temperätures: Highest growthwas obserVed at 30°C (Tab.2; Figs. 5a-d).Temperature:salinity combination - general impacts: Temperature arid saiinitywere associated with signiflcant differences in survival of 2-week-old larVae.Thc best coriditions for 2-week larval survival were at 30°C and saliriity rangesfrom 25 ppt to 30 pPt. Over all 'comiitions highest mean survival was rit 25 pptwith 14% mean surVival (Tab.1).

F. Laie liUVae tiiuijuvenUes 22·25 days alter IUitchiizg:SalinÜy influence on grouith: Salinity effect ori spotted seatrout growth atmctJ~~rphosiswas signÜicant; groWth vades inverselywith saIinity and wasmuch slower at 30 ppt compared to 10 ppt (lfigs. 5a-d).Temperature in{luence on groioth: Metamorphosis to the juvenile stageoccurred 25 days after hatching at 25°C, at 30°C after 22 days. GroWth iricreasedrapidly from flexion to metamorphosis at 25°C, reaching an exponential growthat all temperatures (Figs. 5a-d). Although highest growth rates were shownunder these conditions, high mortaÜty was correlated With high cannibalism atthc end.of the postflexionallarval stage.

DISCUSSION

The irivestigation of tcmperature arid salinity effects on spotted scatroutlarval survival demonstrated that both parameters were impoItarit for 2-weekiarval survivai but not very important for cgg hatching and 24-hour larValsurVival. Spotted seatrout larvae develop successfully to fceding iarvae atsalinities of 15 to 35 ppt. Temperature and salinity effects on egg buoyancydcmonstrated that at O-lli%o eggs sank to the bottoln, above 200/00 egge; floated t()

the surface at a11 tcmperatures. Teniperature-salinity influerice on hatchingsuccess. and larval survival showed paor hatching rates at salinities ~ 10 ppt

over aU teniperattires. Although larVal survival was observed at low salinities

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in thc laboratoi"y; we wöuld expect high mortality of eggs developing ön the

bottom in natural populations. « , I.24-hour larval survival was irinuenced by both temperature and salinity.

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Lower temperaturcs (200 lind 25°C) and low salinities (below 10 ppt) were. I

associatcd With poor surVivaL Best conditions for hatching, 24-hour- arid 2-weeklarval surnval were 25 ppt and 30°C. Tanigilshi (1981) found that eggs could be. .

fertilized at salinities from 5 to 60 ppt, but embryos died after thc 2- to 8-celledstages of de~elopment at 5 ppt and ~ 50 PPt. Hypersalinity (~40 ppt) and atemperature of 20°C adversely affected a redueed hatehing suceess of spottedseatrout cggs (Gray et al. 1991). This study of Gray et ai. i99i eontradiets ourresults and previous ßndings oe Gray and Cohira (1988), who reported 0% hatehat salinities above 45 pPt. Sciaenid eggs ean be affectEid by increased' salinitylevels (MeCarty ct a1. 1986). Studios of temperature and salinity Eiffeets on'spotted seatrout eggs' have focused priinarily on hatehing success, survival, aneigroWth'potential (Tanigushi 1981, Gray anei Colura 1988). Spotted seatrout eggsexpos~d to temperatures ranging from 20 to 32°C died at salinities betweeri 35and·45 ppt (Gray and Colura 1988). Taniglishi found timt saIinities above 50 pptadversely affected development of larVal spotted seatrout. Differences inhatehing suecess may oe due to different methodologies or to mitural variationin the loeal seatrout population.

In this study, spottEid seatrout hirvae dcmonstratEid that temperature andsalinity were assoeiatrid with significant differences in 2-week surviva1. Nolarval survival was ooserved at the lowest temperature (20°C) and at 50 ppt,whereas highest survival rates were at 30°C. Over aIi conditioris highestsurvival was at 25%0. Although relatively few studies have beeil eoneerned Withsalinity effeets on larval spotted seatrout, Taniguehi (1981) reportEid an optimumtemperature of 28.0°C and optimum salinity of 28.1 ppt and predicted 100%survival from 18.6 to 37.5 PPt. Barik~ et al.(1991> demonstrated the efficientosmorcgulation abilities of spotted seatrout larVae, and delimits their narrowesttOlerance range (6.4 to 42.5 ppt), occurring on day 3.

Field da~a provide firm support for spotted seatrout toleranee limits.Estuarine spawners such as spotted seatrout will 1>e subjected to wide rariges iri

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salinity during a long spawning season, however, our studies indieate thatspotted seatrout spawned when tcmperatures range between 25 änd 32°C. Insouth Texas spotted seatrout spawning took place at lower temperaturesbetween 20 and 32°C (Brown-PEiterson Eit al. 1988) and salinities are 30 ppt or

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hfgher (Rice et aL 1988). Arnold et al. (1976) reported spaWning in the laboratoI-y- . . '

at saliriities between 26 and 30 ppt at 26°C. Tucker and Faulkner (1987)documented cond.itions under which Indian liiver spotted seatrout willvoluntary spawn in cäptiVity were toward the high end of the range reported for

.' '- ,natural spawning: 27.7-32.5°C iri 1985 and 28.1-31.9°C in 1986.

Previous field stUdies indicated collections. of larVal spotted seatrout withinthe saliriity Ümits of 8-40 ppt CRutherford et äl. 1986). These values phice. '

seatrout among the more euryhaline sciaenid larvae. .In companson, silverperch (Bairdiella chrysoura) have been collected at salinities vaiying from 2 ­37.4 ppt (johnson i978). Red drum (SCiaenops ocellatus) have been collectedwithin saIinities ranging from 8-35 ppt (Rtitherford et al. 1986) and developsuccessfully to fcedfng larvae at saliriities of 10-40 ppt (Hoit et al. 198i>. Incontrast, the apparently more stenohaline atlaritic croaker (Micropogoniasundulatus) larvae have been captured only on the continentl:l1 shelf at salinitiesof 28:-36 ppt CPowels and Stender i978). Differences in salinity response'could beexpi~i~ed as being pnmadly norigenetic adaptations to the spawning salinity(Kinne i962, Holt et ai. i981). Holt et al. (1981> indicated that red drum eggs

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exposed to different salinities may have been acclim.ated to higher salinities'since salinities were very near the salinities of the maturation and spawningtanks. Altered upper limits to the range tolerated by iarvae from differentspawning saIinities indicated parental and/or early acclimation effects areimporlant (Banks et al. 1991).

Temperature becaniö fncreasingly important· for sUrVival and growth aslarvae develop. Highest 2-wcek hirvai survival was found at 30°C. Spottedseatrout larvae were not able to metamorphose at 20°C; no survival was observedafter 2 weekS. Teniperature and salinity effect ori larval growth rates wassignificant; growth at 20°C was much slower than at 25° or 30°C. Extremelyhigh gröwth rates at 30°C were the resuit of cannibrilism, whicb occurredduring postflexion. Previousiy, carinibalistic behavior was only observed incultured spotted seatrout (Arnold et al. 1978; Tucker 1988), but no evidenceexists, .whetl).er cannibalism occurs in the wiid.

Apparently contradictory results showed salinity efrect on growth which. .

varies inversely with salinity. Thc. question now arises whether highest growthrates are correlated with highest survival rates? Ai:; our studies indicate spotted

... scatrout can more likely adapt to hypcrsalinity conditions (up to 40 ppt) during - ...tbc early larval. stage, but as larvae gl"OW and develop, there is a teridency of

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higher survival at lower saliriities to 10 ppt towards the juvenile stage. Ourprevious stüdies häve shown that spotted seatrout egg diarrieter~ were

" ., .' ." .. Icorielated inversely with. salinities (Alshuth and Gilmore 1993). This mightexpiain different larval growth rates, if totallengths of yolk sac larvae mky also

differ. IOptimal coriditions for·spotted·seatrout eggs arid larirae were found to be at

25° to 30°C tEmiperäture and 20 to 30 ppt salinities. These ranges are veiy nearthe minimu~ and maximum vahies at which wild spotted seatrout eggs and

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larvae have beeri collected in central cast Florida (Alshuth and Gilniore,unpubl.). Indian River Lagoori spotted seatrout spawn froin spririg,~ April­June, to fall, Scptember-October, With principal activity typically occurring inMay/June arid August/September. May/June marks the erid of the c~ol dryseason, water temperatures warm up (morithly means in Indian River Lagoonbetween Sebastiari and St. Lucie Iniets: 25° - 30°C, Gilmore 1977) and salinitiesare niäfine or polyhaline (monthly means in Indian River Lagoon b:etween

. Seba~tian and St. Lucie Inlets: 31 - 35 ppt, ibid.). August/September is the peak. .

of thc wet season when salinities are lowest (monthly means in Iridian RiverLagoon betwecn Sebastian and St. Lucie Inlets: 22 - 30 ppt, ibid~) andtcmpcratures at their annual peak (monthly means in Indian River Lagoonbetween Sebastian and St. Lucie Inlets: 29° - 30°C, ibid.). Subsequentiy,historical mean saliriities range from 22 to 35 ppt and temperatures from 25° to30°C within thc Indiari River Lagoön system during the period spotted s~atrout

spawn~ Field temperatures takeri when plankton tows were made for larVal fishranged from 15.0°C (13 December 1993) to 32.0°C (8 Julyand 4 August 1993),

. .mean of28.3°C, salinities from 12.0 ppt (1 July 1992) to 35 ppt (8 July 1993), meanof25.8 ppt.

Based on these resülts we hypothesize that spotted sEmtrout spawning successand subsequent year-c1ass strength Will be adversely affected by the onset of highwater temperatures.. Our data indicate that a sudden temperattire decrcasefrom 25° to 20°C during the early spawning seasori, which is not unlikely in theIndian. Rivez= Lagoon, will cause high larval Inortality. ~alinity in the natural

situation is likely to fluctuate more rapidly towards brackish than hypersalineconditions during the wet summer season. Thus it is surprising to obserVc that

these larvae show greater ability tri ädapt to hypersaline comiitions dtiring theirearly development than to brackish or lower salinities. On the other hand weorily occasionaIly observed any spawning activity in salinities below 20 ppt

h .•

•

13

(Gilmore 1992) arid this correlates with the adult spawning behavior: soundinvestigations of soniferous spotted seatrout have shown th~lt during salinity

, ,

.declines aduIts usually migiate toward thc ocean inlets for spawning at highersalinities (Gilmore et aI:; in prep.).

. ,..~. '- ,

ACKNOWLEDGMENTS: We would like tri thank John Reimer, CarlosSepulveda a~d Ginny Walker for their help, both in thc field and laboratory.This contrfbutes miscellarieous publication No. 213 to the Harbor BranchOceanographic Instittition~

. .LITERATURE

ALSHUTH, S., GILMORE, R.G. (1993): .. Egg identificatiori, eariy larval. development and ecology of the spotted seatrout, Cynoscion. nebulosus C.

.: '(PISCES: SClAENIDAE). Int. Couric. Explor. Seas; C.M.1993/G:28, Dem;, Fish Cttee., 18 pp..', ,

ARNOLD, C.R., T.D. WILLIAMS, W.A. FABLE, JR., J.L. LASSWELL, W~H.BAILEY (1976): Methods and techniques for spawning arid rearing

: spottedseatrout (Cynoscion nebulosus) in thelaboratOry. Proc. 30th Conf.Southeast. Assoe. Game Fish Comm. 30: 167-178. . ,

BANKS, M.A., G.J. HOLT, J.M~ WAKEMAN (1991): Age-linked changes insalinity tolerance of hlrval spotted seatrout (Cynoscion nebulosus,CuVier). J. Fish BioI. 39: 505-514., , ,

. BROWN, N.J~ (1981): Reproductive biology arid recreational fishery for spottedseatrout, Cynoscion nebi:llosus, in the Chesapeake Bay area; MA Thesis,

. College ofWiIIiam arid Mary"Gloucester Point, VA, 120 pp. , .BROWN-PETERSON, N;, P. THOMAS;. C.R. ARNOLD. (1988): Reproductive

biology of the spottedseatrout, CynosCion nebulosus, iri South Texas.. Fish~ Bull. 86 (2): 373-388. , ., .

CHESTER, A.J.; G.W. THAYER (1990): Distribution of spotted sEmtrout(Cynoscion nebulosus) and gray snapper(Lutjanus griseus) juveniles in

• 0 seagrass habitats ofwesterri Florida Bay. ,BulI: Mar. ScL 46 (2): 345-357.GILMORE, R.G. (1977): Fishes of the Indian River Lagoön und adjacent waters,

" Flonda. Bull. Florida St. Mus. BioI. Sei. 22 (3): 101-147.GILMORE, R.G. (1987): Subtropical-tropical seagrasscommuriities of the

southeastern United States: fishes and fish commuriities. Fla. Mar. res.o Pub!. 42: 117-137. , . .

GILMORE, R.G. (1992): Comprehensive status report: Erivironmentalparameters associated with spawning, larval dispersal and early. life'history of the sJiotted seatrout; Cynoscion nebulosüs (CUVIER).Compreherisive Grant Report; submitted to Department of EnvirorimentalProtcction, St. Pctersburg, Floi-ida~

14

GILMORE, R.G., Y.D. LIN, B.G. GROSSMAN (in prep.): Spawning siteisolation and sound eharaeterization iri soniferous estuarine ifishes

. through a neural network system. . . . . .. "J .. "GRAY, J.D., T.L.KING,· R.L. COLURA (1991): Effeet of temperature and

hypersalinity on hatehing sueeess of spotted seatrout eggs. Prog; Fish-Cult.; 53: 81-84. ,. " ," I

GRAY, J.D., R.L. COLURA (1988): A preliminary analysis of the effeets oftemperature and salinity on hatehing of spotted seatrout. TexasIParkS

" and Wildl. Dep., Coastal Fish~ Braneh, Manag. Data Sero 148, Austin. .GUNTER, G. (1945): Studies on the marine fishes ofTexas. Publ. Inst. Mar. Sei.

Univ. Tex. 1:1-388. .HERALD, E.S.; R.R. STRICKLAND (1949): An annotated list of the fishes of

Homosassa Spririgs; Florida. Quart. J~ Fla~ Acad. Sei. 11: 99-109. ,HOLLIDAY, F.G.T. (1969): The effeets of salinityon the developirig cggs and

larvae of teleosts. In Fish Physiology, Vol. 1 (Hoar, W.S.; D.J. RandaU,eds.), 293-311. , . , '

HOLT, J., R; GODBOUT, C.R; ARNOLD (1981): Effeets of temperature andsalinity on egg hatehing arid hinTal survival of the red drum, Sciaenopsocellata., Fish. Bull. 79 (3), 569-573.-

IVERSEN, E.S., D.C. TABB (1962): Subpopulations based on growth and.: .tagging studies of spotted seatrout, Cynoscion nebulosus; in Floridri.. ' Copeia 3: 544-548. . , " i

JANNKE, T.E. (1971): Abundance of yourig sdaenid fishes in EvergladesNational Park, Florida, in relation to season and other variables. I Univ.Miami, Se Grant Program. 128 pp. '.' , :

JOHNSON, G.D. (1978): Development of fishes of thc mid-Atlantie Bight. Biol.., Servo Program, Fish arid Wildl. Servo 4:1-314. .' 'KINNE, O. (1962): . Irreversible nongenetic adaptation. Comp. Bioehcm.

Physiol. 5: 265-282. .MeCARTY,C.E., J.G. GEIGER, L.N. STURMER", B.A. GREGG, W~P.

RUTLEDGE (1986): Marine finfish culture in Texas: a model for thefuture; in: R.. Stroud; cd.: Fish eulture in fishery management" 249-262.Am. Fish. Soe., Fish Culture Seet. and Fish. Manag. Sec.; Bethesda,

. Maryland. , . . , ",' ,,' ,MeMICHAEL, R.H., KM. PETERS (1989): Early life histOry of spottcd seatrout,

Cynoscion nebulosus (PISCES: SCIAENIDAE), in Tampa Bay, Florida.Estuärlcs 12 (2),98-110. '. .

MOFFETT, A.W~ (1961): .Movcments and growth of spotted seatrout, Cynoscionnebulosus, in west Florida. Fla. Board Conserv. Mar. Res. Lab: Teeh.Sero 36, 3 pp., .. ,

MOK; H.-K; R.G. GILMORE (1983): Analysis of sound produetion in estuanneaggregations of Pogonias cromis, Bairdiella chrysoura, and,Cynoscionnebulosus (SCIAENIDAE). BuH. Inst. Zool.; Academia Sinica 22 (2): 157-186. ,

PEARSON, J.C. (1929): ,Nattiral history arid conservation of redfish and othercommercial schienids on the Texas coast. Bull. U.S. Bur. Fish. 44: 129-

,214. " ". ". ' ,PEEBLES, E.B., ·S.G. TOLLEY (1988): Distribution, gro\Vth and mortality of

larval spotted seatrout, Cynoscion nebulosus: a comparison between two

•

15. ~ .. ;.

adjaecnt estuarine areas of southwest Florida. Bull. Mar. Sei.; 42 (3); 397-410. ....." ",.

POWELL, A.B., D.E. HOSS, W.F. HE'ITLER, D.S. PETERS, S. WAGNER (1989):Abundance and distribution of iehthyoplankton' in Florida Bay and .

, adjaeent waters. BulL Mar. Sei. 44: 35-48. . , 'POWELS, H., V~W~ STENDER (1978): Taxonomie data on thc earIy life history

stages of Sciaenidae of thc South Atlantie Bight of the United States. S.C.. "Mar. Res. Cent. Teeh. Rep. 31. 64 pp.. ".. , ,'. . .

RICE, K W., L.W. MeEACHRON, P.C. HAMMERSCHMIDT (1988): Trends inrelative abundance arid size of seleetcd finfishes in Texas bays: November1975-Deeember 1986. Texas Parks and WildL Dep.; Coastal Fish. Braneh; .

"" " Manag. Data Sero .139, Austin. " . ,RUTHERFORD, E.S., T.W. SCHMIDT, J.T. TILMANT (1986): Tbe early life

history of spotted seatrout, red drum, gray snapper and snook .in theEverglades National Park; Florida. South Florida Research Center

, Report,86-107., 'RUTHERFORD, E.S., T.W. SCHMIDT, J.T. TILMANT (1989): Early life history

of the spotted seatrout (Cynoscion nebulosus) and gray snapper, (Lutjanus.griseus), in Florida Bay, Everglades National Park; Florida. Bull. Mar.

, Scienee 44 (1): 49-64. , .SIMMONS, E.G. (1957): Eeological survey of the upper Laguna Madre of Texas.

, Publ. Inst. Mar. Sei. 4 (2): 156-200.SPRINGER, V.G., K.D. WOODBURN (1960): An eeologieal study of the fishcs of

the Tampa Bay area. Fla. Board ConserV. Mar. Res. Lab. Prof. Pap. Sero1:1-104.

TABB, D.C. (1961): A eontribution to the biology, of thc spotted scat!out,CynosCion nebulosus, of East Central Florida. Fla. State Board ConserV.

. Teeh. Sero 35, 21 pp.. ' .TABB, D.C. (1966): The cstuary as a habitat for spotted scatrout, Cynoscion

, nebulosus. AIll. Fish~ Soe. Spee. PubL 3: 59-67. . ..TANIGUSHI, A;K~ (1981): Survival and growth of larval spottEid s.eatrout

(Cynoscion nebulosus) in relation to temperaturc,. prey abunda~ee, and. stoeking densities. Rapp. P.-v. Reun. Cons. Int. Explor. Mer. 178: 507-508.

TUCKER, J.W., Jr. (1988): GroWth of juvenile spotted seatrout on dry feeds.. " Prog. Fish-Cult. 50: 39-41. ,

TUCKER, J~W~, Jr., B.E. FAULKNER (1987): Voluntary spawriing patterns ofcaptive spottcd seatrout. Northeast Gulf. Sei. 9: 59-63.

16

i';>. N

o

Fig.I: Sampling sites in the Indian River Lagoon, central-east Florida. ..,.' .

ltem •% hateh o 50.1 88.3 95.6 99.3 100 100 99.3 95.6 93 85 78.6 82.9 85.6

48.3 86.6 95.5 98.6 100% 24-h survival

% 2-wk survival

o

o o 2 4.6 8

97 90

14 11.7 5.6

84.7 71.7 50

0.3 0

73.4 73.6 79.0

0.2 4.5 8.3

Tab.I: Mean percentage hatch, 24-h survival, and 2-week survival of spotted seatrout overall conditions.

r

17

100

90

80

'70

60

50

40

30

20

10

o~<:.>

Fig.2: Hatching success at different temperature-salinity conditions.

..... .

Salinity 20° 25° 30°(%c) Mean SO n Mean SO n Mean SO n

10 none survived 5.85 0.165 5 12.675 0.975 6

20 none survived 4.86 ·0.307 16 8.407 2.350 10

25 none survived 4.562 0.823 11 no measurements

30 none survived 4.262 0.632 13 5.98 1.242 13

Tab.2: Totallengths (in milliTneter~) of spotted seatrout larvae that survived 2 ·weeks.

18

100

90

60

__ 5=10%­

-e- S=2O%a

-*-S~

70

~S=1.O%a

-e- S=2O%a

---~

, ,

T=30·C

.5 10 15 20 25 30 35

Age (in days)

35

T=20·C

10 15 20 25 30Af;e (in days)

100

90

80

70

~ 60.,;:,.. 50oe ' ,:::l 40

CD

30

20

10

00

T=2S·C

5 10 15 20 25 30 35Age (in days)

10

O~~~~~~~-~~~o

~GO~"öl 50

-E 40:::ltQ

30

20

10

00 5

100 __ s..1O%a

90 -e- S=2O%a

80---~

70

~60.gi 50

ri3 40

30

20

Fig.3: Relationship between larval survival rates (in %) aTul age in days over a 30:dayperiod at different teinperature-salinity corulition's. ." ..

30

zS

20

15

10

5

~

4<'-~---~--~.~~ .

-""'i:s. ~_...,.

~.;p"'"~

Fig.4: 2-week larval survival at different temperature-salinity coTulitions.

•

r

19

35 35

• S=10%0 • S=10%0

300 S=20%0

30 0 5=20%0

25 0 5=30%0 0 ,.... 25 .Ä. 5=25%0 ®1 ~ 0 5=30%0

ä20T=20°C

-S20A A T=25°C~ ~~ ~ 15~ 15 .....'3 Ci!

+>0 0

E-< 10 E-< 10

5 5

0 00 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Age (in days) Age (in days)

8=30%0

• T=20°C

* T=25°C

000 T=30°C

5

35T;:======:;------~-_,

30• 5=10%0

o 5=20%0

o 5=30%0

35-r::======;-------r7J,.--,

30

5

,....25

~-S20

~.§ 15

:5oE-< 10

353010 15 20 25Age (in days)

5353010 15 20 25Age (in days)

50-f-,-...,...,........1'""T""T""T""T..............,i'""'"T...,...,..-r-.-1'""T""T.............,...,-,~....-l

o

Fig.5: Relationship between total length and age in days over a 30-day period at differenttemperature-salinity conditions. Points are mean values of 10 larvae.