The Effect Of Spatial Scale On Food Web Structure

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Methods Sampling biota The biological community was sampled every two months from June 2014 to April 2015 across three spatial scales in Carlingford lough, Ireland. Sampling took place in Mill Bay (54°03.519 'N, 006°05.687 'W) in June, August, October and December 2014; as well as in February and April 2015 (Figure 1). Figure 1. Sampling occurred at Carlingford lough (a), in the extensive mudflat area of Mill Bay (b), at three spatial scales delineated by differences in mean lag between samples (c). Green: samples collected at the smallest spatial scale (>1 and 10 and 100 but < 1000 m apart, n=4). In order to analyse temporal change in assemblage and food web composition, we used mean monthly surface sea surface temperature (°C)…show more content…
Stomachs of fish were removed and kept on ice until arrival in the laboratory where they were processed immediately. At each quadrat, the benthic fauna was collected using sediment cores (10 cm diameter and 10 cm depth) and preserved in 4% formalin buffered in seawater. On return to the laboratory, sediments were rinsed through 0.5 mm mesh, invertebrates removed, fixed in 70% ethanol, and subsequently identified to the lowest taxonomic level possible using dissecting and compound microscopes. Total biomass (g dry weight) and abundance were recorded and calculated on a square meter basis. Fyke net abundance per m2 was estimated as a function of leader radius. Density estimates for this type of static gear are largely a function of taxon activity levels and therefore challenging to obtain. For our estimates we assumed that a fyke net sampled a circular surface area proportional to the leader length, calculating the circular area sampled in two ways: 1) as a function of fyke net radius, 4 m, providing an estimate of an area of A=50.27 m2; and 2) as a function of net diameter, 8 m, providing an estimate of area A=201.06 m2. Averaging abundance estimates obtained for radii of both 4 and 8 m provided a mean area of sampling equal to A=125.94 m2 with an associated radius of r=6.33 m. Abundances from the fyke nets were then expressed as a function of this integrated area to obtain estimates of fish and crustacean abundances per m2.
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