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MEPS 613:15-47 (2019)  -  DOI: https://doi.org/10.3354/meps12825

Effects of spatial scale, species aggregation and balancing on carbon flows and ecological network analysis indicators of food webs

Victor N. de Jonge1,*, Ulrike Schückel2, Dan Baird3

1Institute of Estuarine and Coastal Studies, IECS, University of Hull, Hull HU6 7RX, United Kingdom
2Schleswig-Holstein Agency for Coastal Defence, National Park and Marine Conservation, National Park Authority, 25832 Tönning, Germany
3Department of Botany and Zoology, Stellenbosch University, Stellenbosch 7600, South Africa
*Corresponding author:

ABSTRACT: The food webs of the 3 main reaches of the Ems estuary were analysed for 1975-1980 using Ecological Network Analysis (ENA). Aspects related to model aggregation at a high species resolution level (ALL SPP) or using functional groups (F-GR) and at 4 spatial scales (3 reaches and entire system) are cast in 24 balanced carbon flow models with 20 to 57 ENA compartments. Highest biomasses are represented by true phytoplankton, resuspended microphytobenthos, microphytobenthos, benthic bacteria, dissolved and particulate organic carbon. The bivalves Limecola balthica and Mya arenaria represent the highest animal biomass, while Crangon crangon plays a central role in the network connections. In an upstream direction, there are clear gradients in the relative overhead (Φ/DC: 0.610-0.599-0.534 [values for the 3 reaches]) and the relative ascendency (A/DC: 0.390-0.401-0.466). The A/DC values decrease whenthe non-living compartments (detritus) as well as the living compartments (species, functional groups) are hand-balanced. The A/DC values increase when the models are balanced by the available AVG2 balancing routine. The Φ/DC values show opposite trends. For the ALL SPP models, the geometric mean trophic efficiencies (MTE) decrease in an upstream direction (2.71-1.01-0.89) while the Finn cycling indices (FCI) increase (10-8.4-16.6%), as do the detritivory/herbivory ratios (3.13-4.33-9.03). Application of ENA to reaches instead of a full system is therefore suggested. Since ENA is sensitive to relatively small quantitative changes in biomass input values, the preferred user protocol is to consider all the relevant species separately, and to hand-balance the flows of living as well as non-living compartments.


KEY WORDS: ENA indices · Assessment · Ecosystem · Indicators · enaR


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Cite this article as: de Jonge VN, Schückel U, Baird D (2019) Effects of spatial scale, species aggregation and balancing on carbon flows and ecological network analysis indicators of food webs. Mar Ecol Prog Ser 613:15-47. https://doi.org/10.3354/meps12825

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