This paper investigates the possible underlying causes of the wide interannual fluctuations in catch of the common octopus Octopus vulgaris Cuvier, 1797 in one of the main small-scale fisheries off the coast of Galicia (northwest Spain). Galicia is at the northern boundary of the Iberian-Canary current upwelling system in the northeast Atlantic Ocean, where local winds induce seasonal upwelling, largely driving the annual cycles of primary and secondary production. We hypothesize that such dynamics are also fundamental for the survival of the planktonic stages of octopus and set the year class strength. We address this hypothesis by investigating the influence of upwelling on time-series of octopus fishery data. Wind stress structure during the spring-summer (prior to the hatching peak) and autumn-winter (during the planktonic stage) was found to affect the early life phase of this species, and explains up to 85% of the total variance of the year-to-year variability of the adult catch. Despite this bottom-up modulation via environmental conditions, our results also provide evidence for a between-cohort density-dependent interaction, probably caused by cannibalism and competition for habitat.KEY WORDS: Octopus vulgaris · Phytoplankton · Zooplankton · Fisheries · Bottom-up control · Upwelling · NE Atlantic Ocean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 362: [181][182][183][184][185][186][187][188][189][190][191][192] 2008 unclear. Nevertheless, some environment -biology links have been found between recruitment or abundance and sea surface temperature (SST) in different areas (Loligo gahi in the southwest Atlantic, Agnew et al. 2000; L. vulgaris and L. forbesi in the English Channel, Robin & Denis 1999). Similarly, catch fluctuations of Thysanoteuthis rhombus are closely related with water temperature, salinity and sea level (Miyahara et al. 2005). Dawe et al. (2007) also documented opposite responses to oceanographic variations of 2 sympatric squid species in the northwest Atlantic Ocean. However, in other squid species, relationships with oceanographic processes remain unresolved (e.g. Martialia hyadesi, González et al. 1997).The common octopus Octopus vulgaris Cuvier, 1797 is one of the best studied cephalopods worldwide and the subject of an active fishery (see Otero et al. 2005 and references therein); however, little is known about the influence of environmental variability on the dramatic annual fluctuations of octopus catch. Year-to-year changes of this species have been related to coastal retention processes (Faure et al. 2000), water temperature (Balguerías et al. 2002) and rainfall (Sobrino et al. 2002). In Galician waters, the reproductive cycle of O. vulgaris appears to be tuned to seasonality in upwelling. There is one peak of spawning in spring time. The embryonic development lasts up to 4 mo, depending on water temperature, and the hatching peak occurs at the end of summer through the beginning of autumn of a given year (Year t)...

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Knowledge on the mechanisms that drive population dynamics and shape community structure is a key issue in ecology. Using wavelet methods, we analyzed 17-yr of monthly time-series of marine zooplankton (taxonomic composition, total abundance, and biomass) and their relationship with environmental factors

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) was observed at the shelfedge station in the autumn-winter period (downscaling season). We hypothesise that the observed reduction in temperature is due to the combined effect of the increase in upwelling events during the downwelling season and the decline of NAO since 1995. No significant temporal trends on an interannual scale were found in salinity values in surface or bottom layers of the stations.