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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 3 | Copyright
Biogeosciences, 15, 905-918, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Feb 2018

Research article | 13 Feb 2018

Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

Caroline Echappé1,2, Pierre Gernez1, Vona Méléder1, Bruno Jesus1,3, Bruno Cognie1, Priscilla Decottignies1, Koen Sabbe2, and Laurent Barillé1 Caroline Echappé et al.
  • 1University of Nantes, Lab. Mer Molécules Santé – EA 2160, 2 rue de la Houssinière, 44322 Nantes CEDEX 3, France
  • 2Ghent University, Department of Biology, Lab. Protistology and Aquatic Ecology, Krijgslaan 281/S8, 9000 Ghent, Belgium
  • 3University of Lisboa, Faculty of Sciences, BioISI – Biosystems & Integrative Sciences Institute, Campo Grande, 1749-016 Lisboa, Portugal

Abstract. Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating on smaller scales however, such as the impact of benthic macrofauna on MPB development, to date remain underinvestigated. In this study, we analysed the influence of wild Crassostrea gigas oyster reefs on MPB biofilm development using multispectral RS. A 30-year time series (1985–2015) combining high-resolution (30m) Landsat and SPOT data was built in order to explore the relationship between C. gigas reefs and MPB spatial distribution and seasonal dynamics, using the normalized difference vegetation index (NDVI). Emphasis was placed on the analysis of a before–after control-impact (BACI) experiment designed to assess the effect of oyster killing on the surrounding MPB biofilms. Our RS data reveal that the presence of oyster reefs positively affects MPB biofilm development. Analysis of the historical time series first showed the presence of persistent, highly concentrated MPB patches around oyster reefs. This observation was supported by the BACI experiment which showed that killing the oysters (while leaving the physical reef structure, i.e. oyster shells, intact) negatively affected both MPB biofilm biomass and spatial stability around the reef. As such, our results are consistent with the hypothesis of nutrient input as an explanation for the MPB growth-promoting effect of oysters, whereby organic and inorganic matter released through oyster excretion and biodeposition stimulates MPB biomass accumulation. MPB also showed marked seasonal variations in biomass and patch shape, size and degree of aggregation around the oyster reefs. Seasonal variations in biomass, with higher NDVI during spring and autumn, were consistent with those observed on broader scales in other European mudflats. Our study provides the first multi-sensor RS satellite evidence of the promoting and structuring effect of oyster reefs on MPB biofilms.

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Using satellite technology and a life-size experiment, we analysed the impact of oyster reefs on mats of microscopic algae that develop within coastal mudflats. We showed that the relationship between microalgae and oysters is not limited to a one-way process where microalgae are a food source to oysters, but that oysters also promote microalgae mats development, presumably by providing nutrients to them. This might yield new insights into coastal ecosystem management.
Using satellite technology and a life-size experiment, we analysed the impact of oyster reefs on...