| 1. |
- Kozlowsky-Suzuki, Betina, et al.
(author)
-
Disruption of the microbial food web and inhibition of metazooplankton development in the presence of iron- and DOM-stimulated Baltic Sea cyanobacteria
- 2007
-
In: Marine Ecology - Progress Series. - 1616-1599. ; 337, s. 15-26
-
Journal article (peer-reviewed)abstract
- Summer N-2-fixing cyanobacterial blooms are a common feature in the Baltic Sea, and the occurrence of Nodularia spumigena toxic blooms is of particular concern. Cyanobacterial blooms can be favoured by certain conditions including high concentrations of dissolved organic matter, which may increase the availability of iron critical for N-2 fixation. Cyanobacteria may negatively affect grazers because many species produce toxins and generally lack fatty acids essential for zooplankton reproduction. In this study we investigated the effect of riverine high-molecular weight dissolved organic matter (DOM-)/iron-stimulated cyanobacteria on the development of proto- and metazooplankton, and evaluated the role of DOM in stimulating the zooplankton part of the microbial food web. A plankton community was incubated in cylinders with either nitrate (NO3) or DOM alone or combined with iron (Fe) or zooplankton >100 mu m (G). The development of proto- and metazooplankton was followed for 10 d. Trophic relationships between metazooplankton taxa and their potential food items were assessed by ordination analysis and by feeding and reproduction bottle incubations with the calanoid copepod Acartia bifflosa. Contrary to our expectations, DOM did not stimulate the microbial food web, and proto- and metazooplankton developed similarly in all treatments until the middle of the experiment. However, by the end of the experiment, the biomass of proto- and metazooplankton as well as the biomass of diatoms and dinoflagellates was greatly depressed in all DOM and NO3Fe treatments. In these treatments, cyanobacterial and bacterial biomasses were highest leading up to phosphate depletion. Plankton development seemed to be bottom-up controlled and to be affected by extracellular compound(s) produced by the dominant cyanobacteria, possibly triggered by phosphate limitation. Diatoms, dinoflagellates, protozoans and metazooplankton were instead stimulated in the NO3 and NO(3)G treatments, where cyanobacterial biomass was low. Accordingly, A. bifilosa reproduction and survival were sustained in NO3 bottles. Deleterious effects of cyanobacteria on metazooplankton were diminished in NO3 and NO(3)G tanks where other food resources were available. Overall, the results suggest that increases in the input of DOM to the Baltic Sea can potentially stimulate cyanobacterial blooms that may disrupt the microbial food web and inhibit metazooplankton development.
|
|
| 2. |
- Müller-Karulis, Bärbel, et al.
(author)
-
Challenges and opportunities of local fisheries management : pikeperch, Sander lucioperca (Actinopterygii: Perciformes: Percidae), in Pärnu Bay, northern Gulf of Riga, Baltic Sea
- 2013
-
In: Acta Ichthyologica et Piscatoria. - 0137-1592 .- 1734-1515. ; 43:2, s. 151-161
-
Journal article (peer-reviewed)abstract
- Background. A local stock of pikeperch, Sander lucioperca (Linnaeus, 1758), is a valuable fishery resource in Parnu Bay, northern Gulf of Riga. Due to the late maturity of pikeperch in the bay, the stock is vulnerable to over-exploitation, whereas recruitment is highly dependent on climate factors. Because of its high market price, fishing pressure on the stock increased considerably in the 1990s, resulting in stock depression. To assist fishery management in Parnu Bay we have simulated the effect of several scenarios (such as: fishing mortality, climate, and young-of-the-year food supply) on the pikeperch stock, catches, and revenues generated by the fishery.Materials and methods. A simulation system consisting of an age-structured population model, a recruitment component, and a forcing module of different climate, food supply to young-of-the-year, and fishing mortality scenarios was used to estimate the equilibrium stock size and catches under varying environmental conditions and exploitation strategies. Economic impacts of these scenarios were assessed based on the first selling price of pikeperch.Results. Under present climate and food supply for pikeperch young-of-the-year, the Parnu Bay pikeperch stock is very sensitive to catches of immature fish. Warmer future climate conditions are likely to be beneficial for the stock, but also prey abundance for young-of-the-year influences potential stock sizes and catches. Compared to targeting its prey species, herring, which has a lower commercial value at current first selling prices, pikeperch acts as a biomeliorator, roughly doubling fisheries revenue in the bay.Conclusion. Flexible adaptive management methods should be used to estimate the yearly allowable pikeperch catch, taking into account food supply to young-of-the-year and climate conditions influencing recruitment.
|
|
| 3. |
- Stolte, Willem, et al.
(author)
-
Stimulation of nitrogen-fixing cyanobacteria in a Baltic Sea plankton community by land-derived organic matter or iron addition
- 2006
-
In: Marine Ecology - Progress Series. - : Inter-Research Science Center. - 1616-1599 .- 0171-8630. ; 327, s. 71-82
-
Journal article (peer-reviewed)abstract
- In the Baltic Sea, floating blooms of nitrogen-fixing cyanobacteria occur yearly during late summer. These blooms can sometimes be limited by iron. Due to extensive foresting around the Baltic Sea, iron is entering the Baltic Sea partly bound to dissolved organic material (DOM) via rivers. An experiment was performed in 300 1 laboratory mesocosms to test the hypothesis that riverine high-molecular weight dissolved organic matter (HMWDOM), extracted by tangential flow filtration > 1000 Da, stimulates the biomass of nitrogen-fixing cyanobacteria, by increasing the availability of iron. The addition of iron/EDTA and of DOM resulted in 5 to 10 times higher biomass of nitrogen-fixing cyanobacteria. Accordingly, higher primary production and particulate nitrogen concentration at the end of the experiment were observed in those treatments compared to the control. The removal of mesozooplankton grazers did not have a significant effect on the microphytoplankton biomass and species composition. Nodularia spumigena biomass was highest in the treatments receiving DOM, but addition of iron alone had no significant effect on this. N. spumigena was less positively affected by iron addition than Anabaena cf. inaequalis, suggesting that N, spumigena is a better competitor for iron. Separate microcosms comparing additions of iron, manganese and cobalt showed that iron was limiting for cyanobacterial biomass development. The results strongly suggest that iron bound to DOM can contribute to the iron demands of nitrogen-fixing cyanobacteria in the Baltic Sea.
|
|
