Structural and functional responses of harpacticoid copepods to anoxia in the Northern Adriatic: an experimental approach

[摘要] Combined in situ and laboratory studies were conducted to document the effects ofanoxia on the structure and functioning of meiobenthic communities, withspecial focus on harpacticoid copepods. In a first step, anoxia was createdartificially by means of an underwater chamber at 24 m depth in the NorthernAdriatic, Gulf of Trieste (Mediterranean). Nematodes were found as the mostabundant taxon, followed by harpacticoid copepods. While nematode densitieswere not affected by treatment (anoxia/normoxia) or sediment depth, thesefactors had a significant impact on copepod abundances. Harpacticoid copepodfamily diversity, in contrast, was not affected by anoxic conditions, onlyby depth. Ectinosomatidae and Cletodidae were most abundant in both normoxicand anoxic samples.

The functional response of harpacticoid copepods to anoxia was studied in alaboratory tracer experiment by adding ¹³C pre-labelled diatoms tosediment cores in order to test (1) if there is a difference in food uptakeby copepods under normoxic and anoxic conditions and (2) whether initial(normoxia) feeding of harpacticoid copepods on diatoms results in a bettersurvival of copepods in subsequent anoxic conditions. Independent of theaddition of diatoms, there was a higher survival rate in normoxia thananoxia. The supply of additional food did not result in a higher survivalrate of copepods in anoxia, which might be explained by the presence of anutritionally better food source and/or a lack of starvation before addingthe diatoms. However, there was a reduced grazing pressure by copepods ondiatoms in anoxic conditions. This resulted in a modified fatty acidcomposition of the sediment. We concluded that anoxia not only impacts thesurvival of consumers (direct effect) but also of primary producers(indirect effect), with important implications for the recovery phase.

[学科分类] 地球化学与岩石