Isopod Saduria Entomon Research Articles

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences.

A significant increase in the infection level of Baltic cod Gadus morhua with the anisakid nematode larvae Contracaecum osculatum and Pseudoterranova decipiens has been recorded during recent years due to the expanding local population of grey seals Halichoerus grypus, which act as final hosts for these parasites. Here, we report from an investigation of 368 cod (total length [TL] 6-49 cm; caught in ICES Subdivision 25) that the infection level of juvenile cod (TL 6-30 cm) with larvae of C. osculatum and P. decipiens is absent or very low, whereas it increases drastically in larger cod (TL 31-48 cm). A third nematode Hysterothylacium aduncum was rarely found. The study indicates that the prey animals for large cod act as transport hosts for the parasite larvae. Analyses of stomach contents of cod caught in the same area (2007-2014) showed that small benthic organisms (including polychaetes Harmothoë sarsi) are preferred food items by small cod, the isopod Saduria entomon is taken by all size classes, and sprat Sprattus sprattus are common prey items for cod larger than 30 cm. Parasitological investigations (microscopic and molecular analyses) of H. sarsi (100 specimens) and S. entomon (40 specimens) did not reveal infection in these invertebrates, but 11.6% of sprat (265 specimens examined) was shown to be infected with 1-8 C. osculatum third stage larvae per fish. Analyses of sprat stomach contents confirmed that copepods and cladocerans are the main food items of sprat. These observations suggest that the C. osculatum life cycle in the Baltic Sea includes grey seals as final hosts, sprat as the first transport host and cod as second transport host. It may be speculated that sprat obtain infection by feeding on copepods and/or cladocerans, which could serve as the first intermediate hosts. One cannot exclude the possibility that the size-dependent C. osculatum infection of cod may contribute (indirectly or directly) to the differential mortality of larger cod (>38 cm) compared to smaller cod (<30 cm) recently recorded in the Baltic cod population.

Effect of Carbon Dioxide-Induced Water Acidification on the Physiological Processes of the Baltic Isopod Saduria entomon

Survival, behavior, hemolymph pH, osmolality, and chloride ion concentration as well the total metabolic rate (heat dissipation rate) of the isopod Saduria entomon from the brackish Baltic Sea were investigated after exposure to carbon dioxide-induced water acidification (pH, 7.5, 7.0, and 6.5; control pH, 8.2) keeping other parameters constant (temperature, 10°C; salinity, 7). The short-term (12 h per each pH treatment) exposure to carbon dioxide-induced water acidification did not cause significant changes (P < 0.05) in the resting metabolic rate or the scope of activity in S. entomon; however, high interindividual variability was observed. The 2-wk exposure to lowered pH values did not affect either the activity of the isopods or their survival rate significantly (P > 0.05), which was greater than 90% in all pH treatments. The hemolymph pH increased significantly (P < 0.05) with a decrease of water pH from a control pH of 8.2 down to a pH of 7.0. Hemolymph osmolality increased significantly (P < 0.05) at pH 7.5, but exposure to pH 7.0 did not cause further increase in this parameter. Reduction of water pH did not affect the hemolymph chloride ion concentration. Obtained results indicated that S. entomon is adapted to large fluctuations of carbon dioxide levels in the water primarily to compensate for acid—base disturbances without additional energetic costs.

Forage fish quality: seasonal lipid dynamics of herring (Clupea harengus L.) and sprat (Sprattus sprattus L.) in the Baltic Sea

Abstract Røjbek, M. C., Tomkiewicz, J., Jacobsen, C., and Støttrup, J. G. Forage fish quality: seasonal lipid dynamics of herring (Clupea harengus L.) and sprat (Sprattus sprattus L.) in the Baltic Sea. – ICES Journal of Marine Science, 71: . This study investigates lipid content and fatty acid composition of two important forage fish, sprat (Sprattus sprattus) and herring (Clupea harengus) in the Baltic Sea ecosystem. Seasonal variation in lipids was studied during three periods following the annual reproductive cycle considering potential differences relating to fish size, sex, and reproductive status. The isopod Saduria entomon, being at times an important prey for predatory fish, was included for comparison. In both sprat and herring, lipid content and absolute contents of essential polyunsaturated fatty acids (PUFAs) varied seasonally with high levels towards the end of the annual zooplankton production cycle, succeeded by a decline. Lipid content and fatty acid composition differed significantly between sprat and herring. Sprat lipid content was higher than herring, increasing with fish size and characterized by large proportions of monounsaturated fatty acids. Herring lipid content was related to the reproductive cycle and proportions of PUFAs were high compared with sprat. Levels of essential PUFAs were high in S. entomon compared with clupeids rendering it a valuable alternative prey species in the Baltic Sea ecosystem. The lipid dynamics of forage fish and benthos, combined with changes in availability and abundance, will affect growth and reproduction of their predators.

Food Composition and Prey Selection of Cod, &lt;I&gt;Gadus Morhua&lt;/I&gt; (Actinopterygii: Gadiformes: Gadidae), in the Southern Baltic Sea

Background. At the end of 1980s, ecological regime shifts occurred in the Baltic. Since, the Baltic fish assemblage has been dominated by sprats, whereas before cod was the dominant fish species. The majority of previous food studies refer to the period before the shift. This raises the question, how changes in the Baltic ecosystem have affected the diet of cod. The aim of the presently reported study was to identify the differences in the food composition of cod depending on the area, depth, season, and the cod size and compare it with the findings from the 1970s and 1980s. Materials and methods. Food composition and selection of prey size for Baltic cod was evaluated by examining the stomach contents of 556 adult cod, collected in 2006 and 2007. Fish stomachs were sampled from research catches within the Polish Exclusive Economic Zone. Results. The main component of the cod diet were the clupeids, constituting more than 67% of the total weight of the food recovered from the specimens studied. Other fishes in the diet represented Gobiidae, Ammodytidae, as well as young cod. The dominant invertebrate in the diet was the isopod Saduria entomon which accounted for 13% of the diet by weight. The weight proportion of larger fish, such as herring, Clupea harengus (L.), and cod, increased with the cod size, while the proportion of small- and medium-sized fish (sprats, gobies) decreased. The food composition of cod varied seasonally. The weight proportion of European sprat, Sprattus sprattus (L.), was much higher in winter (55%) than in fall (27%), while the proportion of cod in the diet was higher in the fall (10%) than in winter (4%). The proportion of sprat in the diet increased with depth, while that of Ammodytidae and Gobiidae showed a decreasing trend. At depths greater than 40 m, the proportion of invertebrates in cod stomachs decreased. This study demonstrated a significant area effect for sprat; year effect for sprat and Saduria entomon; a seasonal effect for young cod and S. entomon; and a depth effect for sprat, young cod, and S. entomon. The occurrences of herring and small cod increased in the stomach as the predator increased, while no significant relation was found for sprat and S. entomon. The data collected do not indicate that cod select a specific size of sprat or herring, though cod were found to use size selection for S. entomon and juvenile cod. Conclusion. The food composition of cod has undergone certain changes compared to results of Załachowski (1977, 1985), which covered the 1970s and 1980s. Currently, the proportion of clupeids in the food is approximately 67% (in weight), while during the 1977–1982 it was in the range of 25%–50% depending on cod length. In 2006 and 2007 sprat was the main cod diet component rather than herring.

Linking lipid dynamics with the reproductive cycle in Baltic cod Gadus morhua

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 471:215-234 (2012) - DOI: https://doi.org/10.3354/meps10012 Linking lipid dynamics with the reproductive cycle in Baltic cod Gadus morhua Maria C. Røjbek1,*, Charlotte Jacobsen2, Jonna Tomkiewicz1, Josianne G. Støttrup1 1National Institute of Aquatic Resources, Technical University of Denmark, Charlottenlund Castle, 2920 Charlottenlund, Denmark 2National Food Institute, Technical University of Denmark, 2800 Lyngby, Denmark *Email: mar@aqua.dtu.dk ABSTRACT: This study describes lipid composition and antioxidants of Baltic cod Gadus morhua L. during the reproductive cycle, and investigates whether they reflect its dominant prey and whether levels of fatty acids important for reproductive performance were low. Reasons for a shift in peak spawning time of Baltic cod from spring/early summer to midsummer since the early 1990s remain unresolved and may partly be diet related. This study demonstrated that a substantial amount of lipid was invested in cod ovarian development, and that lipid composition varied substantially with the reproductive cycle. Selective retention of the essential fatty acids docosahexaenoic acid (DHA) and arachidonic acid (ARA) in ovaries during maturation was evident, but despite mobilization from the liver, ARA levels were low in ovaries during late maturation and spawning. Astaxanthin and α-tocopherol accumulated in cod ovaries and decreased in late maturing and spawning fish, most likely due to their antioxidant protection activity. The fatty acid composition of cod liver reflected its clupeid prey. The ratio of 18:1n-9 to DHA was almost twice as high in sprat as in herring and indicated the ratio of sprat and herring in cod diet, while the level of 16:1n-7 and astaxanthin indicated the presence of the isopod Saduria entomon in cod diet. It is likely that food web alterations in the Baltic ecosystem related to environmental and hydrographic changes caused a decrease in ARA availability. Low ARA content coincides with cod ovarian development in the central Baltic Sea, and may be associated with the delay in spawning and affect egg and larval survival; however, this needs further verification in experimental studies. KEY WORDS: Arachidonic acid · Astaxanthin · Baltic Sea · Fatty acid composition · Maturation · Predator–prey relationship · Reproduction · Trophic interaction Full text in pdf format PreviousNextCite this article as: Røjbek MC, Jacobsen C, Tomkiewicz J, Støttrup JG (2012) Linking lipid dynamics with the reproductive cycle in Baltic cod Gadus morhua. Mar Ecol Prog Ser 471:215-234. https://doi.org/10.3354/meps10012 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 471. Online publication date: December 19, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Diet specialization in a fluctuating population of Saduria entomon: a consequence of resource or forager densities?

Intraspecific competition has been shown to favor diet specialization among individuals. However, the question whether the competition takes the form of interference or exploitative in driving diet specialization has never been investigated. We investigated individual diet specialization in the isopod Saduria entomon, in relation to forager and resource biomasses in a system that exhibits predator–prey fluctuations in density. We found that individual diet specialization was only affected by the biomass of their preferred prey (Monoporeia affinis) and not by Saduria biomass; diet specialization was higher when Monoporeia biomass was low compared to when there were high Monoporeia biomass. Population diet breadth increased at low Monoporeia biomass whereas individual diet breadths were marginally affected by Monoporeia biomass. Overall, this led to the increase in diet specialization at low Monoporeia biomass. This study shows that predator–prey dynamics might influence diet specialization in the predator and that resource biomass, not forager biomass might be important for individual diet specialization.

Distribution and relationships of trace metals in the isopod Saduria entomon and adjacent bottom sediments in the southern Baltic

The concentrations of Ag, Cd, Co, Cr, Cu, Fe, Ni, Pb, Mn and Zn in Saduria entomon and adjacent bottom sediments from the southern Baltic were determined by FAAS. In order to estimate the strength of correlations between accumulated elements in these crustaceans and surficial sediment, bioaccumulation factors (BAFs) were calculated. The results of factor analysis (FA) and the Kruskal-Wallis analysis of variance (ANOVA) clearly indicate geographical differences between the concentrations of these elements. Cd, Co, Fe, Ni, Pb and Zn levels were higher in S. entomon from the Gulf of Gdańsk, whereas Cr and Mn levels were higher in the crustaceans inhabiting open Baltic waters. The concentrations of Ag and Cu were comparable in both regions. There was a tendency for metal concentrations to distinguish organisms inhabiting the muddy bottom from those living in sandy sediments. The granulometric composition of the sediment appears to influence trace metal bioavailability. The results show that S. entomon could be a valuable sentinel organism for biomonitoring heavy metal contamination in the southern Baltic.

Combining stable isotope and intestinal parasite information to evaluate dietary differences between individual ringed seals (Phoca hispida botnica)

The diet and foraging behaviour of nine individual Baltic ringed seals ( Phoca hispida botnica Gmelin, 1785) in the Bothnian Bay were studied by combining results from stable isotope analyses (δ13C and δ15N) with data on intestinal parasites whose occurrence varied among the fish hosts. The patterns of infection with three acanthocephalan parasites, Corynosoma semerme (Forssell, 1904), Corynosoma magdaleni Montreuil, 1958, and Corynosoma strumosum (Rudolphi, 1802), and with a cestode larva, Schistocephalus solidus (Müller, 1776), were examined. The ringed seals become infected with these intestinal parasites by feeding on the fish hosts and hence have different parasite species and different parasite burdens according to their dietary history. δ13C and δ15N values were determined from diaphragm muscle of the seals and from tissues of potential prey items. A dual isotope plot of δ13C and δ15N values for individual seals and mean values for key potential prey species, together with the parasitological data from the seals, allowed inferences to be drawn about the feeding of individual seals. It appeared that two seals foraged particularly on fourhorn sculpin ( Myoxocephalus quadricornis (L., 1758)) and one seal consumed a high proportion of the isopod Saduria entomon (L., 1758). Three seals apparently preferred coastal benthic prey in their diets, while two other seals fed more on pelagic herring ( Clupea harengus membras L., 1761). One older female seal evidently also fed on salmon ( Salmo salar L., 1758).

Modulators of haemocyanin oxygen affinity in the hypoxia- and sulphide-tolerant Baltic isopod Saduria entomon (L.).

Dialysed haemocyanin from the isopod Saduria entomon had a considerably increased oxygen affinity (lower P50) and Bohr factor (-1.71) compared to native haemocyanin (Bohr factor -1.36) indicating that dialysis removes a small molecule size modulating factor decreasing the affinity of native haemolymph. Dialysed haemocyanin had a slightly lower co-operativity (2.42 +/- 0.3) than native haemocyanin (2.9 +/- 0.2). L-Lactate (10 mmol l(-1)) improved oxygen affinity by 1-1.5 torr while urate had no effect. Mg2+ affected affinity in a pH-dependent manner (Bohr-factor increased to -1.67) while Ca2+ had no effect on the Bohr factor but increased affinity with ca 1 torr. Thiosulphate changed the Bohr factor to -1.75 to -1.82, similar to dialysed blood. Co-operativity was in neither case affected. The haemocyanin characteristics of S. entomon are similar to those of crustaceans from hydrothermal vents. These characteristics are probably general for crustaceans that are more or less permanently exposed to sulphide.

Destruction of Sertoli cells and disturbance of spermiogenesis in Saduria entomon L. (Crustacea, Isopoda) from the Baltic infected with the ciliate Mesanophrys

Summary Pathological lesions were observed by electron microscopy in the testicular tubules of the isopod Saduria entomon naturally infected with the ciliate Mesanophrys. Profound and extensive changes were visible in the ultrastructure of both somatic and germinal cells. The cytoplasm of Sertoli cells was electron transparent and there was a drastic reduction in the rough endoplasmic reticulum and Golgi complexes; in addition, their nuclei showed an abnormal arrangement of chromatin. The damaged protrusions of the cells had lost contact with spermatids. In the lumen of the testicular tubules, spermatids at various stages of destruction lay in a loose, chaotic group, as did spermatozoa, which failed to form bundles. Extracellular tubules were missing. Spermiogenesis, if occurring at all, was disturbed. Determination of the level of infection by analysis of the haemolymph revealed that pathological changes intensified with the progress of infection.

How many species are in the genus Mesanophrys (protista, ciliophora, facultative parasites of marine crustaceans)?

Summary The paper presents the morphometric characteristics of the histophagous ciliate Mesanophrys found in the hemolymph of the isopod Saduria entomon from the Baltic Sea. The ciliate is compared with another, very similar one, found free-living on the coast of Vancouver Island, British Columbia, as well as with all literature data on the genus Mesanophrys . The ranges of all morphometric characters among these ciliates and all Mesanophrys species described so far strongly overlap. It seems, therefore, that the available morphological data, in the absence of other criteria, do not justify distinguishing separate species. The two ciliates presented here, as well as all nominal Mesanophrys species, should be referred to M. maggii (Cattaneo, 1888) unless new evidence concerning host specificity, life cycle or biochemical dissimilarity, for example, indicates a taxonomic difference.

Influence of oxygen levels on the predatory behaviour of the isopod saduria entomon

The effect of low oxygen levels on predatory behaviour of the isopod Saduria entomon on its natural prey, the amphipods Monoporeia affinis and Pontoporeiafemorata, was studied in laboratory experiments. The isopod S. entomon consumed the amphipods M. affinis and P. femorata in normoxic experimental conditions. A significantly decreased predation rate was found at 33% oxygen saturation and below. No preference by S. entomon for either amphipod species was detected, and both amphipod species appeared to use a similar behavioural strategy for avoiding predators at low oxygen concentrations. At a low oxygen concentration (8%) S. entomon was mostly immobile on the sediment surface, and its predation rate was low. There was no indication that low oxygen levels increases the vulnerability of M. a ffinis or P. femorata to predation by S. entomon. Instead, the findings suggest decreasing rates of predation as the oxygen concentration declines.

Behavioural responses to chemical cues of predation risk in a three-trophic-level Baltic Sea food chain

Behavioural responses of 2 Baltic benthic crustaceans to chemical substances from predators were studied using infrared video-recording in the laboratory. This is the f~rs t study of behavioural responses to species-specific chemical substances in a 3-trophic-level food chain. Exposure to chemical substances from a predatory fish, the short-horned sculpin Myoxocephalusscorp~us (L.) , ca.used the isopod Saduria entomon (L . ) to remain buried in the sediment most of the time and decreased its foraging success on the amphipod Adonoporeia affinis (Lindstrom). M. a f f ~ n ~ s decreased its swimming activity when exposed to water from S. entomon feeding on M. affinls, whereas water from unfed S, entomon had no such effect.

Behavioural response to gradually declining oxygen concentration by Baltic Sea macrobenthic crustaceans

Behavioural responses to decreasing oxygen concentrations were studied in the amphipods Monoporeia affinis (Lindstrom) and Pontoporeia femorata Kroyer and the isopod Saduria entomon (L.), all benthic macrofauna species from the Baltic Sea. Infrared time-lapse video recording was used. Seven oxygen concentrations were studied, starting near saturation (about 90%), followed by about 65, 49, 33, 16, 8 and 5% oxygen saturation, with each oxygen level maintained for 24 h. M. affinis was more active than P. femorata. The duration of swimming activity of M. affinis was shorter at ≤33% oxygen saturation compared with at the two highest levels. The duration of swimming by P. femorata was longest at 90, 65 and 5% oxygen saturation. For both amphipods the frequency of swimming activity was highest at 5% oxygen saturation. Above 7% oxygen saturation, S. entomon spent most of its time in the sediment, whereas at levels ≤7% it was most often found on the sediment surface. Both amphipods were predominantly night active (nocturnal), whereas no diurnal variation in behaviour was detected for S. entomon. It is suggested that the amphipods minimise the costs associated with obtaining oxygen as well as their risk of predation by moving little on or above the sediment until a lower critical oxygen level is reached. Below this level, they show an oxygen-seeking behaviour. S. entomon also hid in the sediment for as long as possible, suddenly coming to the surface once the oxygen concentration became intolerably low. Its behaviour is also indicative of a trade-off between predation risk and obtaining sufficient oxygen. It is suggested that the change in behaviour shown at about 33% oxygen saturation could lead to a long-term alteration in community structure in the deeper parts of the northern Baltic proper, whereas the change at about 8% oxygen saturation reflects a more acute, short-term response.

Activity and ventilation-induced variations of postbranchial oxygen tensions in the isopod Saduria entomon

Variations in postbranchial oxygen tensions were studied in vivo in the brackish water isopod Saduria entomon collected from the Baltic Sea in 1992. Haemolymph oxygen tensions were highly influenced by activity. Resting isopods showed small and regular variations in haemolymph oxygen tensions, while a sudden burst of activity caused an immediate reduction in oxygen tension. Periods of no ventilation caused anoxic haemolymph in less than 3 to 4 min. Haemolymph oxygen tension responds rapidly, within seconds to minutes, to changes in isopod activity. Oxygen uptake rates calculated from oxygen tension difference, gill area and membrane thickness were compared with measured values. Permeability studies showed that only 30% of the gill area was effective in oxygen transfer. The present study has confirmed earlier measured oxygen uptake rates and reevaluated the role of the gills as respiratory organs. Postbranchial oxygen tension was established as a function of external steady state oxygen tensions and the intrinsic diffusive conductance was estimated.

Predation by the isopod Saduria entomon on the amphipods Monoporeia affinis and Pontoporeia femorata: experiments on prey vulnerability.

Predation by Saduria entomon on the depositfeeding amphipods Monoporeia (=Pontoporeia) affinis and Pontoporeia femorata was studied in laboratory experiments. Prey vulnerabilities were compared in singleprey treatments and in mixed-prey treatments, where the proportions of the two species were varied at one total density. In a pilot experiment, P. femorata was the more vulnerable prey, both in single-prey and mixed-prey treatments. In later experiments, the amphipod species were equally vulnerable in single-prey treatments, while in mixed-prey treatments Saduria preyed preferentially on M. affinis, even when this prey was rare, i.e. it did not "switch". We suggest that the different result in the later experiments may have been due to a change in the search mode of the isopods.

Effects of Cannibalism and Alternative Prey on Population Dynamics of Saduria Entomon (Isopoda)

Field sampling and laboratory experiments were performed to investigate the importance of cannnibalism in the isopod Saduria entomon from the Gulf of Bothnia. In the experiments the vulnerability to cannibalism was high for small individuals. The vulnerable phase lasted °9 mo in the deep zone and 3 mo in the shallow zone. Large S. entomon individuals caught small conspecifics more efficiently than they caught the alternative prey Pontoporeia affinis (Amphipoda), and Neomysis integer (Mysidacea). Both relative and absolute densities affected the number of small conspecifies eaten. The preference for conspecifics increased with decreased with decreasing density of P. affinis. In a behavioral experiment a small but significant proportion of the small S. entomon specimens actively sensed and avoided aggregations of large conspecifics. In contrast to the findings of the laboratory experiments, only a small amount of S. entomon were found in the guts of large conspecifics from the field samples. Pontoporeia affinis was the dominant prey. Due to differences in the life history of S. entomon, conditions for cannibalism differ between shallow and deep zones, favoring higher rates of cannibalism in the deep zone. In the deep zone there were lower densities of alternative prey per predator, the vulnerable phase was three times as long, and the cannibals reached larger sizes. Calculations using information from laboratory data showed that cannabalism has the potential to cause substantial mortality in S. entomon in the deep zone also when inflated mortality rates were accounted for. In the field, the density of small S. entomon was negatively correlated with the density of large conspecifics, but positively correlated with the density of P. affinis. The size distributions of the field samples indicated a high mortality in deep—living young S. entomon. These patterns were consistent with the results of the laboratory predation experiments, which are consistent with the hypothesis that cannibalism produced these patterns.