In-vivo single-cell fluorescence and size-scaling of phytoplankton chlorophyll content

In unicellular phytoplankton, the size scaling exponent of chlorophyll content per cell decreases with increasing light limitation. Empirical studies have ex- plored this allometry by combining data from several species, using average values of pigment content and cell size for each species. The resulting allometry thus in- cludes phylogenetic and size scaling effects. The possibility of measuring single-cell fluorescence with imaging-in-flow cytometry devices allows the study of the size scaling of chlorophyll content at both the inter- and intraspecific levels. In this work, the changing allometry of chlorophyll content was estimated for the first time for single phytoplankton populations by using data from a series of incubations with monocultures exposed to different light levels. Interspecifically, our experiments con- firm previous modeling and experimental results of increasing size scaling exponents with increasing irradiance. A similar pattern was observed intraspecifically but with a larger variability in size scaling exponents. Our results show that size-based pro- cesses and geometrical approaches explain variations in chlorophyll content. We also show that the single-cell fluorescence measurements provided by imaging-in-flow devices can be applied to field samples to understand the changes in the size de- pendence of chlorophyll content in response to environmental variables affecting primary production

Intrusions of warm and salty waters onto the NW and N Iberian shelf in early spring and its relationship to climate variability

Temperature and salinity data from a series of cruises carried out on the NW and N Iberian shelf, between 1987 and 2005 during early spring, were analysed to investigate the inter-annual variability of the intrusions of warm and salty waters into the Cantabrian Sea, and its relationship with the meridional sea surface temperature (SST) gradient in the NE Atlantic and the main modes of climate variability affecting the Northern Hemisphere. A sub-surface front, that separates warmer and saltier (i.e. spicy) waters in the westernmost part of the Iberian shelf from the colder and fresher waters, characteristic of the easternmost part of the southern Bay of Biscay, was observed in all the analysed years. The location of this sub-surface front, which defines the limit of the influence of the Subtropical mode of Eastern North Atlantic Central Water (ENACWst) advected by the Iberian Poleward Current (IPC), varied approximately between Finisterre Cape (43ºN, 9ºW) and Penñas Cape (43.5ºN, 6ºW), being located on average around the Ortegal Cape (43.5ºN, 8ºW). Its position, alongshore the Southern Bay of Biscay shelf, is displaced westward as the spring season progresses, and showed a positive correlation with the summer–autumn (July–October, JASO) meridional SST gradient (measured between 36º N 15º W and 46º N 15º W) of the previous year. This gradient was in turn correlated with the values of the Eastern Atlantic (EA) climate index for the same period.FICY

Hydrographic conditions and mesozooplankton species distribution in the Bay of Biscay shelf during spring 2004

Mesozooplankton community structure on the southern Bay of Biscay shelf and its relationship with environmental conditions was analysed during spring 2004. According to thermohaline characteristics, we observed two frontal zones along the shelf (around 7° and 3°W) that gave rise to three distinct hydrographic regions. The westernmost part of the shelf (WC), defined by the presence of relatively warm and salty water related to the presence of the Iberian Poleward Current (IPC), the easternmost region (EC), characterised by colder and fresher water, and a region in the Central Cantabrian Sea (CC) with thermohaline characteristics in between these two extremes. Besides, a clear coastal-offshore pattern was found in relation to the mixed layer depth (MLD). We observed a good agreement between the aforesaid hydrographic regions and the distribution of zooplankton species. In the WC region, the community structure was dominated by Paracalanus parvus, Oithona helgolandica, Acartia clausii and Clausocalanus pergens, while in the EC region the most dominant species were Noctiluca scintillans and Oncaea media. The CC region showed similar composition of copepods than the WC region but larvaceans (Oikopleura and Fritilaria) were also abundant. Superimposed to this along-shelf pattern, relative abundances differed also between coastal and shelf stations.SARDYN EU –project (QLRT-2001-00818

Mesozooplankton species distribution in the NW and N Iberian shelf during spring 2004: Relationship with frontal structures.

We have analysed the mesozooplankton community structure in the southern Bay of Biscay shelf and its relationship with the hydrographic conditions during spring 2004. According to thermohaline characteristics, we observed two frontal zones of distinct origin along the shelf (around 7° and 3°W), that allowed us to differentiate three different hydrographic domains. The westernmost part of the shelf (WC), defined by the presence of relatively warm and salty water related to the presence of the Iberian Poleward Current (IPC), the easternmost region (EC), characterized by colder and fresher water and subject to the influence of freshwater inputs from the Adour river in the French coast, and a region in the Central Cantabrian Sea (CC), where thermohaline characteristics were intermediate between these two extremes. The mixing layer depth (MLD) regime in these areas was also different: theWCregion was characterized by a mixed water column, whereas in the EC region the river discharges produces stratification of the upper meters of the water column (b10 m); in the CC region, we found a distinct vertical mixing regime that separated coastal (stratification) from shelf (mixed water column) stations, giving rise to a notorious across-shelf front. We found a good match between the aforesaid hydrographic regions and the distribution of mesozooplankton species composition and community assemblages: the Mantel correlation between physical variables and mesozooplankton distribution was highly significant (n=63, r=0.70, αb0.001). In the WC region, the community was dominated by Paracalanus parvus, Oithona helgolandica, Acartia clausi and Clausocalanus pergens, while in the EC region the most dominant species were Noctiluca scintillans, Oncaea media and Temora longicornis. The CC region showed similar composition of copepods than the WC region, but larvaceans (Oikopleura spp. and Fritillaria spp.) were more abundant in the CC region than in the WC region. Within each zone, the relative abundances of the dominant species differed between coastal and shelf locations.SARDYN EUproject (QLRT-2001-00818) Consejería de Educación y Cultura del Principado de Asturias’ (FICYT)

Spring influence of the Iberian Poleward Current into the Bay of Biscay from 1987 to 2006

Publicado

Producción de mielatos en colonias de abejas afectadas por el mal del río en Uruguay

In Uruguay, the excretions of the flatidae Epormenis cestri when located in sarandí colorado trees (Sebastiania schottiana) are the cause of the massive death of young honeybee larvae, a phenomenon that beekeepers call River disease. A strong income of honeydew is frequently observed in these affected colonies despite the con-tinuous loss of bees due to lack of replacement. The aim of this study was to determine a handling of the colonies that allows obtaining honeydew honey. Forty-eight colonies were transported to an apiary affected by River disease and were divided into 5 groups according to the following treatments: Group 1: regular honeydew har-vest, adding of brood and sugar syrup supply (N=10); Group 2: regular honeydew harvest and sugar syrup supply (N=10); Group 3: regular honeydew harvest and adding of brood (N=10); Group 4: regular honeydew harvest (N=10); Group 5: only one harvest of honeydew once the study had finished (N=8). The colonies from groups 1 and 3 produced the biggest amount of honeydew honey, averaging 32.0 and 28.6kg, respectively. The physicochemical analysis of honeydew honey showed characteristics of this product such as high electrical conductivity (0.98-1.14 mS/cm), diastase activity (>50%) and color (71-83 mm Pfund). This study provides the basis of a colony handling that allows beekeepers to obtain important harvests of a honeydew honey not yet known in the international market.En Uruguay, las excreciones de los flátidos Epormenis cestri, cuando se localizan en árboles de sarandí colo-rado (Sebastiania schottiana), causan mortalidad masiva de larvas jóvenes de abejas melíferas, fenómeno que los apicultores denominan «mal del río». Frecuentemente se observa una fuerte entrada de mielatos en las colonias afectadas a pesar del despoblamiento de abejas generado por la falta de reemplazo. El objetivo de este estudio fue determinar un manejo de las colonias que permita obtener mielatos. Se transportaron 48 colo-nias a un colmenar afectado por el mal del río y se dividieron en 5 grupos de acuerdo con el tratamiento: Grupo 1: cosecha regular de mielatos, adición de cría y suministro de jarabe de azúcar (N = 10); Grupo 2: cosecha regular de mielatos y suministro de jarabe de azúcar (N = 10); Grupo 3: cosecha regular de mielatos y adición de cría (N = 10); Grupo 4: cosecha regular de mielatos (N = 10); Grupo 5: solo una cosecha de mielatos una vez finalizadas las secreciones de E. cestri (N = 8). Las colonias de los grupos 1 y 3 produjeron la mayor cantidad de mielatos, con un promedio de 32,0 y 28,6 kg, respectivamente. El análisis fisicoquímico de los mielatos mostró características de este producto, como alta conductividad eléctrica (0.98-1.14 mS / cm), activi-dad diastasa (> 50%) y color (71-83 mm Pfund). Este estudio proporciona la base de un manejo de las colonias que permite a los apicultores obtener cosechas importantes de un mielato aún no conocido en el mercado internacional

Nutrient limitation can explain a rapid transition to synchrony in an upwelling-driven diatom community

Identifying the mechanisms controlling the temporal dynamics of ecological communities is key to understand their vulnerability to natural and anthropogenic impacts and to identify early warnings of critical transitions. At community level, inter-specific synchrony is an important indicator of ecosystem stability and variation in function. Using wavelet analysis on time-series of abundance of 12 dominant diatom species, sampled monthly (1994-2009) in a coastal upwelling embayment at the northern limit of the Canary Current Upwelling System, we find a sudden onset of synchrony between 1998 and 2002, concomitant with an increase in the amplitude of the upwelling index at different temporal scales. To better understand the underlying mechanism that could generate this sudden onset of synchrony among competitors, we analyzed a general model of competition between two species for two essential nutrients (e.g., nitrogen and silicate). We incorporate environmental variation by varying the concentration of one of the essential nutrients entering the system. Increase in the amplitude of environmental variation always leads to greater synchrony among competitors. This occurs because the system shifts from a state in which species are limited by different nutrients to one where species are often limited by the same nutrient. We show that the transition from asynchronous to synchronous dynamics can occur suddenly as the amplitude of environmental variation increases. While it is not possible to rule out alternative mechanisms, our model demonstrates that sudden changes in the extent of synchronization should be a common feature when species compete for essential nutrients in variable environments.En prensa3,38