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- Holmqvist, Niklas, et al.
(författare)
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Lake trophic status and bioaccumulation of polychlorinated biphenyls in benthic organisms: a comparison between littoral and profundal invertebrates
- 2005
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 1205-7533. ; 62:6, s. 1201-1209
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the influence of lake trophic status on accumulation of polychlorinated biphenyls (PCBs) in littoral and profundal invertebrates from 19 lakes in southern Sweden. The PCB concentration in profundal chironomids (Chironomus sp.) was negatively correlated with lake trophy but the concentration in littoral crayfish (Pacifasticus leniusculus) was unrelated to shifting nutrient regimes. PCB concentrations in chironomids were negatively correlated, while crayfish did not correlate with lake total phosphorus. Two findings indicate that different processes determine bioaccumulation in littoral and profundal invertebrates: (i) a lack of correlation between PCB concentrations in crayfish and chironomids within lakes and (ii) some differences in congener distribution in the two species. We suggest a possible explanation in that chironomids are directly exposed to settling material from the pelagic zone, while crayfish are omnivorous and feed mainly in the littoral zone. A intensive investigation on one pond population could not reveal any individual factors, such as lipid content, size, or sex, influencing bioaccumulation of PCBs in crayfish.
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| 3. |
- Stenroth, Patrik
(författare)
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The different roles of crayfish in benthic food webs
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I show that crayfish consume detritus, algae, macrophytes, and an array of invertebrates. Crayfish were found to reduce invertebrate densities. However, prey mobility seemed to be a key factor regulating the strength of interactions between crayfish and prey. Since crayfish seek to maximize growth, they benefit from feeding on invertebrates, shown to promote high growth rates. I found crayfish to increase their intake of invertebrate prey in eutrophic lakes. This suggests that crayfish have different roles in different lakes, they seem to be predators in eutrophic lakes and more like primary consumers in oligotrophic lakes. In lakes where crayfish are predacious they elongate the food chain between basal resources (i.e. detritus and algae) and top predators like perch. This since perch are likely to prey heavily on crayfish when these were available. Moreover, I found crayfish to be larger in eutrophic lakes, this indicates that they grow faster in eutrophic waters. The rationale behind this conclusion is that the mean sizes of crayfish, possible to catch in baited traps, at the beginning of each growing season (summer) would be very similar between populations due to intensive harvest the previous autumn. Consequently, I interpreted the differences in mean size of crayfish at the end of the growing season (when harvest starts) to be a measure of growth differences between populations. Furthermore, the results of this thesis indicate that omnivores like crayfish could derive carbon from some food sources and simultaneously derive nitrogen from other sources. I found periphyton to be the chief ultimate nitrogen source for crayfish in streams. About half of the nitrogen seemed to come from direct consumption of algae and the other half via consumption of invertebrates that in turn relied on periphyton as their chief nitrogen source. In contrast, I found no clear trend regarding ultimate carbon sources for stream crayfish. In addition, these findings suggest that omnivorous organisms potentially could be at different trophic level with respect to different elements.
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