Phytoplankton ecology in the Bay of Biscay
Manuel Varela

General studies on phytoplankton ecology are very scarce, and have been undertaken mostly in the southern part of Bay of Biscay. The annual cycle of phytoplankton is typical of a temperate sea, with some special peculiarities. In winter time the water column is well mixed, and light is the main factor controlling primary production. During spring, water stratification previous to bloom development has a saline origin, in contrast to other areas where this stratification has a thermal origin. In summer, a thermal stratification with a subsurface chlorophyll maximum (SCM) associated to the nitracline was found. Maximum primary production was above the SCM. This situation can be ascribed to the typical tropical structure. Nevertheless, this basic pattern of phytoplankton cycle, is modified by two important processes: the intrusion of saline waters (ENAWt) during winter-spring that when it is strong and extensive, it causes a decrease in the phytoplankton biomass and the pulsating upwelling in summer time connected to the stronger Galician upwelling that causes an elevation of SCM. Both processes greatly influence the phytoplankton dynamics.The classical food web, dominated by autotrophic processes, predominates in periods of high productivity. However, during stratification and saline intrusion the food web based on microbial loop prevails, this system being of great efficiency in nutrient regeneration. The hydrographic events, in particular fronts, play a crucial role as barriers for eggs and larval transport. The success of recruitment of pelagic fishes is highly dependent on spawning taking place in areas where the newly hatched larvae find the appropriate food type and size. The different trophic food webs which characterize both sides of the front were exploited by different fish species for reproduction

Keywords: phytoplankton, fronts, upwelling, food webs, Cantabrian Sea, Bay of Biscay.
Contents of this volume Sci. Mar. 60(Suppl.2) : 45-53 Back PDF
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