Ricardo Anadón

A persistent upwelling off the Central Cantabrian Coast (Bay of Biscay)

Abstract North Atlantic Central Waters were detected near the surface in some locations off the Central Cantabrian Coast (Bay of Biscay). This feature suggests an upwelling process taking place in the season of the thermal stratification which is persistent throughout the summer. The exact mechanism of formation is unknown but the wind driven currents are probably the main force. The prevailing winds off the Cantabrian coast are northeast during summer, generating westward superficial currents that produce an Eckman transport offshore. Factors such as shape of the coast and slope topography maybe modulators. Although the upwelling was subsuperficial, our results suggest that cold and nutrient rich waters reached the surface previously. The biomass distribution of phytoplankton varied according to the upwelling and different populations could be recognized. In stations not affected by upwelling phytoplankton occured mainly on top of the thermocline, whereas in those affected by upwelled waters it was concentrated near the surface. The mean size and composition of the populations were also different, and two distinct types could be recognized and related to nutrient concentrations.

Evidence of heavy predation by Noctiluca scintillans on Acartia clausi (Copepoda) eggs off the central Cantabrian coast (NW Spain)

A large proliferation of Noctiluca scintillans (Dinophyceae: Noctilucidea) was observed in neritic waters off the central Cantabrian coast during late April 1995. Eggs of Acartia clausi (Crustacea: Copepoda) were the most conspicuous prey within vacuoles of Noctiluca. Noctiluca ingested 73 % of the total stock of A. clausi eggs. This intense predation on copepod eggs could potentially affect the recruitment of nauplii. The potential impact on the stock of Acartia clausi eggs and on the daily egg production of the population is discussed. There is a negative correlation between the average number of ingested eggs by a single Noctiluca cell and the abundance of Noctiluca. This fact, coupled with the lack of significant correlation between the former variable and the abundance of Acartia clausi eggs, suggests that interference processes play a major role in regulating the predator-prey interaction between Noctiluca and Acartia eggs.

Seasonal plankton dynamics along a cross-shelf gradient.

Much interest has recently been devoted to reconstructing the dynamic structure of ecological systems on the basis of time-series data. Using 10 years of monthly data on phyto- and zooplankton abundance from the Bay of Biscay (coastal to shelf-break sites), we demonstrate that the interaction between these two plankton components is approximately linear, whereas the effects of environmental factors (nutrients, temperature, upwelling and photoperiod) on these two plankton population growth rates are nonlinear. With the inclusion of the environmental factors, the main observed seasonal and inter-annual dynamic patterns within the studied plankton assemblage also indicate the prevalence of bottom-up regulatory control.

Seasonality of North Atlantic phytoplankton from space: impact of environmental forcing on a changing phenology (1998-2012).

Seasonal pulses of phytoplankton drive seasonal cycles of carbon fixation and particle sedimentation, and might condition recruitment success in many exploited species. Taking advantage of long-term series of remotely sensed chlorophyll a (1998-2012), we analyzed changes in phytoplankton seasonality in the North Atlantic Ocean. Phytoplankton phenology was analyzed based on a probabilistic characterization of bloom incidence. This approach allowed us to detect changes in the prevalence of different seasonal cycles and, at the same time, to estimate bloom timing and magnitude taking into account uncertainty in bloom detection. Deviations between different sensors stressed the importance of a prolonged overlap between successive missions to ensure a correct assessment of phenological changes, as well as the advantage of semi-analytical chlorophyll algorithms over empirical ones to reduce biases. Earlier and more intense blooms were detected in the subpolar Atlantic, while advanced blooms of less magnitude were common in the Subtropical gyre. In the temperate North Atlantic, spring blooms advanced their timing and decreased in magnitude, whereas fall blooms delayed and increased their intensity. At the same time, the prevalence of locations with a single autumn/winter bloom or with a bimodal seasonal cycle increased, in consonance with a poleward expansion of subtropical conditions. Changes in bloom timing and magnitude presented a clear signature of environmental factors, especially wind forcing, although changes on incident photosynthetically active radiation and sea surface temperature were also important depending on latitude. Trends in bloom magnitude matched changes in mean chlorophyll a during the study period, suggesting that seasonal peaks drive long-term trends in chlorophyll a concentration. Our results link changes in North Atlantic climate with recent trends in the phenology of phytoplankton, suggesting an intensification of these impacts in the near future.

Salp distribution and grazing in a saline intrusion off NW Spain

Salp distribution and grazing were studied along three transects (19 stations) and a Lagrangian phase (7 stations) off Galician coast (NW Spain) in November 1999 during GIGOVI 99 cruise. A poleward saline intrusion was detected at the shelf-break, reaching salinity values above 35.90 u.p.s. at 100-m depth. The salp community was dominated by Salpa fusiformis, although Cyclosalpa bakeri, Thalia democratica and Iasis zonaria were also found in the study area. Total salp abundance ranged from 4 to 4500 ind m 2 , representing biomass values between 0.2 and 2750 mg C m 2 . Maximum densities were located in the frontal area separating the saline body from coastal waters. S. fusiformis pigment ingestion was estimated using the gut fluorescence method. Gut contents were linearly related to salp body size. Total pigment ingestion ranged from 0.001 to 15 mg Chl-a m 2 d 1 , with maximum values at the coastal edge of the saline body. Estimated ingestion translates into an average daily grazing impact of 7% of chlorophyll standing stock, ranging from <1% to 77%. D 2003 Elsevier Science B.V. All rights reserved.

Nutrients dynamics in the southern Bay of Biscay (1993–2003): Winter supply, stoichiometry, long‐term trends, and their effects on the phytoplankton community

[1] The southern Bay of Biscay is a very active region in terms of hydrography due to the interannual variations of its Central Waters, the recurrence of mesoscale features such as slope currents and upwellings, and the freshwater discharges from land. This highly dynamic physical environment influences to a great extent the biogeochemical cycles of nutrients beyond the seasonal cycle typical of middle latitudes. By using a monthly time series (1993–2003) of nitrate, nitrite, phosphate, and silicate consisting of three stations placed along a cross-shelf transect, we assess the role of the physical forcing on nutrient seasonal and interannual dynamics within the upper 200 m, as well as the interactions with the biological component. The seasonal cycles of all nutrients and the stoichiometric balances (N:P and Si:N) are characterized along this coastal-oceanic gradient. The year-to-year variations in the extent of the winter replenishment are analyzed in relation to the background Central Waters and presence/absence of the Iberian Poleward Current. In the long term we report decreasing linear trends of nitrate, nitrite, and silicate as well as an uncoupled nonlinear variation (i.e., cyclical) for all nutrients. Furthermore, we investigate the effect of this complex long-term forcing on the phytoplankton: the linear trends are probably related to a decreasing primary production rate, while the nonlinear forcing may be responsible for controlling the community structure of phytoplankton.

The FRUELA cruises.: A carbon flux study in productive areas of the Antarctic Peninsula (December 1995–February 1996)

Abstract The FRUELA (name of an 8th century king of Asturias) project, part of the Spanish contribution to the study of biogeochemical carbon fluxes in the Southern Ocean, was based on two consecutive cruises of the B.I.O.; Hesperides which took place in the Bransfield and Gerlache Straits and Belligshausen Sea between early December and early February of Austral summer 1995–1996. In addition to the cruises, data were obtained from an array of sediment traps deployed for one year in the Western Bransfield Strait Basin. The basic objectives of FRUELA were the quantification of carbon standing stocks and fluxes through the main components of the “biological pump” and the determination of carbon fluxes across different water column boundaries, including the transfer of CO2 between the atmosphere and the ocean, the export of particulate carbon (PC) out of the euphotic zone, the vertical flux of PC in deep waters and the accumulation of carbon in sediments. The main hydrographical features found in the study region were the Southern Boundary of the Antarctic Circumpolar Currrent (SbyACC) and the Bransfield Front. Three major zones, with contrasting physico-chemical and biological characteristics were considered: Bellingshausen, including the Northwest Bellingshausen Sea and comprising the SbyACC, Bransfield, including the Western Bransfield Strait and the northeastern part of the Gerlache Strait, and Gerlache, with the rest of the Gerlache Strait. This paper summarizes the distribution of different properties and rate processes in these zones and discusses the major findings of the cruise concerning carbon fluxes. Our results indicate that, during the summer period, the studied area could be considered as a sink for atmospheric carbon. The amount of PC exported out of the photic layer was a moderate fraction of primary production and a low fraction of the suspended PC; high chlorophyll a systems dominated by microphytoplankton showed higher PC export fluxes than low chlorophyll a systems dominated by small flagellates and cryptomonads. The amount of PC arriving at deep waters or accumulating in the sediments was two to three orders of magnitude lower than that exported from the photic layer, probably due to biological recycling and advection out of the area.

Ingestion, faecal pellet and egg production rates of Calanus helgolandicus feeding coccolithophorid versus non-coccolithophorid diets

Ingestion rates, faecal pellet and egg production were obtained in laboratory experiments with females of the copepod Calanus helgolandicus collected from the English Channel in November 1994. Five different algal monocultures were used as food: Prorocentrum micans (30 µm ESD), Thalassiosira weissflogii (13 µm ESD), Dunaliella tertiolecta (7 µm ESD), Emiliania huxleyi (5 µm ESD) and Coccolithus pelagicus (14 µm ESD). Results obtained suggest the low ingestion efficiency of the copepod when feeding on coccolithophorids during late autumn-early winter. From the five species offered, only the largest non coccolithophorid Prorocentrum micans and Thalassiosira weissflogii supported efficient feeding and calculated respiratory demand for C. helgolandicus. Both coccolithophorids, irrespective of cell size, were ingested at very low rates even when offered at high concentrations (233-468 µg C l(-1)). Besides low ingestion, no egg production was found in the copepods fed with Emiliania huxleyi, although unusual high gross efficiency (reaching 72%) was obtained in experiments performed with Coccolithus pelagicus. The late seasonal timing of the experiments (November) could explain the low ingestion and egg production rates.

Patterns of change in sea surface temperature in the North Atlantic during the last three decades: beyond mean trends

Sea surface temperature (SST) is an important indicator of changes in the climate system and a key driver of marine ecosystems. Here we studied the strength and spatial patterns of changes in North Atlantic SST during the last three decades (1982–2010). Regional and local patterns of change were studied using data derived from the Advanced Very High Resolution Radiometer (AVHRR) sensors. Apart from changes in mean SST, we studied changes in the seasonal cycle, in the spatial patterning of temperature anomalies and in the location of selected isotherms. We quantified the degree of nonlinearity in mean SST as an indicator of the rate at which SST trends changed during the study period. Changes in the timing and intensity of seasonal extremes were explored, and a heuristic method was used to derive the length of the period of stratification and to estimate its variation. Our results were in general coherent with the main impacts predicted by climate change projections, with greatest changes located at northern latitudes and near land. Marked variation in the spatial patterns was also found for different variables, strengthening the view that physical changes could be promoting the arrangement of novel marine biological communities. The observed changes in ocean SST highlighted the need of a more local and regional focus in future climate change studies.

Fucoid assemblages on the north coast of Spain: past and present (1977–2007)

Abstract Fucoid assemblages dominated by Pelvetia canaliculata, Fucus spiralis, F. vesiculosus, and Ascophyllum nodosum located at two sites on the central coast of Asturias (northern Spain) were sampled monthly in 1977. Repeating the same sampling methodology, a resurvey was done in 2007 to detect changes in the abundances of the species using the previous data as a baseline. Annual net primary production was lower for all the species in 2007, and there were differences in the timing of maximum biomass for P. canaliculata and F. vesiculosus, as well as a shortening of the growth period in 2007. Associated fauna also differed between dates. Higher abundances of Gibbula spp. occurred in 2007, whereas littorinid species densities in the upper intertidal were reduced in that year. As a result, the fucoid-grazers balance changed, with P. canaliculata and particularly F. vesiculosus, being the assemblages most sensitive to change. Observed modifications were not merely fluctuations in the biomass patterns of these species, but also responses to increases in air temperature and sea surface temperature and to a shift in the frequency and seasonality of upwelling episodes. Other long-term abiotic fluctuations not directly related to global warming should also be considered as possible drivers for these changes.