| 1. |
- Calliari, D., et al.
(författare)
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Density dependent grazing rates in a natural microzooplankton community
- 2019
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 622, s. 83-92
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Tidskriftsartikel (refereegranskat)abstract
- Density dependence is a common phenomenon that affects individual performance in a wide range of organisms. Negative density dependence involves diminished individual rates, e.g. feeding and growth, under high organismal concentration. Microzooplankton (µZ) are key consumers in marine ecosystems and their grazing is frequently estimated by the dilution technique, which involves experimental manipulation of population concentrations of both grazer and prey. However, the potential interference of density dependent processes on grazing estimates has not been evaluated in the general context of µZ ecology, nor in the specific context of the dilution technique. Density dependent effects on µZ grazing rates were evaluated for a natural community of grazers in the Gullmar Fjord (Skagerrak, Sweden) across a wide but realistic range of µZ densities and under controlled algal prey concentrations. Net algal growth rates (k), grazing rate of the µZ community (G), and per capita grazing rates (SG) by the components of the µZ community were estimated based on algal cell counts and chlorophyll a (as metrics for prey concentration) and µZ counts (as a measure of predator concentration). The 3 responses (k, G and SG) showed clear evidence of negative density dependence under moderate and high levels of µZ concentrations. Results imply that negative density dependent effects on µZ grazing rates may actually occur in marine ecosystems. © Inter-Research 2019.
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| 2. |
- Hansen, Benni W., et al.
(författare)
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In situ and experimental evidence for effects of elevated pH on protistan and metazoan grazers
- 2019
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 41:3, s. 257-271
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Tidskriftsartikel (refereegranskat)abstract
- Plankton succession was studied in a hyper-eutrophic stratified estuary, Mariager Fjord, Denmark. Above the pycnocline (15 m) pH increased from 8.5 to 9.2 and the oxygen increased to super saturation after 5 d of sunny weather due to high primary production. The protistan grazers were dominated by heterotrophic dinoflagellates and mixotrophic and heterotrophic ciliates. Metazooplankton was dominated by meroplankton, rotifers and the copepod, Acartia tonsa, all with a relatively low biomass. Cirriped nauplii occupied the upper strata while polychaete larvae populated the whole water column. Bivalve larvae occurred occasionally above the pycnocline even at very high pH. In pH challenge experiments, the mixotrophic ciliate Mesodinium rubrum was the least pH tolerant species, followed by Strombidium spp., which did not cope well with seawater pH > 8.5. Some heterotrophic dinoflagellates were more tolerant with net growth at pH > 9. The predominant rotifer Synchaeta sp. tolerated up to pH 9.5 and the copepod survived pH 10 but stopped producing eggs at pH 9.5 with unaffected egg hatching success. The polychaete and cirriped larvae tolerated pH 9.5, but bivalve larvae showed decreased survival already at pH 8.5. In situ distribution patterns and pH challenge experiments suggest that pH indeed contribute to structuring zooplankton distribution.
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| 3. |
- Kiorboe, T., et al.
(författare)
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Reply to comment: Prey perception in feeding-current feeding copepods
- 2016
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590. ; 61:4, s. 1169-1171
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Tidskriftsartikel (refereegranskat)abstract
- We reply to the comments of Paffenhofer and Jiang (2016) who argues that remote chemical prey perception is necessary for feeding-current feeding copepods to fulfill their nutritional requirements in a dilute ocean, that remote chemical prey detection may only be observed at very low prey concentrations, and that chemical prey perception is feasible if prey cells release dissolved organic material in short-lasting but intense bursts. We demonstrate that mechanoreception at a very short range is sufficient to sustain a living, even in a dilute ocean. Further, if chemoreception requires that prey cells have short intense leakage burst, only a very small fraction of prey cells would be available to the copepod at any instance in time and, thus would be inefficient at low prey concentration. Finally, we report a few new observations of prey capture in two species of copepods, Temora longicornis and Centropages hamatus, offered a 45-mu m sized dinoflagellate at very low concentration. The observed short prey detection distances, up to a few prey cell radii, are consistent with mechanoreception and we argue briefly that near-field mechanoreception is the most likely and common prey perception mechanism in calanoid copepods.
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| 4. |
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| 5. |
- Selander, Erik, 1973, et al.
(författare)
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Solid phase extraction and metabolic profiling of exudates from living copepods
- 2016
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Ingår i: Peerj. - : PeerJ. - 2167-8359. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Copepods are ubiquitous in aquatic habitats. They exude bioactive compounds that mediate mate finding or induce defensive traits in prey organisms. However, little is known about the chemical nature of the copepod exometabolome that contributes to the chemical landscape in pelagic habitats. Here we describe the development of a closed loop solid phase extraction setup that allows for extraction of exuded metabolites from live copepods. We captured exudates from male and female Temora longicornis and analyzed the content with high resolution LC-MS. Chemometric methods revealed 87 compounds that constitute a specific chemical pattern either qualitatively or quantitatively indicating copepod presence. The majority of the compounds were present in both female and male exudates, but nine compounds were mainly or exclusively present in female exudates and hence potential pheromone candidates. Copepodamide G, known to induce defensive responses in phytoplankton, was among the ten compounds of highest relative abundance in both male and female extracts. The presence of copepodamide G shows that the method can be used to capture and analyze chemical signals from living source organisms. We conclude that solid phase extraction in combination with metabolic profiling of exudates is a useful tool to develop our understanding of the chemical interplay between pelagic organisms.
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| 6. |
- Tiselius, Peter, 1958, et al.
(författare)
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Community cascades in a marine pelagic food web controlled by the non-visual apex predator Mnemiopsis leidyi
- 2017
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 39:2, s. 271-279
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Tidskriftsartikel (refereegranskat)abstract
- Trophic cascades are a ubiquitous feature of many terrestrial and fresh-water food webs, but have been difficult to demonstrate in marine systems with multispecies trophic levels. Here we describe significant trophic cascades in an open coastal planktonic ecosystem exposed to an introduced top predator. The ctenophore Mnemiopsis leidyi was monitored for an 8-year period concurrent with measures of the food web structure of the plankton and strong trophic cascades were evident. In the 5 years when M. leidyi were found, their target prey (grazing copepods) were reduced 5-fold and the primary producers doubled their biomass when released from the grazing pressure. The increased phytoplankton biomass could unequivocally be assigned to grazing release since concurrent measurements of primary production did not differ between years with or without M. leidyi. Copepod biomass prior to the mass occurrence of the ctenophore was important. The years without M. leidyi had significantly higher biomass of copepods in July, the month preceding the outburst of the ctenophore. The profound changes of the pelagic ecosystem faced with a non-selective apex predator shows that marine communities are not exceptions from trophic cascade mechanisms.
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| 7. |
- Tiselius, Peter, 1958, et al.
(författare)
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Daily changes in δ15N and δ13C stable isotopes in copepods: equilibrium dynamics and variations of trophic level in the field
- 2016
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 38:3, s. 751-761
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Tidskriftsartikel (refereegranskat)abstract
- We investigated how fast the δ15N and δ13C stable isotope signature of copepods changes and how fast the isotope signals in microzooplankton and copepods change in the field. In experiments C1, copepodites of the copepod Acartia tonsa raised on Rhodomonas baltica were switched to a diet of Oxyrrhis marina and the δ15N and δ13C signature followed for 8 days. The δ15N increased by 0.18 ± 0.03‰ day−1 in animals fed O. marina while it decreased by 0.14 ± 0.02‰ day−1 with a R. baltica diet and equilibrium was reached after 5 days. Enrichment of nitrogen 15N (Δ15N) was 2.4 ± 0.26‰ with R. baltica and 4.1 ± 0.38‰ with O. marina as food, and corresponding factors for carbon (Δ13C), 1.7 ± 0.38‰ and 2.3 ± 0.30‰. Δ15N in the field, using seston 0–10 µm as the baseline, ranged from 2.4 to 3.1 for copepods and 1.0 to 1.6 for the microzooplankton (10–90 and 90–200 µm). Nitrate input resulted in low Δ15N for copepods (2.4‰) and high for microzooplankton (1.4–1.6‰), indicating that copepods were feeding indiscriminately on phyto- and microzooplankton after the event. The second period showed higher Δ15N (3.1‰) and a higher trophic level of copepods, but lower of microzooplankton (1.0–1.1‰).
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| 8. |
- Tiselius, Peter, 1958, et al.
(författare)
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Primary productivity in a coastal ecosystem: a trophic perspective on a long-term time series
- 2016
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 38:4, s. 1092-1102
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Tidskriftsartikel (refereegranskat)abstract
- To investigate forcing factors on a coastal plankton food web, primary production was measured every 2 weeks for 28 years. On a decadal scale, the North Atlantic Oscillation (NAO) correlated positively to primary production (r = 0.44, P = 0.021) and winter surface nitrate (r = 0.60, P = 0.0014) and phosphate (r = 0.66, P = 0.0003; r = 0.60, P = 0.0014). This suggests that climate forcing through increased wind and vertical mixing leads to higher entrainment of nutrients which stimulate yearly primary production. The highest production occurred in summer (1105 ± 16 mg C m−2 day−1) and correlated positively with zooplankton biomass (r = 0.61, P = 0.037), but showed no relation to phytoplankton biomass. Estimated phytoplankton grazing by copepods was low, but ciliates had the potential to remove all the phytoplankton biomass daily. Copepods, in turn, could exert a strong predation on ciliates which indicates a top-down regulation of phytoplankton biomass. Advection of copepods into the fjord and predation of jellyfish are suggested as the main regulatory factors for the copepod populations. We conclude that climate affects the pelagic ecosystem in the fjord through the NAO, but that biological interactions through grazing and predation by copepods regulate the system on a seasonal scale, indicative of a trophic cascade.
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| 9. |
- Tiselius, Peter, 1958, et al.
(författare)
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Toxicity of treated bilge water: The need for revised regulatory control
- 2017
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Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X .- 1879-3363. ; 114:2, s. 860-866
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Tidskriftsartikel (refereegranskat)abstract
- Water accumulating in the bottom of ships (bilge water), contains a mixture of oil, detergents and other compounds from on board activities. To evaluate ecological effects of released bilge water the chemical composition and toxicity of treated bilge water from seven passenger ships was analysed. The oil content was below 15 mg L− 1, the threshold for legal discharge, in all but one ship. Still, significant reductions in feeding and reproduction of Acartia tonsa were found after 48 h exposure in dilutions with 2.5–5% of bilge water. Mortality was significant at dilutions of 5–10% in 4 of the 5 bilge water samples. Surfactants were the most significant contributor to the toxicity on copepod vital rates and survival. Toxicity was also tested with Microtox where an EC50 was found at dilutions between 4.3% and 52%. The results show that ecological effects might occur also in diluted suspensions of bilge water.
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| 10. |
- Werbrouck, Eva, et al.
(författare)
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Temperature impact on the trophic transfer of fatty acids in the congeneric copepods Acartia tonsa and Acartia clausi
- 2016
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Ingår i: Journal of Sea Research. - : Elsevier BV. - 1385-1101. ; 112, s. 41-48
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Tidskriftsartikel (refereegranskat)abstract
- Copepods of the genus Acartia occur worldwide and constitute an important link to higher trophic levels in estuaries. However, biogeographical shifts in copepod assemblages and colonization of certain European estuaries by the invader A. tonsa, both driven or enhanced by increasing ocean temperature, raise the pressure on autochthonous copepod communities. Despite the profound effect of temperature on all levels of biological organization, its impact on the fatty acid (FA) dynamics of Acartia species is understudied. As certain FAs exert a bottom-up control on the trophic structure of aquatic ecosystems, temperature-induced changes in FA dynamics of Acartia species may impact higher trophic levels. Therefore, this study documents the short-term temperature responses of A. tonsa and A. clausi, characterized by their warm- versus cold-water preference respectively, by analyzing the FA profiles of their membrane and storage lipids under 5 and 15 °C. Copepods that were fed an ad libitum diet of the diatom Thalassiosira weissflogii (bloom conditions) under 15 °C increased their storage FA content substantially. Furthermore, the membrane FA composition of A. tonsa showed a more profound temperature response compared with A. clausi which might be linked with the eurythermal character of the former.
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