Phytoplankton and primary production

There is high confidence that the anthropogenic increase of atmospheric greenhouse gases (GHGs) is causing modifications in the Earth's climate. Coastal waterbodies such as estuaries, bays and lagoons are among those most affected by the ongoing changes in climate. Being located at the land-sea interface, such waterbodies are subjected to the combined changes in the physical-chemical processes of atmosphere, upstream land and coastal waters. Particularly, climate change is expected to alter phytoplankton communities by changing their environmental drivers (especially climate-related), thus exacerbating the symptoms of eutrophication events, such as hypoxia, harmful algal blooms (HAB) and loss of habitat. A better understanding of the links between climate related drivers and phytoplankton is therefore necessary for projecting climate change impacts on aquatic ecosystems. Here we present the case study of the Zero river basin in Italy, one of the main contributors of freshwater and nutrient to the salt-marsh Palude di Cona, a coastal waterbody belonging to the lagoon of Venice. To project the impacts of climate change on freshwater inputs, nutrient loadings and their effects on the phytoplankton community of the receiving waterbody, we formulated and applied an integrated modelling approach made of: climate simulations derived by coupling a General Circulation Model (GCM) and a Regional Climate Model (RCM) under alternative emission scenarios, the hydrological model Soil and Water Assessment Tool (SWAT) and the ecological model AQUATOX. Climate projections point out an increase of precipitations in the winter period and a decrease in the summer months, while temperature shows a significant increase over the whole year. Water discharge and nutrient loads simulated by SWAT show a tendency to increase (decrease) in the winter (summer) period. AQUATOX projects changes in the concentration of nutrients in the salt-marsh Palude di Cona, and variations in the biomass and species of the phytoplankton community.

Some sources and biogeochemical processes of the nitrogen cycle were studied to determine the existing balance of this nutrient in the first 300 m of the water column of Alfonso Basin. The seasonal variability of microbial planktonic abundances were described, as well as, their association to the carbon assimilation (AC) levels, organic production and physicochemical variables. The dynamics of the thermohaline, during the process of winter mixing and the elevation of deep water due to pumping (April to July) of a cyclonic eddy caused a prolonged period of high levels of oxidized nutrients, which resulted in high planktonic abundances. However, this increase generally was restricted to the uppermost layer, where according to canonical correspondence analysis, the planktonic components were positively associated to dissolved oxygen and temperature. Estimated annual AC values in the euphotic zone (Zeu) were substantially higher (6741 kg C ha-1 yr-1) compared to previous reports for the Gulf of California, where the fraction between 0.4 to 20 μm had a contribution of ~ 63 %. At 150 m depth, AC rates fluctuated between 0.26-3.2 mg C m-3 h-1 which were attributed to both the activity of chemolithotrophic organisms, as well as phytoplankton groups adapted to very low irradiances, which were consistent with their densities distribution. Among the evaluated nitrogen inputs, vertical transport of nitrate due to cyclonic eddy was the most important for the Zeu (63 kg N ha-1 yr-1), followed by biological N2 fixation (FBN) and atmospheric deposition of gas + aerosol (26 and 7 kg N ha-1 yr-1, respectively). FBN registered large values compared to previous measurements for the Gulf of California and other coastal and oceanic systems, as well as detection levels at 150 m depth under high concentration of dissolved inorganic nitrogen suggesting a positive feedback due low nitrogen to phosphorus ratio. Between 100-300 m, nitrogen losses by N2 production via denitrification and ANAMMOX were low compared to observed rates in sites of the Pacific oxygen minimum zones. Likewise, ANAMMOX was predominant (79%) relative to denitrification. This characteristic was attributed mainly to the physiological inhibition by relatively high dissolved oxygen content at the site (0.15-1.72 ml O2 l-1), the presence of denitrification inhibitors (e.g. H2S and HS-), and/or unevaluated production and consumption of intermediate forms such as N2O. Nitrification in the aphotic layer as a mechanism for regeneration of dissolved inorganic forms, showed a high contribution to the mobilization of nitrogen (251 kg N Ha-1 yr-1) compared to other physiological rates, and integrated values were similar to previous estimates of nitrification for the Zeu of the Gulf of California and Mexican Pacific Ocean. However, the temporal variability of these rates was strongly associated with the availability of substrates (e.g. nitrite and ammonium) during periods of high biological production. Indirect calculations of assimilation of dissolved inorganic nitrogen from AC rates corroborate the prevalence of this activity in the mobilization of nitrogen in the Zeu (949 kg N ha-1 yr-1). Indirect calculations of dissolved inorganic nitrogen assimilation through AC rates corroborate the predominance of this activity to the mobilization of nitrogen in the euphotic layer (949 kg N Ha-1 yr-1). The nitrogen budget indicated that external inputs and nitrification in the first 300 m depth barely contributed with 53% of the requirement of this element for phytoplankton growth organisms. This suggests the presence of alternative routes or reservoirs associated with the dissolved organic fraction as a nitrogen supply mechanism for mixotrophic populations. Clearly the results provided by this study indicate a highly dynamic cycle of nitrogen and its potential for positive feedback nitrogen inventory to mitigate the N:P unbalance prevailing in Cuenca Alfonso.

"From 1995 to 2000, daily integrated, water column phytoplankton primary production was estimated on a monthly basis at the CaTS (Caribbean Time-Series Station, 17°36’N, 67°00’W) using available algorithms that relate phytoplankton photosynthetic pigment biomass and available photosynthetic radiation (PAR). Average daily integrated primary production was between 132 and 750 mg C m-2 d-1. Annual production was 149 gC m-2 yr-1 and showed maxima in April, July, October and November. SeaWiFS derived chlorophyll-a concentrations for the Northeastern Caribbean Sea followed the same pattern.  Increases in primary production were associated to large PBS (or PBm), alphaB and ā*ph values during maximum influence of Amazon and Orinoco River plume waters. High vertical diffusivity values, kd > 6 X 10-3 m-2s-1, were measured between SEP-DEC 1997 and MAY-OCT 2000 in oceanic waters of the Mona Passage. These elevated diffusivities are associated with the presence of locally generated internal waves of semidiurnal frequency, with a reduction of the Richardson number at the base of the pycnocline, and with increased coastal seiches activity over the southwest coast of Puerto Rico. The patterns of activity are strictly correlated with the lunar cycle and with changes in the stratification of the Caribbean Surface Water (CSW). Increases in the stratification of the water column are due to the influence of the Amazon and Orinoco Rivers. Under the proper astronomical forcing and vertical stratification conditions energy from the barotropic tide at or near the shelf break is transferred offshore towards the generation of internal tides and shoreward into the platform waters consequently increasing the coastal seiche activity. Internal tides of near semidiurnal frequencies were observed in the euphotic zone. The development of K-H instabilities during the breaking of the internal tide can explain the formation of high diffusivity patches. Inside the patches (kd > 0.004 m2 s-1) increments in primary productivity of the order of 0.05 mg C m-3 h-1 were measured. The patches generated a NO3 flux equal to 1.058 x 10-4 mmol m-2 s-1 and can sustain a new production equal to 724 mg C m-2 d-1 or 264 g C m-2 yr-1.

Resumen

La integración vertical a lo largo de todo el día, de la productividad primaria del fitoplancton se estimó mensualmente entre el 1995 y el 2000 en la estación serial del programa CaTS (Caribbean Time-Series Station, 17° 36’ N, 67° 00’ 0) usando los algoritmos disponibles que relacionan la biomasa fotosintética del fitoplancton y la irradianza disponible para fotosíntesis (PAR).  La producción integrada promedio osciló entre 132 y 750 mg C m-2d-1.  La producción anual es alrededor de 149 g C m-2 año-1 y muestra una distribución con máximos cerca de abril, julio, octubre y noviembre.  Concentraciones de clorofila-a del Noreste del Mar Caribe determinadas por el teledetector satelital SeaWiFS imitan el mismo patrón.  Aumentos en productividad primaria se asocian a valores altos de PBS (ó  PBm), alfaB y ā*ph durante las épocas de mayor influencia de las aguas dispersas del Río Amazonas y Orinoco.  Valores altos de difusividad vertical, kd > 6 X 10-3 m2s-1, se registraron entre septiembre y diciembre del 1997 y mayo y octubre del 2000 en aguas oceánicas del Canal de Mona.  Estas difusividades altas están asociadas a la presencia de ondas internas de frecuencia semidiurna que se generan localmente en nuestras aguas, a la reducción en el número de Richardson y los aumentos en la actividad de seiches en la costa suroeste de Puerto Rico.  Los patrones de alta actividad están estrictamente correlacionados con el ciclo lunar y con cambios en la estratificación del agua superficial del Caribe.  Aumentos en la estratificación en la columna de agua se deben a la influencia del Río Amazonas y Orinoco.  Bajo las condiciones astronómicas y de estratificación apropiadas, la energía de la marea barotrópica en y cerca del veril es transferida fuera de la costa para la generación de la marea interna y hacia las aguas de la  plataforma insular provocando aumentos en la actividad de seiches costeros.  El desarrollo de la inestabilidad K-H durante el rompimiento de la marea interna puede explicar la formación de parches de alta difusividad.  Dentro de los parches (kd > 0.004 m2 s-1)  se observaron aumentos en producción primaria del orden de 0.05 mg C m-3 h-1.  Los parches generaron un flujo de NO3 igual a 1.058 x 10-4 mmol m-2 s-1 y que puede sostener una producción nueva de  724 mg C m-2 d-1 ó 264 g C m-2 año-1."

Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper, we present an overview of current trends and future directions in aquatic plant research in the early twenty first century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrates the global relevance of aquatic plant research in the early twenty first century but also the many challenges that this burgeoning scientific discipline must address.

Sedimentation is a major process for removal of particulate material from the water column and important determinant accounting for the stability of aquatic ecosystems. Gross sedimentation rates (GSR) in Lake Kinneret (Israel), regularly monitored from 1999 up-to-date with sedimentation traps, showed salient temporal and spatial variability. In the lake center, the annual mean GSR ranged from 1.9 to 6.0 g m-2 d-1. The accumulation rate of sediments at the lake centrum during the study averaged from 2.6 to 4.3 mm yr-1, in agreement with values obtained by sediment core dating. Organic matter (OM) content comprised 33-42% of the sinking particulate mater in sediment traps located in the lake centre and was 1.5-2 times lesser in peripheral stations. The highest seasonal values of OM content in traps were associated with collapse of algal blooms. Algae and their debris are the main component of OM and their fate in the water column can be well traced by photosynthetic pigments. Chlorophyte signature pigments display much lower degradability in the water column than those of diatoms and dinoflagellates and leave a relatively persistent residue in the buried sediments. Despite large variation in algal community composition, the ratio of OM sedimentation flux to primary production (i.e., the export ratio) alters only slightly throughout the stratified period. Approximately 20% of the OM supplied to the lake by primary production founds its way to the traps. A large decline of water level in recent years affected the processes of particle resuspension and offshore translocation, which caused prominent site-specific impacts on the sedimentation regime. We argue that changes in sedimentation rates observed in the lake are related to fluctuations of loads from the watershed and prominent water level fluctuations.

Bio-optical measurements off Visakhapatnam Coastal Waters (VCW) East
Coast of India along Bay of Bengal (BoB) were carried out over several field
campaigns in 2009 and 2010. These campaigns were performed over different
periods of the year in order to obtain separate samplings of the system’s
seasonal cycles. The goal of these field campaigns is to arrive at a consistent
remote sensing algorithm for the estimation of the chlorophyll concentration in
the Case-2 waters (where optical properties are influenced not just by
phytoplankton and co varying constituents, but also by non-co varying
constituents such as gelbstoff and suspended sediments), of the VCW. The
optical components of these missions included measurements of inherent and
apparent in-situ optical parameters. Preliminary results using profiling
radiometer were carried out for the characterization and classification of the
Visakhapatnam coastal waters. In this presentation focus will be given on the
observation and analysis of variations in the optical constituents and
reflectance characteristics.

The northwestern coast of the Iberian Peninsula is characterized by a high primary production mainly supported
by coastal upwelling, creating an extraordinary commercial interest for fisheries and aquaculture. Considering
chlorophyll-a (Chl-a) as an indicator of primary production, its spatio-temporal variability was researched in
this study in the surface water of this upwelling region from 1998 to 2007. Satellite derived Chl-a, Sea Surface
Temperature (SST) and Ekman transport data as well as the inflow of the main rivers discharging into the
study area were used to investigate the origin of the Chl-a concentration. Empirical Orthogonal Function (EOF)
analysis of weekly Chl-a images was performed, as well as correlation analysis between Chl-a concentration,
Ekman transport and river discharge. EOF results suggest that the highest Chl-a concentration occurs near the
coast up to 60 km offshore. The interannual variability of Chl-a, SST and Ekman transport was also studied considering
summer andwintermonths. Generally, 2005, 2006 and 2007were themost productive years during the
summer months with high Chl-a concentrations along the coast associated to the strong upwelling conditions
observed. Otherwise, 1998 seemed to be themost productive year duringwinter. The absence of upwelling favorable
conditions together with localized lowSST and considerable discharges, suggests that the high Chl-a concentrations
observed during this period are mainly due to the entrance of nutrients through river runoff. However, in
winter, high concentrations of colored dissolved organic matter (CDOM), associatedwith river runoff, are present
in the ocean surface, leading to an erroneous strong signal of the satellite. During winter correlations of 0.58 and
0.49 were found between Chl-a concentration and Douro and Minho discharges, respectively, evidencing that
high Chl-a concentration was related with river runoff. Otherwise, during summer, Chl-a and Ekman transport
exhibited a correlation of −0.38 indicating that high Chl-a is associated to upwelling events. In summary, it
was found that the spatio-temporal variability of Chl-a along the northwestern coast of Iberian Peninsula exhibited
the clear influence of upwelling events during summer. Conversely, the variability during winterwasmainly
due to entrance of nutrients through the rivers discharge which flow into the area.

Particle fluxes at the Cape Verde Ocean Observa- tory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic par- ticle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (mini- mum concentration below 2 μmol kg−1 at 40 m depth) anti- cyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m−2 d−1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ∼ 15 and 13.3 mg m−2 d−1, respectively, were ob- served in February–March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic car- bon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso- pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic car- bon in the deep trap samples might be explained by parti- cle focusing processes within the deeper part of the eddy. Molar C : N ratios of organic matter during the ACME pas- sage were around 18 and 25 for the upper and lower trap
June 2016
samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The δ15N record showed a de- crease from 5.21 to 3.11 ‰ from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in Febru- ary/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid rem- ineralisation of sinking organic-rich particles could have con- tributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from di- atoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indica- tive of the presence of anammox (anaerobic ammonia ox- idation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isore- nieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detec- tion thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below.

To study the ecology of calcareous dinoflagellates we examined the impact of the SW and NE monsoons on cyst formation using sediment trap material, collected at 1032 m water depth, off Somalia from June 1992 to February 1993. The results do not confirm the relationship between cyst production and lower nutrient concentrations, as highest cyst fluxes were recorded during late SW monsoon under the relatively nutrient-rich and less agitated conditions of mature upwelled water. Lowest cyst fluxes were found under strongly stratified, nutrient-depleted surface waters during the inter-monsoon. Although all of the studied species seem to prefer a stratified water column, an elevated concentration of nutrients appears to be necessary to maintain high cyst production. Comparison of the mean cyst flux to the sediment trap with that into the underlying surface sediments reveals a loss of 81-96%, which can be attributed to calcite dissolution. The relatively small spheres of Thoracosphaera heimii are affected more than the cysts of the other species.

Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2 µmol kg<sup>−1</sup> at 40 m depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m<sup>−2</sup> d<sup>−1</sup>, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ∼ 15 and 13.3 mg m<sup>−2</sup> d<sup>−1</sup>, respectively, were observed in February–March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated wi...

The Southern Ocean (SO), an area highly sensitive to climate change, is currently experiencing rapid warming and freshening. Such drastic physical changes might significantly alter the SO's biological pump. For more accurate predictions of the possible evolution of this pump, a better understanding of the environmental factors controlling SO phytoplankton dynamics is needed. Here we present a satellite-based study deciphering the complex environmental control of phytoplankton biomass (PB) and phenology (PH; timing and magnitude of phytoplankton blooms) in the SO. We reveal that PH and PB are mostly organized in the SO at two scales: a large latitudinal scale and a regional scale. Latitudinally, a clear gradient in the timing of bloom occurrence appears tightly linked to the seasonal cycle in irradiance, with some exceptions in specific light-limited regimes (i.e., well-mixed areas). Superimposed on this latitudinal scale, zonal asymmetries, up to 3 orders of magnitude, in regional-scale PB are mainly driven by local advective and iron supply processes. These findings provide a global understanding of PB and PH in the SO, which is of fundamental interest for identifying and explaining ongoing changes as well as predicting future changes in the SO biological pump.

Dissolved iodine speciation in surface seawater at a coastal Antarctic site has been studied over a period spanning three austral summers. The sampling site is biologically productive, with a summertime algal
bloom accompanying strong seasonal variations in physical and chemical parameters. The results suggest a seasonal cycle in which iodide concentrations increase and iodate concentrations decrease during the summer, though the magnitude of these changes appears to be subject to considerable inter annual variability. Iodide concentrations were typically very low, with minimum values of 10 to 20 nM at the beginning and end of the ice-free summer periods and summertime maxima of about 35 nM in 2005/06, 150 nM in 2006/07 and 82 nM in 2007/08. More detailed observations of iodide and iodate concentrations made during summer 2005/06 demonstrated that the accumulation of iodide was strongly correlated with integrated biological primary productivity, with an implied I/C assimilation ratio of 1.6×10−4.

In estuaries, the sources of organic matter, its composition, and its functional role in the coastal ecosystem food web are all influenced by dominant estuarine processes. We investigated seasonal variations in the quantity and composition of dissolved inorganic nutrients, suspended particulate matter (SPM), and phytoplankton across a low-turbidity estuarine-coastal continuum in Gwangyang Bay, South Korea. The narrow estuarine channel has a sharp salinity gradient (from 0 to around 30) and low SPM concentrations (<20 mg L −1). The channel carries river discharge, with a large quantity of nutrients (NO 3 and SiO 2), into the bay. The especially low SPM concentrations in the estuary (range: 2.0-29.1 mg L −1), and generous nutrient source, create an exceptionally low-turbidity condition in the water column and high primary productivity with no conspicuous spatial or seasonal trends. Gradually increasing δ 13 C values, low POC:Chla (<200), and low molar C:N (4-8) in the SPM, together with higher Chla concentrations at low SPM locations along the longitudinal transect, suggest that local production of phytoplankton has a strong influence on the distributional patterns of particulate organic matter. Short water-residence times, within the bay system, impede the accumulation of diverse-origin organic matter. The community composition of phytoplankton, distinguished by their size group, also plays a role in characterizing SPM quantity and composition. The results indicate that autochthonous pelagic production governs biogeochemical features in the low-turbidity estuarine embayment, contrasting with a prevalence of allochthonous organic matter, and its active processing, in highly turbid and/or longer residence-time systems.

Phytoplankton are the base of the Antarctic food web, sustain the wealth and diversity of life for which Antarctica is renowned, and play a critical role in biogeochemical cycles that mediate global climate. Over the vast expanse of the Southern Ocean (SO), the climate is variously predicted to experience increased warming, strengthening wind, acidification, shallowing mixed layer depths, increased light (and UV), changes in upwelling and nutrient replenishment, declining sea ice, reduced salinity, and the southward migration of ocean fronts. These changes are expected to alter the structure and function of phytoplankton communities in the SO. The diverse environments contained within the vast expanse of the SO will be impacted differently by climate change; causing the identity and the magnitude of environmental factors driving biotic change to vary within and among bioregions. Predicting the net effect of multiple climate-induced stressors over a range of environments is complex. Yet understanding the response of SO phytoplankton to climate change is vital if we are to predict the future state/s of the ecosystem, estimate the impacts on fisheries and endangered species, and accurately predict the effects of physical and biotic change in the SO on global climate. This review looks at the major environmental factors that define the structure and function of phytoplankton communities in the SO, examines the forecast changes in the SO environment, predicts the likely effect of these changes on phytoplankton, and considers the ramifications for trophodynamics and feedbacks to global climate change. Predictions strongly suggest that all regions of the SO will experience changes in phytoplankton productivity and community composition with climate change. The nature, and even the sign, of these changes varies within and among regions and will depend upon the magnitude and sequence in which these environmental changes are imposed. It is likely that predicted changes to phytoplankton communities will affect SO biogeochemistry, carbon export, and nutrition for higher trophic levels.

Phytoplankton community and its relationships with environmental factors were investigated in the surface waters from Malacca Strait (MS) to the connected South China Sea (SCS) in May of 2011. Salinity was significantly lower in MS. No significant spatial variations were found for most of the nutrients (except silicate) between MS and connected SCS. Silicate gradually increased from Andaman Sea to the southern MS, and then declined from the southern MS to SCS. Phytoplankton mainly belonged to diatoms and dinoflagellates. The dominant species of diatoms were Skeletonema, Pseudo-nitzschia, Navicula, and Thalassionema. Dinoflagellates were mainly presented by Prorocentrum, Scrippsiella and nano-dinoflagellate. Diatoms contributed to most of the phytoplankton abundance in the middle and south MS. However, dinoflagellates predominated in the side of Andaman Sea or SCS. Chlorophyll a concentration and phytoplankton abundance were the highest in the shallowest sampling station of middle MS. CCA results suggested that salinity and silicate were the most important environmental variables influencing the phytoplankton spatial variation. The prosperity of diatoms in the middle MS may be promoted mainly by the sufficient nutrients brought by the deep-water intrusion or river inflow. Silicate can be considered as an indicator for high phytoplankton biomass, but could not be the limited factor for the phytoplankton growth in MS.

Eutrophication is an increasing global threat to freshwater ecosystems. East Africa's Lake Victoria has suffered from severe eutrophication in the past decades which is partly responsible for the dramatic decline in haplochromine cichlid species diversity. However, some zooplanktivorous and detri-tivorous haplochromine species recovered and shifted their diet towards macro invertebrates and fish. We used four formalin preserved cichlid species caught over the past 35 years to investigate whether stable isotopes of these fish are reflecting the dietary changes, habitat differences and if these isotopes can be used as indicators of eutrophication. We found that d 15 N signatures mainly reflected dietary shifts to larger prey in all four haplochromine species. Shifts in d 13 C signatures likely represented habitat differences and dietary changes. In addition, a shift to remarkably heavy d 13 C signatures in 2011 was found for all four species which might infer increased primary production and thus eutrophication although more research is needed to confirm this hypothesis. The observed temporal changes confirm previous findings that preserved specimens can be used to trace historical changes in fish ecology and the aquatic environment. This highlights the need for continued sampling as this information could be of essence for reconstructing and predicting the effects of environmental changes.

by C. Rodríguez-Benito, J. Pérez-Marrero, L. Maroto y O. Llinás

Se ha calculado la producción primaria integrada en la capa fótica de las aguas del entorno de las Islas Canarias a través de imágenes de color del océano.
El procedimiento consistió en la aplicación de un algoritmo analítico implementado, basado en el modelo de Bedford , según el cual se establece la relación de la biomasa fitoplanctónica, la capacidad
fotosintética de los organismos, la cantidad de luz disponible y la cantidad de carbono incorporada en mgC·m-3·d-1. La implementación concluyo en el desarrollo de la herramienta OPPP. Los trabajos de validación y calibración de la misma se llevaron a cabo con datos históricos del CZCS y datos in situ
contemporáneos de este sensor. En este trabajo se presentan los resultados obtenidos cuando se utilizan nuevos datos de color del océano procedentes del sensor SeaWiFS.

The fertilizing potential of atmospheric deposition on ocean production in the Mediterranean is a matter of debate. In this study, eight years (from 2000 to 2007) of weekly chlorophyll concentration data derived from SeaWiFS satellite observations and dust deposition data provided by the BSC-DREAM8b model are investigated in a basin-wide scale in the Mediterranean Sea to describe the geographical distribution and dynamics of both variables and to find potential relationships between them.
In all analyses the largest positive cross correlation values are found with a time lag of 0 8-d periods. The coupling between annual cycles of chlorophyll and dust deposition may on average explain an 11.5% in chlorophyll variation in a large part of the Mediterranean. The Eastern Mediterranean shows the largest annual correlations, while the responsiveness to large events is small. The contrary is true for the Western and Northwestern Mediterranean where, if anything, only large events may add to the chlorophyll variability. The Central Mediterranean shows the highest responsiveness of chlorophyll to mineral dust deposition with annual contributions from seasonal variability as well as stimulations owing to large events.
These results highlight the importance of dust deposition from African and Middle East origin in the potential stimulation of phytoplankton production in the nutrient depleted surface layers of the Mediterranean Sea.

The composition of particulate organic matter (OM) and photosynthetic pigments (signature of specific algal groups) in sedimentation trap were studied in a deep lake. The export of particulate OM and algal material from the upper productive stratum reflects the seasonal succession of algal community and also depend on physical conditions in the lake. The downward fluxes of different pigments depend on their biodegradability. Despite large variation in algal community composition, the ratio of OM sedimentation flux to primary production (the Export Ratio) alters only slightly throughout the stratified period.

A revised estimate of the relationship between the maximum growth rate (μmax, d−1) of Emiliania huxleyi and temperature (T, °C) was made using quantile regression and literature data from culture experiments (n = 1415). For modeling E. huxleyi bloom formation and coccolithophore functional group growth rate, this relationship is commonly assumed to follow an exponential relationship, as is the case for photosynthetic algal species in general. However, data specific to E. huxleyi show that this relationship is better described by a power function. Direct comparison with growth rate–temperature relationships used to model E. huxleyi from the literature shows that they overestimate growth rate by up to 250% over a wide range of temperatures. It is recommended that the revised relationship of μmax = 0.1419T0.8151 be used in future models incorporating temperature-dependent maximum growth rate estimates of E. huxleyi and of coccolithophores as a functional group.

There is high confidence that the anthropogenic increase of atmospheric greenhouse gases (GHGs) is causing modifications in the Earth&#39;s climate. Coastal waterbodies such as estuaries, bays and lagoons are among those most affected by the ongoing changes in climate. Being located at the land-sea interface, such waterbodies are subjected to the combined changes in the physical-chemical processes of atmosphere, upstream land and coastal waters. Particularly, climate change is expected to alter phytoplankton communities by changing their environmental drivers (especially climate-related), thus exacerbating the symptoms of eutrophication events, such as hypoxia, harmful algal blooms (HAB) and loss of habitat. A better understanding of the links between climate-related drivers and phytoplankton is therefore necessary for projecting climate change impacts on aquatic ecosystems. Here we present the case study of the Zero river basin in Italy, one of the main contributors of freshwater and nutrient to the salt-marsh Palude di Cona, a coastal waterbody belonging to the lagoon of Venice. To project the impacts of climate change on freshwater inputs, nutrient loadings and their effects on the phytoplankton community of the receiving waterbody, we formulated and applied an integrated modelling approach made of: climate simulations derived by coupling a General Circulation Model (GCM) and a Regional Climate Model (RCM) under alternative emission scenarios, the hydrological model Soil and Water Assessment Tool (SWAT) and the ecological model AQUATOX. Climate projections point out an increase of precipitations in the winter period and a decrease in the summer months, while temperature shows a significant increase over the whole year. Water discharge and nutrient loads simulated by SWAT show a tendency to increase (decrease) in the winter (summer) period. AQUATOX projects changes in the concentration of nutrients in the salt-marsh Palude di Cona, and variations in the biomass and species of the phytoplankton community.

High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO&lt;sub&gt;2&lt;/sub&gt; levels ranging from ambient (343&thinsp;μatm) to 1641&thinsp;μatm in six 650&thinsp;l minicosms. Productivity assays were performed to identify whether a CO&lt;sub&gt;2&lt;/sub&gt; threshold existed that led to a decline in primary productivity, bacterial productivity, and the accumulation of Chlorophyll &lt;i&gt;a&lt;/i&gt; (Chl &lt;i&gt;a&lt;/i&gt;) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton co...