Community structure of mesopelagic copepods (>500 μm) in the Ligurian Sea (Western Mediterranean)

Journal of Marine Systems 15 Ž1998. 511–522

Community structure of mesopelagic copepods ž ) 500 mm/ in the Ligurian Sea ž Western Mediterranean/ B. Gasser ) , G. Payet, J. Sardou, P. Nival UniÕersite´ P. and M. Curie (Paris VI), URA 2077, Station Zoologique, BP 28, 06230 Villefranche-sur-Mer, France Accepted 26 September 1997

Abstract The distribution of mesopelagic copepods between 250 and 1000 m depth was studied along a transect off the coast of Villefranche-sur-Mer in June 1991 by means of a BIONESS multiple-net sampler. Among the most abundant species at all stations were Pleuromamma gracilis, Paraeuchaeta acuta and overwintering Calanus helgolandicus CV copepodites, each species inhabiting different depth layers with maximum abundances in the 250–350 m, 450–550 m and the 700–850 m layer, respectively. Cluster analysis of the vertical distribution of all species caught revealed three distinct strata Ž‘TOP’, ‘INTERMEDIATE’, ‘BOTTOM’. consisting of characteristic species that occurred in the same stratum at all stations. Differences in total abundances of the species assemblage occupying each layer are discussed with regard to predation pressure by mesopelagic macroplanktonic crustaceans and fish. We show that each stratum is characterized by distinct trophic interactions and life strategies, which play an important role in the structuring of mesopelagic zooplankton communities. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Copepoda; zooplankton; abundance; vertical distribution community structure; multiple-net sampling

1. Introduction At least since Hutchinson Ž1961. formulated ‘‘the paradox of the plankton’’, the coexistence of species in the pelagic realm has become one of the key questions in studies on the pelagic food web. In oligotrophic oceanic waters, species coexist in a vast space characterized by quite homogeneous physical and chemical conditions, especially at depths below the main vertical gradients of temperature, salinity and nutrients. However, the distribution of organisms

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Corresponding author. Fax: q33-4-93763834. E-mail: [email protected]

within this space is very heterogeneous at different space and time scales ŽHaury et al., 1978; Mackas et al., 1985.. As Longhurst Ž1981. stated, the vertical distribution of species is far more predictable than the horizontal one at the same scale. In fact, excluding competition by vertical separation of species within the water column has been widely considered as an explanation for species coexistence ŽHayward and McGowan, 1979; Ambler and Miller, 1987; Williams, 1988; Mackas et al., 1993.. According to Longhurst Ž1985., the predictability of environmental gradients and discontinuities Žthermo- and nitracline, maximum of chlorophyll, etc.. leads to multi-layered structures by day as well as during the night, since the species of each community can locate the spe-

0924-7963r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 4 - 7 9 6 3 Ž 9 7 . 0 0 0 9 4 - 8

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cific conditions needed for their competitive advantage over other species. It follows that the main components in the organization of zooplankton communities must be looked for along the vertical axis. Vinogradov Ž1970. clearly identified discrete plankton strata in mesopelagic depths and associated their existence to a ladder-like migration pattern of surface, interzonal and deep migrators. Since then, improved sampling techniques have led to more precise descriptions of vertical distribution patterns. Discrete layers of interzonal species related to a deep scattering layer could be identified ŽLonghurst, 1976.. These layers were mainly composed of migrating species and sometimes dominated by a single species ŽLonghurst and Williams, 1979; Weikert and Koppelmann, 1993.. These studies, however, did not pay special attention to the species assemblage of mesopelagic layers, and others related them to physical parameters ŽSameoto, 1986.. In a more global objectif, Koppelmann and Weikert Ž1992. and Roe Ž1988. analyzed

the shape of whole zooplankton profiles and pointed out distinct mesopelagic layers of increased zooplankton biomass and abundance. In the Mediterranean Sea, several studies considered only copepods ŽHure and Scotto di Carlo, 1969; Scotto di Carlo et al., 1984, 1991. or macrozooplankton ŽBaussant et al., 1992a., or they focused on the vertical distribution pattern with respect to other seas ŽWeikert and Trinkaus, 1990.. We present here the results of a sampling program carried out in the Ligurian Sea along a transect crossing a frontal zone, which is characterized by enhanced primary production due to a nutrient enrichment of the surface waters ŽPrieur, 1981.. The zone is considered to be a source of organic matter for midwater tunicates ŽGorsky et al., 1991. and may act on the abundance and vertical distribution of other mesopelagic organisms. The objective of the present study was to detect discrete layers of mesopelagic species assemblages by giving a precise description of the vertical zooplankton distribution.

Fig. 1. Map showing the general study area in the Ligurian Sea Žnorthwestern Mediterranean. and the five sampling stations indicated by their distance in nautical miles from Cap Ferrat. Arrows point in the direction of the oblique tow and their length corresponds to the horizontal distance covered during the sampling time.

B. Gasser et al.r Journal of Marine Systems 15 (1998) 511–522 Table 1 Sampling data. Depth layers sampled Žsee text. are the same at all stations, except for the deepest layer, which extended from 850 m to the lower limit of the total depth range Date

Station Žmiles.

Sampling time GMTq2 Žhh:min.

Total depth range Žm.

June 25, 1991

28 23 18 8 13

9:30–11:10 13:13–14:40 16:43–18:15 11:33–12:35 14:48–16:00

0–960 0–960 0–960 0–1050 0–960

June 26, 1991

The use of nets of 500 mm mesh size was efficient for large size copepods as well as for macroplanktonic crustaceans and fish. They were taken into account in order to discuss the spatial structure of discrete layers of copepod communities. In depths below the euphotic zone, the copepod distribution is more likely to be shaped by predation than by food availability.

2. Material and methods The five stations of the transect lie between 8 and 28 nautical miles off Cap Ferrat, the distance between the sites being 5 miles ŽFig. 1.. A multiple openingrclosing net, the BIONESS ŽSameoto et al., 1980., equipped with 9 nets of a mesh size of 500 mm and a mouth opening of 1 m2

513

was used for plankton sampling. Oblique hauls at an average speed of 1.7 m sy1 Žrange: 0.9–2.0 m sy1 . were carried out from bottom to top at each station in a direction parallel to the coastline and to the frontal zone, in order to minimize horizontal bias due to gradients expected to be encountered along the transect. Each net sampled a different layer of the water column from 1000 m depth to the surface. The sampled layers were: 0–75, 75–150, 150–250, 250– 350, 350–450, 450–550, 550–700, 700–850 and 850–1000 m. A summary of the sampling data is given in Table 1. For technical reasons, the first net not always started at 1000 m but rather between 960 and 1050 m. Filtration performance was measured with an external and an internal flowmeter. The filtered volume was corrected for net pitch variation, the mouth opening being - 1 m2 if the opening is not perpendicular to the direction of the tow track. Volumes varied from 216 to 2234 m3 depending on the trajectory of the BIONESS. Sampling was achieved within two days ŽJune 25–26, 1991. sampling time falling between 9 a.m. and 6 p.m. Parallel echosounder recordings Ž38 and 120 kHz. showed no influence on the sampling by vertical migration of macroplanktonic organisms. On board, the samples were preserved in a 5% Borax buffered formaldehyde solution in seawater. In the laboratory, macroplanktonic organisms of a size ) 2 cm were sorted by eye and identified to species level. For species identification of

Fig. 2. Spatial distribution of Ža. density and Žb. temperature along the transect from station 8 to 28 miles. Density between 0 and 250 m is shown on a zoomed depth scale. Note the changing scale of the isolines above 28.50 kg my3 . Temperature steps are 0.58C from 13.5 to 14.58C and 1.08C thereafter.

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Fig. 3. Vertical distribution of the mean abundance of the three most abundant copepod species at depths below 250 m. Means are calculated from the five sampling stations. Error bars indicate standard deviation.

macroplankton as well as for the remaining mesoplankton, a binocular microscope Žmagnification 8– 35 = . was used. Entire samples of the macroplankton and aliquots of 1r10 to 1r2 of the mesoplankton were counted, and all abundances were then expressed in numbers of individuals per 1000 m3. Following the objectif of the study on mesopelagic zooplankton, we considered only copepod taxa of which the average weighted mean depth ŽWMD. of

the five sampling stations was deeper than 250 m. The following formula presented by Bollens et al. Ž1993. was used to calculate WMD: k

WMDs

Ý

k

nD z D z z i

is1

Ý nD z D z is1

where nD z is the abundance Žno.1000 my3 . in a depth interval D z whose midpoint is z i . Rare taxa

Table 2 Abundance Žno.1000 my3 . of the copepod taxa in each sampled layer. Abundance values are averages over the five sampling stations. Numbers in bold indicate maximum value for each taxon. Nomenclature was given following Razouls Ž1995. Depth layer Žm.:

Pleuromamma gracilis ŽClaus, 1863. Žadult. Pleuromamma abdominalis ŽLubbock, 1856. ŽCV,CIV. Pleuromamma gracilis ŽClaus, 1863. ŽCV. Pleuromamma abdominalis ŽLubbock, 1856. Žadult. Chiridius spp. ŽGiesbrecht, 1892. Eucalanus monachus ŽGiesbrecht, 1888. Euchirella spp. ŽGiesbrecht, 1888. Žcopepodite. Neocalanus gracilis ŽDana, 1849. Žmale. Paraeuchaeta spp. ŽA. Scott, 1909. ŽCV. Paraeuchaeta acuta ŽGiesbrecht, 1892. Žadult. Euchirella spp. ŽGiesbrecht, 1888. Žadult. Eucalanus elongatus ŽDana, 1849. Monacilla typica ŽSars, 1905. Chiridius armatus ŽBoeck, 1872. Calanus helgolandicus ŽClaus, 1863. Žfemale. Calanus helgolandicus ŽClaus, 1863. ŽCV. Gaetanus sp. ŽGiesbrecht, 1888.

0–75

75–150

150–250

250– 350

350– 450

450– 550

550– 700

700– 850

850– 1000

165 15 37 2 6 8 1 2 194 10 28 22 22 4 32 98 2

134 11 19 4 12 0 11 4 178 8 12 8 0 0 5 8 1

644 52 39 0 105 8 29 1 426 12 1 9 0 0 0 1 0

2836 259 30 150 96 32 4 3 247 3 0 2 0 0 0 3 2

994 55 50 199 139 57 45 116 216 81 0 0 1 10 0 21 0

98 8 0 6 7 35 40 258 269 452 32 28 37 7 0 83 3

54 21 1 5 22 12 3 3 39 178 42 45 654 9 2 586 28

30 10 0 6 27 1 0 0 10 6 4 24 253 20 25 1866 68

27 3 0 5 3 2 0 2 27 10 6 5 106 7 16 1301 41

B. Gasser et al.r Journal of Marine Systems 15 (1998) 511–522

never appearing at more than 2 individuals in the counts were also discarded. However, for profile plots and cluster analysis, abundances of the whole water column sampled Ž0–1000 m. were used, so to take into account the broad vertical distribution of many of the taxa. CTD casts were carried out along the same transect between the surface and 1000 m depth at 10 stations, 2.5 miles apart, using a CTD model ‘SeaBird SBE 19’.

3. Results 3.1. Hydrological structure The density and temperature data obtained from the CTD casts revealed steep gradients separating the top 50 m from the rest of the water column ŽFig. 2.. The horizontal gradient marking the frontal zone between 15.5 and 20.5 miles is illustrated by quasi vertical isopycnals in a zoomed view of the density distribution ŽFig. 2a.. At mesopelagic depths, there was hardly any density gradient. But the temperature showed a secondary maximum around 400 m depth at the coast and around 300 m at station 28 miles. Temperatures above 158C at these depths are characteristic of the so-called intermediate water originating in the Levantine basin and commonly observed in this area ŽLacombe and Tchernia, 1960; Bethoux ´ and Prieur, 1983.. 3.2. Distribution of copepods A total of 13 copepod taxa were retained for this study. Nine were identified to species level and 4 to genus. Pleuromamma gracilis and Calanus helgolandicus were by far the most abundant species, with up to 3000 individuals.1000 my3 per sample, while abundances for other species remained - 1000 individuals. The vertical distribution of these two abundant species was very different. C. helgolandicus was mainly found at the bottom and P. gracilis at the top of the water column we are concerned with ŽFig. 3.. Their average maximum abundance at the five stations was 1866 individuals.1000 my3 ŽS.D.s 361. in the 250–350 m layer and 2836 individuals ŽS.D.s 361. between 700 and 850 m depth, respec-

515

tively. A much lower maximum abundance Ž406 ind.1000 my3 ; S.D.s 161. was obtained for Paraeuchaeta acuta, which was located in the 450– 550 m layer. However, P. acuta was the most important species in this depth layer. Table 2 shows the average abundance of copepods calculated from the five stations in each layer. Most of the taxa show a marked maximum abundance in one of the layers below 250 m depth. In almost every layer, a group of taxa with a common depth maximum could be identified. In order to find out if this vertical separation formed a coherent pattern throughout the five staTable 3 Groups of copepod taxa issued from the cluster analysis performed at each station from 8 to 28 miles. Groups are separated by single lines and strata by double lines. Vertical order of the groups follows weighted mean depth Žm. indicated to the right of each taxon. Taxon marked in bold letters appear in the same stratum at all five stations

B. Gasser et al.r Journal of Marine Systems 15 (1998) 511–522

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tions, we performed a cluster analysis. The abundance profiles of each taxon were transformed into depth-dependent percentage distributions. The Euclidean distance was chosen as a measurement of dissimilarity of the percentage between two taxa in each depth layer. Dissimilarity was calculated according to the following formula: n

D 2 Ž x1 , x 2 . s

Ý Ž yi1 y yi2 . 2 is1

x 1 and x 2 being the indices of the two species and yi1 and yi2 their percentage in the ith depth layer. Dendrograms were produced for each station by flexible clustering ŽLance and Williams, 1966.. The results of the clustering are shown in Table 3. Using the same cut-off level, 5 to 9 groups could be

identified at each station. These groups were then ordered according to the weighted mean depth of the different taxa in each group. We defined three distinct strata, in which the majority of the taxa remained throughout the five stations of the transect, even if they switched within distinct groups within the same stratum. Each stratum showed a characteristic species assemblage. Fig. 4 shows the abundance profiles of these communities. They clearly outlined three different depths of maximum abundance. The distribution of the weighted mean depths ŽWMD. over the five stations ŽTable 4. was significantly different Žtest Kruskal–Wallis; p - 0.05. between each community. In the top stratum and especially in the intermediate one, WMDs were shallower at the two coastal near stations than at the three offshore

Fig. 4. Profiles at each station of the cumulated abundances of the copepod taxa classified in the same stratum. The taxa constituting each profile are given in Table 3. Note the equal scale of the x-axis in all strata.

B. Gasser et al.r Journal of Marine Systems 15 (1998) 511–522

517

Table 4 Weighted mean depths Žm., at each station, of the copepod communities obtained from the cluster analysis

3.3. Distribution of macroplankton

Station Žmiles.:

8

13

18

23

28

‘TOP’ ‘INTERMEDIATE’ ‘BOTTOM’

262 473 735

344 480 774

348 525 789

337 527 731

351 531 731

We show here the results of the three most abundant macroplanktonic species found below 250 m, Meganyctiphanes norÕegica, Nematoscelis megalops and Cyclothone braueri. All three showed maximum abundances in the 250–450 and 450–550 m layers ŽFig. 5.. The distribution at mesopelagic depths of the two euphausiids is remarkably similar at all stations, with very low abundances at stations 23 and 28 miles. The maximum abundance around 400 m depth at 8 miles drops to around 500 m at the next station and is maintained along the rest of the transect. At all stations, Nematoscelis megalops was also observed in superficial layers. Cyclothone

stations Ž18–28 miles.. The profiles of the three strata resembled the distribution of the most abundant species Pleuromamma gracilis, Paraeuchaeta acuta and Calanus helgolandicus ŽFig. 3.. Abundances in the intermediate stratum, however, were much lower than in the two other strata.

Fig. 5. Vertical distribution of the abundances of two euphausiid species, Meganyctiphanes norÕegica and Nematoscelis megalops, and of the fish Cyclothone braueri at the five stations of the transect.

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braueri is almost evenly distributed along the transect. Maximum abundances were encountered around 400 m at 8 and 13 miles and 100 m deeper at the other stations. This drop does not correspond to the one observed for the euphausiids.

4. Discussion The distinct vertical pattern observed in the distribution of the zooplankton cannot be associated with the vertical gradients of the hydrological parameters. At mesopelagic depths, there was hardly any density gradient, and we could only identify a slight temperature maximum, indicating the intermediate water. Its depth distribution, rising gradually from around 400 m Ž5.5 miles. to around 300 m depth Ž28 miles. did not correspond to any pattern observed in the plankton distributions. This result is consistent with those obtained by Weikert and Trinkaus Ž1990. in the Eastern Mediterranean. Cummings Ž1983. in a similar hierarchical classification of copepod communities as in the present study, showed sample groups being arrayed primarily according to depth, despite contrasting hydrographic features and seasonal differences in sampling periods. However, we have found that a hydrodynamic discontinuity such as the frontal zone, may act on the depth of the different strata but not on the vertical structure itself of the mesopelagic zooplankton communities. The three layers persisted along the transect but WMDs of the top and the intermediate stratum were on an average some 70 m deeper beyond station 13 miles than on the nearshore side. Baussant et al. Ž1992b. observed this phenomenon in the recordings of a mesopelagic scattering layer during a whole year. It was confirmed in a similar study across the Almerıa–Oran front in the Alboran Sea ´ ŽBaussant et al., 1992a.. The abundant copepods in our samples, Pleuromamma gracilis and Paraeuchaeta acuta, are known to be diel migrants ŽRoe, 1984; Haury, 1988.. Their absence between 250 and 550 m during nighttime would strongly modify the vertical pattern we presented here. Yet, stratification seems to be a permanent feature of the organization of the pelagic ecosystem. Stratification in the epipelagic layer,

where diel migrants are found during nighttime, has been extensively studied and well demonstrated ŽLonghurst, 1985; Mackas et al., 1993.. Some characteristics that distinguish the different daytime layers may as well be attributed to nighttime layers. For example, predation pressure is as well an important factor for spatial separation of species during daytime as during nighttime ŽLonghurst, 1985.. The mesh size of 500 mm used in the present work does not consider small copepods, which can be very abundant also at mesopelagic depths ŽBottger-Schnack, 1994.. However, the same author ¨ reported on distinct meso- and bathypelagic Oncaea species assemblages, which indicates that stratification might apply to all of the pelagic copepods. Former studies carried out in the Mediterranean have mostly identified three strata between the surface and the bottom. But the depth ranges were not very precise as reported by Casanova Ž1970. Ž200– 300 to 600–800 m., or were very large, from 100 to 600 m ŽScotto di Carlo et al., 1984. and from 100 to 1000 m ŽWeikert and Trinkaus, 1990.. These authors mentioned the presence of vertically migrating species, compared abundances with the surface stratum Ž0–100 m. and explained the rarity of individuals at great depths by low surface production and vertical flux. Our results show three strata between 250 and 1000 m depth, WMD ranges being 250–350 m Ž‘TOP’., 400–550 m Ž‘INTERMEDIATE’. and 700–800 m Ž‘BOTTOM’.. The species composition in our samples was similar to previous findings in other Mediterranean areas ŽScotto di Carlo et al., 1984; Weikert and Trinkaus, 1990.. We showed, however, that the main migrating species Pleuromamma gracilis and Paraeuchaeta acuta are vertically separated and each species forms an important part of a distinct stratum with a characteristic species assemblage. These two strata, ‘TOP’ and ‘INTERMEDIATE’, also differed strongly in their abundance maxima, which were some 5 times higher in the first than in the second one. The depth range of the latter corresponds to the range of minimum total abundance found by Scotto di Carlo et al. Ž1984. and Weikert and Trinkaus Ž1990.. We suggest that this minimum reflects the presence of a distinct community, where copepods, in our case Paraeuchaeta acuta, undergo heavy predation pressure by a

B. Gasser et al.r Journal of Marine Systems 15 (1998) 511–522

macroplanktonic predator, the fish species Cyclothone braueri. Yoon Ž1995., in the same study area, has found this copepod to be the major prey of the fish. Palma Ž1990. made the same observation during the month of June. The rest of the year, Pleuromamma gracilis was most frequently found in the fish stomachs. Bennett and Hopkins Ž1989. reported on Pleuromamma from the Gulf of Mexico as being the major prey of midwater fish, both organisms having the same vertical distributions. Generally, C. braueri is known to be an opportunistic predator ŽGjøsaeter and Kawaguchi, 1980. selecting rather size than type of prey ŽRoe and Badcock, 1984.. In the present study, Pleuromamma gracilis is likely to be a prey of C. braueri, since their depth distributions overlap. Still, the copepod was most abundant, which we believe, is due to avoiding predation by inhabiting depths above the maximum occurrence of the fish. This direct relationship is confirmed by a consistent vertical pattern between the two species along the transect ŽFig. 6.. The switch from an upward to a downward extension of the abundance peak of P. gracilis at station 18 miles around the frontal zone, occurs at the same time as the deepening of the maximum abundance of C. braueri. The same relationship was not observed between euphausiids and copepods. Vertical migration is known for Meganyctiphanes norÕegica and for a part of the Nematoscelis megalops population in our study area ŽAndersen and Sardou, 1992. and also

519

elsewhere ŽMauchline, 1980.. They are not likely to exert a considerable predation pressure on the copepods since the feeding activity tends to be low during the day, due to a diurnal feeding rhythm of M. norÕegica ŽSimard et al., 1986. and to a behavioural response of N. megalops to low food concentrations at mesopelagic depths ŽBarange et al., 1991.. In our study area, Yoon Ž1995. obtained similar results for both euphausiid species. Low predation pressure is probably also undergone by the copepods in the bottom stratum, which is indicated by high abundances of Calanus helgolandicus CV copepodites and by the absence of abundant predators. All individuals of C. helgolandicus showed a large oil sac filling out most of their body, which indicated their overwintering state. The overwintering at depths below 500 m of this species is commonly known ŽVives, 1978; Hirche, 1983; Williams and Conway, 1988. and seems to be a successful strategy. The presence of distinct zooplankton layers within a rather homogeneous water body has been interpreted as the result of avoiding competitive interaction through vertical partitioning of the pelagic habitat ŽAmbler and Miller, 1987.. Both niche separation and avoiding competitive exclusion are frequently used to explain the paradox of the plankton. However, Peters Ž1995. described the niche concept and the competitive exclusion principle as ‘‘ecological non-theories’’. Such theories are not precise in predicting the future state of a system, since they are

Fig. 6. Profiles at the five sampling stations, of a vertically migrating copepod, Pleuromamma gracilis, and of the non-migrating fish, Cyclothone braueri. For direct comparison, abundance values of both species have been standardized to depth-dependent percentage distributions, the whole profile being 100%.

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unrestrictive. Any set of observations will match them or be irrelevant to them. However, a good ecological theory predicts a single possible state and excludes all others. As Peters Ž1995. further states, to improve this theory or to develop a better one, it must be possible to prove its failings. The fundamental problem behind Peters’ conclusions has been evoked by Ghilarov Ž1984.. He stated that theory in ecology includes a number of concepts easily treatable in terms of mathematics, but that this theory cannot necessarily be related to the generalization of empirical data. Hutchinson Ž1958. had already distinguished between the ‘fundamental niche’ defined by the n-dimensional hypervolume, in which a species can exist and the ‘realized niche’ as the hypervolume reduced by competition and other interactions, in which a species may be observed. In a similar way, the concept of competitive exclusion involving just two species that cannot occupy the same fundamental niche, emerges again from the abstract formalization of the niche concept. As Peters Ž1995. argues, the confirmation of the above mentioned fundamental concept by data on the vertical partitioning of the pelagic habitat is relatively uninformative. In fact, there is a considerable gap between the spatial andror temporal scales, to which the concepts and the data sets refer. Instead of trying to explain the paradox of the plankton, we may consider our results as evidence for the coexistence of species. As Ghilarov Ž1984. summarized, such an approach is much better adapted to discuss data sets like ours. It allows to analyze processes that govern the coexistence and to identify interactions between communities of coexisting species, as was reported by Williams Ž1988. in a study on niche differentiation in populations of four copepod species. Our results revealed discrete layers of different communities, each community being characterized by distinct types of life strategies and trophic relationships. This is still far from identifying the processes that lead to the establishment of discrete layers. But it underlines the importance of biotic factors involved in these processes. Acknowledgements We fully acknowledge the efficient work and help of the captain and the crew of R.V. ‘Georges Petit’,

as well as the competence of Marc Picheral in programming and running the BIONESS. Helpful comments by three anonymous reviewers are appreciated. This is a contribution to the ‘MBP-Front’ programme of research unit URA 2077.

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