composition, abundance, distribution and seasonality of larval fishes in the sundays estuary, south...

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Composition, Abundance, Distribution and Seasonality of LarvalFishes in the Sundays Estuary, South AfricaAuthor(s): K. Sutherland, N.A. Strydom & T.H. WooldridgeSource: African Zoology, 47(2):229-244. 2012.Published By: Zoological Society of Southern AfricaDOI: http://dx.doi.org/10.3377/004.047.0220URL: http://www.bioone.org/doi/full/10.3377/004.047.0220

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Composition, abundance, distribution andseasonality of larval fishes in the Sundays Estuary,

South AfricaK. Sutherland, N.A. Strydom* & T.H. Wooldridge

Department of Zoology, Nelson Mandela Metropolitan University, P.O. Box 1600, Port Elizabeth, 6000 South Africa

Received 2 April 2012. Accepted 9 July 2012

The larval fish assemblage was studied in the permanently open Sundays Estuary on thesoutheast coast of South Africa. Seasonal samples were collected between winter 2007 andautumn 2009 at eight sites along the estuary by means of boat-based plankton tows using twomodified Working Party 2 (WP2) nets. Salinity ranged from 1.5–36.5 and temperaturefrom 11.6–26.8°C during the study period. A total of 8174 larval and early juvenile fishes werecaught, representing 12 families and 23 taxa. The Clupeidae, Gobiidae and Blenniidae were thenumerically dominant fish families. Common species included Gilchristella aestuarias(Clupeidae), Omobranchus woodi (Blenniidae), Caffrogobius gilchristi, Glossogobius callidus(Gobiidae), Liza dumerilii and Myxus capensis (Mugilidae), largely reflecting the adult assem-blage of the estuary. Catches varied significantly between seasons, but not between sites andsalinity zones within the estuary. Highest catches were recorded in summer (mean of 464and 928 larvae per 100 m3 in 2008 and 2009, respectively). Species diversity also variedseasonally, with highest diversity occurring during summer. Highest larval fish densityoccurred in the euhaline zone while the oligohaline zone supported the highest diversity.Estuarine-resident species (category I) dominated the system (91%). The preflexion stage ofdevelopment dominated the catches suggesting a high degree of local production in theSundays Estuary. Larval sizes of the estuarine-resident G. aestuarias and catadromous speciesM. capensis tended to increase towards the middle and upper reaches of the estuary. Importantvariables regulating larval fish dynamics in the Sundays Estuary included salinity, temperatureand turbidity.

Key words: estuary-dependent, nursery, salinity zones, developmental stage.

INTRODUCTIONFish species worldwide make extensive use ofestuarine systems as settlement, spawning, feed-ing and nursery areas (Whitfield 1985; Harris &Cyrus 1995; Whitfield 1998; Strydom et al. 2003;Berasategui et al. 2004; Able et al. 2006; Aceves-Medina et al. 2008). Estuarine nursery areas aretherefore crucial habitats for the survival of manyendemic fish species. The study of larval fishes isthe basis for understanding fish assemblagesoccurring in estuaries. For those species enteringestuaries to use them as nurseries, many do notonly enter estuaries during their juvenile stages,but also during their larval stages (Strydom et al.2003). Postflexion larvae of estuarine-dependentmarine species recruit from marine breedinggrounds into estuarine nurseries. Passive tidalentrance of preflexion larvae of certain fish speciesinto estuaries is also known to occur (Beckley 1985;Whitfield 1989a; Strydom 1998; Strydom &Wooldridge 2005). The recruitment of postflexion

larvae also includes certain estuary-resident speciesafter an obligatory marine phase during flexion(Beckley 1985; Whitfield 1989a). Worldwide, factorsdriving the recruitment process and the dynamicsof the use of estuaries by these early developmentalstages have been the focus of much research atten-tion (Neira & Potter 1994; Barletta-Bergan et al.2002; Hagan & Able 2003; Faria et al. 2006; Ramoset al. 2006; Aceves-Medina et al. 2008).

South African larval fish studies have includedboth single (Melville-Smith & Baird 1980; Strydom& Whitfield 2000; Pattrick et al. 2007; Wassermanet al. 2010) and multiple estuary studies (Harris &Cyrus 2000; Strydom et al. 2003; Montoya-Maya &Strydom 2009). In these studies aspects such as theinfluence of estuary type (Strydom et al. 2003),tidal exchange (Beckley 1985; Whitfield 1989a;Strydom & Wooldridge 2005) and the effects ofaltered freshwater input (Strydom & Whitfield2000; Strydom et al. 2002; Vorwerk et al. 2008) onspecies distribution and success in estuaries wasassessed.

African Zoology 47(2): 229–244 (October 2012)

*Author for correspondence. E-mail: [email protected]

In the Sundays Estuary, previous studies includethose on the juvenile (Beckley 1984) and adult(Marais 1981) components of the fish community.Harrison & Whitfield (1990) complemented thesestudies with an analysis of the larval fish composi-tion, distribution and abundance of the SundaysEstuary fish community. The effects of freshwaterinputs on larval and juvenile marine fishes and thebiomass and consumption of zooplankton by theClupeidae, Gilchristella aestuarias were studied byWhitfield (1994a) and Whitfield & Harrison (1996),respectively.

To understand the dynamics of the fish assem-blage occurring in an estuary the study of larvalfishes is imperative. Longer-term studies on larvalfish communities of estuaries are lacking andalthough short-term investigations are availablefor some estuaries, most South African estuarieslack basic information. The objective of this studywas to describe the spatio-temporal dynamics ofthe larval fish assemblage in the Sundays Estuaryover a two-year period. The specific aims were toidentify the species composition, abundance,distribution and seasonality of the larval fishcommunity in the estuary and relate this to thephysico-chemical variability within the system.

MATERIALS & METHODS

Study areaThe Sundays Estuary is a permanently open

system located on the southeast coast of South

Africa (Fig. 1). It rises in the Karoo (south-centralSouth Africa), draining a catchment area of20 729 km2 before flowing into Algoa Bay (33°04’03”S, 25°05’01”E) (Beckley 1984). The Sundays Es-tuary is part of the Addo Elephant National Park(AENP). The estuary is channel-like along themajority of its 21 km length with a depth variationfrom 5 m in the lower and middle reaches to lessthan 2 m in the upper reaches (Wooldridge & Eras-mus 1980; Whitfield & Harrison 1996). The estuaryis approximately 800 m at its widest point nearthe mouth, becoming increasingly narrower toapproximately 20 m wide at the head of the estu-ary (Marais 1981; Whitfield & Harrison 1996).

The Sundays Estuary is characterized by steepbanks (about 3–4 m high) with limited marginalvegetation. There is an absence of salt marshes orlarge mud flats (Beckley 1984). Submerged macro-phytes such as Potamogeton crispus occur at thehead of the estuary while Phragmites australis occursin the upper reaches. Benthic algae dominate themiddle reaches and a small bed of Zostera capensissometimes establishes itself near the mouth (Har-rison & Whitfield 1990). Hilmer (1990) recordedhigh chlorophyll-a levels in the middle and upperreaches extending into the lower reaches of theestuary during summer. This is due to intenseagricultural practices along the river contributingto generally high nutrient levels (Emmerson 1989).

The estuary has continuous freshwater inflow(Jerling & Wooldridge 1995) supplemented by aninter-basin water-transfer scheme (Pech et al.

230 African Zoology Vol. 47, No. 2, October 2012

Fig. 1. Geographical position of the Sundays Estuary showing location of larval fish sampling stations used in thestudy.

1995). The mean annual rainfall in the region is323 mm with a mean annual runoff of approxi-mately 200 × 106 m3 (Whitfield & Harrison 1996).Spring tidal range is about 1.2–1.5 m and at neaptide 0.1–0.3 m (Harrison & Whitfield 1990). Watertemperatures range from 13°C in winter to 26°C insummer (Jerling & Wooldridge 1991). The estuarydisplays a full salinity gradient linked to theinter-basin water-transfer scheme and returnflows from the citrus farming practices above theestuary (Wooldridge & Bailey 1982; MacKay &Schumann 1990). Salinity levels are highest nearthe mouth of the estuary due to the permanentconnection with the ocean.

Field samplingPlankton tows took place at eight GPS-fixed sites

along the length of the Sundays Estuary at seasonalintervals during July 2007 and 2008, October 2007and 2008, January 2008 and 2009 and April 2008and 2009. Two slightly modified Working Party 2(WP2) plankton nets (570 mm mouth diameterand 0.2 μm mesh aperture size) fitted withKahlsico 005 WA 130 flowmeters were used(Strydom et al. 2003). Sampling commencedc. 30 min after nightfall on the new moon. Netswere simultaneously lowered and towed along-side the boat for 3 min at a speed of 1–2 knotssampling the subsurface layer (Strydom et al.2003). After each tow, flowmeter readings weretaken to determine the water volume filtered.Samples were preserved on-site in 10% bufferedformalin.

Vertical temperature (°C) and salinity (expressedas practical salinity units) profiles were obtained ateach site using a YSI 6600 multi-parameter instru-ment. Recordings were conducted at intervals of0.5 m between the surface and bottom of the watercolumn (Strydom & Whitfield 2000). Integratedvalues were used for analyses. Water transparencymeasurements were taken at all sites using aSecchi disc. All Secchi disc depth measurementswere converted into an extinction coefficient (k)using methods described by Dawes (1981)where k = 1.7/D (Secchi depth in cm) (Strydomet al. 2003).

Larval identificationIn the laboratory, larval fishes were first sorted

from plankton samples then identified andcounted. Identification was completed to the low-est possible taxon using Smith & Heemstra (1986),Neira et al. (1998) and Leis & Carson-Ewart (2000)

amongst others. Larvae were measured to thenearest 0.1 mm body length (BL) using an eye-piece micrometer for larvae <10 mm and Verniercallipers for larger specimens. This representsnotochord length in preflexion and flexion larvae,and standard length in postflexion larvae (Neiraet al. 1998). Larvae that were positively identifiedwere grouped into estuary-dependence catego-ries (Whitfield 1998). Categories are defined asfollows: Ia, estuarine species that breed only inestuaries; Ib, estuarine species that breed in estuar-ies and in the marine environment; IIa, euryhalinemarine species that usually breed at sea but thejuveniles are dependent on estuaries as nurserygrounds; IIb, euryhaline marine species that usuallybreed at sea, with the juveniles occurring in estu-aries but also found at sea; IIc, euryhaline marinespecies that usually breed at sea, with the juvenilesoccurring in estuaries but being more abundant atsea; III, marine stragglers not dependent onestuaries; IV, freshwater species able to penetrateinto estuaries from rivers based on their salinitytolerance; V, catadromous species. Larval fishdensity (number of larvae/100 m3) was calculatedusing a simple formula based on a predeterminedcalibration value for each flowmeter used: Totalnumber of fish larvae/100 m3 = [total number oflarvae caught per haul/(revolutions on flowmeter/predetermined calibration value in m3) × 100].

Data treatment and analysisSample sites were categorized into salinity zones

based on an adaptation of the Venice system(Strydom et al. 2003) (Table 1). Homogeneity ofvariance and normality tests were completed forphysical and biological data, using a Levene’s testand normal probability plot. Square-root transfor-mations were also used. The data did not conformto parametric test assumptions and thereforenon-parametric tests were used.

Larval fish density was assessed for differences

Sutherland et al.: Larval fishes in the Sundays Estuary, South Africa 231

Table 1. Adaptation of the Venice system for the classifi-cation of South African salinity zones in estuaries(Strydom et al. 2003).

Salinity zone Salinity range (psu)

Fresh 0–0.49Oligohaline 0.5–4.9Mesohaline 5.0–17.9Polyhaline 18.0–29.9Euhaline 30.0–35.9Hypersaline —36

between seasons, sites and salinity zones using thenon-parametric Kruskal-Wallis test and betweenyears using the Mann-Whitney U-test. Seasonaldifferences between salinity, temperature andturbidity were also assessed using the Kruskal-Wallis test.

Multiple linear stepwise regression for para-metric data was used to determine the relation-ship between environmental variables and larvalfish density. A reduced significance level of P <0.01 was used for this analysis.

PRIMER statistical software package v5.2.9 (Clarke& Warwick 1994) was used to conduct communityanalysis and to calculate diversity indices (Marglef’sspecies richness and Shannon-Wiener diversity).These were compared between seasons, sites andsalinity zones. Larval fish density data were Log10

(x + 1) transformed prior to community analysis.A separation was made between estuarine-resident species (category I) and marine-spawned,estuarine dependent and catadromous species(categories II, III, V) and a Bray-Curtis similaritymatrix was generated for each of these datagroups. ANOSIM was used to detect differencesbetween groups in each analysis. The SIMPERroutine was applied to determine the relative con-tribution of key species to the similarity betweengroups assigned. A significance level of P < 0.05was used.

RESULTS

Environmental variability

Seasonal physico-chemical variability was appar-ent in the Sundays Estuary. Salinity rangedfrom 1.5 to 33.7 in summer, 1.7 to 32.6 in autumn,1.9 to 36.5 in winter and 2.0 to 32.9 in spring. How-ever, differences in mean salinity between seasonswere not significant (H = 2.69, P = 0.44).Vertical sa-linity stratification was evident, with stratificationmost prominent in summer and autumn at lowerestuary sites. A significant difference (H = 97.86,P < 0.01) was found in mean water temperaturebetween all seasons except spring and autumn.Water temperature ranged from 20.2–26.8°C insummer, 18.0–23.0°C in autumn, 11.6–15.8°C inwinter and 20.1–22.5°C in spring. Stratification ofwater temperature was weak, occurring at lowersites in summer and autumn. A significant differ-ence (H= 41.72, P < 0.01) in water transparency(k) was also found between summer and winter,autumn and winter, autumn and spring andwinter and spring (Fig. 2).

Species composition

A total of 8174 larval and early juvenile fisheswere caught, representing 12 fish families and23 species. Gilchristella aestuarias, the only repre-sentative species of the Clupeidae family, domi-nated the catch, comprising 59.2% of the totalcatch. Gobiidae comprised 22.0% of the catch, withCaffrogobius gilchristi (19%) being the dominantspecies. Omobranchus woodi (Blenniidae) contributed10% of the total catch. Liza dumerilii and Myxuscapensis of the family Mugilidae (6.7%) comprised4.3% and 2.1% of the total catch, respectively. Allother fish family contributions were less than 1%(Table 2). The largest portion of the catch (91%)comprised estuary-resident species (category I).Marine dependents (category II) and catadromousspecies (category V) followed, contributing 6%and 2% of the total catch, respectively.

Seasonal trends

The highest mean larval fish density was recordedin summer 2008 (464 larvae per 100 m3) and 2009(928 larvae per 100 m3) (Table 4, Fig. 4).The highestnumber of species (16 species in 2008 and10 species in 2009), species richness (2.44 in 2008)and diversity (1.44 in 2009) were also recorded insummer (Table 4). Evenness was higher in springand autumn, whereas winter was dominated byG. aestuarias (Fig. 5).The estuarine-resident speciesG. aestuarias, C. gilchristi and Psammogobiusknysnaensis and the marine-spawned L. dumeriliiand Rhabdosargus holubi occur throughout the year.

Spatial trends

Although no significant difference was foundbetween larval fish density and different sites(H = 14.62, P > 0.05), there was a clear shift inlarval fish species density between the lower andupper reaches (Fig. 3). Omobranchus woodi (cate-gory Ia) and C. gilchristi (category Ib) dominatedthe lower four sites near the mouth; however,C. gilchristi also occurred at site 8 in the upperreaches. Gilchristella aestuarias (category Ia)showed highest densities at sites 3, 5, 6 and 7.Glossogobius callidus (category Ib), L. dumerilii(category IIb) and M. capensis (category V) occurredin highest densities in the middle and upperreaches (sites 5–8).

Although no significant difference betweenlarval fish densities and salinity zone was found(H = 10.15, P > 0.05), the euhaline zone had thehighest mean density of larval fishes (627 larvaeper 100 m3). This was followed by the mesohaline,



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oligohaline and polyhaline zones (378, 299 and 263larvae per 100 m3, respectively) (Table 4). SIMPERanalysis revealed that C. gilchristi (in spring 2008,summer 2009 and autumn 2009), G. aestuarias (inautumn 2009) and O. woodi (in summer 2009) at thepreflexion stage of development contributed tothe high density of larval fish in the euhaline zone.Also evident was a spatial difference in speciesrichness and diversity. Highest species richnessoccurred at site 1 near the mouth and highestspecies diversity occurred at site 8 in the upperreaches. Compared with other salinity zones, theoligohaline zone showed highest species richnessand diversity followed by the polyhaline zone(Table 4).

Temporal and spatial variation in

development stage, body length

and estuary association

The larval fish assemblage in the Sundays Estuarywas dominated by preflexion larvae. The highestpercentage of preflexion and flexion larvae wasrecorded in summer. Postflexion larvae and earlyjuveniles increased in autumn and winter (Fig. 6).On a spatial scale, lower estuary sites (sites 1–4)were dominated by preflexion larvae. The greatestpercentage of flexion and postflexion larvae wasrecorded at site 5. Early juvenile fishes increased inabundance with distance up the estuary (Fig. 7).Size ranges for larval fishes collected in theSundays Estuary are shown in Table 2.


Table 4. Mean, median, range, species richness index (d ) and species diversity index (H ’) for the larval fishassemblage recorded in the different seasons and salinity zones in the Sundays Estuary between 2007 and 2009.

Density (no. per 100 m3)

Mean Median Range Species richness (d ) Species diversity (H ’)

SeasonWinter ‘07 232 27 0–1194 0.92 0.08Spring ‘07 43 29 0–113 2.13 1.41Summer ‘08 464 145 6–2625 2.44 1.01Autumn ‘08 373 211 0–996 1.35 0.90Winter ‘08 49 32 0–207 2.05 0.60Spring ‘08 177 130 20–764 1.55 0.99Summer ‘09 928 782 47–3171 1.32 1.44Autumn ‘09 346 153 28–2476 0.86 0.47

Salinity zoneEuhaline 627 311 28–3171 0.93 0.97Polyhaline 263 62 0–1316 2.51 1.08Mesohaline 378 155 4–2625 1.52 0.24Oligohaline 299 82 0–2476 2.63 1.38

Table 3. Multiple linear regression statistics for the relationship between larval fish density and environmentalvariables (salinity, temperature and water transparency) for all taxa combined and the dominant species inthe Sundays Estuary. r 2 = Coefficient of determination; r = correlation coefficient;F = F-statistic;Sa = salinity;Te = tem-perature.

Taxon r 2 r F Significant variable

All taxa 0.10 0.32 4.80 Te*

Dominant speciesGilchristea aestuarias 0.04 0.19 1.59Caffrogobius gilchristi 0.13 0.37 6.36 Sa*, Te*Omobranchus woodi 0.15 0.39 7.31 Sa**, Te*Liza dumerilii 0.10 0.31 4.51 Sa*Glossogobius callidus 0.11 0.33 5.07 Sa*

Significance levels: * = P < 0.01, ** = P < 0.001

Marine-spawned species that only occurred inthe summer season include Unidentified goby,Pomadasy solivaceum, Liza richardsonii, L. tricuspidens,Solea turbynei and Diplodus capensis. Estuarine-resident species (category I) were present everyseason (2007–2009) and at all sites. Estuarine de-pendents (category II) were most abundant atsites 5, 6 and 8 and were also present every season(2007–2009). Marine stragglers (category III) and

the freshwater migrant (category IV) were onlypresent during summer 2008 at site 1 and autumn2008 at site 6, respectively. Catadromous species(category V) were absent in the winter seasons andshowed highest densities at site 7.

Community analysis

Cluster analysis grouping indicated that forboth estuarine-residents and marine-spawned


Fig. 4.Mean larval fish density recorded consecutively per season and at all sites along the Sundays Estuary between2007 and 2009.Sp = spring, Su = summer, Au = autumn, Wi = winter. ‘07 = 2007, ‘08 = 2008, ‘09 = 2009.Bars indicaterange.

Fig. 3. Percentage contribution of larval fish species at sites along the length of the Sundays Estuary between2007 and 2009. Only species which contributed over 2% individually to the total catch were included. Rare speciescontributing less than 2% were grouped as other marine-spawned or estuarine-resident species as their contributionto overall catch was negligible. Site 1 occurs at the mouth of the estuary.

species there were no clear patterns associatedwith selected factors (Fig. 8). Groups formed at50% similarity, generally contained a variety ofseasons and sites. Group 5, however, mainly con-tained summer and spring samples. MDS plots

were excluded as these showed similar patterns tothe cluster analysis, thereby not adding any valueto the community analysis. Species compositionby seasons and sites using density data was inves-tigated using a community analysis approach


Fig. 5. Rank abundance curve representing larval fish species richness (d ), diversity (H ’) and evenness (J ) for theSundays Estuary in summer, autumn, winter and spring between 2007 and 2009.

Fig. 6. Temporal trends in larval fish development stages present in the Sundays Estuary between 2007 and 2009.Sp = Spring, Su = Summer, Au = Autumn, Wi = Winter. ‘07 = 2007, ‘08 = 2008, ‘09 = 2009. Due to low numbers of theglass eel developmental stage these are not visible on the figure.

Fig. 7.Spatial variation of larval fish developmental stages at all sites in the Sundays Estuary between 2007 and 2009.Due to low numbers of the glass eel developmental stage these are not visible on the figure.


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(Table 5). SIMPER analysis revealed that theestuarine residents G. aestuarias and C. gilchristiwere the dominant contributing species to dissim-ilarity between seasons and sites (Table 5). Otherestuarine-resident species contributing to thisdissimilarity include P. knysnaensis, O. woodi andG. callidus. The marine-spawned M. capensis,R. holubi and L. dumerilii were the dominant con-tributing species to dissimilarity between seasonsand sites (Table 5). Mugilcephalus, L. tricuspidensand Pomadasys commersonnii also contributed tothis dissimilarity.

Relationships with environmental variables

A weak positive regression relationship wasevident between all taxa, dominant species andenvironmental variables. Larval fish density, inthe Sundays Estuary showed a significant rela-tionship with temperature (P < 0.01). At the com-munity level, salinity and water transparency didnot show any significant relationship with larvalfish density. At the species level, C. gilchristi andO. woodi were significantly influenced by salinityand temperature (P < 0.01). Salinity also had apositive relationship with L. dumerilii and G. calli-dus (P < 0.01) (Table 3).

DISCUSSIONNoting that the number of taxa is a function ofsampling effort, catches of larval fishes in thisstudy (23 taxa representing 12 fish families) wasslightly higher than that recorded in the estuaryby Harrison & Whitfield (1990) (18 taxa represent-ing 10 fish families). In other warm-temperateestuaries including the Kromme Estuary (Strydom& Whitfield 2000) and Breede Estuary (Montoya-Maya & Strydom 2009) 29 and 27 taxa wererecorded. Typically a decrease in the number oftaxa is found in cool-temperate estuaries, noted byMontoya-Maya & Strydom (2009) in the OlifantsEstuary where 12 taxa were recorded. The numberof taxa typically increases along the east coast ofSouth Africa with an example of 40 taxa recordedin the Nxaxo-Ngqusi Estuary on the subtropi-cal–warm-temperate boundary (Wasserman et al.2010).

South African estuaries are typically character-ized by having low species diversity and a domi-nance by relatively few species (Whitfield 1994b).Similar trends were found for the larval fish assem-blage in the Sundays Estuary in the present study.The families Clupeidae, Gobiidae and Blenniidaedominated the estuary together contributing 92%


Table 5. ANOSIM and SIMPER test results for estuarine-resident and marine-spawned species in the SundaysEstuary.

Factor ANOSIM SIMPERSeason P R-statistic Estuarine-resident species Marine-spawned species

(% contribution to dissimilarity) (% contribution to dissimilarity)

Winter–Spring <0.01 0.39 Gilchristella aestuarias (34.0) Myxus capensis (18.9)Caffrogobius gilchristi (22.3) Rhabdosargus holubi (8.0)Psammogobius knysnaensis (2.67) Mugilcephalus (2.5)

Winter–Summer <0.01 0.26 Gilchristella aestuarias (32.8) Liza dumeril (10.1)Caffrogobius gilchristi (16.1) Liza tricuspidens (3.5)Omobranchus woodi (14.3) Rhabdosargus holubi (2.8)

Winter–Autumn <0.01 0.21 Gilchristella aestuarias (48.7) Liza dumeril (6.7)Caffrogobius gilchristi (15.7) Pomadasys commersonnii (4.5)Glossogobius caidus (7.6) Myxus capensis (3.6)

Spring–Summer <0.01 0.22 Gilchristella aestuarias (27.9) Myxus capensis (10.0)Caffrogobius gilchristi (19.8) Liza dumeril (8.6)Omobranchus woodi (13.1) Rhabdosargus holubi (3.8)

Spring–Autumn <0.01 0.22 Gilchristella aestuarias (38.3) Myxus capensis (13.4)Caffrogobius gilchristi (19.9) Liza dumeril (5.6)Glossogobius caidus (6.1) Rhabdosargus holubi (4.8)

Summer–Autumn >0.05 0.06 Gilchristella aestuarias (34.0) Liza dumeril (10.5)Caffrogobius gilchristi (17.1) Myxus capensis (3.1)Omobranchus woodi (12.8) Liza tricuspidens (2.5)

of the total catch. Analogous family dominancehas been found in estuaries worldwide (Neira &Potter 1992; Marques et al. 2006). The three dominanttaxa, Gilchristella aestuarias (59.2%), Caffrogobiusgilchristi (19%) and Omobranchus woodi (10%)together comprised more than 88% of the SundaysEstuary larval fish community. This high domi-nance of estuary-resident species of larval fish istypical for permanently open estuaries in SouthAfrican and temperate Australia (Melville-Smith& Baird 1980; Harrison & Whitfield 1990; Neiraet al. 1992; Harris & Cyrus 2000; Strydom et al.2003).

The dominant family of estuarine-dependentswas Mugilidae, also found in the Kowie and GreatFish estuaries by Whitfield et al. (1994) and in thesouth and west coast estuaries by Montoya-Maya& Strydom (2009). In the Sundays Estuary thisfamily was primarily represented by the speciesLiza dumerilii. Other species contributing to thecatch are Myxus capensis, Psammogobius knysnaensis,Pomadasys commersonnii, Glossogobius callidus andRhabdosargus holubi also found by Harrison &Whitfield (1990) and Strydom et al. (2003).Estuarine-dependent species are subject to highermortality rates and therefore show lower numberswhen compared to estuary-resident species(Harrison & Whitfield 1990; Strydom et al. 2003).The larval fish assemblage includes all speciesoccurring in the system as juveniles, indicating theuse of the estuary as a nursery. Many of thesespecies also enter the estuary as adults for feedingpurposes (Marais 1981).

Water temperature showed seasonal variationand had the greatest influence on the larval fishassemblage of the estuary probably as a result ofwarmer temperatures coinciding with the breed-ing season for most coastal fishes. Seasonal fluctua-tions in larval fish species density and diversitywere recorded in the Sundays Estuary, with high-est mean density and diversity occurring in sum-mer. Summer peaks in catches coincide with peaksin primary and secondary production and withpeaks in recruitment for most fish species(Whitfield & Marais 1999; Hagan & Able 2003).This pattern is characteristic for South Africanestuaries (Strydom et al. 2003; Montoya-Maya &Strydom 2009) and estuaries worldwide (Neiraet al. 1992; Ramos et al. 2006).

Gilchristella aestuarias, C. gilchristi, O. woodi,L. dumerilii and G. callidus were most abundant insummer. Harrison & Whitfield (1990) also measuredhighest densities of G. aestuarias in summer, corre-

sponding to the peak in the main spawning periodfor this species. These peaks in productivity areassociated with lower salinities which triggerspawning of this species (Strydom et al. 2002).Past studies have found that high densities ofG. aestuarias are found in areas of low salinity andin freshwater-rich systems (Strydom et al. 2002;Pattrick et al. 2007). In the Swartkops Estuary,Melville-Smith (1978) recorded C. gilchristi inspring, with large numbers occurring throughoutthe summer season. Similarly, C. gilchristi wasfound to be most abundant in early spring to latesummer in the present study. Rhabdosargus holubioccurred in highest densities in summer (Harrison& Whitfield 1990) in the Sundays Estuary with adecline in densities in winter in the SwartkopsEstuary (Melville-Smith 1978). However, in thepresent study, highest densities (although nothighly abundant) of R. holubi were recorded inspring.

Zooplankton standing stock in the SundaysEstuary attains highest biomass in summer(Wooldridge & Bailey 1982). This is primarily dueto the abundance of the dominant copepodsAcartia longipatella and Pseudodiaptomus hessei(Sutherland et al. 2010). Therefore, the seasonalfluctuations positively correlate to copepod abun-dance, increasing potential growth and survival oflarval fish (Harrison & Whitfield 1990).

Salinity zones play an important role in thestructuring of species density in estuaries(Strydom et al. 2003). In the present study, highestmean density occurred in the euhaline zone. Thisis predominantly due to the high densities of theestuarine residents G. aestuarias, O. woodi andC. gilchristi. High mean larval fish density in theeuhaline zone corresponds with highest meanzooplankton density (primarily due to thecopepod A. longipatella) that was found in thissalinity zone (Sutherland et al. 2010). Typically,highest mean densities of larval fish occur in themesohaline zone of most estuaries due to its asso-ciation with the river-estuary interface (REI), thisbeing an area of high primary and secondary pro-ductivity (Wooldridge & Bailey 1982; Jerling &Wooldridge 1991; Snow et al. 2000; Strydom et al.2003).

Highest larval fish diversity was found in theoligohaline zone and in the upper reaches of theestuary (site 8). SIMPER revealed that this highdiversity was attributed to high numbers ofG. aestuarias, G. callidus, M. capensis and L. dumerilii.Hilmer & Bate (1990) recorded chlorophyll-a and


nitrate maxima not only in the mesohaline but alsoin the oligohaline zone of the Sundays Estuary.Maximum primary productivity in these regionsresults in elevated zooplankton productivity,particularly copepods (Wooldridge & Bailey 1982;Jerling & Wooldridge 1991). High densities of thecopepod P. hessei were recorded in the upperreaches of the estuary (Sutherland et al. 2010).Therefore high larval fish diversity in the oligohalinezone may be explained through feeding implica-tions for larval fish such as G. aestuarias, G. callidus,M. capensis and L. dumerilii.

Gilchristella aestuarias spawn in the upperreaches of open estuaries and larvae extend downinto the estuary as they develop. This explains thedominance of G. aestuarias in the middle stations 3and 5 and upper reaches (stations 6 and 7) in theSundays Estuary. Similar spatial distribution ofG. aestuarias was found by Melville-Smith (1978)and Whitfield (1989b) in the Swartkops andSwartvlei estuaries. Harrison & Whitfield (1990)found largest abundance of O. woodi and C. gil-christi in the lower reaches of the estuary. Similarresults were found in the present study; however,C. gilchristi also occurred in higher densities in theupper estuary (site 8).

Estuarine-resident species (category I) comprisedthe largest portion of the larval fish assemblage inthe Sundays Estuary. The dominance of estuarine-resident species in open estuaries was also notedby Strydom et al. (2003) and Montoya-Maya &Strydom (2009). The trend of freshwater speciesbeing restricted to the upper reaches and marinestragglers to the lower reaches (Strydom et al. 2003;Pattrick et al. 2007) was not as clear in the SundaysEstuary. Estuarine-dependent and catadromousspecies occurred throughout most of the estuary.This is probably attributable to the high freshwaterinflow from the IBWTS and a more uniform chan-nel like estuary providing marginal refuge with-out the high degree of habitat structuringoccurring in other systems that are less uniform inchannel structure. Inter-basin water transferschemes tend to alter the natural longitudinalstructuring of young fish assemblages when ele-vated freshwater supply affects water chemistryand flow dynamics as has been observed in theGreat Fish Estuary (Strydom et al. 2002). It is highlyprobable that seasonal productivity is artificiallyprolonged throughout the year through the inter-basement transfer of nutrients.

A high dominance of preflexion larvae in summercoincides with peaks in spawning of most species.

This suggests a high degree of local productionoccurring in the Sundays Estuary. Highest densi-ties of early juveniles occurred in winter, whichmay be attributable to grow-out of estuarine-resi-dent species (e.g. G. aestuarias) that make use of theestuary throughout their life cycle. Preflexionlarval fish dominated the lower reaches of theestuary, mainly attributable to C. gilchristi andO. woodi. There is evidence that these species,which have a marine larval phase, show synchro-nized hatching that coincides with strong ebbtidal currents in order to be carried into the sea(Whitfield & Marais 1999). A trend of expansioninto the middle and upper estuary as larvaedevelop, is seen. Similar trends were noted byStrydom (2003) where postflexion larvae maketheir way up into the estuary through activemigration and flood tidal movement.

In conclusion, the Sundays Estuary plays animportant role as a nursery area in the early lifehistory of many fish species, including marinespecies as well as estuarine-resident species. It isan area of high primary production and an assess-ment of the larval fish assemblage occurring in theSundays Estuary facilitates a holistic understand-ing of the plankton in this estuarine system. Animportant finding in the present study is thereduction in larval fish density in areas predictedto be high and an increase in larval fish density inthe lower reaches of the estuary. Such anomalousfindings may be related to water quality problemsin the low salinity waters. Low oxygen levels havebeen observed in conjunction with low catches oflarval fishes (Strydom et al. 2003) that is likelylinked to eutrophication from agricultural run-off.This has as yet not been further explored in thesystem but will be the focus of upcoming research.

ACKNOWLEDGEMENTS

The authors wish to acknowledge the SouthAfrican National Parks for funding the researchproject. The National Research Foundation inSouth Africa is thanked for supplementary fund-ing. Fieldworkers are thanked for their valuedassistance.

REFERENCES

ABLE, W.A., FAHAY, M.P., WITTING, D.A., McBRIDE,R.S. & HAGAN, M. 2006. Fish settlement in the oceanvs. estuary: comparison of pelagic larval and settledjuvenile composition and abundance from southernNew Jersey, U.S.A.. Estuarine, Coastal and Shelf Science66: 280–290.

ACEVES-MEDINA, G., SALDIERNA-MARTINEZ, R.,


HINOJOSA-MEDINA, A., JIMENEZ-ROSENBERG,S.P.A., HERNANDEZ-RIVAS, R. & MORALES-AVILA, R. 2008. Vertical structure of larval fishassemblages during diel cycles in summer and winterin the southern part of Bahia de La Paz, Mexico.Estuarine, Coastal and Shelf Science 76: 889–901.

BARLETTA-BERGAN, A., BARLETTA, M. & SAINT-PAUL, U. 2002. Structure and seasonal dynamics oflarval fish in the Caete River Estuary in North Brazil.Estuarine, Coastal and Shelf Science 54: 193–206.

BECKLEY, L.E. 1984. The ichthyofauna of SundaysEstuary, South Africa, with particular reference to thejuvenile marine component. Estuaries 7(3): 248–258.

BECKLEY, L.E. 1985. Tidal exchange of ichthyoplanktonin the Swartkops estuary mouth, South Africa. SouthAfrican Journal of Zoology 20: 15–20.

BERASATEGUI, A.D., ACHA, E.M. & FERNANDEZARAOZ, N.C. 2004. Spatial patterns of ichthyo-plankton assemblages in the Rio de la Plata Estuary(Argentina-Uruguay). Estuarine, Coastal and ShelfScience 60: 599–610.

BOEHLERT, G.W. & MUNDY, B.C. 1988. Roles of behav-ioural and physical factors in larval and juvenile fishrecruitment to estuarine nursery areas. AmericanFisheries Society Symposium 3: 51–67.

CLARKE, K.R. & WARWICK, R.M. 1994. Change in MarineCommunities: an Approach to Statistical Analysis andInterpretation. Plymouth Marine Laboratory, Plymouth,U.S.A.

DAWES, C.J. 1981. Marine Botany. John Wiley and Sons,New York.

EMMERSON, W.D. 1989. The nutrient status of theSundays River estuary. South African Water Research23(8): 1059–1067.

FARIA, A., MORAIS, P. & CHICHARO, M.A. 2006.Ichthyoplankton dynamics in the Guadiana estuaryand adjacent coastal area, south-east Portugal.Estuarine, Coastal and Shelf Science 70: 85–97.

HAGAN, S.M. & ABLE, K.W. 2003. Seasonal changes inpelagic fish assemblage in a temperate estuary.Estuarine, Coastal and Shelf Science 56: 15–29.

HARA, T.J. 1992. Fish chemoreception: overview andintroduction. In: Fish Chemoreception, (ed.) T.J. Hara,pp. 1–12 Chapman and Hall, London.

HARRIS, S.A. & CYRUS, D.P. 1995. Occurrence of fishlarvae in the St Lucia Estuary, KwaZulu-Natal, SouthAfrica. South African Journal of Marine Science 16:333–350.

HARRIS, S.A. & CYRUS, D.P. 2000. Comparison of larvalfish assemblages in three large estuarine systems,KwaZulu-natal, South Africa. Marine Biology 137:527–541.

HARRISON, T.D. 2004. Physico-chemical characteristicsof South African estuaries in relation to zoogeographyof the region. Estuarine, Coastal and Shelf Science 61:73–87.

HARRISON T.D. & WHITFIELD, A.K. 1990. Composi-tion, distribution and abundance of ichthyoplanktonin the Sundays River estuary. South African Journal ofZoology 25(3): 161–168.

HILMER, T. 1990. Factors influencing the estimation ofprimary production in small estuaries. Ph.D. thesis,University of Port Elizabeth, Port Elizabeth, SouthAfrica.

HILMER, T. & BATE, G.C. 1990. Covariance analysis ofchlorophyll distribution in the Sundays River Estuary,eastern Cape. South African Journal of Aquatic Sciences16: 37–59.

JAMES, N.C., COWLEY, P.D., WHITFIELD, A.K. &KAISER, H. 2008. Choice chamber experiments to testthe attraction of postflexion Rhabdosargus holubilarvae to water of estuarine and riverine origin.Estuarine, Coastal and Shelf Science 77: 143–149.

JERLING, H.L. & WOOLDRIDGE, T.H. 1991. Populationdynamics and estimates of production for theCalanoid copepod Pseudodiaptomus hessei in a warmtemperate estuary. Estuarine, Coastal and Shelf Science33: 121–135.

JERLING, H.L. & WOOLDRIDGE, T.H. 1995. Planktondistribution and abundance in the Sundays RiverEstuary, South Africa, with comments on potentialfeeding interactions. South African Journal of MarineScience 15: 169–184.

LEIS, J.M. & CARSON-EWART, B.M. 2000. The Larvae ofIndo-Pacific Coastal Fishes: An Identification Guide toMarine Fish Larvae. Koninklijke Brill, Leiden.

MARAIS, J.F.K. 1981. Seasonal abundance, distribution,and catch per unit effort using gill-nets, of fishes inthe Sundays Estuary. South African Journal of Zoology16: 144–150.

MARQUES, S.C., AZETTEIRO, U.M., MARQUES, J.C.,NETO, J.M. & PARDAL, M.A. 2006. Zooplankton andichthyoplankton communities in a temperate estuary:spatial and temporal patterns. Journal of PlanktonResearch 28: 297–312.

MELVILLE-SMITH, R. 1978. Aspects of ecology of fishlarvae in the Swartkops Estuary, Port Elizabeth. M.Sc.thesis, University of Port Elizabeth, Port Elizabeth,South Africa.

MELVILLE-SMITH, R. & BAIRD, D. 1980. Abundance,distribution and species composition of fish larvae inthe Swartkops estuary. South African Journal of Zoology15: 72–78.

MONTOYA-MAYA, P.H. & STRYDOM, N.A. 2009.Description of larval fish composition, abundanceand distribution in nine south and west coast estuariesof South Africa. African Zoology 44(1): 75–92.

NEIRA, F.J., MISKIEWICZ, A.G., TRNSKI, T. 1998. Larvaeof Temperate Australian Fishes, Laboratory Guide forLarval Fish Identification. University of Western Aus-tralia Press, Nedlands.

NEIRA, F.J. & POTTER, I.C. 1992. Movement of larvalfishes through the entrance channel of a seasonallyopen estuary in Western Australia. Estuarine, Coastaland Shelf Science 35: 213–234.

NEIRA, F.J. & POTTER, I.C. 1994. The larval fish assem-blage of the Nornalup-Wapole Estuary, a permanentlyopen estuary on the southern coast of WesternAustralia. Australian Journal of Freshwater Research 45,1193–1207.

NEIRA, F.J., POTTER, I.C. & BRADLEY, J.S. 1992.Seasonal and spatial changes in larval fish faunawithin a large temperate Australian estuary. MarineBiology 112: 1–16.

PATTRICK, P., STRYDOM, N.A. & WOOLDRIDGE, T.H.2007. Composition, abundance, distribution and sea-sonality of larval fishes in the Mngazi Estuary, SouthAfrica. African Journal of Aquatic Science 32(2): 113–123.


PECH, G.A., McCOURT, B. & KEMPER, N.P. 1995.Orange River development project, replanningstudy. Environmental overview of the Eastern CapeRivers. Department of Water Affairs and Forestry,Ninham Shand Incorporated Report No. 2357, CapeTown, South Africa.

POTTER, I.C., BECKLEY, L.E., WHITFIELD, A.K. &LENANTON, R. 1990. Comparison between the rolesplayed by estuaries in the life cycles of fishes intemperate Western Australia and southern Africa.Environmental Biology of Fishes 28: 143–178.

RAMOS, S., COWEN, R.K., RE, P. & BORDALO, A.A.2006. Temporal and spatial distributions of larval fishassemblages in the Lima estuary (Portugal). Estuarine,Coastal and Shelf Science 66: 303–314.

SMITH, M.M. & HEEMSTRA, P.C. 1986. Smith’s Sea Fishes.Macmillan South Africa, Johannesburg.

SNOW, G.C., ADAMS, J.B. & BATE, G.C. 2000. Effectof river flow on estuarine microalgal biomass anddistribution. Estuarine, Coastal and Shelf Science 51:255–266.

STRYDOM, N.A. 1998. Fish larval dynamics in themouth region of the Gamtoos Estuary. M.Sc. thesis,University of Port Elizabeth, Port Elizabeth, SouthAfrica.

STRYDOM, N.A. 2003. An assessment of habitat use bylarval fishes in a warm temperate estuarine creekusing light traps. Estuaries 25: 1310–1318.

STRYDOM, N.A. & WHITFIELD, A.K. 2000. The effectsof a single freshwater release into the KrommeEstuary. 4: Larval fish response. Water SA 26(3):319–328.

STRYDOM, N.A., WHITFIELD, A.K. & PATERSON, A.W.2002. Influence of altered freshwater flow regimes onabundance of larval and juvenile Gilchristellaaestuarias (Pisces: Clupeidae) in the upper reaches oftwo South African estuaries. Marine and FreshwaterResearch 53: 431–438.

STRYDOM, N.A., WHITFIELD, A.K. & WOOLDRIDGE,T.H. 2003. The role of estuarine type in characterizingearly stage fish assemblages in warm temperateestuaries, South Africa. African Zoology 38(1): 29–43.

STRYDOM, N.A. & WOOLDRIDGE, T.H. 2005. Diel andtidal variations in larval fish exchange on a neap andspring tide in the mouth of the Gamtoos Estuary,South Africa. Journal of Aquatic Science 30: 143–152.

SUTHERLAND, K., WOOLDRIDGE, T.H. & STRYDOM,N.A., 2010. The dynamics of larval fish and zooplank-ton assemblages in the Sundays Estuary, SouthAfrica. M.Sc. thesis, Nelson Mandela MetropolitanUniversity, Port Elizabeth, South Africa.

VORWERK, P.D., FRONEMAN, P.W., PETERSON, A.W.,STRYDOM, N.A. & WHITFIELD, A.K. 2008. Biologi-cal responses to the resumption in river flow in afreshwater deprived, permanently open southernAfrican estuary. Water SA 34(5).

WASSERMAN, R.J., STRYDOM. N.A. & WOOL-DRIDGE, T.H. 2010. Larval fish dynamics in theNxaxo-Ngqusi Estuary Complex in the warm tem-perate–subtropical transition zone of South Africa.African Zoology 45(1).

WHITFIELD, A.K. 1985. The role of zooplankton in thefeeding ecology of fish fry from some southernAfrican estuaries. South African Journal of Zoology 20:166–171.

WHITFIELD, A.K. 1989a. Ichthyoplankton interchangein the mouth region of a southern African estuary.Marine Ecology Progress Series 54: 25–33.

WHITFIELD, A.K. 1989b. Fish larval composition, abun-dance and seasonality in a southern African estuarinelake. South African Journal of Zoology 24: 217–224.

WHITFIELD, A.K. 1994a. Abundance of larval and 0+juvenile marine fishes in the lower reaches of threesouthern African estuaries with differing freshwaterinputs. Marine Ecology Progress Series 105: 257–267.

WHITFIELD, A.K. 1994b. Fish species diversity in southernAfrican estuarine systems: an evolutionary perspec-tive. Environmental Biology of Fishes 40: 37–48.

WHITFIELD, A.K. 1998. Biology and ecology of fishes insouthern African estuaries. J.L.B. Smith Institute ofIchthyology. Ichtyological Monographs of the J.L.B.Smith Institute of Ichthyology No. 2.

WHITFIELD, A.K. & HARRISON, T.D. 1996. Gilchristellaaestuarias (Pisces: Clupeidae) biomass and consump-tion of zooplankton in the Sundays estuary. SouthAfrican Journal of Marine Science 17: 49–53.

WHITFIELD, A.K. & MARAIS, J.F.K. 1999. TheIchthyofauna. In: Estuaries of South Africa, (eds) B.RAllanson & D. Baird, pp. 209–233. Cambridge Univer-sity Press, Cambridge.

WHITFIELD, A.K., PATERSON, A.W., BOK, A.H. & KOK,H.M. 1994. A comparison of the ichthyofaunas in twopermanently open eastern Cape estuaries. SouthAfrican Journal of Zoology 29(2): 175–185.

WOOLDRIDGE, T.H. & BAILEY, C. 1982. Euryhalinezooplankton of the Sundays estuary and notes ontrophic relationships. South African Journal of Zoology17: 151–163.

WOOLDRIDGE, T.H. & ERASMUS, T. 1980. Utilization oftidal currents by estuarine zooplankton. Estuarineand Coastal Marine Science 11: 107–114.


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