Realm: Marine
Climate: Temperate
Biome: Temperate shelf and seas ecoregions
Central latitude: 44.775118
Central longitude: -2.829299
Duration: 6 years, from 1995 to 2004

9059 records

66 distinct species

Across the time series Microsetella is the most frequently occurring species

Methods

The samples were obtained during Bioman surveys covering the southeast of theBay of Biscay in spring from 1998 to 2006 (see Table 1 and Fig 1 for dates. number ofsamples and coverage of each cruise). These cruises generally take place in May. at thepeak spawning period and covering the spawning area of anchovy in the Bay of Biscay.The objective of the cruises is to evaluate anchovy biomass using the DEPM method. Asynthesis of the anchovy spawning areas. larvae and juvenile distribution. and hypothesesabout recruitment mechanisms can be found in Irigoien et al (2007). Stations were locatedevery 3 nautical miles (nm) along transects 15 nm apart perpendicular to the coast. Avertical plankton haul was made at each sampling station. using a 150?m PairoVET net (2-CalVET nets. Smith et al.. 1985). The net was lowered to a maximum depth of 100 m or 5m above the bottom at shallower stations. Samples were preserved in 4% formaldehydebuffered with sodium tetraborate. Samples were stored in 150 ml jars. The sample wasthoroughly mixed in a measuring cylinder. the total volume measured (usually around 150ml) and an aliquot of 6 ml was taken with a pipette from each sample. The average numberof organisms counted in each plate with this sub sampling set up is around 400 individuals.The aliquot was stained for 24 hours with 4 ml 1% eosin. which stains the cell cytoplasmand the muscle protein. This stain creates sufficient contrast to be recognised by imageanalysis and reduces counting of detrital material. The sub-samples were scanned onpolystyrene plates (12.7 x 8.5 cm) in 24 bit colour. at a resolution of 600 dpi using an HPScanjet8200 series scanner (reflective). The samples were not manually separated.Preliminary work (unpublished) has shown that as long as the percentage of the imagecovered by the sample remains below 3 % there is a linear relation between the number ofitems and the automatic counting. Over that threshold the percentage of organisms touchingeach other increases and results in an underestimation of the abundance. For samples fromthe Bay of Biscay the aliquot taken and the plastic plate size assures that this limit is notreached. These images were analyzed using Zooimage (www.sciviews.org/zooimage). Atotal of 17 classes were selected combining expert opinion and the class selection methodproposed by Fernandes et al. (2008). Classification was carried out using a Random Forestalgorithm which provided the best results with an estimated accuracy 88.23% using 10 foldcross-validation. Accuracy for each of the classes and the confusion matrix are provided inTables 2 and 3. The spatial distribution of the classes that were rare and resulted in poorclassification is not presented. However. because individual biomass were estimated basedon the size ? biomass relationship provided by Alcaraz et al (2003) which is not taxonspecific. all individuals were used for total biomass estimation. Three classes wereexcluded from the biomass estimation because these particles are not zooplankton:?scanning artefacts?. ?marine snow? and ?small marine snow?. Mean abundances andbiomass (Table 4) were calculated for a common area corresponding to the area of the yearwith the minimum coverage (1999). Unit of abundance = AggregatedPresence, Unit of biomass = NA

Citation(s)

"Zooplankton in the Bay of Biscay (1995-2004, yearly DEPM surveys)". Available at: http://www.emodnet-biology.eu/component/imis/?module=dataset&dasid=2774, accessed 2012.