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The colonization success of non-indigenous species (NIS) of copepods that arrived in the estuaries of Bilbao and Urdaibai (Bay of Biscay) and other expanding species (OES) of copepods that arrived in the former estuary during the 1998–2015 period, as well as the impact of such species on the density and seasonal patterns of congeneric species, total copepods and total zooplankton have been analysed. The estuary of Bilbao was successfully colonized by the NIS Acartia tonsa and Oithona davisae (since 2003) and by the NIS Pseudodiaptomus marinus and the OES Calanipeda aquaedulcis (since 2010), coinciding with the progressive improvement of environmental conditions in the rehabilitation process of this estuary. The three NIS species also arrived in the estuary of Urdaibai during the same time period, but only A. tonsa became abundant, likely due to inherent natural constraints for the other two species. A. tonsa in both estuaries, and O. davisae and C. aquaedulcis in the estuary of Bilbao became influential in the density, composition and dynamics of total copepods and zooplankton in water-masses of 33 or lower salinity. The highest impact was found in the inner estuary of Bilbao, where total copepods and zooplankton reached densities comparable to those of the outer estuary and copepod maxima moved from spring to summer due to the contribution of the colonizing copepod species. The congeneric species most affected by the NIS were the neritic species Acartia clausi and Oithona nana in the estuary of Bilbao, and the brackish species Acartia bifilosa in the estuary of Urdaibai.

Since 2007, the non-indigenous calanoid copepod Pseudodiaptomus marinus Sato, 1913 has been increasingly recorded in numerous European sites, spreading at an unexpectedly fast pace over a short time-span. This species presents specific biological and behavioural traits which make it of particular interest for ecological and applied research topics. On 29–30 January 2018, 29 scientists from nine European Countries established the EUROBUS (Towards a EURopean OBservatory of the nonindigenous calanoid copepod Pseudodiaptomus marinUS) Working Group (WG). This WG aimed at creating a European network of institutions and researchers working on the various aspects of the biology and ecology of P. marinus, with an open forum where sharing experience and know-how among WG participants. This brought to an updated distribution map of P. marinus in European waters, as well as to the identification of priority research lines and potential joint initiatives under the WGEUROBUS umbrella. This contribution, stemming from the experts participating at the WG, represents the manifesto of the current and future initiatives developed within WGEUROBUS. info:eu-repo/semantics/publishedVersion

Zooplankton seasonality and its environmental drivers were studied at four coastal sites within the Northeast Atlantic Shelves Province (Bilbao35 (B35) and Urdaibai35 (U35) in the Bay of Biscay, Plymouth L4 (L4) in the English Channel and Stonehaven (SH) in the North Sea) using time series spanning 1999–2013. Seasonal community patterns were extracted at the level of broad zooplankton groups and copepod and cladoceran genera using redundancy analysis. Temperature was generally the environmental factor that explained most of the taxa seasonal variations at the four sites. However, between-site differences related to latitude and trophic status (i.e. from oligotrophic to mesotrophic) were observed in the seasonality of zooplankton community, mainly in the pattern of taxa that peaked in spring-summer as opposed to late autumn-winter zooplankton, which were linked primarily to differences in the seasonal pattern of phytoplankton. The percentage of taxa variations explained by environmental factors increased with latitude and trophic status likely related to the increase in the co-variation of temperature and chlorophyll a, as well as in the increase in regularity of the seasonal patterns of both temperature and chlorophyll a from south to north, and of chlorophyll a with trophic status. Cladocerans and cirripede larvae at B35 and U35, echinoderm larvae at L4 and decapod larvae at SH made the highest contribution to shape the main mode of seasonal pattern of zooplankton community, which showed a seasonal delay with latitude, as well as with the increase in trophic status.

Seasonal and interannual variations of total mesozooplankton abundance and community variability were assessed for the period 1998–2005 at 3 salinity sites (35, 33 and 30) of the estuaries of Bilbao and Urdaibai (southeast Bay of Biscay). Spatial differences in mesozooplankton seasonality were recognized, both within and between estuaries, related to differences between sites in hydrodynamic features and anthropogenic nutrient enrichment that drive phytoplankton biomass seasonal cycles. The within estuary seasonal differences in mesozooplankton community were mainly shown through seaward time-advances in the seasonal peak from summer to spring along the salinity gradient, linked to differences in phytoplankton availability during the summer, in turn, related to nutrient availability. These differences were most marked in the estuary of Urdaibai, where zooplankton seasonal pattern at 35 salinity (high tidal flushing) resembled that of shelf waters, while at 35 of the estuary of Bilbao zooplankton showed an estuarine seasonal pattern due to the influence of the estuarine plume. Cirripede larvae contributed most to the mesozooplankton seasonal variability, except at the outer estuary of Bilbao, where cladocerans and fish eggs and larvae were the major contributors, and the inner estuary of Urdaibai, where gastropod larvae contributed most. Total mesozooplankton increased at 30 salinity of the estuary of Bilbao and 35 salinity of the estuary of Urdaibai. Interannual variability of mesozooplankton at the lowest salinity of the estuary of Bilbao was mainly accounted for by copepods due to the introduction of non-indigenous species during estuarine rehabilitation from intense pollution. However, bivalve larvae and gastropod larvae showed the highest contributions at 35 salinity of the estuary of Urdaibai. At the rest of sites, the opposite interannual trends of polychaete larvae and hydromedusae generally made the highest contribution.

The rapid warming of the wolrd’s oceans during the last few decades has affected distributional patterns of marine planktonic communities. Here, we analyse links between sea warming and changes in copepod community composition over the last 3 decades (1980−2012). We used zooplankton time-series data which included 79 species of copepods collected at 3 sites in the eastern North Atlantic (Bay of Biscay and the Kattegat Sea) and the Mediterranean Sea (Gulf of Saronikos). First, using community β-diversity metrics, we analysed temporal patterns of copepod community composition changes over time and its relation to local environmental conditions. Second, to test whether the changes in copepod community composition correspond to community thermal preferences, we used the community temperature index (CTI) and compared CTI interannual changes with local temperature trends. The β-diversity analysis reveals a high temporal turnover in the copepod community composition at the 3 sites (30−45%), with a significant similarity decrease over time (‘decay’) associated with both niche descriptors and demographic stochastic processes. CTI results reveal that both in the Kattegat and Saronikos, where the ocean warming rate was the highest amongst sites, copepod community changes are linked to temperature variability, suggesting that the community is tracking their thermal niche over time. Our findings unveil the fundamental role of abiotic factors structuring copepod biodiversity over time and reveal that the local velocity of ocean warming and the species thermal thresholds are key to rearranging copepod community composition in coastal ecosystems.

Feeding is critical for larval survival and it becomes a determining factor in the annual recruitment in species such as European anchovy Engraulis encrasicolus. Additionally, since differences in the plankton community may affect the larval feeding patterns, an interregional comparative study may contribute to understand these patterns concerning larval development and environmental features. The diet, feeding pattern and prey selectivity in relation to the ontogeny of the larval anchovy in the Cantabrian Sea (inner Bay of Biscay) and the Catalan Sea (NW Mediterranean) were compared in this study. Larvae fed preferentially on copepod eggs, nauplii and calanoid postnauplii, selecting them actively. Larval diet was similar before notochord flexion in the two areas. Nonetheless, for larvae of comparable size, prey preferences skewed towards small preys in the Cantabrian Sea, and towards large preys in the Catalan Sea. Differences appeared in the middle-sized larvae (6.5–9 mm) due to prey size and type. Diet differences were attributable (a) to the ability of the Catalan Sea larvae to capture bigger preys at a smaller individual size; and (b) to differences in prey preferences and availability. Therefore, geographic variety in larval populations and food environment features may promote variability in the larval anchovy diet.

Variations in mesozooplankton abundance and community structure in response to water quality improvement and to variations in hydro-climatic conditions were studied in the inner estuary of Bilbao from 1998 to 2011. A process of recolonization was observed with a marked increase in copepod abundance and a smaller increase in the abundances of appendicularians, meroplanktonic bivalves and gastropods, at the expense of the decrease in groups of gelatinous predators. Within the copepods, an initial phase in this recolonization occurred through an increase in neritic copepods. However, in a second phase, the non-indigenous species Acartia tonsa and Oithona davisae increased and became dominant. In the last 2 years, a third non-indigenous species Pseudodiaptomus marinus was observed in lower densities, and Calanipeda aquaedulcis abundance increased becoming co-dominant with A. tonsa. All non-indigenous copepod species had summer/autumn peaks and were characteristic of brackish conditions, which suggests that unsaturated ecological niches in brackish waters were important for the settlement of non-indigenous species. Pollution abatement allowed for zooplankton recolonization, but variations in community structure, both at the broad taxonomic group and at the copepod species level, were greatly influenced by hydro-climatic factors, temperature being the single best explanatory variable of zooplankton variations.

Background: The introduction of NIS to estuaries and coastal embayment is of great concern. Commercial ships’ ballast water discharge and the northwards progression of species due to the ongoing climate change arise as the main factors explaining the rising occurrence of NIS species in Northern Atlantic waters. In this regard, regular monitoring of the plankton communities is paramount as to be able to respond properly to this potential issue. Results: While monitoring the invasive copepod Acartia tonsa populations in the estuaries of Bilbao and Urdaibai (Basque country, Spain), we report here the Asian copepod Pseudodiaptomus marinus for the first time in the Iberian Peninsula waters. Individuals from both species were collected from July to October, 2013 for DNA sequencing of mitochondrial cytochrome c oxidase subunit I gene (MT-CO1). Phylogenetic analysis of MT-CO1 confirmed P. marinus identity. Conclusions: Phylogeographic distribution of A. tonsa haplotypes in Europe along with the Bilbao port traffic patterns suggested a secondary invasion from an European source to Basque estuaries. The successful establishment of the A. tonsa population and the appearance of Pseudodiaptomus marinus confirm the need for regular plankton monitoring of estuarine and port waters. This applies also to nearby systems as these populations could represent a source of future dispersal. DA’s work was supported by the ZabaldUz Program (PhD fellowship). SGIker technical and human support (UPV/EHU) is gratefully acknowledged. Thanks to T. Matellanes (Bilbao Port Authority) for providing maritime traffic data. Special thanks to the anonymous reviewers that greatly improved the different manuscript versions. The sampling program received funds from the University of the Basque Country (UFI11/37) and the Basque Government (GIC10/168).

Metabarcoding is becoming an increasingly valuable alternative approach to biodiversity assessment, due to the combination of extreme sensitivity and potential for the highest taxonomic resolution in a cost- and time-effective methodology. To evaluate the capacity of metabarcoding for estuarine plankton monitoring, a comparison between the results obtained with this approach were compared with those based on traditional taxonomic analysis (microscopy). Database incompleteness, one of the main limitations of metabarcoding, was somewhat overcome by the addition of DNA sequences for local species, which increased the taxonomic assignment success from 23.7 to 50.5 %. When the communities were studied along with environmental variables, similar spatial and temporal trends of taxonomic diversity were observed for metabarcoding and microscopic studies of zooplankton, but not for phytoplankton. This is most likely attributable to the lack of representative sequences for phytoplankton species in current databases. In addition, there was high correspondence in community composition when comparing abundances estimated from metabarcoding and microscopy, suggesting semiquantitative potential for metabarcoding. Furthermore, metabarcoding allowed the detection and identification of two non-indigenous species (NIS) found in the study area at abundances hardly detectable by microscopy. Overall, our results indicate that metabarcoding is a powerful approach with excellent possibilities for use in plankton monitoring, early detection of NIS and plankton biodiversity shifts.

Seasonal, interannual and spatial variabilities were analysed for the > 100 μm and > 200 μm zooplankton assemblages in the estuary of Bilbao throughout 1997–2000, and related to hydroclimatic and water-quality factors. Seasonal and interannual patterns of abundance differed between assemblages, and only the abundance of the > 100 μm zooplankton was correlated with temperature. The large-sized zooplankton decreased more drastically than the small-sized zooplankton with decreasing salinity, and showed highest correlations with dissolved oxygen and water transparency. Seasonal changes were the major variability mode of zooplankton composition in both assemblages. Interannual changes associated to phytoplankton biomass and temperature were more evident in the small-sized zooplankton, whilst spatial differences related to oxygen depletion were more evident in the large-sized zooplankton. This indicates that small zooplankton was more sensitive to climate-related factors, while large zooplankton was more sensitive to water quality. Small copepods, cirriped larvae, appendicularians and Noctiluca were the main taxa responsible for the interannual variations in the > 100 μm assemblage. In the > 200 μm assemblage, large copepods were the main zooplankton responsible for the spatial variability related to oxygen depletion. Cnidarians and cladocerans responded mainly to decreases in salinity, and polychaete larvae were found to be unaffected by the decrease in dissolved oxygen and salinity. Results suggest that size-related differential responses of zooplankton should be considered when zooplankton monitoring is performed to assess the effect of climate forcing and pollution in coastal and estuarine environments.

13 pages, 7 figures, 1 table, Feeding ecology was analysed for the first time in the larvae of the European hake (Merluccius merluccius) to determine whether their diet and selectivity were constrained by environmental conditions and how these feeding characteristics were related to ontogeny, prey availability and visual capabilities. Larvae collected during both day and night were analysed, and it was found that feeding incidence was high, regardless of the time of day. Examination of the visual system corroborated the hypothesis that hake larvae should be able to cope with a wide range of photic conditions and to forage even at low light intensity. A clear preference for adult calanoid copepods and, especially, for Clausocalanus spp. was observed in all sizes analysed. Prey number increased with larval size, but prey size did not. This finding indicates that hake larvae behave as selective and specialist predators that consume an increasing number of prey rather than larger prey during larval growth, The research was funded by projects CTM2004-03510 C02-01/MAR and CTM2004-03510-C02-02/MAR. E. Morote acknowledges predoctoral FPI Fellowship support from Spain’s Ministry of Education and Science

Sardine larvae are forced to grow as fast as possible to reduce larval mortality. Thus, changes in biochemical composition during the first steps of sardine larval growth are intended to maximize larval growth rate efficiency and survival. Protein and RNA weight-specific growth rates were the highest and their corresponding doubling times the shortest among all the biomolecules, reflecting the importance of fast growth during early stages of larval development. The protein percentage increased and the carbohydrate and lipid percentages decreased during early growth until they reached, respectively, a percentage of 73.7, 3.1 and 18.0%. These percentages would represent the optimal proportion of biochemical components in sardine early larvae and they are the result of the trade-off between, in the short term, the protein proportion necessary to optimize larval movement and growth and, in the long term, the minimum lipid percentage necessary to guarantee energy reserves to fuel metamorphosis. RNA/DNA ratio increases during larval growth up to an asymptotic optimal value of ≈3.5 in postflexion larvae. Nutritional condition of sardine larvae was good and was influenced by the parental effect through the egg biochemical composition and by the growth trajectory determined by the actual environmental conditions.

The effect of environmental factors (river discharge, water temperature and dissolved oxygen saturation) on the abundance and distribution of Acartia populations and the interactions between their congenerics was evaluated by means of transfer function (TF) models in the estuary of Bilbao during the period 1998–2005. The recorded species were Acartia clausi, Acartia tonsa, Acartia margalefi and Acartia discaudata. Acartia clausi dominated in the entire euhaline region of this estuary until 2003 when it was displaced from the inner part by A. tonsa. This invasive species (A. tonsa) was found for the first time in 2001 and colonized successfully the inner (salinity 30) and intermediate (salinity 33) waters of this estuary since 2003. The TF models revealed an immediate and negative effect of A. tonsa on A. clausi in the intermediate salinity (33) waters, where these species showed the highest spatial overlap. The results indicate that environmental changes from 2003 influenced the abundance of Acartia species, being unfavourable for A. clausi. The decrease of A. clausi abundance in low salinity waters was related to a significant decrease of dissolved oxygen saturation levels, whereas the increase of temperature was linked to a significant increase of A. tonsa. Acartia margalefi and A. discaudata were scarce over the entire period, but they were found to be valuable indicators of hydrological changes, which were associated to climate factors. These two latter species increased in abundance and expanded their seasonal distribution, and in the case of A. margalefi also its spatial distribution, in 2002, coinciding with the period in the time-series when autumn–winter rainfall and summer temperatures were lowest, and dissolved oxygen saturation levels were highest.

The growth strategies of pelagic larvae of 3 fish species from the Bay of Biscay belong- ing to 2 different shape groups, the eel-like anchovy Engraulis encrasicolus and sardine Sardina pilchardus, and the tadpole-like horse mackerel Trachurus trachurus, are compared in terms of changes in their biochemical composition and energy allocation. In anchovy and sardine, the relative amount of protein increased and relative amounts of carbohydrates and lipids decreased throughout their growth. The biochemical composition in horse mackerel did not change significantly during growth. Differences between the 2 shape groups could be associated with the various energy alloca- tion patterns related to dissimilar growth strategies. Although the patterns of change in biochemical composition during growth are different in the 2 shape groups, they show a very similar biochemical composition at the notochord flexion stage, indicating convergences in life-history patterns of the dif- ferent species.

This study is a part of the zooplankton monitoring program carried out in the euhaline region of the estuaries of Bilbao and Urdaibai (Basque coast, Bay of Biscay), and analyses between-estuaries differences in zooplankton spatial and temporal patterns in relation to environmental conditions between July 1999 and May 2001. Environmental variables measured were water temperature, dissolved oxygen saturation (DOS), Secchi disk depth (SDD) and chlorophyll a. Relationships between zooplankton community and environmental variables were analysed using canonical correspondence analysis; between-estuaries differences in environmental conditions and distribution of zooplankton taxa in relation to salinity were tested using Mann― Whitney U-test. Spatial differentiation of the zooplankton community was higher in the estuary of Bilbao, with the relative abundance of most of the taxa decreasing more pronouncedly towards the upstream estuary than in the Urdaibai related to significantly lower values of DOS and SDD, reflecting the higher degree of pollution, in the Bilbao estuary. However, the successful establishment of the Acartia discaudata and A. margalefi populations, and the first records of another Acartia species, Calanipeda aquaedulcis and Eurytemora affinis in the Bilbao estuary, along with the increasing similarity between zooplankton assemblages of the Bilbao and Urdaibai estuaries in relation to the period 1997―1999, represent a new step in the recovery of the zooplankton community in the estuary of Bilbao responding to the improvement of water quality.

Growth and condition of larval Engraulis encrasicolus larvae in the Bay of Biscay were analysed relative to their biochemical composition. Protein, carbohydrate, lipid, DNA and RNA contents of larvae were quantified during larval ontogeny to analyse changes associated with growth. Proteins were the main organic component of E. encrasicolus at every larval stage, followed by lipids and carbohydrates. The increase in relative protein content in terms of protein percentage (P%) and the decrease in lipid relative content (L%) of the total organic matter (OM) with size observed are consistent with the definition of Type 1 larvae. Protein relative content increased until the P% in larvae reached ~71%, whereas L% and carbohydrate relative content (CH%) declined, exhibiting minimum values of ~20, and ~6%, respectively. In general terms, the feeding condition of larvae, as defined by their RNA/DNA ratio, was good. Food did not seem to be a major factor limiting larval growth in the study area throughout late spring and early summer. The RNA/DNA ratio was size-related and increased during larval growth up to an asymptotic optimal value of ~3.6 in postflex- ion larvae in relative protein content, in terms of protein percentage (P%). The 'actual' RNA/DNA ratios found in a given larval population when compared with the 'starving' RNA/DNA ratio, and using an 'absolutely optimal' value as complementary information, could be used to determine the overall status of the population. Parental effect of low egg quality is a possible explanation of delayed ontogenetical development of larvae from July 2000.

The nutritional environment for fish larvae is analysed for the Basque continental shelf (Bay of Biscay), during the main anchovy-spawning period (spring) over two years. The quantity and quality of Suspended Particulate Matter (seston) is analysed for total particles, microparticles (20–200 μm) and mesoparticles (200–1000 μm). Separately, the characterisation of the

The abundance and hatching success of Acartia bifilosa resting eggs in subtidal sediments of the Urdaibai estuary was analysed in the context of a study on the spatial and temporal dynamics of this species. Two sediment cores of 20 to 30 cm depth were obtained at two sites of the middle zone, where the accumulation of mud and organic particles is favoured. Laboratory incubations were performed to determine the hatching success of eggs and identify newborns. Resting egg abundance was around 107 eggs m -2 , and was higher at the site where the A. bifilosa population maintains an optimal position in the water column. The lower egg abundance in upper layers, as corresponds to winter, was associated with the seasonal dynamics of planktonic populations. On average, the hatching success was >50% at both sites. The lack of significant differences in the hatching success according to sediment depth suggests that eggs remain viable after being buried for a long-time in anoxic conditions. This enables us to infer that the benthic egg bank of A. bifilosa in this estuary is a safe source of recruits into the planktonic population, and plays a crucial role in recuperationand maintenance of the population.

Variations in prosome length and width, dry weight and condition factor of female Acartia clausi copepods were studied at three salinities (35, 34 and 33 psu) in the euhaline region of two estuaries (Bilbao and Urdaibai) of the Basque coast, with different level of anthropogenic impact. Effect of the environmental variables upon the morphology of A. clausi females on a small geographic scale is discussed. In general, biometric variables showed no significant differences between the two estuaries, but dry weight and condition factor were significantly higher in the estuary of Urdaibai at 35 and 34 psu, whilst at 33 psu they were higher in Bilbao. Body dimensions decreased significantly with decreasing salinity in both estuaries, however, no similar trends were observed for dry weight and condition factor. Temperature appeared the main variable to account size variations, but once eliminated seasonal effect of the temperature body size was related with oxygen concentration in the estuary of Bilbao and with salinity in Urdaibai. This study reveals that morphological characteristics of A. clausi not are only dependent on the temperature, but also, within a limited geographical zone, on local differences in environmental variables, mainly salinity and oxygen concentration.

The abundance and spatial distribution of copepod species were compared in the euhaline region of the polluted estuary of Bilbao [mean biological oxygen demand (BOD): 49748.05 kg day -1 in 1996] and the unperturbed estuary of Urdaibai. Sampling was performed at fixed salinity sites, where data of temperature, dissolved oxygen saturation, particulate organic matter, Secchi disk depth and chlorophyll were also obtained. Differences between the estuaries and within the estuaries for environmental variables and copepod abundances were tested statistically. The dominant species Acartia clausi and Paracalanus parvus differed significantly in abundance between estuaries, and most of nerilic species diminished more drastically with decreasing salinity in Bilbao by the effect of pollution. The different responses observed among species in relation to pollution and water desalination are discussed. The lack of the brackish-water species in Bilbao indicated that water quality worsening upward the estuary of Bilbao not only limited the penetration of neritic species but also prevented the development of autochthonous estuarine species. At the outer euhaline region of Bilbao, however, pollution was found to be low enough to enhance the development of tolerant neritic species that are favoured under moderate pollution conditions. Results indicate that comparisons of copepod abundances and distributions with salinity in estuaries may he a useful tool to evaluate the health of the different estuarine pelagic habitats.

The fecundity and hatching success of Acartia clausi were analysed at fixed salinity sites (35, 34 and 33 psu) in two nearby estuaries (Bilbao and Urdaibai, Basque coast, Bay of Biscay) from March to June 1997. Field incubations were conducted to estimate egg production rates and hatching success, and the size of eggs and experimental females measured. Water temperature and dissolved oxygen saturation were also determined, as well as seston samples to quantify food abundance and quality. Between-estuary and within-estuary differences were tested statistically, and correlation and regression analyses were used to determine relationships between reproductive and environmental variables. Egg production rates were higher in the organically enriched estuary of Bilbao; this denoting that food supply controls the fertility of A. clausi in these systems. Temporal patterns of egg production differed between estuaries, and were associated with different nutritional factors in each estuary. Within the salinity range analysed, egg production reached higher values at intermediate salinity (≈34 psu) in both estuaries. This was interpreted as the result of the interaction between the positive effect of food increase, and the negative effect of physicochemical conditions with decreasing salinity. Egg size variations mainly occurred temporally in relation to female size, but no clear trade-off between egg size and egg number was observed in any case. A drop in hatching success in Bilbao, mainly in waters of

The reproductive response involving egg number and size was studied for the egg carrying copepod Euterpina acutifrons in two estuaries with different nutritional environment (Bilbao and Mundaka). To characterise the available food for copepods, the concentration of particulate organic matter (POM), the combined concentration (PGL) and proportion of particulate protein, carbohydrate and lipids and the concentration of chlorophyll a were measured in the

The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994, Food availability was evaluated by analysing the chlorophyll a (Chi a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increase, in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63 x 10(-3) day(-1)) than in the Gironde (ranging from 0 to 0.13 x 10(-3) day(-1)), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive con-elation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chi a/SPM: 10 to 1870 mug g(-1)) and gut fluorescence (between 0, 12 and 0,38 ng Chi a Eq ind(-1)) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chi a/SPM: 10 to 80 mug g(-1) GF: 0.09 and 0.25 ng Chi a Eq ind(-1)), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton ere responsible for the observed changes in egg production, Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries. (C) 2002 Elsevier Science B.V All rights reserved.

The grazing activity of nanozooplankton natural assemblages on phytoplankton was analysed in the polyhaline and euhaline zones of the estuary of Mundaka throughout the spring–summer–autumn period. Grazing experiments were conducted in situ using the dilution method. Incubations occurred within a relatively wide range of initial chlorophyll concentration (1–10 μg chl l −1 ), but saturated feeding kinetics were not observed in most experiments. The heterotrophic nanoplankton grazed on average between 43 and 51% (mean values from all dilutions data and the 3 more diluted data, respectively) of the phytoplankton stock in the polyhaline zone, and between 36 and 43% in the euhaline. The grazing impact on primary production averaged around 65% in both zones, but showed higher variability in the euhaline (0–223%) than in the polyhaline (15–117%). Herbivore pressure was found to be higher in polyhaline waters on average, but between-zone differences were not significant. The nanozooplankton herbivory was not clearly related to water temperature, nor to phytoplankton biomass (expresed as chlorophyll concentration), and the coupling between production and consumption was weak, being more unbalanced in the euhaline zone. Nanozooplankton grazing was sometimes found to cause phytoplankton decline, while at other times its impact was negligible. In addition, indirect evidence suggests that nanozooplankton grazing activity may be affected by predation pressure from mesozooplankton in the polyhaline zone. Seasonal patterns of phytoplankton exploitation by heterotrophic nanoplankton differed among saline zones, suggesting that the fate of phytogenic carbon in the estuary of Mundaka may be highly variable both spatially and seasonally.

18 pages, 13 figures, 8 tables, The abundance, composition and mesoscale variability of the microplankton (53-200. μm) and the mesoplankton (0.2-2. mm) fractions in relation to oceanographic factors and phytoplankton biomass were compared off the Catalan coast (NW Mediterranean) during the summer stratification (June) and autumn mixing (November) periods in 2005. This work aims to determine whether the two plankton fractions that more contribute to fish larval diet respond to a common variable environment, and this study constitutes the first attempt to analyse, in parallel, the spatial structure of both fractions in this area. From June to November microplankton abundance increased mainly by the increase of dinoflagellates, tintinnids and radiolarians, and mesoplankton decreased due mainly to the decrease of long-horned dinoflagellates, cladocerans, doliolids and appendicularians. Plankton mesoscale variability in relation to environmental variables showed higher complexity in June, where environmental horizontal and vertical gradients were more marked than in November. In June, the major mode of variability of the microplankton was mainly accounted by the patchy distribution of several tintinnid species dominated by Rhabdonella spiralis associated to the subsurface phytoplankton biomass. The main mode of variability of the mesoplankton was related to the intrusion of the Ebro river plume and the related aggregation of doliolids and cladocerans, dominated by Evadne spinifera. In November, the major variability pattern in both fractions was a combination of inshore-offshore and eastern-western gradients in taxa distributions shaped mainly by the course of the Catalan Current along the shelf-break. Spatial differences in planktonic food pathways in each period are discussed on the basis of literature on plankton feeding habits and types, and on the diet of fish larvae of the main species from the same surveys. © 2014 Elsevier B.V., This research was funded by the CTM2004-03510-C02-01 and 02 ⁄MAR Project. The team of the UPV/EHU also received finnancial support for this work from the Basque Government (GIC10/168) and the University of the Basque Country (UFI11/37)

12 pages, 7 figures, 4 tables, The feeding ecology of the larvae of the two most important small pelagic species in the western Mediterranean, anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus), is investigated. Samples were collected in early summer (anchovy) and autumn (sardine). Composition of the diet and prey selectivity were compared over the course of ontogeny in anchovy (2.7-14.5 mm standard length, SL) and sardine (5.5-15.8 mm SL) larvae. Anchovy larvae begin feeding on prey items >150 m at smaller sizes than sardine larvae, and the diets of both species are based mainly on copepod nauplii and postnauplii. Seasonal differences in the composition of the plankton influenced the contributions of prey types to the diets of the two species, e.g. the cladoceran Evadne spp. in anchovy and the tintinnid Codonellopsis sp. in sardine. Although copepod eggs are generally present in the diets of larval clupeoids, they were not major components of the diets of the species considered here. Despite morphological similarity, selection patterns were different between the species and changed through ontogeny. © 2009 International Council for the Exploration of the Sea, The research was funded by projects CTM2004-03510-C02-01/MAR and CTM2004-03510-C02-02/ MAR. EM acknowledges predoctoral FPI Fellowship support from Spain’s Ministry of Education and Science

10 pages, 7 figures, 2 tables., The present study analyses for the first time the diet of larvae of the clupeid Sardinella aurita in the NW Mediterranean. Gut contents of larvae from first feeding (3.9 mm) to early postflexion stages (14.7 mm) were analysed. The type and abundance of ingested prey were related to the plankton composition in the environment in order to determine prey-type selectivity. The feeding incidence observed was among the highest reported for clupeid larvae, with higher values during the day (68.6%) than at night (7.7%), indicating that Sardinella aurita larvae are diurnal predators. The mean number of ingested prey was 3.3 (±2.51). The width of the prey increased from < 30 to 410 μm with the development of the larvae, but the niche breadth did not vary with the size of the larvae. The diet was based on different stages of copepods (nauplii and postnauplii) and cladocerans (mainly Evadne spp.), though the preference for each type of prey varied, with higher preference for copepod nauplii in larvae < 8 mm and a higher preference for Evadne spp. in larvae ≥ 8 mm. The copepod based diet of S. aurita larvae is very similar to that reported for Engraulis encrasicolus larvae in the Mediterranean, indicating a possible competition for food between the first-feeding larvae in situations of low prey abundance., This research was funded by the CTM2004-03 510-C02-02/MAR Project. E.M. acknowledges the predoctoral FPI Fellowship support from Spain’s Ministry of Education and Science.