|Functionele redundantie in mariene voedselwebben: voedingsexperimenten met harpacticoide copepoden en diatomeeën|
Heynssens, E. (2007). Functionele redundantie in mariene voedselwebben: voedingsexperimenten met harpacticoide copepoden en diatomeeën. MSc Thesis. Universiteit Gent. Faculteit Wetenschappen: Ghent. 62 pp.
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VLIZ: Non-open access 121445
|Document type: Dissertation|
Carbon isotope ratio; Feeding; Food webs; Harpacticoida [WoRMS]; Copepoda [WoRMS]; Bacillariophyceae [WoRMS]; ANE, Netherlands, Westerschelde, PaulinaPolder; ANE, Poland [Marine Regions]; Marine
This paper consisted of two major parts. The first experiment compared the feeding ecologyof harpacticoid copepods in a species–rich community versus a species–poor community.The second one dealt with functional redundancy of harpacticoids through an interspecific and an intraspecific interaction experiment.The first experiment was conducted in Kuźnica and Hel (Poland). Undisturbed sediment wascollected at both sites. Two treatments were applied. In the first treatment, 13C enrichedSeminavis robusta was added at the upper layer of the sediment. In the second treatmentthe upper layer (0–3 cm) was removed and the enrichment took place at the –3 cm level.After 50 h of incubation, the experiment was ended by decantation and maintained informaldehyde–solution (4%). Meiofauna was extracted from the sediment (only for Kuźnica) by means of Ludox centrifugation. Subsequently, 20 individuals of each species from everysample were prepared for analysis. In Kuźnica 4 different species were identified:Paraleptastacus spinicauda, Nitokra spinipes, Huntemannia jadensis, and a bulkgroupconsisting of the species Halicyclops neglectus (Cyclopoida). In Hel only two species werecollected in sufficient numbers: P. spinicauda and Typhlamphiascus typhlops. Beyond the –3cm layer of Kuźnica there were not enough individuals present for an analysis at specieslevel.We found a significant enrichment for all copepods, except for H. jadensis and for T. typhlopsindividuals beyond the –3 cm layer when labelling was performed on the upper layer (0 cm).The organisms on the lower layer when labelling was performed at –3 cm, showed higher 13Cvalues than the organisms from the labelled top layer. In the lower layer there is less organicmaterial, and thus less non–enriched food. This increased the chance for a copepod feedingon the applied enriched diatoms. Paraleptastacus spinicauda is significantly more enriched inKuźnica then in Hel. This difference can be explained by the presence of T. typhlops in Hel.The latter species has about the same size, and thus will probably be a bigger competitorthan the species from Kuźnica.The second experiment existed of two parts and was conducted with three selected speciesfrom Paulina intertidal flat (The Netherlands): Ameiropsis longicornis, Microarthridion littoraleen Amphiascoides cfr. subdebilis. The first part was an interspecific experiment in which anartificial community, containing 3 species, was composed as treatment 1. Here there were 20individuals of every species present in one experimental unit, so the total was 60 individuals.Treatments 2–4 contained three different combinations of 2 species, with 30 individualseach. In treatments 5–7 there were 60 individuals of only one species that was present in thepetridish. The total amount of copepods was kept constant in order to exclude densitySummary - IX -effects. These treatments were established in petridishes with 13C enriched Naviculaphyllepta cells and artificial seawater. After 96 h of incubation the experiment was ended byfreezing the experimental units at –28 °C. Afterwards, 20 individuals per species were sortedrandomly from the dish, and prepared for further analysis.The outcome showed a significant enrichment for each species in comparison with thecontrol. Although the M. littorale uptake was obviously much lower then the uptake from theother two species. Microarthridion littorale showed a slightly larger uptake in treatment 1, soit is positively influenced by the presence of A. longicornis and A. cfr. subdebilis. The uptakeof A. cfr. subdebilis hardly showed any difference between the treatments. Amphiascoideslongicornis showed a decrease in uptake in combination with M. littorale, and thus wasnegatively influenced by the absence of A. cfr. subdebilis.The second part was an intraspecific experiment where for each species two densities arecompared. Each treatment contained only one species and the same amount of food (10 6 cells Navicula phyllepta). Treatments 1–3 were the same as treatment 5–7 in previousexperiment, here there were 60 individuals of each species in the dish. The remaining threetreatments contained 20 individuals of each species. This experiment lasted for 96 h and wasended by freezing the experimental vessels at –28 °C. Afterwards, 20 individuals were sortedrandomly and were prepared for analysis.This experiment showed no significant difference between both treatments for M. littorale andA. cfr. subdebilis. This may indicate that food was unlimited in the experimental unit. For A.longicornis an increased uptake was shown in the high density treatment. This surprisingresult may be explained by the fact that it is harder to find food when more copepods are inthe same dish or the rise of a stressfactor. So the search for food continued and more energywas needed, justifying a higher food–uptake.In general the first experiment concludes that the structure of a rich community, has apositive influence on the food uptake of a species (eg. P. spinicauda).The second experiment shows that only one of the three examined species is redundant, inspite of the fact that they all graze on diatoms. The absence of M. littorale leads to a higherspecific uptake for both remaining species. This concludes that M. littorale is redundant inthis artificial community. From this results it is impossible to conclude that M. littorale isredundant in its natural habitat, because also competition can play a major part.
- Functional redundance in marine food webs: feeding experiments with harpacticoid copepods and diatoms, more