Mesopodopsis Slabberi Research Articles

Türkiye’nin Akdeniz Kıyılarında Mesopodopsis slabberi (Van Beneden, 1861) (Crustacea: Mysida)’nin varlığı

Mysid, Mesopodopsis slabberi (Van Beneden, 1861) was for the first time recorded in İskenderun Bay (eastern Mediterranean). A total of 10 specimens belong to M. slabberi was collected at the depths between 0 and 2 m. This paper is on the first record of M. slabberi from the Levantine coast of Turkey.

The effects of mercury on the dynamics of the peracarida community in a temperate coastal lagoon (Ria de Aveiro, Portugal)

This study focuses on the impact of mercury on the dynamics and bioaccumulation patterns of suprabenthic peracarida community along a mercury gradient. Suprabenthic peracarida was negatively affected in terms of biomass, diversity and productivity. Mysids including Mesopodopsis slabberi dominated the community, presenting a regular distribution along the Hg gradient, so are considered tolerant species to mercury. Then, isopods, the second most abundant group, dominated in the most contaminated areas being considered also a tolerant group. Contrarily, amphipods were negatively correlated with higher Hg concentrations, dominating in the intermediate areas, thus are considered more sensitive species. In addition, isopods and amphipods were the taxa with higher mercury body burden, followed by mysids. This paper highlights the importance of suprabenthic peracarida as a vehicle of mercury transference through the estuarine trophic web since it is a main link between benthic and pelagic levels and an essential food resource for numerous fish species.

Organic matter exploitation in a highly turbid environment: Planktonic food web in the Charente estuary, France

Abstract Estuaries are highly dynamic systems where multiple organic matter sources coexist and where complex biogeochemical processes greatly affect their fate. Although zooplankton plays a key role of in the energy fluxes between primary sources and exploited macrofauna, there is still a critical lack of field information concerning the spatio–temporal variability of the trophic pathways supporting its high biomasses in estuaries. From January 2007 to January 2008, suspended matter, microphytobenthos and zooplankton were sampled along the salinity gradient of the Charente estuary to determine their carbon and nitrogen stable isotope composition. The relative homogeneity of the δ 13 C values of particulate organic matter (POM) all along the estuary (−23.6 to −26.5‰ except in March and June, ∼ −28.5‰) was attributed to physical mixing of marine and terrestrially derived organic matter with the great load of tidally resuspended particles. The five zooplankton taxa analysed displayed a wide range of δ 13 C (from −34.9 to −17.4‰) and δ 15 N values (3.4–15.2‰) over the year, providing strong evidence for high selectivity toward different organic matter sources and reinforcing the idea that a spatio–temporal succession of species assemblages lead to multiple trophic pathways and may stabilize the estuarine trophic network. The high δ 15 N values of Eurytemora affinis in the maximum turbidity zone were believed to reflect a higher carnivorous tendency as a functional response to the strong decrease of phytoplankton availability. Conversely, Acartia spp. appeared unable to change their diet in the same way and was thus unable to colonize upstream areas. Stable isotope analysis also revealed that Mesopodopsis slabberi mostly relied on fresh phytoplankton and microphytobenthos while Neomysis integer presented a clear carnivorous tendency toward copepods, at least during the warm period. Additionally evidence was provided for passive (downstream advection of freshwater cladocerans with river runoffs) and active (coast-estuary seasonal migration of M. slabberi ) longitudinal movements in estuarine organisms.

Effects of freshwater inputs on the lower trophic levels of a temperate estuary: physical, physiological or trophic forcing?

The aim of this 6 year study was to assess whether freshwater inputs (rainfall and dam discharges) were acting as physical, physiological or trophic forcing factors on phytoplankton pigment concentrations and the dominant mysids of a temperate estuary (Guadalquivir estuary; SW, Spain). The effects of natural and human-controlled freshwater inputs modified the physico-chemical conditions and consequently biological production (bottom up control). Nutrient (nitrogen hypernutrification), suspended particulate matter and allochthonous photosynthetic pigment imports linked to freshwater inputs from adjacent habitats were observed, as well as light-limited autochthonous primary production. Seasonal and/or spatial patterns were shown by all study variables, including mysids. Freshwater management effects on dominant mysids differed depending on the species’ salinity tolerance (physiological forcing) and preferred prey availability (trophic forcing). Moreover, high inorganic matter content had a negative effect on the density of Mesopodopsis slabberi (physical forcing), which led to an increased detritivory/herbivory ratio (Neomysis integer/M. slabberi ratio). In conclusion, freshwater inputs appeared to effect estuarine lower trophic levels via a combination of different forcing mechanisms. Although several general patterns can be derived, the response of the system to freshwater inputs was not always univocal.

The impact of extreme turbidity events on the nursery function of a temperate European estuary with regulated freshwater inflow

Estuaries are used as nursery grounds by numerous marine species despite being usually subject to strong anthropogenic disturbances. Abundances of marine recruits (fish and crustacean decapods) and their main prey (mysids) were monitored by monthly sampling, from June 1997 to February 2009, in the lower reaches of the Guadalquivir estuary (SW Spain). During that period, unusually high and persistent turbidity events (HPTEs) were observed twice. Both HPTEs started with strong and sudden freshwater discharges after relatively long periods of very low freshwater inflow. Data from this time-series were used to test the hypothesis that HPTEs may negatively impact the nursery function of estuaries either by decreasing prey availability or by decreasing survival/arrival of marine recruits. During HPTEs, the commonest mysid ( Mesopodopsis slabberi), a key species in the estuarine food web, showed a significant decrease in abundance. Likewise, some marine recruits that prey on M. slabberi and whose peaks of abundance within the estuary occur in summer–autumn ( Engraulis encrasicolus and Pomadasys incisus) were less abundant during HPTEs. It is also suggested that HPTEs might have triggered a shift in the distribution of the most euryhaline prey ( Neomysis integer) and predator ( Dicentrarchus punctatus and Crangon crangon) species, towards more saline waters. This could have contributed to an increase in the inter-specific competition (for food/habitat) within the estuarine nursery area. The results discussed in this study call attention to the need to reduce as much as possible the anthropogenic pressures that may stimulate the occurrence of high and persistent turbidity events (HPTEs) in order to preserve the nursery function of temperate estuaries.

Use of Amphipods as alternative prey to culture cuttlefish ( Sepia officinalis) hatchlings

The effects of feeding two alternative live prey (exclusively caprellids ( Caprella equilibra) or several species of gammarids, mainly Ericthonius brasiliensis, Jassa marmorata and Elasmopus sp.), to cuttlefish hatchlings were compared to feeding mysids ( Mesopodopsis slabberi), which are normally used during the first weeks of the life cycle. Weight (g) and growth rates (GR, % BW d − 1 ) were determined. Cuttlefish hatchlings fed with mysids and gammarids grew faster (6.7 ± 0.4 and 5.7 ± 0.9% BW d − 1 , respectively) compared to caprellids (1.6 ± 0.2% BW d − 1 ). Survival was higher (96.7 ± 5.8%) for hatchlings fed mysids, compared to 83.3 ± 15.3% and 76.7 ± 5.8%, for those fed gammarids and caprellids, respectively. According to the results obtained, gammarids could be used as an alternative prey to mysids, while Caprella equilibra did not deliver appropriate growth rates and should be disregarded as alternative prey for rearing early stages (hatchlings) of Sepia officinalis. This is the first study revealing a successful use of amphipods, mainly gammarids, as alternative prey for cuttlefish hatchlings.

Ecology of mysid shrimps in the Bornholm Basin (central Baltic Sea)

Mysid shrimps are an important trophic link in the food web of the Baltic Sea. In 2002 and 2003 we investigated species composition, distribution, life cycle and prey in the Bornholm Basin (central Baltic). Three species and one genus were identified: Mysis mixta, Neomysis integer, Mesopodopsis slabberi and Praunus sp. The dominant M. mixta and N. integer occurred in the whole study area but were more abundant in the peripheral, more shallow regions. Size frequency distribution indicated one generation for M. mixta and probably two for N. integer. Main prey of all size classes in both species was the cladoceran Bosmina coregoni maritima during summer and autumn. In spring and winter also copepods of the species Temora longicornis and Pseudocalanus acuspes were important prey items. Detritus and phytoplankton cells were of minor importance and many individuals had empty guts. Mysid shrimps in the deep basin might be advected from more shallow areas, as the abundance of all species was much lower than in coastal regions. The deep Bornholm Basin does not seem to be a favourable habitat, probably due to the inaccessibility of the oxygen deficient bottom layer. Under current hydrographic conditions mysids are probably not important predators of zooplankton and thus not competitors of planktivorous fish in the Bornholm Basin.

Inter- and intra-specific differences in euryhalinity determine the spatial distribution of mysids in a temperate European estuary

Mysids are an important component of estuarine hyperbenthos and a major prey item in the food web of many estuaries. Understanding the abiotic and biotic mechanisms determining mysid distributions is therefore important to comprehend the general processes structuring estuarine communities. We carried out field surveys and exposure-survival experiments for three species of mysids, Neomysis integer Leach Mesopodopsis slabberi van Beneden and Rhopalophthalmus tartessicus Vilas-Fernandez, Drake and Sorbe, to link salinity tolerances of different sex and life stages (adults and juveniles) to their spatial distributions within the Guadalquivir estuary, SW Spain. Despite being euryhaline, the three species of mysids were unevenly distributed along the saline gradient, with salinity being the environmental variable which best explained structure changes in the estuarine mysid assemblage. R. tartessicus remained confined to the outer and more marine part of the estuary and showed a higher temporal variation in its salinity-related distribution (position within the salinity gradient). M. slabberi and N. integer displayed wider estuarine distributions but remained associated with intermediate and low salinities, respectively. We found considerable inter- and intra-specific differences in tolerance to sudden salinity changes: N. integer, and juveniles of M. slabberi and R. tartessicus, showed a high tolerance to sudden salinity changes, whereas adults of M. slabberi and R. tartessicus were only tolerant to salinities close to their isosmotic points. For the less euryhaline species M. slabberi and R. tartessicus acclimation to unfavourable salinities decreased survival after exposure to sudden salinity changes. Both location and strength of the salinity gradient were important factors in determining spatial distribution, either directly to avoid osmotic stress and mortality risk ( R. tartessicus and M. slabberi) or indirectly to reduce inter-specific mysid competition ( N. integer). We suggest inter- and intra-specific euryhalinity differences determine the spatial distribution of mysids and the specific strategies they use to maintain this spatial structure in a highly variable environment.

Growth and survival of adult long snout seahorse ( Hippocampus guttulatus) using frozen diets

This investigation examined the effect of using three different natural frozen diets; shrimp ( Palaemonetes varians), mysids ( Mesopodopsis slabberi) and adult Artemia on the fitness condition of adult long snout seahorse ( Hippocampus guttulatus). At the end of the 12 week experimentation, significant differences on the final wet weight were found between the animals fed with the three different treatments ( F 3,54 = 33.31, P < 0.0001). Significant differences were found between the animals fed with adult Artemia and the ones fed with either mysids or shrimp ( P < 0.001), but no significant differences were found between the shrimp and mysid treatments ( P > 0.05). Seahorses fed with the shrimp and mysid treatments had an increase of 58.9% and 52.2%, respectively, between the initial and final wet weight, while for the animals fed adult Artemia there was a decrease in their final wet weight. Condition Factor (CF) and Weight Gain (WG) showed the same pattern of statistical significance. Significant differences were found between treatments (CF; F 3,54 = 11.49, P < 0.0004, WG; F 3,54 = 71.19, P < 0.0001), with the seahorses from the shrimp treatment having a higher CF and WG than those from the adult Artemia treatment ( P < 0.001), but not from the mysid treatment ( P > 0.05). The comparison of mean daily SGR and the FCR revealed similar results, as significant differences were found between treatments (SGR; H = 23.33 P < 0.0001, FCR; H = 23.84, P < 0.0001). Seahorses fed shrimp had higher SGR and better FCR than the ones fed adult Artemia ( P < 0.001), but weren’t different from the ones fed mysids ( P > 0.05). In this study, the Atlantic ditch shrimp ( P. varians) was successfully used as a frozen diet for H. guttulatus. Although no significant differences have been found between the shrimp and mysid treatments, the WG, CF, SGR and FCR were higher for the animals fed with shrimp. Results thus suggest the adequate use of these two frozen diets to improve the fitness condition of adult H. guttulatus.

Functional response of early stages of the cuttlefish Sepia officinalis preying on the mysid Mesopodopsis slabberi

The functional response of Sepia officinalis early stages, preying on mysids of the species Mesopodopsis slabberi was investigated. The effects of five prey densities (12.5, 25, 37.5, 50 and 125 mysids l−1) and two hatchling ages (1-day-old and 7-day-old) on consumption rate and the frequency of non-feeding animals were tested. Older animals were approximately 50% heavier than newly hatched ones. Hatchlings were individually assayed under 0.25 W m−2 natural light, 37.8 psu in salinity and 19°C. The effect of prey density on consumption rate was highly significant and no effect of age was detected within the age range tested. Maximal values recorded for consumption rate were about 0.45 mysids h−1. The frequency of non-feeding individuals was strongly reduced at saturating prey densities. The functional response curve showed an interval of prey densities for which density-dependent prey mortality is probable.

Spatio‐temporal distribution of early life stages of the European anchovy Engraulis encrasicolus L. within a European temperate estuary with regulated freshwater inflow: effects of environmental variables

The spatio‐temporal distribution of the anchovy Engraulis encrasicolus in its early life stages was related to environmental conditions within the Guadalquivir River estuary (south‐west, Spain) by monthly field surveys during nine periods of recruitment (May 1997 to December 2005). Anchovy post‐larvae showed a consistent seasonal pattern of abundance throughout the study period: each year, a high anchovy recruitment period (HARP) occurred from late May to November, with a main peak in July, coinciding with the period when environmental conditions were more stable. Results of stepwise multiple regression analysis indicates that density of its main prey, Mesopodopsis slabberi, explained 45% of total anchovy density variance. Furthermore, after removing the effect of this variable, interannual differences in the anchovy estuarine recruitment were not significant. Clear spatial and tidal trends were also observed for both prey and predator: at each sampling date, density decreased from the outer to inner estuary; at each sampling site, density was higher during ebbs than during floods. Field distributions related to environmental gradients during HARP indicated that the populations of E. encrasicolus and M. slabberi seemed to hold a steady position at a point on the salinity gradient by longitudinal displacement within the estuary. Since freshwater management actions affect the longitudinal position of the salinity gradient as well as the input of nutrients to the estuary and adjacent coastal areas, it is hypothesized that this factor may also be relevant to anchovy recruitment.

Enrichment of aquaculture earthen ponds with Hediste diversicolor: Consequences for benthic dynamics and natural productivity

The present work analysed the potential impacts of the enrichment of semi-intensive production earthen ponds with the ragworm Hediste diversicolor in the benthic dynamics and natural productivity. The macrobenthos and sediment characteristics were analysed in two enriched ponds and two control ponds in May, June and September 2005. The number of species, Margalef species richness and biomass (AFDW) were generally significantly higher in enriched than in control ponds, while for abundance no clear pattern was visible. Multivariate analysis showed differences in macrobenthic community structure of control and enriched ponds. Differences were also visible when the introduced species was removed from the data set, indicating that differences were mainly due to changes in other species abundance. In general, gastropods ( Akera bullata, Jujubinus striatus, Hydrobia ulvae, Rissoidae), bivalves ( Abra ovata, Cerastoderma spp.), crustaceans ( Ampithoe rubricata, Dexamine spinosa, Gammarus insensibilis, Gammarella fucicola, Iphinoe tenella), and also some polychaetes ( Desdemona ornata, Terebella spp., Syllis gracilis and Neanthes caudata) greatly increased their abundances in enriched ponds. On the other hand, the abundance of Tubificidae, Capitella spp., Pseudopolydora paucibranchiata, Corophium acherusicum, and Mesopodopsis slabberi decreased. The organic matter content was significantly lower in enriched ponds, probably due to the positive impact of the polychaetes on sediment reworking, resulting in higher organic matter mineralization. Overall the present study indicates that stocking of earthen production ponds with H. diversicolor significantly altered community structure of benthic invertebrates and may improve environmental conditions for fish production by reducing the organic matter accumulation in pond sediments.

Oxygen Consumption and Osmoregulatory Capacity in Neomysis integer Reduce Competition for Resources among Mysid Shrimp in a Temperate Estuary

Results of field surveys and laboratory measurements of oxygen consumption and body fluid osmolality at different salinities in the mysids Neomysis integer, Mesopodopsis slabberi, and Rhopalophthalmus mediterraneus from the Guadalquivir estuary (southwest Spain) were used to test the hypothesis that osmotic stress (oxygen consumption vs. isosmotic points) was lowest at salinities that field distributions suggest are optimal. The three species showed overlapping spatial distributions within the estuary but clear segregation along the salinity gradient: N. integer, M. slabberi, and R. mediterraneus displayed maximal densities at lower, intermediate, and higher salinities, respectively. Adults of N. integer were extremely efficient hyperregulators (isosmotic point 30 per thousand) over the full salinity range tested (3 per thousand-32 per thousand), and their oxygen consumption rates were independent of salinity; adults of M. slabberi were strong hyper- and hyporegulators at salinities between 7 per thousand and 29 per thousand (isosmotic point, 21 per thousand) and showed higher oxygen consumptions at the lowest salinity (6 per thousand); adults of R. mediterraneus hyperregulated at salinities between 19 per thousand and seawater (isosmotic point, 36 per thousand), with the lowest oxygen consumption at salinity around their isosmotic point (35 per thousand). Thus, the osmoregulation capabilities of M. slabberi and R. mediterraneus seem to determine the salinity ranges in which most of their adults live, but this is not so for adults of N. integer. Moreover, maximal field densities of M. slabberi (males and females) and R. mediterraneus (males) occur at the same salinities as the lowest oxygen consumption. In contrast, field distribution of N. integer was clearly biased toward the lower end of the salinity ranges within which it osmoregulated. We hypothesize that the greater euryhalinity of N. integer makes it possible for this species to avoid competition with R. mediterraneus by inhabiting the more stressful oligohaline zone.

Phylogeographic patterns of the mysid Mesopodopsis slabberi (Crustacea, Mysida) in Western Europe: evidence for high molecular diversity and cryptic speciation

The phylogeographic patterns among populations of Mesopodopsis slabberi (Crustacea, Mysida), an ecological important mysid species of marine and estuarine habitats, were analysed by means of DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) and the 16S ribosomal RNA genes. Samples of M. slabberi collected from five Atlantic and two Western Mediterranean populations were investigated. Very high levels of within-population molecular diversity were observed in all samples (mean h=0.807 and π=0.0083), with exception of the Mediterranean Ebro population which contained only one haplotype. Differentiation among populations was high, and a clear phylogeographic break was observed between the Atlantic and Mediterranean populations. Moreover, a strong differentiation was detected between both populations in the Western Mediterranean Sea (Alicante and Ebro delta), while two divergent lineages occurred in sympatry within the Atlantic Mondego estuary. The high congruence between both the COI and 16S rRNA sequence data, the reciprocal monophyly of the different mitochondrial clades and the levels of nucleotide divergence between them suggest the presence of a complex of cryptic species within M. slabberi. Estimations of divergence time between the different mitochondrial lineages indicate that a split occurred during the late Miocene/early Pliocene. Such a divergence could be concordant with vicariant events during sea-level drops within the Mediterranean region at that time. However, within the Mediterranean Sea, the potential of divergence through ecological diversification cannot be ruled out.

Morphological Differentiation Between Geographically Separated Populations of Neomysis integer and Mesopodopsis slabberi (Crustacea, Mysida)

Morphological variation was examined in Neomysis integer and Mesopodopsis slabberi, two abundant, low dispersal mysid species (Crustacea, Mysida) along the European coasts. Both species dominate the hyperbenthic communities in the northeast Atlantic, and M. slabberi is also widely distributed in the Mediterranean and Black Sea. Three populations of these species were sampled throughout their distribution range; samples of N. integer were collected in the northeast Atlantic Eems-Dollard, Gironde and Guadalquivir estuaries; in the case of M. slabberi, mysids were sampled in two northeast Atlantic estuaries (Eems-Dollard and Guadalquivir) and one Mediterranean site (Ebro Delta). A total of 12 morphometric and 2 meristic characters were measured from 30–64 mysids per sample. Multivariate analysis showed clear morphometric differences between populations of both species. The morphological differentiation within M. slabberi was highly concordant with the available genetic data from mitochondrial loci, pointing to a large divergence between the Atlantic and Mediterranean populations. However, due to some overlap of individuals between the different populations, the present morphometric analysis does not suffice to assign the different populations to a separate (sub)species status. In the case of N. integer, the morphometric patterns showed a divergence of the Gironde population. Differentiation of populations within this mysid, as in M. slabberi, were mainly related to eye and telson morphology. Potential interactions of the mysid morphology and environmental conditions are discussed.

Long-term changes of the zooplankton variability in a turbid environment: The Gironde estuary (France)

Zooplanktonic variability at the maximum turbidity zone was investigated for the Gironde estuary for 18 years. This ecosystem is characterized by a high concentration of suspended matter and five dominant zooplankton species: the copepods Eurytemora affinis, Acartia bifilosa, A. tonsa and the mysids Neomysis integer and Mesopodopsis slabberi. Four major sources of variation in density were analyzed: (a) spatial variation (vertical and longitudinal variability) and (b) temporal variation (seasonal and annual variability) in the oligo-mesohaline area of the estuary. Temporal variability was related to environmental parameters: temperature, salinity, suspended matter concentration and active chlorophyll in the water column. Seasonal and annual variability were identified as significant sources of variation which explains the fluctuations of all zooplankton densities. No long-term trend was observed for zooplankton densities except for A. tonsa, a species recently introduced into the oligo-mesohaline area of the estuary. Temperature and salinity were important factors explaining the interannual variability of E. affinis as well as of both mysids. Suspended matter concentration controlled the long-term trends of E. affinis and A. tonsa. Annual variability of A. bifilosa and both mysid species was also explained by the proportion of active chlorophyll. Seasonal variability, calculated as the between-month variation, represented the dominant type of variability for all species. Seasonal variations of copepods were essentially explained by salinity. N. integer was significantly correlated with temperature and copepod densities, whereas M. slabberi was correlated with temperature and salinity. Zooplankton also showed significant spatial variation. Mysids demonstrated significant differences between surface and bottom densities whereas vertical variability of copepod densities did not represent a significant source of variation. In terms of longitudinal variability, density of E. affinis was similar along the salinity gradient, whereas Acartia spp. and mysids occurred at significantly greater densities at the downstream station. The high turbidity, which characterizes the Gironde estuary, seems to be a determining factor that acts directly on copepod temporal variability and indirectly on mysid long-term fluctuations by limiting the nutritional quality of the environment.

Suprabenthic biodiversity of Catalan beaches (NW Mediterranean)

Abstract An analysis of the suprabenthos has been carried out on 13 diverse type beaches in Catalonian coast (NE of Spain). A total of 29 717 specimens, belonging to 145 species and eight different zoological groups (mysids, amphipods, cumaceans, isopods, tanaidaceans, decapods, pycnogonids, and teleostean fishes) were obtained. The suprabenthos of Catalan beaches were characterized by a mean density of 40 ind. m–2, by the abundance of Mysids (75% of the total density) and by the higher diversity of Amphipods (64 species). Five population species were considered as typical of suprabenthic assemblages: Schistomysis assimilis, Mesopodopsis slabberi, Atylus guttatus, Pontocrates altamarinus, and Cumopsis goodsir. Four main types of beaches with different number of suprabenthic species and densities and three main faunistic groups are described and related to environmental physical factors of the analysed beaches (morphodynamics, exposure, etc.). The macrofaunal trend about to that the species richness decrease from dissipative to reflective beaches is confirmed for the suprabenthic communities.

Temporal variation in feeding rhythms in a tidal marsh population of the common goby Pomatoschistus microps (Kroyer, 1838)

Pomatoschistus microps (Teleostei, Gobiidae) intensively uses the mesohaline marsh of Westerschelde estuary as a nursery and foraging ground. The sampling campaign covered the semi-lunar, diel and tidal cycles. The density of P. microps and potential hyperbenthic prey species in the marsh creek, fullness index, evacuation rates and daily ration of common goby were calculated. Mesopodopsis slabberi, Neomysis integer and Corophium volutator were the most dominant prey items in terms of biomass. Numerically, copepods dominated the diet. Migrating fish enter the marsh creek with a relatively empty stomach and leave the marsh with a higher stomach content. Pomatoschistus microps seemed to feed more intensively during the day than the night, however the influence of the diel cycle is inferior in comparison with the tidal influence on the feeding behaviour of the common goby. A significant difference in foraging activity occurred between the spring and neap tide. The common goby migrated in lower abundance into the creek during spring tide but foraged more intensively. At both spring and neap tide, a significant difference was found in the fullness index between day and night. At spring tide, gobies feed more during the day, while they forage more intensively at night at neap tide. All the three cycles (tidal, diel and semi-lunar) influenced the feeding rhythm of the common goby. The tidal influence is superior over the diel variation, while the explanation of the combined effect of diel and semi-lunar cycle needs further studies.

Mesopodopsis slabberi (Crustacea: Mysidacea): can it be used in toxicity tests?

Mesopodopsis slabberi is a euryhaline and suprabenthic mysid with a wide geographic distribution and one of the most important mysid species in coastal shallow waters. Nevertheless, no references were found to its uses in ecotoxicological experiments (TOXNET, AQUIRE, ISI Web of Knowledge). This work is part of an ecotoxicological study, representing the first step in establishing a description of this species’ tolerance to chemical pollutants typical of estuarine environments. It is possible to assert that acclimation was achieved, for it occurred during a period of time, with a low mortality. Due to the short life cycle of M. slabberi it is strongly believed that 12 days of acclimation is a far too long time, when experiments are to be made after this period. This species is suitable for acclimation in the laboratory, tolerant, and easy of handling. Logistics and materials used to maintain the acclimation system as described are simple and not costly and could easily be used in other laboratories.

Histochemistry and histology in planktonic ecophysiological processes determination in a temperate estuary (Mondego River estuary, Portugal)

Zooplankton communities in temperate climates exhibit well documented seasonal variability. The reasons proposed to explain this kind of behaviour range from the effect of physical-chemical conditions (salinity, nutrients, temperature) growth rates, mortality, migration rates, food availability and predation. It is noticeable that the majority of the factors mentioned are external to the organisms, being environmental factors responsible for time dependent changes in zooplankton abundance. A question may arise from this conclusion, namely, “Could zooplankton blooms, in temperate climates, be mainly modelled by the internal physiological predispositions of the individual organisms?” Or, in a more “functional” formulation, “Could gonads be the baseline regulators of zooplankton abundance?”. This study answers this pertinent question, assuming as a basic assumption that the reproductive potential of these organisms is constant, being controlled by extrinsic factors. For this purpose, histological and histochemical techniques were applied to the mysid Mesopodopsis slabberi, a key species in the Mondego River estuary, in order to establish a scale of gonadic development that would allow comparisons between high and low density periods. Histology reveals itself as the ideal base to establish a tool for the evaluation of the gonadic masses by allowing to calculate oocyte dimensions (trough biometry) and determine its maturity status through calculation of the N/C ratio and histochemical analysis (PAS and Tetrazonium reaction for proteins). Upon creation, validation and application of the formerly described tool, the most prominent result emerging from this study is the confirmation of the initial assumption: seasonal variability in zooplankton densities reflects advantageous or disadvantageous external factors acting over a latent reproductive potential. Moreover, this work confirms histology and histochemistry as valuable approaches to the determination of planktonic ecophysiological processes.