Reference : The secret life of a Mediterranean seagrass litter macrofauna community : a history o...
Scientific congresses and symposiums : Unpublished conference/Abstract
Life sciences : Aquatic sciences & oceanology
http://hdl.handle.net/2268/191993
The secret life of a Mediterranean seagrass litter macrofauna community : a history of oxygen
English
Remy, François mailto [Université de Liège > Département de Biologie, Ecologie et Evolution > Océanologie >]
Michel, Loïc mailto [Université de Liège > Département de Biologie, Ecologie et Evolution > Océanographie biologique >]
Sturaro, Nicolas mailto [Université de Liège > Département de Biologie, Ecologie et Evolution > Océanographie biologique >]
Mascart, Thibaud mailto [Universiteit Gent - Ugent > Marine Biology Research Group > > >]
Lepoint, Gilles mailto [Université de Liège > Département de Biologie, Ecologie et Evolution > Océanographie biologique >]
12-Feb-2016
No
No
Vliz 16th Marine Scientists Day
12 février 2016
Bruges
Belgique
[en] Marine ecology ; Invertebrates ; Seagrasses ; Phytodetritus ; Detritus ; Oxygen level ; Oxygen concentration ; Experimental ecology ; Experiment ; Oceanology
[en] Most of the foliar primary production of Posidonia oceanica, a major Mediterranean seagrass, sheds in autumn and is exported from the meadow to adjacent areas to form "Exported Macrophytodetritus Accumulations", EMAs. These EMAs are a habitat, shelter and feeding place for an abundant and diverse community of macrofauna. Being very dynamic places and potentially playing a role of transition compartment between water column and sediment, EMAs present high variability in term of physicochemical conditions and more specifically in term of oxygen concentration. Mild to severe hypoxic periods (2 - 0.01 mL O2.L-1) can be observed in situ at different moments of the year, and this variability thus potentially play a structuring role on the macrofauna community. During this study, our main specific questions were (1) Does oxygen stratification occur inside EMAs? (2) If present, how long does it take to observe this stratification? (3) Is the macrofauna impacted and do the dominant species occupy defined positions inside the different micro-habitats?

To assess the importance of this impact, an experimental study was conducted in October 2014 near the STARESO oceanographic station (Calvi, Corsica) using an original "layer-sampling" design. The experimental construction was put underwater inside an EMA for 48 hours at a depth of 8m. Samples were collected (N=8) in a 20cm thick EMA using "sealed" boxes to sample every 5cm, from the sediment, to the water column. Oxygen, nutrients and of course the litter itself (containing the macrofauna) were sampled carefully to make sure no exchange occurred between the 4 different layers.

After data analysis, the assessment was clear: oxygen stratification occurred in less than 48h and oxygen level inside the layer close to the sediment experienced a fast decrease below the hypoxia threshold (2 mL O2.L-1). Diversity was highly impacted, showing a clear positive link with oxygen concentration. Macrofauna also appeared to follow this oxygen stratification but this response was very species specific. Some species didn't follow oxygen and are present in every layer and most of them were strongly positively linked to oxygen concentration.
But a few (Nebalia strausi and Athanas nitescens) were strongly negatively linked to oxygen concentration and were present only in the more hypoxic layers.

This experimentation thus confirmed our in situ observations. Oxygen stratification occurred quickly (< 48h) when EMAs were experiencing calm weather. This stratification observed from the water column to the sediment was very marked. Diversity and abundance of most abundant macrofauna species were drastically influenced by this stratification, showing the importance of these micro-habitats in structuring of this macrofauna community.
Laboratoire d'Océanologie, ULg
Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS
La théorie des pulses peut-elle être appliquée aux macro-invertébrés des accumulations de macrophytodétritus marins en Méditerranée ?
Researchers ; Professionals
http://hdl.handle.net/2268/191993

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