Reference : Has oxygen depletion an impact on nutrients and macrofauna in a highly dynamic macrop...
Scientific congresses and symposiums : Poster
Life sciences : Environmental sciences & ecology
http://hdl.handle.net/2268/168604
Has oxygen depletion an impact on nutrients and macrofauna in a highly dynamic macrophytodetritus accumulation?
English
Remy, François mailto [Université de Liège - ULg > Département de Biologie, Ecologie et Evolution > Océanologie >]
Mascart, Thibaud mailto [Université de Liège - ULg > Département de Biologie, Ecologie et Evolution > Océanologie >]
Dauby, Patrick mailto [Université de Liège - ULg > Département de Biologie, Ecologie et Evolution > Systématique et diversité animale >]
Gobert, Sylvie mailto [Université de Liège - ULg > Département de Biologie, Ecologie et Evolution > Océanologie >]
Lepoint, Gilles mailto [Université de Liège - ULg > Département de Biologie, Ecologie et Evolution > Océanologie >]
6-May-2014
A0
No
No
International
46th GHER Liège International Colloquium 2014
du 5 mai 2014 au 9 mai 2014
Liège
Belgique
[en] Low oxygen conditions ; Hypoxia ; Nutrients
[en] Posidonia oceanica is an endemic Mediterranean highly productive seagrass. Depending on the ability of the primary consumers to digest it alive, a generally important part of its foliar primary production falls in autumn, to decay inside the meadow or to be exported to sand patches to form “exported litter accumulations”. These accumulations are highly dynamic depending on hydrodynamics and seafloor geomorphology. Literature says that low O2 conditions might occur inside litter accumulations, but the annual oxygen dynamics or its impact on the litter-associated macrofauna has never been measured. We focused on 2 exported litter accumulations in Calvi Bay (Corsica), during 2 years for a total of 8 seasons. For each season, we collected water samples (n=6) from 3 different strata: Water Column (WC), Water Just Above the litter (WJA) and Water Inside the litter (WI). Oxygen was measured for each replicate using a Winkler-based automated routine for oxygen concentration measurements on micro-volumes. At the same time, nutrients concentrations (PO4, NH4, and NO2+NO3) were measured in WC, WJA and WI, but also in the Interstitial Water (IW) using a spectrophotometric continuous flow analyzer (adapted for low nutrients level in an oligotrophic environment). In parallel, macrofaunal (size >500µm) samples (n=3-6) were also collected, counted and identified to the specific level.

Our results show significant differences between O2 concentrations/saturation from WI and the two other strata. Significant differences were detected between seasons, sites and years for WI which is the only stratum where really low O2 conditions can be observed. Significant differences were also detected between seasons for both WC and WJA but no differences between sites and years. On the other hand no significant differences were detected between WC and WJA.
A similar observation was made for the nutrients at the annual, seasonal and spatial level. Moreover differences are also observed between the nutrients themselves.
Our data shows no correlation between WI O2 concentrations and saturation, and global macrofauna abundance or biodiversity. Results are more contrasting at an individual specific level for the 4 most dominant species. For two amphipod species, Gammarella fucicola (55% of the global abundance) and Gammarus aequicauda, no significant correlations were detected between their abundance and O2. For the leptostracan species, Nebalia strausi, a significant negative correlation with O2 concentration was detected. For the last amphipod species, Melita hergensis, a significant positive correlation was observed.
Our analyses also show significant correlations between WI O2 concentration/saturation, and WI / IW nutrients concentration.


To conclude, this work shows that WI is a very particular and dynamic environment considering O2 concentration and saturation. Low O2 conditions can be observed in WI but never in WC or WJA showing that internal processes and relations with the sediment determine the O2 dynamics in WI and showing a potential “barrier” effect between WI and WC. Moreover O2 dynamics and its consequences may play a role in the nutrients dynamics and cycles.
It is clear that faunal responses to low O2 conditions are not identifiable at a global community level. At a specific level, we show a more complex situation: some species do not seem to be impacted by low O2 conditions, but some present a significant positive, or a significant negative response.
This shows the existence and complexity of species-dependent low O2 tolerance/adaptation, and the importance of a specific level data analyses to detect responses of dominant litter associated macro- invertebrates to O2 concentration and saturation variations.
Laboratoire d'Océanologie, Liège
Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS ; Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture (Communauté française de Belgique) - FRIA
La théorie des pulses peut-elle être appliquée aux macro-invertébrés des accumulations de macrophytodétritus marins en Méditerranée?
Researchers ; Professionals ; Students
http://hdl.handle.net/2268/168604

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