Vincent Escaravage

Influence of seagrass beds and oyster parks on the abundance and biomass patterns of meio- and macrobenthos in tidal flats

In Arcachon Bay, on the south-west coast of France, the intertidal area is mainly occupied by sandbanks, oyster parks (Crassostrea gigas) and mud flats covered with seagrass beds (Zostera noltii). In order to estimate the relative contribution of meio- and macrofauna to the benthic ecology of these tidal flats, seven stations were studied seasonally for a year. Relationships between faunal density and biomass, and external factors such as sediment structure, benthic chlorophyll and seagrass debris were investigated. A comparison was made between bare sands, oyster beds and vegetated sediment in semi-exposed conditions and in sheltered areas. Using a stepwise method of multiple linear regression it was shown that high densities of macrobenthos are mostly explained by high quantities of plant debris. For meiofauna, together with plant debris, other effective variables are involved: silt content, organic carbon, chlorophyll pigments. On an average, a correlation between macro- and meiofaunal abundances could be found. However, this general pattern is modified by the biogenic structure created by the oysters and seagrass. When compared to the adjacent sandbanks, oysters clearly enhanced meiofaunal abundance (from 1130–4170 individuals 10 cm−2) but depressed macrofaunal densities (from 640-370 individuals 400 cm−2). The organic-rich oyster biodeposits probably favour meiofauna by an increase of the trophic resources but do not favour macroinfauna by inducing low oxygen concentrations. Moreover, it is likely that macrofauna is more sensitive to predation than meiofauna both in sandbanks and in oyster parks. For both meio- and macrofauna the highest incidences (7200 individuals 10 cm−2 and 2470 individuals 400 cm−2, respectively) are recorded in seagrass bed sediments. Zostera induces an enhancement of organic detritus and provides a refuge against predation. In terms of biomass, the macrofauna/meiofauna ratio is 25·1 in sandbanks, 1·5 in oyster parks and 4·2 in seagrass bed sediments. Macrofaunal biomass is more variable both spatially and temporally than meiofauna biomass. It is likely that the macrofauna is more sensitive to external factors such as predation, anoxia, exposure, than the meiofauna. Meiofauna abundance and biomass are more usually a function of food abundance and physical properties of the sediment.

Secondary Production of the Brackish Copepod Communities and Their Contribution to the Carbon Fluxes in the Westerschelde Estuary (the Netherlands)

The zooplankton community of the brackish part of the Westerschelde estuary (November 1989–October 1990) was dominated by two calanoid copepods, Eurytemora affinis and Acartia tonsa. Eurytemora was present during a longer period of the year and was much more important in terms of total abundances and biomasses than Acartia.The secondary production of these species was estimated by means of the growth rate method, using weight-specific growth rates obtained from laboratory cultures (Eurytemora) or from the literature (Acartia).Due to the substantially higher growth rates of Acartia compared to Eurytemora, total yearly productions of both communities were comparable, notwithstanding the large discrepancies in biomass. They amounted to about 5 and 6 g C m−2 y−1 by Acartia and Eurytemora respectively.The food needed to realise this production was estimated to be about 14 and 17 g C m−2 y−1 by Acartia and Eurytemora respectively. Provided that the copepods are able to selectively ingest the phytoplankton, in situ net production provides sufficient carbon for zooplankton demands for a short period of the year only. As phytoplankton standing stock is very low and net phytoplankton productivity is negative from late fall to early spring, nutritional demands of the copepods have to be fulfilled by other than algal food at least during this period of the year.Although the copepods in the brackish part can have an important impact on some food items, their contribution to total carbon fluxes in the brackish zone is negligible: each year some 6% of all consumed carbon in the brackish part of the estuary passes through the copepod food web.

Data integration for European marine biodiversity research: creating a database on benthos and plankton to study large-scale patterns and long-term changes.

The general aim of setting up a central database on benthos and plankton was to integrate long-, medium- and short-term datasets on marine biodiversity. Such a database makes it possible to analyse species assemblages and their changes on spatial and temporal scales across Europe. Data collation lasted from early 2007 until August 2008, during which 67 datasets were collected covering three divergent habitats (rocky shores, soft bottoms and the pelagic environment). The database contains a total of 4,525 distinct taxa, 17,117 unique sampling locations and over 45,500 collected samples, representing almost 542,000 distribution records. The database geographically covers the North Sea (221,452 distribution records), the North-East Atlantic (98,796 distribution records) and furthermore the Baltic Sea, the Arctic and the Mediterranean. Data from 1858 to 2008 are presented in the database, with the longest time-series from the Baltic Sea soft bottom benthos. Each delivered dataset was subjected to certain quality control procedures, especially on the level of taxonomy. The standardisation procedure enables pan-European analyses without the hazard of taxonomic artefacts resulting from different determination skills. A case study on rocky shore and pelagic data in different geographical regions shows a general overestimation of biodiversity when making use of data before quality control compared to the same estimations after quality control. These results prove that the contribution of a misspelled name or the use of an obsolete synonym is comparable to the introduction of a rare species, having adverse effects on further diversity calculations. The quality checked data source is now ready to test geographical and temporal hypotheses on a large scale.

Daily cycles of dissolved oxygen and nutrient content in a shallow fishpond: The impact of water renewal

This study was conducted in a shallow fishpond located on the eastern side of Arcachon Bay, France.Dissolved oxygen, pH and nutrient content (NH4, NO2, NO3 and PO4) showed pronounced diel variations.These phenomena seemed to be directly controlled by biological processes. Microbially mediated degradation of organic matter constitutes the main source of nutrients in the water column and primary producers consume the major part of these products. These processes are closely coupled to the light-dark cycle.Man-induced water renewal caused low modifications in nutrient concentration and did not alter its temporal dynamics.

Benthic respiratory potential with relation to sedimentary carbon quality in seagrass beds and oyster parks in the tidal flats of Arcachon Bay, France

Relationships between sedimentary organic carbon quality and the benthic response were checked in tidal sediment of Arcachon Bay, France. Pigment and easily extractable macromolecular contents were used as indicators of the quality of particulate organic carbon (POC) while respiratory electron transport system (ETS) activity was chosen as an indicator for benthic response. The study was carried out in seven stations representing strongly different facies; these stations were sampled seasonally. Total ETS-activity includes the respiratory potential of various benthic compartments (phytobenthos, meiofauna, protozoa and bacteria). The importance of each of these components was calculated using conversion factors between ETS and biomass parameters. It was shown that ETS-activity due to phytobenthos was relatively high (up to 87% of total ETS) in stations under intense hydrodynamic conditions, but low (less than 23%) in the most sheltered stations. The impact of meiofauna was very low in all stations (less than 15% of heterotrophic ETS). Total and heterotrophic ETS activities were highly correlated with either POC, macromolecular content or protein. The slopes of the curves were compared with the ratios known for living organisms. The ETS/POC ratio in sediment was much lower than that in living matter while ETS/macromolecules and especially ETS/protein in sediment were of the same order as that in living material. We conclude that the degradable organic matter, (i.e. easily extractable biopolymers) could be mainly biomass and that detrital degradable molecules could be rapidly incorporated in biomass and not accumulate.

A mixed modeling approach to predict the effect of environmental modification on species distributions

Human infrastructures can modify ecosystems, thereby affecting the occurrence and spatial distribution of organisms, as well as ecosystem functionality. Sustainable development requires the ability to predict responses of species to anthropogenic pressures. We investigated the large scale, long term effect of important human alterations of benthic habitats with an integrated approach combining engineering and ecological modelling. We focused our analysis on the Oosterschelde basin (The Netherlands), which was partially embanked by a storm surge barrier (Oosterscheldekering, 1986). We made use of 1) a prognostic (numerical) environmental (hydrodynamic) model and 2) a novel application of quantile regression to Species Distribution Modeling (SDM) to simulate both the realized and potential (habitat suitability) abundance of four macrozoobenthic species: Scoloplos armiger, Peringia ulvae, Cerastoderma edule and Lanice conchilega. The analysis shows that part of the fluctuations in macrozoobenthic biomass stocks during the last decades is related to the effect of the coastal defense infrastructures on the basin morphology and hydrodynamics. The methodological framework we propose is particularly suitable for the analysis of large abundance datasets combined with high-resolution environmental data. Our analysis provides useful information on future changes in ecosystem functionality induced by human activities.

Potenties voor herstel getijdenatuur in het Haringvliet, Hollands Diep en de Biesbosch

In verband met de verwachte positieve effecten op de natuur, met name het herstel van vismigratie, gaan vanaf 2018 de Haringvlietsluizen op een kier. Als gevolg van deze aanpassing kan er tijdens vloed zoutwater binnendringen in het westelijk deel van het Haringvliet. Het verder openzetten van de Haringvlietsluizen dan alleen op een kier, biedt ook de mogelijkheid voor meer getijdynamiek in het Haringvliet, maar ook verder landinwaarts, het Hollands Diep en de Biesbosch, waardoor er meer intergetijdengebied ontstaat. In deze studie is een verkenning gedaan naar de mogelijkheden van het herstel van getijdenatuur in het Haringvliet, Hollands Diep en de Biesbosch. In deze studie zijn vijf varianten doorgerekend: (1) Huidig beheer, (2) Kierbesluit, (3) 80 cm getij, (4) Stormvloedkering en (5) Klimaatscenario (met stormvloedkering).