De Troch, M.

Heylen, K.

Sabbe, K.

Stock, W.

Willems, A.

Open Marine Archive

Copepods promote nitrogen retention in estuarine sediments
Stock Willem' , Kim Heylen2, Koen Sabbe3, Anne Willems2 and Marleen De Troch1
1 Marine Biology, Biology Department, Ghent University, Krijgslaan 281 -  S8, B-9000 Ghent, Belgium 
E-mail: Willem.Stock@Uqent.be
2 Laboratory o f M icrobiology (LM-UGent), Department o f Biochemistry and Microbiology, Ghent 
University, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium
3 Laboratory o f Protistology and Aquatic Ecology, Biology Department, Ghent University 
Krijgslaan 281 -  S8, B-9000 Gent, Belgium
During the past century anthropogenic activities have dramatically increased the am ount o f reactive 
nitrogen on Earth. It has been estimated that nitrogen inputs have increased as much as ten-fo ld  in 
coastal ecosystems. As a result, these orig inally n itrogen-lim ited areas have become severely 
eutrophied.
Denitrification is an essential step in the nitrogen cycle as it is capable o f counteracting 
eutrophication by removing the excess o f reactive nitrogen from  the ecosystem. In the past 
decades, much research has been devoted to  unravelling which organisms affect nitrogen cycling in 
intertida l sediments. Until now, these studies almost exclusively focussed on the influence o f 
m icrophytobenthos or macrofauna on den itrification. The effects o f meiofauna (e.g. nematodes and 
copepods), the intermediate troph ic level, on the N fluxes have alm ost completely been neglected, 
notw ithstanding the fact that these abundant organisms interact in numerous ways w ith bacteria, 
m icrophytobenthos and macrofauna.
The aim o f th is study was to investigate the impact o f the meiofauna and its interactions with 
diatoms and bacteria on den itrification in marine sediments.
To th is end, we used a microcosm approach in which (1) copepods, (2) spent medium from  
copepods, (3) diatoms (Navicula  sp.) or (4) a combination o f copepods and diatoms were added to 
defaunated estuarine sediments. The microcosms were incubated fo r seven and a half days, after 
which the nutrient concentrations and den itrifica tion potential (a proxy fo r the den itrification 
activity in the microcosm) were measured. The excretion products o f copepods proved to be an 
im portant source o f both ammonium and phosphate. Furthermore, the presence o f copepods and 
the ir excretion products reduced den itrifica tion rates in the microcosms. By providing the system 
with more nutrients through the ir excretions and reducing the amount o f active nitrogen that was 
lost through denitrification, copepods seemed to enhance eutrophication. This would benefit the 
copepods as it w ill promote the growth o f the ir food sources, i.e. bacteria and diatoms. However, 
these findings should be interpreted w ith care, as fie ld verification remains necessary. This is the 
firs t study that provides clear evidence fo r the impact o f meiofauna on denitrification.
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Copepods promote nitrogen retention in estuarine sediments

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