Bay of Biscay
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Gijón is the latest station to be added to the temporal dataseries project RADIALES (Instituto Español de Oceanografiía). This monthly survey consists of three sampling stations, of which only Station 3 (43 46.7'N 5 30.3'W) data were used for this site summary.
Zooplankton samples were collected on board the RV Jose de Rioja by means of vertical hauls from 100 m to surface using a triple WP-2 net (38 cm diameter, 200 µm mesh) and then preserved with 4% formalin in sodium borate-buffered seawater for posterior laboratory analysis. To estimate total zooplankton biomass, samples were fractionated into three size ranges (200-500 µm, 500-1000 µm, and >1000 µm) using sieve cups equipped with Nitex screens. The samples were then rinsed with 0.2 µm filtered seawater, filtered onto pre-combusted (450 C, 24 h) preweighted Whatman GF/A filters, and dried at 60 C. After 24 hours, total dry weight is measured with a Sartorius microbalance.
The hydrographic conditions in the northern Iberian coast demonstrate a marked seasonality, driven by the cycle of mixing-stratification that is characteristic of temperate seas. Additionally, other specific oceanographic structures influencing the planktonic dynamics can be found, such as the warm, saline IPC flowing eastwards during winter months along the Cantabrian continental shelf and slope, or the entrainment of waters from the subtropical (colder and saltier) and Subpolar gyres of the Northeast Atlantic.
Total zooplankton abundance demonstrates a bimodal distribution, in which spring (March-May) and autumn (September-October) peaks are separated by summer intermediate and winter low values (Figure 7.6a). The rise in both zooplankton abundance and dry weight is already apparent in February (Figure 7.6a and b), although abundance values peak a month earlier than biomass, coinciding with the chlorophyll maximum of March (Figure 7.6c).
Temperature and salinity have been steadily increasing off Gijón since the start of this time-series (Figure 7.6d and e).