Spatial and temporal distribution of zooplankton related to the environmental conditions in the coral reef lagoon of New Caledonia, Southwest Pacific

Marine Pollution Bulletin 61 (2010) 367–374

Contents lists available at ScienceDirect

Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

Spatial and temporal distribution of zooplankton related to the environmental conditions in the coral reef lagoon of New Caledonia, Southwest Pacific L. Carassou a,*, R. Le Borgne b, E. Rolland a, D. Ponton a a b

IRD, UR128, BP A5, 98 848 Nouméa Cedex, New Caledonia IRD, UR103, BP A5, 98 848 Nouméa Cedex, New Caledonia

a r t i c l e

i n f o

Keywords: Prey of fish larvae Meso- and micro-zooplankton Environmental conditions Coral reef Bays Lagoon

a b s t r a c t The distribution of zooplanktonic prey of fish larvae was examined in three bays and two lagoonal stations in the Southwest lagoon of New Caledonia. Water column conditions were characterized by increasing chlorophyll a and particulate organic matter (POM) concentrations from the lagoon to the estuarine bay. The mean zooplankton settled volume and total density were significantly higher in the estuarine bay, reaching 35.1 mL m3 and 3.5  105 individuals m3, respectively. The total zooplankton density also progressively increased along the sampling period. The composition of assemblages differed between the lagoon and the bays, and was similar in the three bays. Wind speed, surface temperature, chlorophyll a and POM explained these variations, as revealed by a co-inertia analysis (COIA). The prey preferred by fish larvae, i.e. small crustaceans and small copepods, were more abundant in bays. Sheltered bays, most influenced by terrigenous inputs, are likely to provide the best feeding conditions. Ó 2010 Published by Elsevier Ltd.

1. Introduction Understanding the relationships between environmental factors and the structure of zooplankton assemblages is a crucial challenge. It may help determine the origin of spatial and temporal variations in food availability for fish larvae, and thus identify the habitats and water masses in which fish larvae find the most suitable and abundant food (Cushing, 1996; Fortier et al., 1992). It may even contribute to make possible the prediction of fluctuations in recruitment for commercially exploited species (Castonguay et al., 2008). In tropical areas, apart from a few descriptions of seasonal variations in mesozooplankton assemblages (Binet and Le Borgne, 1996; D’Croz et al., 2005; McKinnon et al., 2005), these issues have rarely been examined, and the relationship between the small-scale spatial and temporal patterns in zooplankton composition and the environmental conditions remains unknown so far. The lagoon of New Caledonia, Southwest Pacific, is the ideal place to examine the differences in zooplankton biomass and composition in contrasted, spatially variable, trophic conditions. New Caledonia is influenced by a tropical climate with two contrasted seasons: a warm and wet period from mid-November to mid-April, when high rainfalls and tropical depressions occur, and a cool and drier period from mid-May to mid-October (ORSTOM, 1981; Le Borgne et al., 2010). Its lagoon extends over approximately 19 000 km2, the barrier reef lying at a distance of one to 65 km from the coast in some places (Andrefouet and Torres-Pulliza, * Corresponding author. Tel.: +687 26 07 23; fax: +687 26 43 26. E-mail address: [email protected] (L. Carassou). 0025-326X/$ - see front matter Ó 2010 Published by Elsevier Ltd. doi:10.1016/j.marpolbul.2010.06.016

2004). The size of the lagoon results in strong contrasts between near shore waters and the lagoonal waters located further from the coast. Shore waters are subject to the effect of terrigenous inputs leading to higher chlorophyll a concentrations (Tenório et al., 2005; Jacquet et al., 2006) and zooplankton densities (Champalbert, 1993; Binet and Le Borgne, 1996). Conversely, lagoonal waters are influenced by oceanic flows with oligotrophic characteristics (Ouillon et al., 2005). Depending on weather conditions, the spatial extension of these two different water masses and the intensity of lagoonal waters enrichments will vary (Le Borgne et al., 2010). The present study was therefore conducted in three stages: (1) the observation of the environmental conditions encountered within the warm season in three bays characterized by different geomorphologies and levels of exposure to terrigenous inputs on the one hand, and in two lagoonal sites situated at different distances from the shore on the other hand, using various meteorological and water column parameters; (2) the observation of the biomass, density and composition of micro and mesozooplankton in each location; (3) the identification of the environmental parameters which influence the spatial and temporal variations in micro and mesozooplankton distributions, using multivariate statistical methods. 2. Material and methods 2.1. Study sites and periods Sampling took place in two sites of the Southwest lagoon of New Caledonia: Ouano, near La Foa, located 100 km north of

368

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

discharge of La Dumbéa River (Fig. 1b). Eight stations were sampled in this bay, four of which were sheltered from the prevailing winds from the South-East by the nearby islets and the coastal ranges (Fig. 1b). Depending on their exposition to the prevailing winds, on the occurrence of fresh water discharges and the resulting hydrodynamic conditions encountered at each site during sampling, all stations were grouped within four zones (Fig. 1) as follows: Chambeyron (3 stations), Ouaraï (3 stations), lagoon and barrier (2 stations), Dumbéa exposed (4 stations), and Dumbéa sheltered (4 stations). Since this study aimed at studying the availability of prey for larval fish in the lagoon, sampling took place during the warm season, when larval fish are most abundant in the lagoon, and during the new moon periods, when larval fish sampling is optimized (Carassou and Ponton, 2007). A total number of eight monthly campaigns were thus performed from December 2004 to January

Nouméa, where the barrier reef lies approximately 7 km from the coast (Fig. 1a); and Dumbéa, just a few km north of Nouméa, where the barrier reef lies approximately 20 km from the coast (Fig. 1b). In Ouano, three stations were positioned in the Bay of Chambeyron, which is characterized by muddy bottoms and exposed to the prevailing winds from the South-East (Fig. 1a). Three other stations were sampled in the nearby muddy Bay of Ouaraï, more protected from the prevailing winds from the South-East by the Lebris peninsula, and is submitted to the freshwater inputs of the La Foa River (Fig. 1a). Two more stations were positioned in the lagoon, one near an islet in the intermediate lagoon, where bottoms consist of sandy mud with scattered seaweeds, and the other close to the barrier reef, where bottoms consist of a coral pavement covered by coral rubbles and scattered live corals (Fig. 1a). In Dumbéa, all the stations were located in the large Bay of Dumbéa, which is characterized by muddy bottoms covered by living colonies of branched corals and is submitted to the freshwater

NEW N

CALEDONIA

20°

Coral Sea 0

22°S

50km 164°E

166°

(a) OUANO

168°

(b) DUMBÉA

165°40'

165°50'

166°20'

La Dumbéa River

21°42'

166°30' 22°11'

La Foa River

Ouaraï Bay

21°46'

NOUMEA 22°15'

Lebris peninsula

21°50'

Barrier

Dumbéa Bay

Chambeyron Bay Lagoon

0

5 km 22°19'

21°54' 0

5 km

Fig. 1. Position of the sampling stations in the Bay of Chambeyron (black stars), in the Bay of Ouaraï (white stars) and in the lagoon and at the barrier reef (grey stars) at Ouano (a) and in the exposed part (black stars) and sheltered part (white stars) of the Bay of Dumbéa (b), Southwestern New Caledonia. Dark grey zones on the maps indicate the mangroves; dotted lines represent the location of coral reefs.

369

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

2005 and from September 2005 to February 2006 in Ouano and Dumbéa. Each station was sampled at the beginning of the night, four nights per month in Ouano and two nights per month in Dumbéa. 2.2. Sampling design The zooplanktonic prey of fish larvae, which, according to Sampey et al. (2007), are represented by assemblages of micro- (i.e. 20– 200 lm) and meso-zooplankton (i.e. 200–2000 lm, UNESCO, 1968), were collected by horizontal hauls of a 60 lm mesh, 1.60 m long and 20 cm in diameter plankton-net. Since larval fish are known to feed on the surface of the water column during the night (Hunter, 1984), the net was towed approximately 0.5 m

below the surface for 2 min, at about two knots, along a semi-circular trajectory. A General OceanicÒ flowmeter, set near the plankton-net mouth, provided filtered volume measurements (in m3), assuming 100% filtering efficiency. The plankton-net samples were immediately preserved in a 10% formaldehyde solution. Three water samples were collected at each station with a Niskin bottle, in order to assess the level of trophic enrichment (or eutrophication) of the water column by measuring: (1) the concentration of chlorophyll a (Chl, in lg L1), (2) the relative abundance of pheopigments (%pheo, in%), (3) the concentration of particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively, in lM), and (4) the carbon/nitrogen ratio (C/N, in lM). The water samples were collected at the surface, at middepth, and 1 m above the bottom, the three samples being mixed

Table 1 Main categories of zooplankton sampled in the two studied sites from November 2005 to January 2005 and from September 2005 to February 2006, with corresponding description and abbreviations. Categories are ranked in increasing order of their maximum width (including the appendages), except for the ‘‘others” category that contains several types of organisms rarely encountered. Description of categories

Abbreviations

Copepod nauplii Echinoderm pluteus Eggs and lumps (mainly copepod eggs) Gastropod veligers Bivalve veligers Appendicularians Small copepods (mainly copepodids) Unidentified small crustaceans (include all small articulated and chitinous organisms) Large copepods (mainly adults) Chaetognaths ‘‘Large” larvae (include fish larvae, crustacean zoe larvae, cirrhiped larvae, annelid trocophore larvae) Unidentified large crustaceans (include small shrimps and crabs) Others (i.e. miscellaneous) (include radiolarians, tintinnids, siphonophores, cladocereans)

naup echi eggs lgas lbiv appe scop scru Lcop chae larv Lcru othe

Width (lm) Mean

Min

Max

65.4 70.2 75.4 89.9 105.6 125.4 154.9 176.7 185.4 282.7 349.3 354.5 154.9

47.2 42.3 43.4 62.1 50.9 26.4 39.6 60.4 113.2 90.6 84.9 175.4 39.6

95.6 78.9 113.5 119.8 228.5 312.5 392.3 338.5 460.2 750.9 903.5 692.3 392.3

Table 2 Mean and range (min–max) of environmental values for (a) meteorological variables measured in Ouano and Dumbéa, and of (b) water column variables measured in the Bay of Chambeyron (Cham), the Bay of Ouaraï (Ouar), and in the lagoon and the barrier reef zones (Lag&bar) at Ouano, and in the exposed zone (Dum_exp) and sheltered zone (Dum_shel) of the Bay of Dumbéa. Variable

Code

Unit

Ouano Cham

(a) Meteorological variables Daily rainfall

Rain

mm d1

Daily solar radiation duration

Sol rad

min d1

Daily mean wind speed

Wind speed

km h1

Direction of the maximum wind observed over periods of 10 min

Wind dir

°

(b) Water column variables Temperature 0–5 m

Temp

°C

Salinity 0–5 m

Sal

Turbidity 0–5 m

Turb

FTU

Concentration in chlorophyll a

Chl

lg L1

Proportion of pheopigments

%pheo

%

Carbon/nitrogen ratio

C/N

Particulate organic carbon concentration

POC

lM L1

Particulate organic nitrogen concentration

PON

lM L1

Particulate organic phosphorous concentration

POP

lM.L1

Dumbéa Ouar

Lag&bar

Dum_exp

5.1 (0.0–50.5) 397.1 (0.0–763.1) 10.2 (5.0–14.8) 132 (83.3–235.8) 25.9 (21.0–31.2) 35.8 (31.3–37.1) 2.1 (0.7–8.9) 0.7 (0.4–1.1) 28.8 (20.8–36.1) 7.4 (3.3–10.8) 19.9 (10.3–28.3) 2.8 (1.7–4.6) 0.1 (<0.1–0.2)

25.7 (21.4–29.5) 35.3 (30.1–36.7) 3.1 (1.1–9.3) 0.9 (0.4–1.6) 27.1 (18.5–42.3) 8.2 (4.4–10.6) 28.2 (8.8–79.4) 3.7 (1.3–18.0) 0.2 (0.1–0.4)

Dum_shel 1.9 (0.0–8.8) 465.3 (0.0–774.0) 20.8 (11.9–30.2) 104.1 (58.8–206.3)

24.8 (21.9–27.6) 35.3 (33.5–36.2) 1.0 (0.2–8.8) 0.3 (0.1–0.6) 33.7 (21.3–53.9) 8.6 (1.7–14.2) 11.0 (5.2–23.1) 1.4 (0.5–5.8) 0.1 (<0.1–0.2)

25.6 (21.9–28.3) 35.6 (33.3–36.5) 3.2 (0.4–19.3) 0.6 (0.2–0.9) 26.8 (19.0–35.5) 8.7 (3.5–13.7) 12.2 (6.9–21.4) 1.4 (0.6–2.1) 0.1 (<0.1–0.1)

25.3 (21.9–27.8) 35.5 (32.4–36.3) 2.6 (0.6–11.9) 0.5 (0.2–0.9) 29.1 (22.1–36.5) 9.2 (4.9–12.8) 10.5 (7.3–19.9) 1.2 (0.6–2.3) 0.1 (<0.1–0.1)

370

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

in order to provide a mean value for the water column. Sampling took place at dawn and samples were kept in a cooler. Sub-samples varying from 250 to 700 mL were filtered on 25 lm GF/F Whatman filters. These were immediately frozen and later analyzed following Aminot and Kérouel (2004). The temperature (in °C), salinity and turbidity (FTU) were also recorded at dusk and at dawn at each sampling station within the 5 m surface layer of the water column, using a SBE19 Seabird CTD. The meteorological conditions encountered during the sampling period were obtained for each site from the closest MétéoFrance meteorological stations: La Tontouta for Ouano, and Nouméa for Dumbéa. These data included daily rainfall (mm d1), solar radiation duration (min d1), mean wind speed (km h1) and wind direction of the maximum wind over periods of 10 min (°). 2.3. Laboratory work For each sample, an estimate of the total zooplankton biomass was obtained by measuring the volume of solid matter deposited (hereafter called ‘‘settled volume” or Vs, in mL) in a graduated test-tube. Vs was then divided by the volume of water filtered by the net, Vf (in m3). Zooplanktonic organisms were identified and counted under a microscope (magnification 125) on three 101.8 mm3 sub-samples poured in a Palmer nanoplankton counting slide (Thomas Scientific, Philadelphia, USA). Because the objective was the assessment of the spatial and temporal distribution of potential prey for larval fish, and not an exhaustive study of zoo-

plankton diversity, 13 coarse categories of zooplankton were defined according to both taxonomic criteria and abundances in the samples (Table 1). The density (N m3) of each zooplankton category (Di) was calculated as:

Di ¼

ni  V o Vs  Vf

with ni being the total number of individuals of category i in the three sub-samples, Vo, the total volume of the three sub-samples (0.3054 mL), Vs, the settled volume of the sample (500 mL) and Vf, the water volume filtered by the net (m3). In addition, digital images of 20–30 organisms per prey category and sample were taken with a Scion digital camera (model CFW-1308 M) and processed so as to provide an estimate of the prey size, since the latter parameter is considered as a major determinant of larval fish feeding success (Bremigan and Stein, 1994; Pepin and Penney, 1997). Thus, the critical dimensions of the organisms for their ingestion by fish larvae, i.e. their maximum width, including appendages (Hunter, 1984), were obtained by the Image J software. The 13 zooplanktonic categories retained were then classified according to their maximum width (Table 1). 2.4. Data analysis The spatial and temporal variability in the environmental conditions was described using a normed principal component analysis, PCA (Legendre and Legendre, 1998). After data had been tested

(a) W

d Sol ra

-1

1 -1

1

in d ee

ur

d

N

Sal

sp C

T

C PO PON Chl POP

b

W

ph

eo

Temp

in d di r Rai n

PC2: 19.09%

(b)

de ds

o c

(c)

3.4 -3.3 11 -5.8

PC1: 29.01%

3.4 -3.3 11 -5.8

d5 j6 s5 d4 n5 o5

PC1: 29.01%

f6

PC2: 19.09%

lb

j5

Fig. 2. Results of the PCA on environmental variables, with (a) correlations between variables; (b) projection of the observations grouped by zones, i.e. Bay of Chambeyron (c), Bay of Ouaraï (o), lagoon and barrier (lb), Dumbéa exposed (de) and Dumbéa sheltered (de); (c) projection of the observations grouped by months, i.e. from December 2004 (d4) to January 2005 (j5) and from September 2005 (s5) to February 2006 (f6). Sum of variance explained by the two components is 48.10%. See Table 2 for the meaning of the abbreviations.

371

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

for normality (Kolmogorov–Smimov test), one-way analyses of variance (ANOVAs) followed by Bonferroni and Tukey tests (Scherrer, 1984) were used to test for significant differences between zones for each month and between months for each zone, respectively, for the mean settled volume and total density of zooplankton. The relative proportions of the different categories in zooplankton assemblages were then compared between zones and between months, using a factorial correspondence analysis, CA (Legendre and Legendre, 1998), based on the relative densities (% of the total density) of categories in the samples. Co-inertia analyses (COIA) were then used to examine the relationship between the composition of zooplankton assemblages and environmental variables. The co-inertia analysis is based on the matching of a normed PCA on environmental data and a centered PCA on faunistic data (PCA-PCA-COIA; Dray et al., 2003). A Monte–Carlo test based on 1000 permutations between observations was used to confirm the significance of the co-inertia results (Fixed D test; Dray et al., 2003). All statistical tests and multivariate analyses were performed with Systat 10.2 and ADE-4 (Thioulouse et al., 2001), respectively.

3. Results 3.1. Environmental conditions The meteorological and water column conditions appeared variable spatially and temporally over the sampling period. Wind speeds were higher and rainfalls lower in the Bay of Dumbéa than in Ouano, whereas high rainfall events (i.e. >50.0 mm d1) were observed in Ouano in January 2005 and February 2006 (see Table 2 for mean values and Fig. 2a and 2b). These strong rainfall events were associated with low wind speeds (i.e. 65.0 km h1), high

values of wind direction, i.e. winds blowing from the West (Fig. 2a and c), and low salinities (i.e. 30.1). The water column conditions encountered during sampling were found to vary according to a gradient of turbidity, chlorophyll and particulate organic matter stretching from the lagoon and the barrier zone to the Bay of Ouaraï, with the Bay of Chambeyron presenting intermediate values (Fig. 2a and b; Table 2). No differences between the exposed and the sheltered parts of the Bay of Dumbéa were observed for any variable (Fig. 2a and b; Table 2). 3.2. Zooplankton settled volume and total density The quantity of zooplanktonic organisms collected also varied between zones and months (Fig. 3a and b). Indeed, the mean biomass (i.e. settled volume) and total density of zooplankton were higher in the Bay of Ouaraï (means = 35.1 mL m3 and 3.5  105 ind m3, respectively) than in all the other zones (ANOVAs and Bonferroni tests, P < 0.05; Fig. 3a and b). The mean biomass showed erratic temporal variations, with a minimum of 5.7 mL m3 observed in February 2006 and a maximum of 33.8 mL m3 observed in December 2005, while the density progressively increased during the sampling period, with a minimum of 3.3  104 ind m3 in December 2004 and a maximum of 3.63  105 ind m3 in January 2006 (ANOVAs, Tukey tests, P < 0.05; Fig. 3a and b). 3.3. Composition of zooplankton assemblages The quality of zooplankton assemblages, i.e. their relative composition, varied between zones and months (Table 3). The relative densities (in%) of zooplanktonic categories were found to differ between bays and lagoonal zones, whereas similar compositions characterized the three coastal zones under study (see Table 3

Mean total zooplankton density (nb.m-3)

Mean settled volume (mL.m-3)

(a) 80

A

B

A

A

A

80

70

70

60

60

50

50

40

40

30

30

20

20

10

10

0

B

A

A

B

A

B

A

A

d4

j5

s5

o5

n5

d5

j6

f6

A

A

A

A

B

B

C

C

o5

n5

d5

j6

f6

0 Cham

Ouar

A

B

Dum_exp Dum_shel

Lag&bar

(b) 5

12.10

A

A

A

5

12.10

5

10.10

5

5

8.10

5

5

6.10

5

4.10

5

4.10

5

2.10

5

2.10

5

10.10 8.10

6.10

0

0 Cham

Ouar

Dum_exp Dum_shel

Zones

Lag&bar

d4

j5

s5

Months

Fig. 3. Means and standard deviations of settled volume (a) and total zooplankton density (b) for each zone (left column) and for each month (right column). See Table 2 for the meaning of the zones abbreviations and caption of Fig. 2 for that of months abbreviations.

372

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

and salinity were high and the proportion of pheopigments was low. The density of large unidentified crustaceans alone appeared to increase with wind direction and rainfall (Fig. 5a and b).

for mean proportions and Fig. 4a and b for variability between zones and months). Relative densities of large copepods, gastropod larvae and ‘‘large” larvae were higher in the lagoonal zones, where they represented more than 4%, 7% and 5% of the total density in the lagoonal zones, respectively, than in coastal zones, where they reached only 0.6–1.3%, 2.3–4.4% and 2.1–2.9%, respectively (Table 3; Fig. 4a and b). Conversely, relative densities of small copepods and unidentified small crustaceans were higher in the bays (>35% and P0.5%, respectively) than in lagoonal zones (23.8% and 0.2%, respectively, Table 3; Fig. 4a and b). The relative density of echinoderm larvae appeared higher in December 2004 and January 2005 (Fig. 4a and c).

4. Discussion In the present study, nauplii of copepods and copepods (i.e. copepodids and adults) represented a large part of the total density of zooplankton (34.7% and 40.7%, respectively). These proportions are close to those reported by Le Borgne et al. (1989) in the Tikehau atoll (Tuamotu archipelago, French Polynesia), where nauplii and copepods represented 39.2% and 30.6% of the total zooplankton biomass, respectively. In our study, bivalve larvae represented 3.9% of the total density of zooplankton, versus only 0.2% in the open atoll of Ouvéa, New Caledonia (Le Borgne et al. 1997), and up to 19.8% in the Tikehau atoll, French Polynesia (Le Borgne et al. 1989). The differences in the proportions of molluscs larvae observed in these different studies may be accounted for by the seasonal spawning patterns of adults. It is also possible that the net used in the present study, i.e. with a diameter of 20 cm and fitted with a 60 lm mesh, may have under-estimated the density of larger zooplankton due to net avoidance. However, these larger organisms are poorly consumed by larval fish, which feed upon organisms ranging from 50 to 150 lm in width (Carassou, 2008). One main result of this study is that zooplankton assemblages differ in composition between bays and lagoonal waters, suggesting

3.4. Relationship between zooplankton assemblages and environmental conditions The variations in zooplankton composition between zones and months were found to correlate with the environmental conditions encountered in the four zones during the sampling period. The relative densities of chaetognaths, small copepods, ‘‘large” larvae, and appendicularians increased with surface temperature, chlorophyll and particulate organic matter concentrations (Fig. 5a and b). The relative densities of bivalve larvae, nauplii of copepods and gastropod larvae were positively related to variations in wind speed, solar radiation duration and carbon/nitrogen ratio, and negatively related to wind direction and rainfall. Eggs, unidentified small crustaceans and the ‘‘other” category increased when turbidity

(a) 0.6 -1.1 1.1 -1.7

n a up c h ae eggs appe

larv

lbiv

FC1: 19.13%

scop

lgas othe scru echi

(b)

Lcru

FC2: 15.73%

Lcop

(c) 0.6 -1.1 1.1 -1.7

0.6 -1.1 1.1 -1.7 n5

c ds4 de o lb

FC1: 19.13%

j6

o5 d5

f6

FC1: 19.13%

s5

FC2: 15.73%

FC2: 15.73%

d4 j5

Fig. 4. Results of the CA on the relative densities (%) of zooplankton categories, with (a) projection of the zooplankton categories; (b) projection of the observations grouped by zones; (c) projection of the observations grouped by months. Sum of variance explained by the two axes is 34.96%. See Table 1 for meaning of the zooplankton categories abbreviations; see caption of Fig. 2 for meaning of the zones and months abbreviations.

373

appe Lcru

echi scop Lcop axis 1: 72.74 %

axis 2: 14.15 %

lgas

eggs scru othe

naup

lbiv

Fig. 5. Result from the co-inertia analysis (PCA-PCA-COIA) coupling environmental variables (a) and relative densities of zooplanktonic categories (b). Total inertia is 5.83, and the variance explained by the two axes is 86.89%. See Table 1 and Table 2 for meaning of the abbreviations.

that fish larvae may find different prey in the lagoon and in the bays. Cross-shelf variations in zooplankton assemblages structure and abundance such as those observed in the present study appear typical of continental shelves, including tropical coral reef lagoons, since they have also been observed in the North-West shelf and in the Great Barrier Reef of Australia (McKinnon and Thorrold, 1993; Wilson et al., 2003), in Namibia (Olivar and Barangué, 1990) and Brazil (Ekau, 1999). Similar relationships have been observed in the Mediterranean coastal areas (Siokou-Frangou et al., 1998). The present study also revealed that biomass and densities of zooplankton are significantly higher in the estuarine Bay of Ouaraï. This might be accounted for by the abundance of particulate organic matter in this bay. Le Borgne et al. (1989) demonstrated the important effect of particulate organic matter concentration on the structure of zooplankton assemblages in the Tikehau atoll (Tuamotu archipelago, French Polynesia), where particulate organic matter constitutes the main source of food for the first consumers in the planktonic food web. The confinement of bays and the induced higher residence time of waters (Jouon et al., 2006) as well as the nature of terrigenous inputs have indeed been shown to have a strong influence over zooplankton biomass in New Caledonia (Binet, 1986). Similarly, terrigenous inputs associated with rainfall events have also been shown to influence zooplankton abundance in Australia, the Caribbean Sea and South Africa (McKinnon and Thorrold, 1993; Wilson et al., 2003; Froneman, 2004; D’Croz et al., 2005).

40.7 34.7 8.4 3.9 3.5 2.8 1.9 1.6 1.2 0.7 0.3 0.1 <0.1 Dum_shel

38.4 (9.1–100.0) 35.1 (0.0–64.2) 7.6 (0.0–17.6) 4.9 (0.0–16.7) 3.2 (0.0–10.5) 4.0 (0.0–45.5) 2.9 (0.0–50.0) 0.9 (0.0–3.1) 1.8 (0.0–13.7) 0.8 (0.0–7.5) 0.3 (0.0–1.4) 0.2 (0.0–1.0) 0.1 (0.0–1.1) 36.8 (9.3–66.1) 35.o (9.4–56.0) 9.3 (2.8–24.7) 5.7 (0.0–24.0) 3.3 (0.0–15.8) 2.8 (0.0–15.8) 2.1 (0.0–13.5) 1.3 (0.0–12.5) 2.8 (0.0–26.3) 0.6 (0.0–10.7) 0.2 (0.0–1.4) 0.1 (0.0–0.6) 0.1 (0.0–2.3)

chae

Dum_exp

0.5 -0.6 1.2 -0.5

larv

23.8 (0.0–75.0) 33.8 (0.0–62.4) 12.1 (0.0–78.3) 1.8 (0.0–14.7) 7.1 (0.0–29.4) 7.7 (0.0–27.3) 5.2 (0.0–27.3) 3.2 (0.0–16.2) 0.2 (0.0–5.6) 4.1 (0.0–30.9) 0.3 (0.0–3.8) 0.9 (0.0–11.5) 0.2 (0.0–3.3)

(b)

45.9 (22.8–86.9) 30.6 (0.0–55.0) 8.2 (0.0–25.0) 2.2 (0.0–13.8) 4.9 (0.0–28.4) 2.3 (0.0–13.2) 2.4 (0.0–12.5) 1.2 (0.0–5.5) 0.5 (0.0–6.3) 1.3 (0.0–12.6) 0.4 (0.0–3.4) 0.2 (0.0–6.3) 0.1 (0.0–4.2)

Wind speed

37.1 (6.0–67.7) 34.8 (2.0–63.3) 9.8 (1.5–33.3) 3.4 (0.0–13.4) 3.5 (0.0–44.8) 4.4 (0.0–17.1) 2.3 (0.0–9.0) 2.8 (0.0–16.2) 0.5 (0.0–7.2) 0.7 (0.0–5.4) 0.3 (0.0–3.9) 0.3 (0.0–11.9) 0.1 (0.0–3.7)

CN

8.5  104 7.2  104 1.7  104 8.2  103 7.4  103 5.9  103 3.9  103 3.4  103 2.6  103 1.4  103 6.0  102 2.0  102 1.8  102

Sol rad

Small copepods Copepod nauplii Eggs and lumps Bivalve veligers Others Gastropod veligers ‘‘Large” larvae Appendicularians Unidentified small crustaceans Large copepods Chaetognaths Unidentified large crustaceans Echinoderm pluteus

axis 2: 14.15 %

Sal

DUMBÉA

axis 1: 72.74 %

Turb

Lag&bar

pheo

Ouar

POC

Chamb

Chl

PON

OUANO

Temp

Proportions for all zones (%)

POP

Proportions for each zone (%)

Rain

Mean density (ind m3)

0.5 -0.6 1.2 -0.5

Wind dir

Zooplankton category

(a)

Table 3 Mean density and mean and range (min–max) proportions of each zooplankton category (in% of the total density) observed in the Bay of Chambeyron (Cham), the Bay of Ouaraï (Ouar), in the lagoon and the barrier reef zones (Lag&bar) at Ouano; in the exposed zone (Dum_exp) and sheltered zone (Dum_shel) of the Bay of Dumbéa, and for all zones considered together. Estimates of total zooplankton density and biomass are given in Fig. 3. See Table 1 for details on zooplankton categories. Categories are ranked in decreasing order of their mean density.

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

374

L. Carassou et al. / Marine Pollution Bulletin 61 (2010) 367–374

The third most important result of our study is that variations in zooplankton composition appear mostly related to the variations in wind speed, water temperature, and concentration in chlorophyll and particulate organic matter. In the North-West shelf of Australia, these spatial patterns in assemblages distribution have been related to variations in water temperature and chlorophyll concentration, both under the influence of season and wind speed in the area (Wilson et al., 2003). Similarly, McKinnon et al. (2005) reported greater abundances and biomass of copepods, nauplii of copepods, and molluscs larvae in the coastal waters of the Great Barrier Reef, where their respective proportions presented seasonal variations. This preliminary study shows that the compositions of zooplankton assemblages differ between bays and lagoonal waters and vary with environmental conditions in the bays. Therefore, fish larvae may not find identical feeding conditions in these two water masses, or between seasons in the same location. Fish larvae in the lagoon of New Caledonia have been shown to prefer prey of a 150– 200 lm width (Carassou, 2008). Small copepods and unidentified small Crustaceans constitute the positively selected prey among the 13 categories of zooplankton examined in this study. Since the relative densities of both these categories were found to be higher in bays, these areas appear more favorable to the feeding of fish larvae. Among these bays, those most influenced by terrigenous inputs, associated with a high water residence time, such as the Bay of Ouaraï, are likely to provide the best feeding conditions. Acknowledgements This study was funded by IRD, The Programme d’Évaluation des Ressources Marines de la Zone Économique de Nouvelle-Calédonie (ZoNéCo), and the Programme National Économique Côtier (PNEC). We are very grateful to J. Baly for field and laboratory work. We thank N. Favéro, S. Hénin, A. Bertaud, M. Imirizaldu and M. Pruneddu for sorting out, counting and measuring zooplankton samples. P. Gérard (IRD) performed the chemical measurements. N. Deschamps (Météo-France) provided the meteorological data. We also thank the different captains of the NO Coris and Aldric, M. Clarque, N. Colombani and S. Tereua. A.M. Lassallette helped in editing the English text. References Aminot, A., Kérouel, R., 2004. Hydrologie des écosystèmes marins. Paramètres et analyses. Ed. Ifremer, Brest. Andrefouet, S., Torres-Pulliza, D., 2004. Atlas des récifs coralliens de NouvelleCalédonie. IFRECOR Nouvelle-Calédonie-IRD, Nouméa, p. 26 + ill. Binet, D., 1986. Note sur l’hypothèse d’une influence de la nature géologique et pédologique des terrains côtiers sur la biomasse zooplanctonique dans le lagon de Nouvelle-Calédonie. Océanographie Tropicale 21, 99–110. Binet, D., Le Borgne, R., 1996. La station côtière de Nouméa : dix ans d’observations sur l’hydrologie et le pelagos du lagon Sud-Ouest de Nouvelle-Calédonie. Archives ORSTOM Sciences de la Mer Biologie Marine 2, 37. Bremigan, M.T., Stein, R.A., 1994. Gape-dependent larval foraging and zooplankton size: implications for fish recruitment across systems. Canadian Journal of Fisheries and Aquatic Sciences 51, 913–922. Carassou, L., 2008. Les assemblages de larves de poissons dans le lagon de NouvelleCalédonie: structure spatio-temporelle et relations avec les facteurs abiotiques et biotiques de l’environnement. Ph.D. Dissertation, École Pratique des Hautes Études, Perpignan, France, p. 300. Carassou, L., Ponton, D., 2007. Spatio-temporal structure of pelagic larval and juvenile fish assemblages in coastal areas of New Caledonia, Southwest Pacific. Marine Biology 150, 697–711.

Castonguay, M., Plourde, S., Robert, D., Runge, J.A., Fortier, L., 2008. Copepod production drives recruitment in a marine fish. Canadian Journal of Fisheries and Aquatic Sciences 65, 1528–1531. Champalbert, G., 1993. Plankton inhabiting the surface layer of the southern and southwest lagoon of New Caledonia. Marine Biology 115, 223–228. Cushing, D.H., 1996. Towards a science of recruitment in fish populations. In: Kinne, O. (Ed.), Excellence in Ecology. Ecology Institute of Oldendorf-Luhe, Germany, p. 175. D’Croz, L., Del Rosario, J.B., Góndola, P., 2005. The effect of fresh water runoff of dissolved inorganic nutrients and plankton in the Bocas del Toro Archipelago, Caribbean Panama. Caribbean Journal of Science 41, 414–429. Dray, S., Chessel, D., Thioulouse, J., 2003. Co-inertia analysis and the linking of ecological tables. Ecology 84, 3078–3089. Ekau, W., 1999. Topographical and hydrographical impacts on zooplankton community structure in the Abrolhos Bank region, East Brazil. Archive of Fishery and Marine Research 47, 307–320. Fortier, L., Levasseur, M.E., Drolet, R., Therriault, J.C., 1992. Export production and the distribution of fish larvae and their prey in a coastal jet region. Marine Ecology Progress Series 85, 203–218. Froneman, P.W., 2004. Zooplankton community structure and biomass in a southern African temporally open/closed estuary. Estuarine Coastal and Shelf Science 60, 125–132. Hunter, J.R., 1984. Feeding ecology and predation of marine fish larvae. In: Lasker, R. (Ed.), Feeding Ecology and Predation of Marine Fish Larvae. Washington Sea Grant Programme, Washington, pp. 33–77. Jacquet, S., Delesalle, B., Torreton, J.P., Blanchot, J., 2006. Response of phytoplankton communities to increased anthropogenic influences (southwestern lagoon, New Caledonia). Marine Ecology Progress Series 320, 65–78. Jouon, A., Douillet, P., Ouillon, S., Fraunié, P., 2006. Calculations of hydrodynamic time parameters in a semi-opened coastal zone using a 3D hydrodynamic model. Continental and Shelf Research 26, 1395–1415. Le Borgne, R., Blanchot, J., Charpy, L., 1989. Zooplankton of Tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter. Marine Biology 102, 341– 353. Le Borgne, R., Rodier, M., Le Bouteiller, A., Kulbicki, M., 1997. Plankton biomass and production in an open atoll lagoon: Uvea, New Caledonia. Journal of Experimental Marine Biology and Ecology 212, 187–210. Le Borgne, R., Douillet, P., Fichez, R., Torréton, J.P., 2010. Hydrography and plankton temporal variabilities at different time scales in the southwest lagoon of New Caledonia: a review. Marine Pollution Bulletin 61, 297–308. Legendre, P., Legendre, L., 1998. Numerical Ecology. Elsevier Science, Amsterdam. p. 853. McKinnon, A.D., Thorrold, S.R., 1993. Zooplankton community structure and Copepod egg production in coastal waters of the central Great Barrier Reef. Journal of Plankton Research 15, 1387–1411. McKinnon, A.D., Duggan, S., De’Ath, G., 2005. Mesozooplankton dynamics in nearshore waters of the Great Barrier Reef. Estuarine, Coastal and Shelf Science 63, 497–511. Olivar, M.P., Barangué, M., 1990. Zooplankton of the northern Benguela region in a quiescent upwelling period. Journal of Plankton Research 12, 1023–1044. ORSTOM, 1981. Atlas de la Nouvelle-Calédonie et dépendances. Editions ORSTOM Paris. Ouillon, S., Douillet, P., Fichez, R., Panché, J.Y., 2005. Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia. Comptes Rendus Géosiences 337, 1509–1517. Pepin, P., Penney, R.W., 1997. Patterns of prey size and taxonomic composition in larval fish: are there general size-dependent models? Journal of Fish Biology 51, 84–100. Sampey, A., McKinnon, A.D., Meekan, M.G., McCormick, M.I., 2007. Glimpse into guts: overview of the feeding of larvae of tropical shorefishes. Marine Ecology Progress Series 339, 243–257. Scherrer, B., 1984. Biostatistique. Gaëtan Morin Editions, Boucherville. p. 850. Siokou-Frangou, I., Papathanassiou, E., Lepretre, A., Frontier, S., 1998. Zooplankton assemblages and influence of environmental parameters on them in a Mediterranean coastal area. Journal of Plankton Research 20, 874–880. Tenório, M.M.B., Le Borgne, R., Rodier, M., Neveux, J., 2005. The impact of terrigeneous inputs on the Bay of Ouinné (New Caledonia) phytoplankton communities: a spectrofluorometric and microscopic approach. Estuarine Coastal and Shelf Science 64, 531–545. Thioulouse, J., Chessel, D., Dolédec, S., Olivier, J.M., Goreaud, F., Pelissier, R., 2001. ADE-4. Ecological Data Analysis: Exploratory and Euclidean Methods in Environmental Sciences. Ó CNRS 1995–2000. UNESCO, 1968. Zooplankton Sampling. United Nations Educational, Scientific and Cultural Organization, Genève. Wilson, S.G., Carleton, J.H., Meekan, M.G., 2003. Spatial and temporal patterns in the distribution and abundance of macrozooplankton on the southern North West Shelf, Western Australia. Estuarine, Coastal and Shelf Science 56, 897–900.