Mesoscale variations in the assemblage structure and trophodynamics 1 of mesozooplankton communities of the Adriatic basin ( Mediterranean 2 Sea ) 3

Zooplankton are critical to the functioning of ocean food webs because of their utter abundance and vital 11 ecosystem roles. Zooplankton communities are highly diverse and thus perform a variety of ecosystem functions, thus 12 changes in their community or food web structure may provide evidence of ecosystem alteration. Assemblage structure 13 and trophodynamics of mesozooplantkon communities were examined across the Adriatic basin, the northernmost and 14 most productive basin of the Mediterranean Sea. Samples were collected in June-July 2019 along coast-offshore transects 15 covering the whole western Adriatic side, consistently environmental variables were also recorded. Results showed a 16 clear separation between samples from the northern-central Adriatic and the southern ones, with a further segregation, 17 although less clear, of inshore vs. off-shore stations, the latter mostly dominated in the central and southern stations by 18 gelatinous plankton. Such patterns were mainly driven by chlorophyll-a concentration (as a proxy of primary production) 19 for northern-central stations, i.e. closer to the Po river input, and by temperature and salinity, for southern ones, with the 20 DistLM model explaining 46% of total variance. The analysis of stable isotopes of nitrogen and carbon allowed to identify 21 a complex food web characterized by 3 trophic levels from herbivores to carnivores, passing through the mixed feeding 22 behavior of omnivores, shifting from phytoplankton/detritus ingestion to microzooplankton. Trophic structure also 23 spatially varied according to sub-area, with the northern-central sub-areas differing from each other and from the southern 24 stations. Our results highlighted the importance of environmental variables as drivers of zooplanktonic communities and 25 the complex structure of their food webs. Disentangling and considering such complexity is crucial to generate realistic 26 predictions on the functioning of aquatic ecosystems, especially in high productive and, at the same time, overexploited 27 area such as the Adriatic Sea. 28 Key-words: mesozooplankton, community composition, environmental drivers, food webs, stable isotopes, Adriatic Sea 29 https://doi.org/10.5194/bg-2021-240 Preprint. Discussion started: 1 October 2021 c © Author(s) 2021. CC BY 4.0 License.


Introduction 30
In an oligotrophic system, such as the Mediterranean Sea, coastal productivity largely depends on inputs from rivers and 31 areas of high productivity are mainly restricted to waters close to major freshwater inputs (D'Ortenzio and Ribera d'Alcalà, 32 2009, Ludwig et al., 2009). Here, the Adriatic basin represent an anomaly, with the northern Adriatic being one of the 33 most productive Mediterranean areas. While the northern part is a shallow sub-basin, characterised by inputs of several 34 rivers, with the Po representing the major buoyancy input with an annual mean discharge rate of 1500~1700 m 3 s -1 , and 35 accounting for about one third of the total riverine freshwater input in the Adriatic (Raicich, 1996), the southern part is 36 characterized by highly saline and oligotrophic waters (Franco and Michelato, 1992;Boicourt et al., 1999). Thus, a trophic 37 gradient, decreasing from northwest to southeast, is typically observed in the basin, in which the nutrient-rich waters Zooplankton is a link between primary producers of organic matter and the higher-order consumers, it provides grazing 45 control on phytoplankton blooms (Kiørboe 1993) and helps regulating fish stocks (Beaugrand et al. 2003), being this last 46 aspect of crucial importance in the Adriatic basin. Because of these important zooplankton functions, a better 47 understanding of their distribution and the patterns of their response to changes in the chemical and physical properties 48 of marine waters is essential, especially under a global warming scenario, being zooplankton sensitive beacon of climate 49 change (Richardson, 2008). Moreover, trophic relationships in pelagic ecosystems are complex and complicated by the 50 large degree of omnivory of most zooplanktonic species (Bode and Alvarez-Ossorio, 2003), which may feed on similar 51 diets composed of a mixture of phytoplankton, detritus, and microplankton (e.g., Stoecker and Capuzzo, 1990;Irigoien 52 et al., 1998;Batten et al., 2001). Several experimental studies allowed zooplankton (mostly copepods) to be categorised 53 from pure carnivores to omnivores with a variety of mixtures of algae and animal prey up to strictly herbivore species 54 (Irigoien et al., 1998;Batten et al., 2001;Halvorsen et al., 2001). Such variety in the diet makes the quantification of 55 flows between compartments or trophic levels difficult. In the last decades, stable isotope analyses (SIA) have been widely 56 used in food-web studies, different studies dealt with high taxonomical groups of zooplankton (Burd et al., 2002;57 Blachowiak-Samolyk et al., Tamelander et al., 2008), while few investigations were focused on low taxonomical 58 resolution (Koppelmann et al., 2003;Rumolo et al., 2017), essential to disentangle the food web structure of pelagic 59 communities (Fanelli et al., 2011). Analysis of stable isotope composition provides indications of the origin and 60 transformations of organic matter. Stable isotopes of carbon and nitrogen integrate short-term variations in diet and thus 61 The southern sub-basin is characterized by a wide depression about 1200 m in depth. Water exchange with the 84 Mediterranean takes place through the Otranto Strait, which has an 800 m deep sill (Artegiani et al., 1997;Marini, 85 Bombace and Iacobone, 2017). The Adriatic is a temperate warm sea, with surface temperature ranging from 6 ºC in the 86 northern part in winter to 29 ºC, in summer. Even the temperatures of the deepest layers are, for the most part, above 10 87 ºC. The South Adriatic is warmer than its central and northern parts during winter. In other seasons, the horizontal 88 temperature distribution is more uniform (Artegiani et al., 1997 Anderson et al., 2008) and if 130 no significant differences were found, sub-areas were merged for the following analyses. 131 Selected zooplankton samples were analysed in the laboratory to characterize the planktonic community. First, the frozen 132 sample was defrosted and filtered with 200 µm sieve and the obtained mass was weighted. Then samples were quickly 133 sorted, and larger animals isolated for first and placed in Petri dishes located on ice, in order to preserve tissue integrity. 134 Individuals were than identified to the lowest taxonomic level possible and stored for subsequent analysis. About 10% of 135 the sample was therefore weighted and all organisms in the sub-sample were identified to the lowest taxonomic level 136 possible. 137 All identified taxa were then counted and weighted with an analytical weight scale, to obtain abundance and biomass 138 estimations. 139

Samples preparation for stable isotope analyses 140
The most abundant taxa in each sample were prepared for stable isotope analyses. Selected taxa were oven-dried for 24 141 hours at 60 °C. Dried samples were converted to a fine powder with a mortar and pestle. For each taxon, three replicates 142 (when possible) were weighted (ca 0.3-1.3 mg) and placed into tin capsules. Since it was not possible to obtain enough 143 material of a single taxon for stable isotope analyses from stations 22_17 and 38_17, a bulk of the whole mesoplankton 144 community of the stations was prepared for the analyses. Acidification of samples prior to stable isotope analyses is 145 usually regarded as a standard procedure, since inorganic carbon could lead to an increase of δ 13 C, because it is 146 isotopically heavier than most carbon of organic origin and could reflect the isotopic signature of environmental carbon 147 (Schlacher and Connolly, 2014). However, for this study, no acidification was carried out, as this procedure generally 148 reduces sample biomass, leading to too little matter available for isotope analyses. Moreover, some authors revealed 149 negligible differences between acidified and not acidified samples (Rumolo et al., 2018). However, in order to have an 150 indication of the possible bias, only one species was acidified, Euchaeta sp., which is a very abundant copepod in Adriatic 151 communities. This taxon was also chosen because it has a more calcified exoskeleton and it was abundant enough to 152 undergo this process. Half of the sample was acidified with HCl 1M, by adding it drop by drop to the sample until bubble 153 https://doi.org/10.5194/bg-2021-240 Preprint. as several studies demonstrated that the acidification procedure can alter nitrogen isotopic signature (Kolasinski,Rogers 155 and Frouin, 2008). Then, six replicates of each sub-samples were prepared for isotope analyses. Samples were analysed 156 through an elemental analyser (Thermo Flash EA 1112) for the determination of total carbon and nitrogen, and then 157 analysed for δ 13 C and δ 15 N in a continuous-flow isotope-ratio mass spectrometer (Thermo Delta Plus XP) at the 158 Laboratory of XX of the University of Palermo (Italy). Stable isotope ratio was expressed, in relation to international 159 standards (atmospheric N2 and PeeDee Belemnite for δ 15 N and δ 13 C, respectively), as:

Community data analyses 165
Zooplankton abundance and biomass were standardized to a constant value. The adopted constant was the volume of 166 water filtered by the net, calculated as follows: 167 where A is the number of spins from the flowmeter, B is the number of meters travelled with each spin (given by the 169 manufacturer) and C is the area of the net mouth (m 2 ). When flowmeter data were not available (due to misfunctioning), 170 the volume was calculated as a mean value of similar nearby stations. Zooplankton abundance was expressed as number 171 of individuals per m 3 , while zooplankton biomass was expressed as mg of wet weight (WW) per m 3 . 172 First, the Shannon-Wiener diversity index of each station was calculated. Then, total biomass, total abundance and H' 173 diversity index were tested by univariate PERMANOVAs. Tests were run on Euclidean distance resemblance matrixes 174 of untransformed data and using a two-way design with sub-area as a fixed factor with three levels (GSA17N, GSA17C-175 S and GSA18) and inshore-offshore location as a fixed factor with two levels (inshore vs. offshore), crossed within each 176 other, in order to assess the presence and significance of differences between stations. As the preliminary analyses showed 177 no significant differences between samples from GSA17C and GSA17S, these two sub-areas were merged, allowing to 178 use a crossed design, otherwise impossible due to the absence of the "inshore" level within the sub-area GSA17S. 179 Univariate PERMANOVA test were run under 9999 permutations, with permutation of residuals under a reduced model, 180 as permutation method, significant p-values were set at p<0.05. 181 In order to test for differences among areas and inshore vs. offshore communities a PERMANOVA test was performed 182 on the Bray-Curtis resemblance matrix of 4 th -root transformed abundance zooplankton data, using the same design 183 https://doi.org/10.5194/bg-2021-240 Preprint. 2003) was then run to visualize the observed pattern, on the factor found to be significant by PERMANOVA. 185 A SIMPER analysis was carried out according to the same sampling design to identify the most typifying taxon 186 contributing to the average similarity/dissimilarity among sub-areas and inshore vs. offshore locations. This was 187 conducted using Bray-Curtis similarity, with a cut-off for low contribution at 60%. 188 In order to identify the environmental drivers of zooplanktonic communities and their structure across the sampling area, 189 biotic data were correlated to environmental variables. Environmental data considered were pressure (db), temperature 190 (°C), fluorescence (µg/l), turbidity (NTU), dissolved oxygen (expressed as ml/l and saturation percentage), salinity (PSU) 191 and density (km/m 3 ). All data were collected through a CTD for each station. Environmental data were tested for  . In 205 particular, the normalization was applied to samples with a C/N ratio > 3, according to Post et al. (2007). 206 A hierarchical cluster analysis (Euclidean distance, average grouping methods) on the bivariate matrix of δ 13 C and δ 15 N 207 mean values of each taxon was performed in order to elucidate the planktonic food web structure. Obtained clusters were 208 also compared with literature data on the trophic guild of analysed taxa. Five main trophic groups were established a 209 priori: primary consumers (PC), omnivores of type 1 (OMN1), encompassing mostly herbivore species, but that can feed 210 also small particles and ciliates, omnivores of type 2 (OMN2), similarly to OMN1 but with greater preference for small 211 zooplankton, carnivores (CAR) and parasite species (PAR). Differences among groups were tested by means of a one-212 way PERMANOVA test with "trophic group" (with four levels) as fixed factor. 213 The trophic level of the different species was estimated according to Post (2002)  and here is assumed to be 2.54 for low trophic level species, according to Fanelli et al (2009;, and  is the trophic 219 position of the baseline, which is 2 in our case. 220 Then, differences in the isotopic composition of the overall communities by sub-area and inshore vs. offshore 221 communities were tested by two-way PERMANOVA on the same design used for assemblage analysis. The same 222 procedure was also used to perform univariate two-way PERMANOVA and one-way PERMANOVA with pairwise test 223 for the δ 13 C and δ 15 N values, separately.

Zooplankton community and spatial changes 239
A total of 52,016 specimens belonging to 113 taxa were collected through the WP2 sampling (Table S1). Zooplanktonic 240 communities in the whole area were dominated by small copepods of the genus Acartia (mostly A. tonsa), Oncaea, 241 Oithona (mainly O. similis) and copepodites. Abundant large copepods were Calanoida belonging to the genera Euchaeta, 242 Calanus, Centropages and Temora. Since samples were frozen on board after collection, a quite considerable number of 243 specimens (particularly amphipods and mysids and those taxa/specimens characterized by soft carapace) were damaged 244 and therefore hard to identify at species level. Generally, they were identified to order level or indicated as "damaged 245 unid." in Table S1. Other common crustaceans were hyperiids, such as Lestrigonus schizogeneios and Phronima 246 https://doi.org/10.5194/bg-2021-240 Preprint. Discussion started: 1 October 2021 c Author(s) 2021. CC BY 4.0 License. atlantica, decapod larvae (mainly zoeae and megalopae), mysids and euphausiids. Among non-crustaceans, molluscs 247 were quite common, both as larvae of benthic organisms and adult pteropods. Chaetognatha were also locally abundant. 248 Gelatinous zooplankton was represented mainly by thaliaceans and calycophorans, while ichthyoplankton was not very 249 abundant, with few fish eggs and larvae found. 250 Zooplankton abundance and biomass varied according to geographic sub-area decreasing from the Northern to the 251 Southern Adriatic (Figure 2a-b), being significant only differences in abundance, while inshore-offshore differences were 252 not, neither for abundance nor for biomass ( Table 1)   PERMANOVA revealed that differences in zooplanktonic communities, based on geographic sub-areas and inshore-266 offshore factor were significant, while any significant differences occurred for the interaction factor (Table 2a-b). 267 The CAP plot showed a clear separation between samples from the GSA17N and all the other stations, on the first axis 274 (Figure 3). 275  (Table 3a) showed that Acartia sp., Oithona sp., unidentified Calanoida, mostly composed by 281 copepodites, mainly contributed to dissimilarity from GSA17N vs. GSA17C-S. Bivalve and gastropod larvae, together 282 with Acartia sp., Oithona sp. and unidentified Calanoida were the main responsible for the dissimilarity between the 283 subareas GSA17C-S and GSA18. Overall, the inshore zooplanktonic communities were mostly typified by Acartia sp., 284 gastropod larvae, copepodites, Podon sp. and Centropages typicus, while the offshore ones were mainly characterised by 285 Calycophorae, Calanus helgolandicus and Evadne tergestina (Table 3b).

Correlation between zooplankton data and environmental variables 297
Draftsman plot allowed to assess collinearity between pair of variables at >0.7. DO concentration (ml/l) and % of oxygen 298 saturation covaried, as well as density and pressure, therefore, only temperature, fluorescence, turbidity, DO and salinity 299 were used for DistLM analysis. 300 DistLM results showed that 26.9% of the variance was explained by salinity, 11% by fluorescence and 8.6% by DO, those 301 three variables cumulatively accounting for 46.5% of variance (Table 4).

Stable isotope composition of zooplankton 306
Stable isotope analyses provided δ 13 C and δ 15 N values of 26 different taxa ( Table 5) Cluster analysis allowed to group animals according to their δ 13 C and δ 15 N values, and partially with the trophic groups 314 previously established, based on literature data when available (Figure 4). One-way PERMANOVA test run on factor 315 "trophic groups-TG" proved significant differences (pseudo-F5,28=2.57, p=0.02), with primary consumers being 316 significantly different from omnivores of type 2 and carnivores (PC vs.

324
The estimates of Trophic Levels (TLs), considering the δ 15 N value of Gaetanus spinosus as baseline, allowed to assign 325 zooplanktonic taxa to 3 TLs from herbivores located at TL 2 to carnivores at TL 4 ( Table 5). 326 Overall, the  15 N of the mesozooplanktonic community was greater in the GSA17N, both for inshore and offshore 327 communities (Figure 5). Similarly, the median  13 C value was similar among the different sub-areas, although in the 328 GSA17N both the greater and lower values were found in the GSA17N than in the other sub-areas, although, than for the 329 other communities (Figure 5) Table 6a). The pairwise comparison on sub-area factor, considering only comparisons between contiguous sub-336 areas showed a significant separation between the isotopic composition of zooplanktonic taxa from the GSA17N vs. 337 GSA17C-S, but not between the GSA17C-S and GSA18. The pairwise test run on the interaction factor for pairs of level 338 of factor "inshore vs. offshore" provided evidence for significant variations in the isotopic composition between inshore 339 and offshore communities only for the GSA17C-S. One-way PERMANOVA tests run separately on δ 15 N values showed 340 significant variation only for factor sub-area (Table 6b)  Finally, the SIBER method for calculating ellipse-based metrics of niche width provided evidence of larger niche width for 349 the zooplanktonic community from GSA17N than GSA17C-S and GSA18 (Figure 6 and Table 7). Estimated overlap by 350 Bayesian inference evidenced almost null overlap between GSA17N and GSA17C-S (<10 -15 ), while a high overlap existed 351 between GSA17C-S and GSA18 (0.26). The greater d15N_range was observed for GSA17C-S and GSA18 communities, while 352 the higher d13C_range occurred in GSA17N communities, where also CD value was the greatest ( Table 7).

Mesoscale variations in zooplankton biomass, abundance and composition 372
Overall, 113 taxa and 57 species have been identified during June-July 2019 in the Adriatic basin (Table S1). These values 373 were only slightly lower than those observed for the Central Adriatic at 0-50 m depths where 150 taxa were counted (Hure et 374 al., 2018). Such differences maybe only apparent and attributable to the storage method we used, as samples were kept frozen 375 for subsequent stable isotope analyses, determining a damage in many organisms, which were impossible to identify to species 376 or even genus level (Fanelli et al., 2011). In terms of species abundance, the most representative species were Acartia tonsa, 377 Zooplankton biomass and abundance were higher in the Northern Adriatic Sea and slowly decreased moving towards the 381 Southern Adriatic. This trend was also observed by Fonda Umani (1996)  Although, in the north-western Adriatic offshore waters are less productive than inshore coastal waters and productivity of the 396 inshore zone decreases southward away from the Po Rivers' nutrient influx (Vollenweider et al., 1998), here we did not find 397 significant differences in terms of abundance and biomass between inshore and offshore communities or for the interaction 398 factors. Such differences were instead observed when we compared zooplanktonic communities' composition. Indeed, 399 multivariate analyses evidenced a clear separation of samples as function of sub-area and inshore vs. offshore locations, and 400 especially between the mesozooplanktonic community of the Northern Adriatic from the other two. This was not surprising as 401 the northern Adriatic is characterised by shallower and colder waters than the rest of the basin and under the influence of 402 riverine input, thus hosting a typical neritic community with coastal and estuarine elements. This area was dominated also by 403 Acartia clausi, Oithona similis, cladocerans (mostly Evadne spinifera), copepodites (here comprised within the "Copepoda 404 unid." group), gastropod larvae with some differences with respect to previous studies (Bernardi Aubry et al., 2012), in terms 405 of temporal shift of species maximum abundance. This could be related to the peak in primary production occurring in May 406 2019, quite delayed with respect to the usual pattern of the area (Kamburska and Fonda-Umani, 2009) (see Figure 7). Conversely, the southern Adriatic basin, except for the Gargano promontory, being characterised by a narrow continental shelf 408 and a steep slope, reaching high depths close to the coasts, was dominated by typical offshore species such as tunicates, 409 chaetognaths, siphonophores and Euchaeta spp. These results were supported by Fonda Umani (1996) These two variables were mainly linked to freshwater inputs from the Po River and were responsible of the main separation 425 between the Northern Adriatic, more coastal-estuarine zooplanktonic communities, from the central and southern Adriatic, 426 more oceanic zooplanktonic communities. On the other hand, changes in DO which decreased southward from a mean value 427 of 5.32 ml/l recorded in GSA17N stations to 4.36 ml/l were observed in GSA18 CTD casts. This is in full agreement also with 428 the decreasing trend in zooplankton biomass from the GSA17N to GSA18. Several studies indicated that oxygen concentration 429 could be a limiting factor for zooplankton growth and survival (Olson, 1987;Moon et al., 2006), with inhibition of egg hatching 430 in some copepod species (Roman et al., 1993). DO was found to be also the driving factor of zooplanktonic communities in 431 the strait of Sicily (Rumolo et al., 2016) 432

Food web structure of zooplankton communities 433
The trophic groups highlighted by cluster analysis fully agreed with putative trophic groups established a priori based on 434 literature information and allowed to assign species with unknown feeding ecology to a trophic group. Two main groups were 435 evident, a first one grouping primary consumers (i.e. herbivore/filter feeder taxa) and copepodites assigned to omnivore of 436 level 1, i.e. taxa that may act both as primary consumer eating phytoplankton or detritus particles or shifting to small prey, i.e. 437 microzooplankton. Taxa with unknown feeding mode such as Gaetanus tenuispinus and small calanoids (including 438 https://doi.org/10.5194/bg-2021-240 Preprint. should be a carnivorous species, feeding on salp tissue (Madin and Harbison, 1977). However, Elder and Seibel (2015) also 441 reported feeding on host mucus, which could lower their trophic position, being more similar to the basal source, i.e. the 442 particulate organic matter or POM (Fanelli et al., 2011). Zoeae of Thalassinidea and Brachyura were also placed in this group, 443 close to thaliaceans, that are herbivorous filter feeders (Madin, 1974). 444 The second group encompass different taxa mostly carnivores and omnivores of both level 1 and 2, i.e. taxa that mostly prefer 445 animal prey but that can shift to phytodetritus when prey was scarce or competition was high (Fanelli et al., 2011). This is the 446 case of Meganichtyphanes norvegica which can vary its diet regionally and with growth, showing a preference for 447 phytoplankton in certain areas, seasons or when juveniles (Schmidt, 2010;Fanelli et al., 2011), or preying exclusively on 448 calanoids when adults or depending on energy requirements (McClatchie, 1985). Other examples of this kind are represented 449 by the calanoid Calanus helgolandicus or Centropages typicus. C. typicus is an omnivorous copepod that feeds on a wide 450 spectrum of prey, from small algae (3-4 μm equivalent spherical diameter) to yolk-sac fish larvae (3.2-3.6 mm length). It uses 451 both suspensivorous and ambush feeding strategies, depending on the characteristics of the prey (Calbet et al., 2007) Although 452 C. helgolandicus was described as an herbivore species (Paffenhoffer, 1976) some authors described density-dependent 453 mortality through cannibalism in Calanus spp., as a form of population self-limitation (Ohman and Hirche, 2001), thus pointed 454 out to an omnivorous feeding behaviour. Omnivorous copepods can display increased predatory behaviour in the absence of 455 other food (Daan, 1988), and may actively target eggs even when phytoplankton is not limiting (Bonnet et al. 2004). Finally, 456 a mixed group formed by the mysid Leptomysis gracilis, the copepod Acartia tonsa and the hyperiid Lestrigonus schizogeneios, 457 clustered close to other carnivore species. Hyperiids generally use gelatinous substrate for reproduction and feeding, some of 458 them living in symbiosis (Gasca and Haddock, 2004) other being parasite such as the genus Hyperia (now Lestrigonus). A. 459 tonsa may display both predatory and suspension feeding behaviour (Saiz and Kiorboe, 1995), similarly to L. gracilis (Fanelli 460 et al., 2009) and accordingly to their isotopic composition and position in the zooplanktonic food web. 461 The average enrichment between the different plankton taxa was greater than the mean value of 2.56 expected between adjacent 462 trophic levels (e.g. carbon moving from inshore to offshore waters, and/or to different trophic dynamics between costal and oceanic food webs. 475 Here  13 C values were highly variable in accordance with the wide array of food sources (i.e., marine and continental) available 476 in the area due to the riverine inputs. Accordingly, the niche width of zooplanktonic community in the area is the greatest and 477 SEAc decreased southward, where zooplanktonic community were likely sustained mostly by marine sources (Coll et al., 478 2007

Conclusions 485
This study represents the first application of the stable isotope approach to the analysis of the mesozooplanktonic food web at 486 Adriatic basin scale including both coastal and offshore communities. The results unveiled the presence of significant 487 differences in zooplankton abundance, biomass, and community composition at mesoscale level, with the main differences 488 observed between the Northern Adriatic and the rest of the basin, due to the peculiar oceanographic conditions (i.e., cold 489 waters) and the strong influence of the Po river. Such differences were also particularly evident in terms of isotopic 490 composition, where a further separation between offshore and inshore communities were evident for the progressive increase 491 of marine contribution to food sources for zooplankton in offshore communities. Such findings may represent a valuable 492 baseline for food web studies encompassing lower to high trophic level species and against changes in oceanographic 493 conditions under a climate change scenario, considering the rapid response of zooplankton communities to global warming. 494 Author contribution 495 IL, AdF and SM designed the survey and carried it out. EF conceived the experimental design. EF and SM analysed the 496 samples. EF analysed the data and prepared the manuscript with contributions from all co-authors. 497

Competing interests 498
The authors declare that they have no conflict of interest.

Data availability 500
Data can be requested to the corresponding author upon reasonable request. 501