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PAOLO GUIDETTI, PAOLO D’AMBROSIO
Laboratorio di Zoologia e Biologia Marina, Dipartimento di Scienze e Tecnologie Biologiche
ed Ambientali, Università di Lecce, Via Prov.le Lecce-Monteroni, 73100 Lecce, Italy
SPATIALDISTRIBUTION PATTERNS OF CORIS JULIS AND
THALASSOMA PAVO (PISCES, LABRIDAE)
ALONG THE SOUTH-EASTERN APULIAN COAST (SE ITALY)
SUMMARY
Distribution patterns of two labrid fish, namely Coris julis and Thalassoma pavo,
were assessed by visual census in autumn 2000 at four locations (with three sites
per location), and at different depth levels (from 0 to about 30 m depth) in SE
Apulia (SE Italy). Total abundance and juvenile density of T. pavo tended to be
greater in shallow waters to about 10 m depth, in spite of some differences occur-
red at the scale of sites. Conversely, C. julis showed low densities in waters shal-
lower than 5 m, and higher values from 5 down to about 30 m depth. In the case of
C. julis, differences in the pattern related to depth occurred at both the spatial sca-
les examined (among locations and among sites within location). The patterns
observed for the two species concerned both adult and juvenile fishes, which sug-
gests the absence of evident ontogenetic shifts in habitat use during their life
history. The results presented here suggest that the two species could segregate
according to depth. T. pavo, due to its well known thermophily, could thus over-
compete C. julis at very shallow depths where seawaters are warmer because of the
seasonal thermocline (at least during the period of the year when sampling was
performed). The patterns observed in this study may also provide useful informa-
tion about the scenario that could take shape in areas of the NW Mediterranean,
such as the Ligurian Sea, where T. pavo started increasing in abundance in the
recent years.
RIASSUNTO
Le modalità di distribuzione di due specie ittiche appartenenti alla famiglia dei
labridi, Coris julis eThalassoma pavo, sono state indagate tramite visual census
nell’autunno 2000 presso 4 località (con 3 siti presso ogni località) e 4 differenti
livelli batimetrici (tra 0 e circa 30 m) nella Puglia sud-orientale. L’abbondanza tota-
le e quella dei giovanili di T. pavo è risultata maggiore nelle acque poco profonde
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fino a circa 10 m, malgrado una certa variabilità osservata alla scala dei siti. Per
contro, C. julis ha mostrato densità minori a profondità inferiori ai 5 m e valori più
elevati tra i 5 ed i 30 m. Nel caso di C. julis, le differenze nella distribuzione in rela-
zione alla profondità sono risultate chiare ad entrambe le scale spaziali indagate (tra
località e tra siti presso ogni località). Le modalità osservate per le due specie hanno
riguardato sia gli individui adulti sia i giovanili: ciò suggerisce l’assenza di eviden-
ti ‘shift’ ontogenetici nell’uso degli habitat durante il ciclo vitale. Questi risultati
suggeriscono che le due specie potrebbero segregarsi in relazione alla profondità. T.
pavo, a causa della sua ben nota termofilia, potrebbe così risultare competitiva-
mente superiore a C. julis a basse profondità dove le acque sono più calde a causa
del termoclino stagionale (almeno durante i periodi dell’anno in cui i campiona-
menti sono stati eseguiti). Tali risultati possono anche fornire utili indicazioni sul
possibile scenario che potrebbe verificarsi nelle aree del mediterraneo nord-occi-
dentale, come il mar Ligure, dove T. pavo ha cominciato ad aumentare in abbon-
danza in anni recenti.
INTRODUCTION
Coris julis and Thalassoma pavo are small protogynous labrid fishes widespread in
the Mediterranean littoral. Coris julis lives in seagrass beds, rocky and sandy habi-
tats down to 50 m depth, although it can also be found in deeper areas. T h a l a s s o m a
p a v o chiefly inhabits rocky habitats and seagrass beds from shallow depths down to
25 m (BINI, 1968; TO RTONESE, 1975). As far as the geographic distribution in the
Mediterranean Sea is concerned, C. julisis reported as fairly evenly distributed in the
basin, without any evident latitudinal gradient (BINI, 1968; TO RTONESE, 1975).
Thalassoma pavo, instead, is classically reported as more common along the south-
eastern coasts of the basin (BINI, 1968; TO RTONESE, 1975), which leads to consi-
der this fish as a thermophilic species (see GUIDETTI et al., 2002). In the northern-
most areas of the western basin, such as the Ligurian Sea, it was regarded as rare in
the past (TO RTONESE, 1975). In the recent years, instead, T. pavohas progressively
expanded northwards, an event which was related to the ongoing water warming in
the Mediterranean (GUIDETTI et al., 2002 and references therein).
Most of the previous research on such labrid fishes has focused on sex-inversion
and the influence of population density on mating systems (REINBOTH, 1975;
BRUSLÉ, 1987; WERNERUS and TESSARI, 1991). In recent years, nevertheless,
T. pavo received an increasing attention due to its potential role as an indicator of
climate changes. A number of studies have thus been carried out on its distribution
patterns, ecological requirements, reproductive behaviour, recruitment and early
mortality rates (VACCHI et al., 1999; SARA and UGOLINI, 2001; GUIDETTI,
2001, 2002; GUIDETTI et al., 2002).
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The fact that the two aforementioned species have the same size and may poten-
tially overlap in habitat and trophic requirements suggests possible competition for
resources (e.g., space, food). This involves that some changes could be expected in
areas, such as the north-western Mediterranean, where the two species did not
coexist in the past and where T. pavo is currently increasing in abundance at shal-
low depths (FRANCOUR et al., 1994; VACCHI et al., 1999; GUIDETTI et al.,
2002). To improve understanding of what is happening in the areas recently con-
cerned by increasing density of T. pavo, it could be useful to know what happens in
areas where the two species live together.
This study, therefore, is aimed at investigating distribution patterns of Coris julis
and Thalassoma pavo in SE Apulia, where the two species coexist.
MATERIALS AND METHODS
Sampling areas
Visual census surveys were carried out in early autumn 2000 at four locations,
namely Torre del Serpe (thereafter TS), Torre Minervino (TM), Zinzulusa (ZN), and
Ciolo (CL), situated along the south-eastern Apulian coasts (SE Italy; Fig. 1).
The region is characterised by gently-medium sloped calcarenitic plateau and sub-
vertical rocky slopes. From the water surface to about 5-6 m depth the rocky substrate
is medium-steeply sloped and covered by articulated Corallinaceae and C y s t o s e i r a
spp. From 6-7 m to about 12-15 m depth there is a gentle-medium slope covered by
photophilic algae (e.g., Dictyotales) with numerous medium- and large-sized boul-
ders. Deeper, sub-vertical slopes may be found from about 15 m to 22-25 m, where
the substrate is
mainly constituted
by bio-construc-
tions (the so-cal-
led “coralligenous
formations” in the
Mediterranean).
At about 25-30 m
depth, the slope
decreases and the
“ c o r a l l i g e n o u s
formations” alter-
nate with sand
patches domina-
ting in deeper
a r e a s .
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Fig. 1 - Sampling areas with locations (TS: Torre del Serpe; TM: Torre
Minervino; CL: Ciolo; ZN: Zinzulusa
Sampling method, experimental design and data analysis
Visual censuses were carried out along transects 25 m long and 5 m wide (see HAR-
MELIN-VIVIEN et al., 1985). Transects were randomly placed at four bathymetric
levels: 0-2 m (level A), 5-7 m (B), 12-15 m (C), 25-28 m (D) depth. Three sites were
investigated at each of the four locations, with four replicates at each site and depth
for a total of 192 visual censuses.
Abundance estimates of Coris julis and Thalassoma pavo were expressed as num-
ber of individuals 125 m-2.Analysis of variance (three way ANOVA, using GMAV
5 from University of Sydney) was used to assess differences in mean abundances of
the two species (of both the entire populations and juveniles). “Location” was con-
sidered as a random factor, “Site” as random factor nested in “Location”, and
“Depth” as fixed and orthogonal. Cochran’s test was employed to assess the homo-
geneity of variances. Whenever transformations did not produce homogeneous
variances, ANOVA was used, nevertheless, after setting a= 0.01 in order to com-
pensate for the increased likelihood of Type I error. When appropriate, the SNK test
was used for a posteriori comparisons of the means after an analysis of variance
(UNDERWOOD, 1997).
RESULTS
The general structure of ANOVAs performed in this study is shown in Table 1.
The average abundances of the two species at the four locations surveyed in rela-
tion to depth (total density and average abundance of juvenile specimens) are repor-
ted in Fig. 2 and 3.
Statistical analyses performed on abundances of Coris julis revealed that differen-
ces among depths were not the same at the spatial scales of locations and sites (inte-
ractions ‘Location x Depth’ and ‘Site (Location) x Depth’ were significant at
p<0.001 level for both total densities and juveniles). As a general rule, nonetheless,
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Source of variation
Location = L
Site(Location) = S(L)
Depth = D
L x D
S(L) x D
Residual
Total
d. f.
3
8
3
9
24
144
191
Tab. 1 - General structure of ANOVAs performed in the present study. d.f. = degrees of freedom.
the lowest values were observed in the shallowest transects, with a sudden increase
in abundances (for both the entire population and juveniles) at the deeper levels (B,
C and D; Fig. 2).
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Fig. 2 - Mean abundances of Thalassoma pavo and Coris julis among depths at the four locations stu-
died.
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Fig. 3 - Mean abundances of juveniles of Thalassoma pavo and Coris julis among depths at the four
locations studied.
Analyses of variance carried out on Thalassoma pavo also provided evidence of
similar distribution patterns for both the entire population and juveniles. The signifi-
cant interactions ‘Depth x Site (Location)’(at p<0.001 level for both the whole popu-
lation and juveniles) revealed that the differences among depth strata were not the
same among sites within location. The pattern among depths, instead, was similar at
the spatial scale of location. Except for some discrepancy at some sites, T. pavo d e n-
sities at levels Aand B were higher than those observed at levels C and D (Fig. 3).
DISCUSSION
The coexistence of similar species within the same ecosystem may occur owing to
different use of and/or access to resources (SCHOENER, 1974). From this per-
spective, resource partitioning in terms of food, habitat, depth, and time partitioning
in their use have been extensively documented among fishes in temperate rocky
reefs (e.g. LOVE and EBELING, 1978; HIXON, 1980; LARSON, 1980;
Y O S H I YAMA, 1980; HALLACHER and ROBERTS, 1985; EBELING and
LAUR, 1986; HOLBROOK and SCHMITT, 1986). In the Mediterranean Sea,
nevertheless, resource partitioning has classically received little attention (see for
instance MACPHERSON, 1981, and HARMELIN-VIVIEN et al.,1989; SALAand
BALLESTREROS, 1997) and few studies have been carried out on small sedentary
fishes (ZANDER, 1982; MACPHERSON, 1994).
The present study provides suggestive evidence of depth segregation between the
two labrid fishes Thalassoma pavo and Coris julis in rocky reefs in SE Apulia.
Depth, however, explained only partially the distribution patterns of the two species
as differences among depths were not always coherent at the two spatial scales exa-
mined (100s metres and 10s kilometres, i.e. among sites within location and among
locations, respectively). The decrease/increase in abundance of the two fishes, in
addition, were not linearly related to depth. Thalassoma pavo, in fact, appeared to
live in similar numbers from the surface to approximately 10 m depth, while avera-
ge abundance suddenly declined in deeper areas. This pattern could be related to the
existence of the seasonal thermocline (still present in early autumn) in the
Mediterranean waters, and to the fact that T. pavo is a thermophilic fish (see GUI-
DETTI et al., 2002 and references therein). Coris julis, conversely, was fairly rare
in the shallowest areas (<5 m depth), whereas approximately comparable densities
were recorded from 5 m depth to the deepest transects down to about 30 m depth.
Another outcome deserving to be considered is that adults and juveniles of both spe-
cies substantially displayed the same distribution patterns. This result, nevertheless,
is consistent with the patterns showed by several labrid species in the Mediterranean
and elsewhere, which usually do not show evident ontogenetic shifts in the habitat
use during their life histories (GARCIA-RUBIES and MACPHERSON, 1995;
GREEN, 1996).
Data about distribution patterns of the two investigated labrids have previously
been reported by other authors in the frame of wider studies about fish assemblages
in several areas of southern Italy, where T. pavois usually dramatically abundant in
shallow rocky-reefs (e.g., MAZZOLDI and DE GIROLAMO, 1998; VACCHI et
al., 1998). Only VACCHI et al. (1997), nevertheless, suggested the possibility of
competition (and consequent depth segregation) between the two species to explain
differences in their bathymetric distribution, an issue which became even more
important when T. pavo started expanding northwards its distribution limits (GUI-
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DETTI et al., 2002 and references therein). It has to be taken into account, in fact,
that C. julis is one of the most common fish even in the shallowest rocky reefs in
the Ligurian Sea (see for instance TUNESI and VACCHI, 1992), where T. pavowas
fairly rare since few years ago (TORTONESE, 1975). As aforementioned, mean
abundance of T. pavo increased more and more in this area, although densities still
remain far lower than those found in the south-western Mediterranean (GUIDETTI
et al., 2002). All the above issues suggest that T. pavo could competitively exclude
C. julis from shallow stands. Conversely, at depth levels where the waters are col-
der (e.g. under the seasonal thermocline) the thermophilous T. pavo could not be
able to overcompete C. julis.
Whether such patterns are actually due to competitive exclusion or not, however,
cannot be said only on the basis of the data presented in this study. From this point
of view, for example, specific investigations on the diets of the two species would
be necessary in order to observe whether there could be an overlap in the use of
food resources. Similar observations, in addition, should be repeated in time to
observe whether they are temporally coherent or not. It has to considered, from this
perspective, that we sampled the two species in a period of the year corresponding
to the end of the reproductive season (usually summer), and distribution patterns of
adults may change during spawning periods. Long-term data in regions of recent
spreading of T. pavo should also be collected for assessing putative changes in time
in the distribution patterns of the two studied fish species.
ACKNOWLEDGEMENTS
This study was carried out in the framework of INTERREG (Italy-Greece) and
SINAPSI (Seasonal, INterannual and decAdal variability of the atmosPhere,
oceanS and related marIne ecosystems; AdP CNR-MURST L. 95/95) Research
Projects.
REFERENCES
BINI G., 1968 - Atlante dei Pesci delle Coste Italiane. Osteitti, vol. 5. Mondo
Sommerso Editore, Roma: 175 pp.
BRUSLÉ S., 1987 - Sex-inversion of the hermaphroditic, protogynous teleost Coris
julis L. (Labridae). J. Fish Biol., 30: 605-616.
EBELING A.W., LAUR D.R., 1986 - Foraging in surfperches: resource partitioning or
individualistic response? Eviron. Biol. Fishes, 16: 123-133.
-88 -
FR A N C O U R P., BO U D O U R E S Q U E C . F., HA R M E L I N J.G., HA R M E L I N- VI V I E N M . L . ,
Quignard J.P., 1994- A re the Mediterranean Waters Becoming Wa r m e r ?
Information from Biological Indicators. Mar. Poll. Bull., 28 (9): 523-526.
GARCIA-RUBIES A., MACPHERSON E., 1995 - Substrate use and temporal pattern of
recruitment in juvenile fishes of the Mediterranean littoral. Mar. Biol., 124: 35-
42.
GREEN A. L., 1996 - Spatial, temporal and ontogenetic patterns of habitat use by
coral reef fishes (Family Labridae). Mar. Ecol. Prog. Ser., 133: 1-11.
GUIDETTI P., 2001 - Population dynamics and post-settlement mortality of the orna -
te wrasse, Thalassoma pavo, in the Tyrrhenian Sea (western Mediterranean).
Ital. J. Zool., 68: 75-78.
GU I D E T T I P. , 2002 - Temporal changes in density and re c ruitment of the
Mediterranean ornate wrasse Thalassoma pavo (Pisces, Labridae). Arch. Fish.
Mar. Res., 49: 259-267.
GUIDETTI P., BIANCHI C.N., LAMESA G., MODENA M., MORRI C., SARA G., VACCHI
M., 2002 - Abundance and size structure of Thalassoma pavo (Pisces: Labridae)
in the western Mediterranean Sea: variability at different spatial scales. J. Mar.
Biol. Ass. U.K., 82 (3): 495-500.
HALLACHER L. E., ROBERTS D. A., 1985 - Differential utilisation of space and food
by the inshore rockfishes (Scorpaenidae: Sebastes) of Carmel bay. Environ.
Biol. Fishes, 12: 91-110.
HARMELIN-VIVIEN M.L., HARMELIN J.G., CHAUVET C., DUVAL C., GALZIN R.,
LEJEUNE P., BARNABE G., BLANC F., CHEVALIER R., DUCLERC J., LASSERRE G.,
1985 - Evaluation des peuplements et populations de poissons. Méthodes et pro -
blemes. Rev. Ecol. (Terre Vie), 40: 467-539.
HARMELIN-VIVIEN M. L., KAIM-MALKA R. A., LEDOYER M., JACOB-ABRAHAM S. S.,
1989 - Food partitioning among scorpaenid fishes in Mediterranean seagrass
beds. J. Fish Biol., 34: 715-734.
HIXON M. A., 1980 - Competitive interaction between California reef fishes of the
genus Embiotoca. Ecology, 31: 918-931.
HOLBROOK S. J., SCHMITT R. J., 1986 - Food acquisition by competing surfperch on
a patchy environmental gradient. Environ. Biol. Fish., 16: 135-146.
LOVE M. S., EBELING A. W., 1978 - Food and habitat of three switch feeding fishes
in the kelp forest of Santa Barbare, California. Fish. Bull. US, 76: 257-271.
MACPHERSON E., 1981 - Resource partitioning in a Mediterranean demersal fish
community. Mar. Ecol. Prog. Ser., 4: 183-193.
MACPHERSON E., 1994 - Substrate utilisation in a Mediterranean littoral fish com -
munity. Mar. Ecol. Prog. Ser., 114: 211-218.
MAZZOLDI C., De Girolamo M., 1998 - Littoral fish community of the Island
Lampedusa (Italy): a visual census approach. Ital. J. Zool., 65: 275-280.
-89 -
REINBOTH R., 1975 - Spontaneous and hormone-induced sex-inversion in wrasses
(Labridae). Pubbl. Staz. Zool. Napoli 39 (suppl.): 550-573.
SALA E., BALLESTREROS E., 1997 - Partitioning of space and food resources by three
fish of the genus Diplodus (Sparidae) in a Mediterranean rocky infralittoral eco -
system. Mar. Ecol. Prog. Ser., 152: 273-283.
SARA G., UGOLINI U., 2001 - Recent naturalization of the warm-water wrasse
Thalassoma pavo (Pisces, Osteichthyes) in the Ligurian Sea. Atti XIV AIOL,
Garda (VR) 14: 249-258.
SCHOENER T. W., 1974 - Resource partitioning in natural communities. Science,
185: 27-39.
TORTONESE E., 1975 - Osteichthyes - Pesci ossei (parte seconda). Fauna d’Italia
(Vol. XI). Calderini, Bologna: 636 pp.
TUNESI L., VACCHI M., 1992 - Indagini visuali in immersione nell’area marina di
Portofino: applicazione di un metodo per lo studio dei popolamenti ittici.
Biologia Marina, 1: 355-360.
UNDERWOOD A. J., 1997 - Experiments in Ecology: their logic design andinterpre -
tation using analysis of variance. Cambridge (University Press): 504 pp.
VACCHI M., LAMESA G., LAMESA M., 1997 - Studio preliminare del popolamento
ittico costiero delle Isole Eolie (Tirreno Meridionale, Mediterraneo). Atti del
XII Congresso AIOL (Piccazzo M., ed.), 1: 489-497.
VACCHI M., BUSSOTTI S., GUIDETTI P., LAMESA G., 1998 - Study of the coastal fish
assemblage in the marine reserve of the Ustica Island (southern Tyrrhenian
Sea). Ital. J. Zool., 65: 281-286.
VACCHI M., SARA G., MORRI C., MODENA M., LAMESA G., GUIDETTI P., BIANCHI, C.
N., 1999 - Dynamics of marine populations and climate change: lessons from a
reef fish in the Ligurian Sea (N-W Mediterranean). PMNHS Newsletter, 3: 13-
17.
WERNERUS F., TESSARI V., 1991 - The influence of population density on the mating
system of Thalassoma pavo, a protogynum Mediterranean labrid fish. P.S.Z.N.:
Mar. Ecol., 12: 361-368.
ZANDER C. D., 1982 - Feeding ecology of littoral gobiid and blennoid fish of the
Banyuls area (Mediterranean Sea). 1-Main food and trophic dimension of niche
and ecotope. Vie Mileu, 32: 1-10.
- 90 -
