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- Ehrenberg, Sigrid Z., et al.
(author)
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Daily activity pattern of the sand goby, Pomatoschistus minutus (Pisces), at low light intensity.
- 2008
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In: HYDROBIOLOGIA. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 603, s. 129-137
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Journal article (peer-reviewed)abstract
- In autumn and winter, the sand goby (Pomatoschistus minutus) in the Baltic Sea is to a large extent found on soft bottoms deeper than the summer thermocline. Although P. minutus are numerous during a large part of the year in these areas, most studies on this species have been performed on very shallow bottoms. Here we study the activity of P. minutus in autumn using video recordings in the laboratory, under light (1.5-2 lux) and temperature conditions prevailing at ca. 30 m depth. We propose that the results can be used to evaluate in situ abundance censuses. P. minutus had the same nocturnal activity pattern in low light intensity as described for light intensities found in shallow water. The fish swim significantly more in darkness than in light, and bury in the sediment mainly at day. These behaviours, recorded in the absence of predators, are suggested to be adaptations to avoid predators.
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- Ehrenberg, Sigrid Z., 1964-
(author)
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The neglected ecology of the sand goby: Abundance and feeding in the Baltic sublittoral
- 2008
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Doctoral thesis (other academic/artistic)abstract
- I investigated the ecology and population density of the sand goby, Pomatoschistus minutus, at sub-thermocline depth in the north-western Baltic proper. Most previous research on the sand goby, and the co-occurring closely related common goby, P. microps, has focused on their stay in shallow waters, while important parts of their life cycles have been largely neglected.Photography was used to assess goby population density and size distribution, a basis for estimations of the potential annual food consumption of the goby community. Diet analysis of the most abundant goby, the sand goby, was combined with the population censuses to estimate the contribution of different prey to the goby consumption. Both benthic and pelagic prey were consumed, including two non-indigenous species. The amphipod Monoporeia affinis was by far the most important prey for the overall consumption, while pelagic and benthic copepods, and naidid oligochaetes were important prey for sand gobies < 3.5 cm. Goby predation is likely to influence the populations of naidid oligochaetes and the amphipod M. affinis, as large parts of their production may be consumed.The potential goby consumption was calculated to be about 72 kJ m-2 yr-1, which corresponds to 14-60 % of the annual production on soft bottoms in the area. In a laboratory study of the sand goby activity, active swimming occurred preferentially at night and burying in the sediment mostly at day. Both behaviours may lead to underestimates in photographic censuses of up to 40 %. The goby community in the sublittoral links the benthic and pelagic sub-systems in the area by being able to remove a substantial amount of energy from the benthic production, by inclusion of pelagic prey, and by holding an intermediate position in the coastal marine food web of the Baltic Sea. Consequently, their role in the flow of energy, elements and substances, some potentially harmful, between the pelagic and benthic ecosystem should be further investigated.
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- Ejdung, Gunilla, et al.
(author)
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Predation by crustaceans on native and non-native Baltic clams
- 2009
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In: Aquatic biology. - : Inter-Research Science Center. - 1864-7790 .- 1864-7782. ; 6, s. 15-24
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Journal article (peer-reviewed)abstract
- We studied the effect of crustacean predators on native/non-native Macoma balthica bivalves in aquarium experiments. North Sea M balthica (NS Macoma) were recently observed in the southern Baltic Sea. They differ genetically and in terms of morphology, behaviour and evolutionary history from Baltic Sea M balthica (BS Macoma), and this may affect predation pressure and community structure. We hypothesised that predators consume more of the prey they co-exist with. NS Macoma and BS Macoma were exposed to crustacean predators common in the North Sea (Carcinus maenas and Crangon crangon) and in the Baltic Sea (C. crangon and Saduria entomon). Contrary to our hypotheses, the North Sea predators ate more BS Macoma, and S. entomon ate more NS Macoma. The crush-limited C. maenas preyed more on globular BS Macoma, whereas S. entomon, which do not crush but pry open the bivalve shell, ate more NS Macoma, which have a lighter (thus probably thinner) shell than BS Macoma. When NS and BS Macoma were offered together, BS Crangon ate more NS Macoma. We also studied BS Crangon consumption of M. balthica to assess whether sizes offered fall within the size spectrum that C. crangon can eat. Small (20 to 40 mm long), medium (40 to 50 mm) and large (50 to 60 mm) C. crangon especially ate small M. balthica. Differences in shape, size and meat/shell weight ratio between the BS and NS Macoma partly explained the differences in the susceptibility to predation by native and non-native predators.
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- Ejdung, Gunilla, 1953-
(author)
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Predatory processes in Baltic benthos
- 1998
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Doctoral thesis (other academic/artistic)abstract
- The Baltic soft-bottom community is uniquely simple, with only a few benthic macro-faunal species, and is therefore well suited for mechanistic studies of inter-specific interactions. Two of the dominating organisms in this benthic community are the amphipod Monoporeia affinis and the bivalve Macoma balthica. Field surveys have shown that M. balthica is generally absent or scarce when the density of M. affinis is high. The hypothesis that adult M. affinis kill the newly settled bivalves was confirmed experimentally in the laboratory, and it was also shown that adult Pontoporeia femorata amphipods have a negative impact on bivalve survival. Further experiments, showed that juvenile M. affinis, contrary to earlier beliefs, can kill and presumably eat the newly settled M. balthica. The response of M. affinis to increased bivalve densities was a type III like functional response, indicating that bivalves at low densities find a partial refuge from amphipod predation.The effect of the predatory isopod Saduria entomon on the Macoma balthica population was assessed both in the laboratory and the field. In the laboratory, the presence of the isopod did not affect the small just settled bivalves (0.3 mm), whereas slightly larger and larger bivalves (>0.8 mm) suffered from increased mortality, as did bivalves in the three month long field study. The isopods are physically capable of opening quite large bivalves, a 34 mm long isopod can break open a 17 mm long bivalve, but given a choice, smaller bivalves are selected. When S. entomon is offered the two prey species, Monoporeia affinis and M. balthica, the amphipod is preferred, leaving the bivalve relatively safe from predation.In the aquatic environment, chemical substances released by predators or their activities can convey information, to which prey can respond, for example, by a change in behaviour. In a three-trophic-level food chain, species-specific chemical substances from a predatory fish, the short-horned sculpin (Myoxocephalus scorpius), directly affected the behaviour of the isopod Saduria entomon. The isopod remained buried in the sediment longer, and fewer prey amphipods, Monoporeia affinis, were eaten. Further, exposure to chemical substances from isopods feeding on amphipods, lead the amphipod to lower their swimming activity, whereas water from non-feeding isopods did not have this effect.
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- Ejdung, Gunilla, et al.
(author)
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Uptake of diatoms in Baltic Sea macrozoobenthos during short-term exposure to severe and moderate hypoxia.
- 2008
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In: Aquatic Biology. - : Inter-Research Science Center. - 1864-7790 .- 1864-7782. ; 3:1, s. 89-99
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Journal article (peer-reviewed)abstract
- he effect of severe and moderate hypoxia on food uptake of benthic macrofauna was studied in the laboratory. The hypothesis was that low oxygen concentrations negatively affect feeding at oxygen levels that have little effect on the studied animals' survival. The bivalve Macoma balthica, the priapulid Halicryptus spinulosus, the amphipods Monoporeia affinis (subadult & juvenile) and Pontoporeia femorata (subadult) were offered the C-14-labelled diatom Skeletonema costatum in 0.8 to 10.6 mg O-2 l(-1). Feeding was measured as radioactivity uptake. Subadult amphipods were studied one species at a time (single) or together (mixed). Feeding changed in all amphipods at the lowest oxygen concentrations, but no effect was found for M. balthica and H. spinulosus. At the lowest concentration (0.8 mg O-2 l(-1)) feeding by subadult M affinis (single) was only 17% of the full oxygen saturation (10.6 mg O-2 l(-1)), and, at 1.6 mg O-2 l(-1), 14% of the feeding at 8.9 mg O-2 l(-1). Juvenile M affinis consumed more labelled algae at 3 Mg O-2 l(-1) than at higher oxygen concentrations. M balthica feeding was not affected. Little radioactivity uptake was registered for H. spinulosus at any oxygen concentration, showing that H. spinulosus is not a surface deposit feeder. The amphipods were the most sensitive to week-long oxygen deficiency. Survival decreased significantly in the lowest oxygen concentrations (0.8; 1.6 mg O-2 l(-1)). Of the subadult M. affinis 15 and 65%, respectively, survived, compared with 0 and 58% for P. femorata. Juvenile M. affinis mortality was high in all oxygen concentrations, whereas most M balthica and H. spinulosus survived.
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