The Abundance and Diversity of Larval and Juvenile Fish in a Tropical Estuary

Estuaries Vol. 17, No. 16, p. 216-225 March 1994

t i t i The Abundance and Diversity of Larval and i i Juvenile Fish in a Tropical Estuary i i i t ‘1.TITO DE hlORUS i L. TITODE bfoRXrs i Hjdrobiologie-UR 2C Centre Orstom de Cajenne BP 163 97323 Cajenne Cedex i France 3 L .%ESTRACT: The larval and juvenile fish of the Cayenne river estuary (French Guiana, South herica) were sampled at two stations from June 1989 until October 1990. A total of 52,989 individuals from 39 species, some still incompletely identified, were collected. Three families, Engraulidae, Gobiidae and Sciaenidae, accounted for over 97% of the total number of juveniles. The analysis of data over his period showed low diversity, and a difference in diversity benveen i the two sampling locations (H = 1.24 and 1.68). The results conform to some theoreticd models of abundance that suggest a relative equilibrium of juvenile assemblages. In contras, the seasonal variations in diversity and abundance and the results of a correspondence analysis showed significant differences in species distribution and in their relative abundance at the two sampling locations at certain periods, mainly in the rainy season. Our study indicates that. in spite of an apparent stability, the year to year variation in salinity and freshwater inputs could affect juvenile recruitment of some species and induces modifications in the composition of larval and juvenile estuarine fish assemblages.

Introduction tive descriptions of assemblages, but they contain no biological information. Theoretical species X number of studies deal with fish communiries I within estuaries and coastal lagoons (see reviews by abundance models attempc to describe the infor- ! Yanez-Arancibia 1985; Day 1989). Such systems are mation gathered in a community (Poole 1974; Ma- known as major nursery grounds for many aquatic gurran 1958) and to explain the spatial distribu- i species. Generally rich in food, they also provide tion of the species within a given habitat and the i protection against predators of larvae and juve- sharing of the available resources (Magurran 1988). I niles, thus allowing both rapid growth and a low ! rate of mortality. However, little is known about To what extent can some of the observed varia- I abundance and diversiry of ichthyoplankton in es- tions be related to simple factors like rainfall and tuaries, and spatiotemporal variation in these as- salinity? semblages is poorly understood. Materials and Methods Our study was carried out in the Cayenne River 1 estuary in French Guiana. Estuaries may be consid- STUDYSITE I ered “unpredictable environments” in which phys- The study was conducted in the Cayenne River ical and chemical factors vary widely in space and estuary (French Guiana, South America, 4O80’N if time (Bruton 1989; Whitfield 1990). The goals of 52“20‘W), an area 3 km in length and 1-13 km in ! our study were to characterize this variation in the width. There is considerable tidal influence (inter- Cayenne estuary and to answer the following ques- tidal range up to 3 m). It is an “homogenous” tions about ichthyoplankton assemblages in this estuary (Yanez-Arancibia 1987) having almost no environment: vertical saliniv gradient. The rainv season occurs Is the larval and juvenile fish assemblage a stable from December to June, with maximum rainfall communiy within an unstable environment? If generally observed in &fay and June. only biotic factors, such as interspecific competi- tion, play a role in the composition of a commu- StmtPLINc METHODS nity,. such a community is at an equilibrium of spe- Two locations were chosen based on differences cies richness. Yet an equilibrium may never be in physical characteristics (position, types of bot- reached if abiotic factors are predominant. tom, and water depth). The first (hereafter named Can this assemblage be described by any of the middle), located in the middle of the estuary, is species abundance models currently in use (Poole characterized by a mud bottom and an average 19‘74; Magurran 1988)? Species richness, species depth of 5 m at low tide. The second location diversity, and equitability provide partial quantita- (called sandy). near the river mouth and 2.5 km

1994 Estuarine Research Federation 216 O160-8347/94/01E0216-1 0$01.50/0 O, R.S.T.O.M. Fends Documentaire N” i 45at50 downstream from the first location. is character- rayes of beins easv to calculate and of sivin: ari ized bv a sandv bottom 2nd an average depth of intuitive image of species distribution. N,,,,,is the 1-'2 in deep at low tide. Sainplin:, conducted $,vith number of individuals of the most abundant spe- --a 1,N)O-pm mesh conical zooplankton net rk.ith a cies: N is the Cotai number ûf iiidi\iduals. , o-cm dianieter mouth, was done once a niorith durin: spring tides from J~iiielcJS9 to October 1990..A 3-min sample (horizontal surface hnull U'AS taken howl\. during one 12-h tidal cvcle at each location and the sample \vas then preseiyed in 55 formalin. The volurne of filtered sb':uer !vas mea- w-ed usin? 1 mechmical RmvuiPrPr, .ind salinir:. readinss $$'ere taken ;+,¡th an .kT.AG(I) refrrnctome- ter.

ID ESTIFICXTION Lnr.al and juvenile fish were cateyJrized accord- ing- to Hubbs' [ 194Yi terminoloy. ijmenile period begins when the fins are full-,, differentiated). The captured fish ranged from 3 mm to abolit 70 mm J'.T,~~~~~.&\II L..UXl..kL .kSSES[BLACES: in >tandard length. -41juseniles Mere identified io (zO rW.ÆSPU ND ESCE ;L\ii\LiS I5 species and lanae to faniilv. The Inn-al component beins iinpi~rtantin some The adult kevr used to make fainils-level identi- samples, a correspondence anal\-sis I C.li, using the fications were from Eigenrnann 119121, Pavo program .lDD;U3 [.'issociation pour le Develop- (194.9),Le Bail et al. (1954.a. bi, and Rojas-Beltran pemenc De I'.-'mal~se de Donnees], was done on I 198-I.i. Species identification (whenever possible I the monthlv mean densities including juveniles was done usinq FV3itehead 119731 and Cen-igon md lamae froin both locations [monchly densities 119871 for Engraulidae. and Chao 19731 and Fi- of 53 taxa (JV~I'17 mol. This essentiails descriptive scher t 13751 For Sciaenidae. multivariate method has the advantage of simpli- hing larse data sets wich little loss of information CH;IIL-\CTERIZATION OF JL~XENILE and identifiing interrelations among variables. .~SSE?.~B LAG ES : (~TRALLD .ATA The analvsis produces composite factors: che first Shannon-Wiener diversitv indices i H';(3larqa- explains the nia-uimum of :-ark" (or inertial in lef 1955) cvere calculated (total number of juve- the dacn set along a sinsle axis, and all subsequent niles of each species in each jlte) and compared factors esplain the masimum amount of the re- using a Student i-test i Hutcheson 1970). maining variance. These new factors i or axes I al- Total nimber of juvendes caughr. at each loca- low plottin9 nf the variabilis of multidimensional tion and che percentage of each specie5 $-%erecal- data in .z reduced space. culated to plot ab~indancelog cumes, and ficted. if possible. to species abundance models (Poole Resuits 1974: Magurran 19EiSi. JCXXILE .~SSEMBLACES ?If.ONTHLY D.4T.i [hvfid1Dnm-AbunÙunr~ and Di-Jtns.itv Monthlv calculations of several diversin indices The list 13f different species collecred, the total were used to highlight seasonal variations. each in- number of juveniles per species. and their relative dex being more sensitive to a different component abundance and ranking are $ven in Table 1. .A of diversitv: total of 33.361 juseniles (and 19,629 larvae, from 59 species from both locacions were collected and Sp7pnt.s Ririinrss: .S sorted. Three families, Engraulidae, Cobiidae and This index Sives only rough information and Sciaenidae, comprised oser 97'% of the total num- does not take into account the second component ber of juseniles. ,>f diversit.:. the relative Lbundance of different Diversic.? indices i H'ì calculated for the middle species. Ihchness is calculated 3s the number of I H' = 1.24) and iandv IH'= l.68i locacions dif- species. fered iiqnificanrlv IC = 3.14: with df = 31,379: critic4 value at 1%: 2.5761. .+i a rule, Shannon 3~ry~-P,~rkm'sDommnnre h&x: ii = "4 diversitv indices ~3rvfrom 1.3 to 3.5 in che field This indes is more sensitive to the rtbundance !hIar?alef 1972I. The Casenne River esruan is the inox cornmon species 3nd has rhe ndvan- thus a lo>%densirt. habitac:vlch respecr io the num- 21 8 A. Tito de Morais and L. Tito de Morais

T=\BLE 1. List of the species collected ac the middle and at the sandy locations. Number of individuals of a given species (N), total of juveniles (Nj), percent of a given species (N/NJ %), and rank.

Sfiddlc Sandy Specics (juveniles) N N/y x Rank N N/X: "o Rmk Anchoviella lepidentostob 10,539 67.688 1 7,106 39.942 1 r -- Anchoa spinifer 1,980 12.717 2 1,347 i.3il S Cobiidae sp. 2. 1,316 8.452 3 5,809 32.651 2 Gobiidae sp. 1 487 3.128 4 1,173 6.593 4 Stellijèr rastrifn 35 1 2.254 3 110 0.618 11 Engraulidae sp. 4 194 1.246 6 270 1.518 'i Otlontognathus mucmnatus 123 0.790 m 18 0.101 19 Engraulidae sp. 2 120 0.7771 8 412 2.316 6 htherinidae 113 0.526 9 133 0.748 9 Gobiidae sp. 4 , 56 0.360 10 35 0.197 13 Macrodon anc1;lodon 49 0.315 Il 29 0.163 14 Gobiidae sp. 3 . 44 0.283 12 53 0.298 12 Colomesus psittacus 32 0.206 13 146 0.521 8 Micropogonias furnieri 23 0.145 14 782 4.395 5 Congridae 21 0.135 15 15 0.084 22 Isopisthus panJi$innis 19 0.122 16 24 0.135 16 Amu sp. 1 12 0.077 17 17 0.096 21 Soleidae 11 0.071 18 1s 0.101 19 Oligoplites saliens 10 0.064 19 12 0.067 24 Lycengraulis sp. 8 0.05 1 20 14 0.059 23 C?nosczon acoupa 6 0.039 21 126 O.Ï08 10 .Vlugil curema 6 0.039 21 25 0.141 15 Belonidae 5 0.032 23 22 0.124 17 Cynoglossidae 3 0.032 23 20 0.112 18 Amphichtys cyptocentrus 4 0.026 25 7 0.039 25 Serranidae 4 0.026 25 6 0.034 26 Stellfër microps 3 0.019 27 5 0.028 29 Trachinotus cayennensis 3 0.019 27 2 0.011 36 Trichiunus lepturus 3 0.019 27 O - - Bochidae 2 0.013 SO 4 0.02 33 Murenosocidae 2 0.013 30 2 0.011 36 Sardinella sp. 2 0.013 30 1 0.006 40 Ariussp. 2 2 0.013 30 1 0.006 40 Selene uomm 2 0.013 30 O - - Aspredinichtysjlammtosus 1 0.006 35 6 0.034 26 Spheroides mannoratus 1 0.006 35 5 0.028 29 Unidentified/38 1 0.006 35 3 0.017 34 Arius sp. 3 1 0.006 35 3 0.017 34 Lonchum lanceotatus 1 0.006 35 1 0.006 40 Anchouiella guinnensis 1 0.006 35 1 0.006 40 Ancliovia sunnamensis 1 0.006 35 1 0.006 40 Pimelodus blochii 1 0.006 35 O - - Unidentified/42 1 0.006 35 O - - Scorn bridae 1 0.006 35 O - - Unidentified/ll 1 0.006 35 O - - Brachyplatytoma uailhntii 1 0.006 35 O - - Naannostomus SQ. 1 0.006 35 O - - Chloroscombrus chrysurus O - - 6 0.034 36 Aspredo aspredo O - - 5 0.0'28 29 Rerengraulis athm'noides O - - 5 0.028 29 Arius sp. 5 O - - 2 0.011 36 Polydactylus sp. O - - 2 0.011 36 Unidentified/27 O - - 1 0.006 40 Unidentified/40 O - - 1 0.006 40 Aspredinidae sp. 3 O - - 1 0.006 40 drimsp. 4 O - - 1 0.006 40 Gramlatus O - - 1 0.006 40 Unidentified/ 19 O - - 1 0.006 40 Pleuronectidae O - - 1 0.006 40 Total of juveniles (Nj) 15,570 100 - 17,791 1O0 - Total of larvae 13,313 - - 6,3 16 - - Larvae and iuveniles 28,883 - - 24,107 - - Juvenile Flsn Assemclages 21 9

(a) Middle

ib) Sanay

f:16 j !- madis ----- sandy I 0 001

1 11 Il li 41 Abundance rank

Fie. :, Rank abundance ?lors ni middle nnd sand\. loeauonb. ber of individuals collected. Fifty-nine taxa were collected, thoiigh most were represented bv only 1 or 2 individuals. These can be considered as "incidental". Xs the Shannon-Weaver indes is particularlv sensitive to the presence of rare species. this measure probahlv overestimated diversity in our scud\.. Fig 2. !.fiddle i ai 2nd ;an& 1 hi ipeclej abundance and Icig- senes disnibution. The number ?f species obsened In 13 abun- The abundance of each species is plotted on 3 dance clabws IS plotted ayxnsr the number of .;pecies predicred logarithmic scale against the species' rank. from bv the lo+eries model. the most abundanc tn the least abundant species (Fig. 1). It should be noted that abundance ranks for single species differed bemeen locations (see mai distribution. onfv nbunclance in che sandv io- also Table 1). cation.fit at che 3% lesel (wich df = 10; middle: c-7 The abundance curves are obriouslv not straiyhc = 13.96: sandv: cl? = 15.21; critical value at 5% = lines I i.e.. thev do noc fit a geomecric series). >Iod- 15.30). els predict that such abundance cumes occur in J. The log-series model is more zdapted to less di- situation in which species arrive Xt an unsaturated verse communities than is the los-normal model habitat at reqular intends of time, and occupv [hlaqurran 1985). In our case, the goodness-of-fit fractions of the remainins niche h\perspace 1x12- of ahnolance in the sandv iocarion was hest ivith prran 1955). the loq-normal distribucion and thac of the middle In Fig. 2. the observed values xecompared trich abi~ndancewas best with the !og-series model. the theoretical log-series model. This pattern Tsuuld result if Lhe intenals benveen the arrival of the species were random rather than regular i >la- The monthly mean densities ofjuieniles for the zurran 1958). In both the sandv and :he middle most common species are siven in Table 2. T19o locations. the obsened vaìues fitted the log-senes specie? uere hi5his dominmt in che samples: An- model (with df = 12; middle: c:! = 17.53; sandv: cho7wlLa /+zdmtodr.

ways A. lepidentostole except when Gobiidae sp.2 predominated at the sandy location in August, Sep- tember, and December 19S9 and at both locations in January and February 1990. Of the other En- graulidae, only Anchoa spinvo, which is an eu?- x- -- haline species (Whitehead 19'73; Cervigon 198'ï),

5 ?I ?I = m c,3 7 was well represented. Sciaenidae as a whole (of - '3 r- '3 L-: ?¡ In- which the adult population is activelv fished on a - small scale by local Cayenne fishermen) dominated in June, Jdy, and August 1989. The bvo main - P. 31 31 * G. Lc: T. - -3- u 3 species collected were Micropogonias j%mien' and Stellyo mstnjèr. Figure 3 gives the variations over time for several diversity indices. Species richness (the number of collected species) showed monthly variations be-

31 73e c -7 31 I tween 9 and 17 at the middle location and from 7- ul '3 - 10 to 22 at the sandy site. The number of species found at the sandy location was significantly higher (AYOVA on species richness: df = 1.32; Fs = 11.96; critical value at 5%: 4.15). All the other indices showed similar trends. The Shannon diversity index varied from 0.5 to 2, and evenness varied from 0.2 (the clear dominance by a single species) to 0.7 (a more homogenous distribution of species). Indices calculated for the sandy location were generally close to or superior to those for the middle one, except in December 1989 and January and February 1990. Shannon indices (H') differed significantly between the two locations for these months (critical value at the 5% level = 1.96 with df = m; December 1989: t = 2-07; January 1990: t = 6.56; February 1990, t = 10.51). These differences reflect the species distribution and the relative dominance of Gobiidae sp.2. The total number of species collected at the sandy location was high in January and February 1990, but Gobiidae sp.2 dominated to such a degree that diversity remained low. Although Gobiidae sp.2 also dominated at the middle location, other species were also abundant and the diversity indices were higher.

LARVAL AND JUVENILE tbSEMBL4GE.S- CORRESPONDENCEANALYSIS A total of 19,629 larvae accounted for 37% of the total number of individuals. The distribution of larvae and juveniles of the three main families from the two sampling locations showed a consis- tently higher percentage of larvae at the middle location (Table 3). The first three axes in the correspondence analysis accounted for 68% of the total inertia (respec- tively 34%, 19%, and 15%). They are retained hereafter to interpret the variance within the data. The most important contributions of species to total variance of each axis are given in Table 4: Go- Juvenile Fizk Assemolages 221

(b) Berger-Parker index (a) Species richness r-----l

months

(d) Shannon evenness (c) Shannon index

'*O0 .r 2

1.5

0.5

months 222 A. Tito de Morais and L. Tito de Morais

TABLE 3. Larvae and juvenile distribution at the ovo sampling - locations. N = total number; Percent = 100.N/(N larvae + N SB8 SB6 juveniles).

~ ~- Middle Smdv MEZ MA1 2 N Percent ?J Percent 584 Engraulidae larvae 11,309 47 4,776 34 I LESMAS / Engaulidae juveniles 12,843 53 9,156 66 Sciaenidae larvae 1,993 S2 1,538 38 Sciaenidae juveniles 452 13 1,099 42 Atiidae larvae 11 42 34 Ariidae juveniles 15 58 54 96 Total larvae 13,313 50 6,316 3s Total juveniles 13,310 50 10,309 62 biidae sp.2 contributed to 68% of the inertia of the first axis. Contributions of stacions to axes are also given in Table 4 (samples from the sandy location are indicated by S and those from the middle location by hl; 1989 by A and 1990 by B). For example, the samples of sandy location in June 19S9 (SA6: S = sandy location; A = 1989; 6 =June) contributed to ‘75% to the total variance of axis 2. Figure 4 shows the factorial plans 1 and 2, where seasonal differences between the two locations are particularly enhanced (codes as in Table 4). On axis 1, there is a contrast between the sandy and middle samples in September (SA9 vs hM9) and in December (SA12 vs hW12) 19S9, and in January (SB1 vs MB1) and in February (SB2 vs MB2) 1990. These four samples from the sandy location account for 72% of the variance of axis 1 (Table 4) Fig. 4. Correspondence analysis performed on both stations: and are the months wich high densities of Gobiidae relative position of the monchlv samples (total number of larvae sp.2. On axis 2 there is a contrast between the and juveniles captured per 1,000 md in each month) on the sandv and middle locations in June (SA6), July axes 1 and 2. Codes: M (middle), S (sandy), X (1989), B (1990), 1-12 (months) (see text). (SX7), and August (SX8) 1989 (months with the highest numbers of iV1. furnima?. M. furnieri; a ben- thic species (Isaac 1988), was clearly dominant in nieri were present in 1990). Precipitation during June 1989, having an important juvenile recruit- the rainy season was much greater in 1989, with ment. This was not observed the following year in much higher freshwacer inputs than in 1990. Ob- the Cayenne River (no similar contrast on axis 2 served salinities were thus lower in 1989 than in was observed during the same period as no M. fur- 1990 (Table 5). In contrast to the Cayenne River, recruitment of IM. funaim’ was observed in the Sin- namary River estuary (100 km east of the Cayenne TABLE 4. Results of correspondence analysis. Contributions of River) in 1990 (unpublished data). The Sinnamary the main species to che variance of each axis (in percentj (i.e.. River is larger than the Cayenne River and has a inertia (or variance) explained by species to total inertia of one much greater freshwater flow, so freshwater input axis). Contributions of the main samples CO the variance of each xis (in percent) (i.e., variance explained by samples to total was considerable even in the less severe rainy sea- variance of one axis). Samples and species are independent. son in 1990. High-level recruitment ofjuveniles of itl. &mieri and other Sciaenidae (e.g., S. rastnj¿¿) .kWS Spectrs Percent Samples Percent seemed to be dependent on low salinity water (see .Axis 1 Cobiidae sp. 2 68 SA9 30 periods of low salinities in Table 5). SAI2 14 SB1 15 Two taxa contribute to the variance of axis 3, A. SB2 --13 lepidentostole and uniden tified Engraulidae larvae Avis 2 M. funti” 59 SA6 13 (the majority are probably A. lepidentostole). The bis 3 Engraulid lame 50 hP.6 18 peak of abundance of larvae was in June 1989 ‘4. &pidenimto& 19 SB6 11 (1”6), with smaller peaks in January (PylB1) and jnnuan Febnisri March ; 582 .kQIll SE1 MA: II a\- June Juh Augus September 0x0ber Sovember December I safi I

Fis 5. Correspondence analvsis performed on hoch stations: I I i llav A[B3 1990 at the middle location top of Fi%. relarive position of che monchl:. samples I cora1 number nt Ìarvae 5 1. These are periods of hea1-s rains in the ner. xa- and juveniles i3prured per I.OW m' in e3ch montht on the son. :: 2nd 3. Cades: 11 imiddle1.5 ctandvi..i 119Si.E 119901, 1-12 (months: :jet fest]. Concfusions Results from Shannon disersin indices and from models of ahundance suggest a relatise equilibri- els t5Iayurran 1SSSi. The second npe of hypoth- um of species at the two locations. The sanav lo- esis emphasizes the role of phvsical and (chemical cation seemed to be more diverse and this :vas also factors that are seldom stable enoush to allow the confirmed bv the abundance models. In a different settlement of a stable cornmuniK. tropical svstem, Pinto :19SSt studied ali adult fish Compared to other environments. estuaries are communitv in a relauvelv stable environment ia known as unpredictable environments where un- Philippines mangrose svstem I. He showed that spe- stable phvsical conditions do not fasor stable com- cies abundance conformed to the 2oS-normal mod- munities. This '.vas shown for adult fish ssem- el except when an important environmental dis- blases by TV-hitfìeld [ 1990). and seems to be e7;en turbance (3Ophoon) disrupted the cornmunit>-. more important for assemblap of juvenile fish: Correspondence analvsis and seasonal .;ariadons Schlosser I 1985i showed that phVsica1 (i.e., sto- of' diversity indices shocz.ed significant dit'ferences chastic! facrors are importanc to riverine juvenile in species distribution and in the relative abun- fish abundance. species richness, and species com- dance of species 3t the n\.o samplinz locations .It position; older aze classes are more influenced bv certain periods. Our ~nalysisindicates that saliniri. biological [i.e.. deterministicr factors. Freeman et and freshwater inputs plaved an important role. 31. I 1988) obtained similar rewits \+henchanSes in Based 1311 a study of a tropical brackish-water la- Stream flow apparen tlv affected ~.uun~+f-the-vear Foon in %'est .ifriCa, Albaret 2nd Ecoutin I 199Oi recruitment. Our study had indicated a relative sta- snowed that seasonal changes in the composition biliw over all the period. but war-to-war variations and the structure of fish communities are induced in the int.ensin. of the ramv season and the level of mainiv by abundance and discriburion of freshwa- freshwarer inputs mav dfec: juvenile recruitment fer inputs. Similarlv, different field studies in South of some species and lead to modifications in the .African estuaries have showm effects of' the occur- composition of larval and juvenile fisn assem- rence and severin of floods on ichthvofaunal com- blages. munities i Plumstead 1990). T,vo &-pes of' hvpotheses, deterministic and sto- .hXVOWLE DG1EXTS chastic. have been considered ro esplain the reg- \Ve thank F. Lhomme and J. Lits I3lii-eira for ihar help in ulation of fish assemblages iCrossman et al. 1982; sampling dar3 coilecriuns 2nd O. \rlcI;es for ret.isinS [he rest. Herbold 1984; Rahe1 et al. 1984: Yant et al. 19%). The former npe emphasizes the rolc ~f biotic fac- LITEKATI:RE CITED tors like interspecific competiuon chat 3re more .~R.A.?ET.j.-J. a.\n j.-;1. EI.:OCTIN. iWo. Intluence des mwns cr. favorable to [he settlement of a stable assemblaSe. des variations climatiques >ur les peuplements de pi-iisons d'une lagune rropic3ie rn ilnqtie de I'(3uesr. .A¿

native Life-history Styles of Animals. ECluwer Academic Pub- POOLE. R. W. 1974. An Introduction to Quantitative Ecoloe. lishers, Dordrecht. McGraw Hill, New York. CERWGOX,G. 1955. Las especies del genero Anchoviella de PLTO,J. 1949. Faune de l’Empire français. XII: Poissons de la Venezuela (Pisces: Engraulidae). Contribuciones Cientificas, Guyane Française. ORSTOM, Paris. 280 p. Centro de Investigaciones Cienuficas, U.D.0,No 14. 54 p. ~L~CURRAU,h. E. 1988. Ecological Diversity and Its Measure- CHAO,L. N. 1978. A basis for classifymg western Atlantic ment, Princeton University Press, Princeton, New Jersev. Sciaenidae (Teleostei: Perciformes). National Oceanic and 179 p. Atmospheric Administration Technical Reports, circular no. MARG~LEF,R. 1958. Information theory in eco1o.g. Genmal sJx- 415. 64 p. tem 3:3&41. DAY,J. H. 1989. Estuarine Ecology. Wey, London. 560 p. ?AARCALEF, R. 1972. Homage to Evelyn Hutchinson, or why is ElGEssuux, C. H. 1912. The freshwacer fishes of British Cuia- there an upper limit to diversity. Transactions of the Connectzml na. including a study of the ecological grouping of species Academ? of A7t~and Science 442 11-235. and the relation of che fauna of the plateau to that of the PISTO, L. 1988. Population dynamics and community structure lowlands. Carnegie Museum. Pittsburgh. 358 p. of fish in the mangroves of Pagbilao, Philippines. Journal O/ Fish 33(A):33-43. FISCHER,W. 1978. FAO species identifications sheets for fish- Biology WEL,F. J., J. D. LYONS, &VD A. P. COCHRAN. 1981. Stochastic eries purposes. Western Central Atlantic. Vol. 4. Food and or deterministic regulation of assemblage structure? It may Agriculture Organization, Rome. depend on how the assemblage is defined. American ivaturulist FREEMAN,M. C., M. K CRAWFORD,J. C. BARET, D.E. FACEY,M. 124583-589. C. FLOOD,J. Hu,D. J. STOUDER,.LUD G. D. CROSSXUU. 1988. ROHLF, F. J. AKD R. R. Sow. 1981. Statistical Tables. W. H. Fish assemblage stability in a southern Appalachian stream. Freeman and Company, New York. 219 p. CanadianJournal of Fishm’es and .-Lquatic Science 45:1949-1958. ROJAS-BELTR~\N,R. 1981. Clé de déterminacion des poissons GRoSsh~w,G. D.,P. B. MOPLLE,ANDJ. O. WHITTAKER.1982. Sto- continentaux et côtiers de Guyane. Bulletin de Liaison chasticity in structural and funcrional characteriscics of an In- C.R.A.A.G., I.N.R.A. 9. 63 p. diana stream assemblage: A test of community theory. Ameri- ROJAS-BELTFLW, R. 1986. Rôle de la mangrove comme noum- can Naturalist 120:423454. cerie de crustacés et de poissons en Guyane, p. 95-110. In HERBOLD,B. 1984. Structure of an Indiana stream fish associ- Sepanguy Sepanric (ed.), Le Littoral Guyanais. Cavenne. ation: Choosing an appropriate model. Amm.can Naturalist SCHLOSSER,I. J. 1989. Flow regime, juvenile abundance, and 124:561-372. the assemblage structure of stream fishes. Eco103 66:1484- HUBES, C. L. 1943. Terminology of early stages of fishes. Copeia 1490. 4260. WHITEHEAD,P. J. P. 1973. The clupeoid fishes of the Cuianas. HUTCHESON,K. 1970. A tex for comparing diversities based on Bulletin of the British Museum (Natural Histq) Zoology. Supple- the Shannon formula. Journal of Theroetical Biology 29:151-154. ment 3. 27p. IS;L\C,V. J. 1988. Synopsis of biological data on the whitemouth WHITFIELD, .A. EL 1990. Life-history styles of fishes in South A€- croaker. Sli~@ogoni~fumimi (Desmarest, 1823). F,40 Fish- rican estuaries. Environmental Biology of Fishes 285.95-308. eries Synopses No. 150. Food and Agriculture Organization, YAUEZ-i\RX”ICIBlA, A. 1985. Fish community ecolog). in estuaries Rome. 33 p. and coasd lagoons. Dirrecion General de Publicaciones, Universidad Nacional Autononoma de Mexico. 633’~. LE BAIL, P. PLANQUETTE,AND G. GERY. 1984a. Clé de P. Y, YbEz-rlRtUcmA, A. 1987. Lagunas cosieras F estuarios: Cro- détermination des poissons continentaux et còtiers de Guya- nologia, criterios y conceptos para una clasificacion ecologica ne. Bulletin de Liaison C.R.AAG., I.N.R.A. 6. 63 p. de sistemas cosceros. Ecossistemas Costeros, Academia de LE BAIL, P. Y., P. PLANQUETTE,.AND G. GERY. 1984b. Clé de Ciencias São Paulo, Publicações ACESP 54:l-38. détermination des poissons continentaux et côtiers de Guya- YmT, P. R., J. R KARR, AVD P. L. ;\NCERILWIER. 1984. Scochas- ne. Bulletin de Liaison C.RA.A.G., I.N.R.A. 8. 6ï p. ticíty in sueam fish communities: An alternative interpreta- PLUXSTMD, E. E. 1990. Changes in ichthyofaunal diversity and tion. Avmican ~Vafuralist124573-382. abundance within the Mbashe estuary, Transkei. following construcdon of a river barrage. South African foumal of Marine Received for consideration, Januav 6, 1992 Science 9:399407. Accepted Jw publication, .+rd 10, 1993 Juvenile Fish hssemblages 225

.AzFEND[S. Ta\onomic list of the collected species. isis unidentihed jpK1i.S are nor listed. See Tahle l.Ì

Order Fainilv joew,. ;inSuiIliformes Consndw One unidentidrd species Sturenosocidae One unidenrificd species

Lehiasinidac in idle

Pimelodidat.

Eatrnchnididae Belonidne Xrhennidae

Sciaenidse

Pieurnnecdinrmes