Antonio Tovar-Sánchez

The impact of surface-adsorbed phosphorus on phytoplankton Redfield stoichiometry

The Redfield ratio of 106 carbon:16 nitrogen:1 phosphorus in marine phytoplankton is one of the foundations of ocean biogeochemistry, with applications in algal physiology, palaeoclimatology and global climate change. However, this ratio varies substantially in response to changes in algal nutrient status and taxonomic affiliation. Here we report that Redfield ratios are also strongly affected by partitioning into surface-adsorbed and intracellular phosphorus pools. The C:N:surface-adsorbed P (80–105 C:15–18 N:1 P) and total (71–80 C:13–14 N:1 P) ratios in natural populations and cultures of Trichodesmium were close to Redfield values and not significantly different from each other. In contrast, intracellular ratios consistently exceeded the Redfield ratio (316–434 C:59–83 N:1 intracellular P). These high intracellular ratios were associated with reduced N2 fixation rates, suggestive of phosphorus deficiency. Other algal species also have substantial surface-adsorbed phosphorus pools, suggesting that our Trichodesmium results are generally applicable to all phytoplankton. Measurements of the distinct phytoplankton phosphorus pools may be required to assess nutrient limitation accurately from elemental composition. Deviations from Redfield stoichiometry may be attributable to surface adsorption of phosphorus rather than to biological processes, and this scavenging could affect the interpretation of marine nutrient inventories and ecosystem models.

A trace metal clean reagent to remove surface-bound iron from marine phytoplankton

Many recent studies have investigated Fe biogeochemical cycling, chemical speciation, and limitation of phytoplankton growth in the ocean. In current models of marine iron biogeochemistry, however, two critical parameters remain uncertain. These are the partitioning of particulate iron into scavenged and interior pools, and the iron quotas (Fe/C ratios) of natural plankton communities. These values have not been measured in natural samples, because the only reagent that is available to remove surface adsorbed Fe from cells and other particles (Ti(III) citrate/EDTA [Limnol Oceanogr 34 (1989) 1113]) contains substantial levels of contaminating Fe, and is therefore useful only for Fe radiotracer experiments. We developed a new reagent that differentiates between intra- and surface adsorbed Fe pools in marine phytoplankton as effectively as the Ti wash, but that is also trace metal clean, chemically stable, and harmless to cells. This reagent uses oxalate as a reductant to remove surface adsorbed Fe from phytoplankton cells and other particles. A simple cleaning protocol reduces Fe concentrations in the oxalate solution to levels suitable for trace metal clean field measurements. The oxalate reagent was used to measure scavenged and interior Fe pools in suspended particles collected at four stations in the Southern Ocean. Sixteen percent to eighty-six percent of the total Fe associated with these samples was found to be surface-adsorbed. The oxalate reagent provides a new tool to accurately measure the physical partitioning of Fe in marine particles and could be used along with appropriate corrections for lithogenic Fe to estimate the intracellular Fe quotas of natural plankton communities.

Aerosol inputs enhance new production in the subtropical northeast Atlantic

Received 21 November 2005; revised 13 May 2006; accepted 30 June 2006; published 10 November 2006. [1] Atmospheric deposition is an important source of limiting nutrients to the ocean, potentially stimulating oceanic biota. Atmospheric inputs can also deliver important amounts of organic matter, which may fuel heterotrophic activity in the ocean. The effect of atmospheric dry aerosol deposition on the metabolic balance and net production of planktonic communities remains unresolved. Here we report high inputs of aerosol-bound N, Si, P, Fe and organic C to the subtropical NE Atlantic and experimentally demonstrate these inputs to stimulate autotrophic abundance and metabolism far beyond the modest stimulation of heterotrophic processes, thereby enhancing new production. Aerosol dry deposition was threefold to tenfold higher in the coastal ocean than in the open ocean, and supplied high average (±SE) inputs of organic C (980 ± 220 mmol C m 2 d 1 ), total N (280 ± 70 mmol N m 2 d 1 ), Si (211 ± 39 mmol Si m 2 d 1 ), and labile Fe (1.01 ± 0.19 mmol Fe m 2 d 1 ), but low amounts of total P (8 ± 1.6 mmol P m 2 d 1 ) to the region during the study. Experimental aerosol inputs to oceanic planktonic communities from the studied area resulted, at the highest doses applied, in a sharp increase in phytoplankton biomass (sevenfold) and production (tenfold) within 4 days, with the community shifting from a dominance of picocyanobacteria to one of diatoms. In contrast, bacterial abundance and production showed little response. Primary production showed a much greater increase in response to aerosol inputs than community respiration did, so that the P/R ratio increased from around 0.95 in the ambient waters, where communities were close to metabolic balance, to 3.3 at the highest nutrient inputs, indicative of a high excess production and a potential for substantial net CO2 removal by the community in response to aerosol inputs. These results showed that aerosol inputs are major vectors of nutrient and carbon inputs, which can, during high depositional events, enhance new production in the NE subtropical Atlantic Ocean.

Sunscreen Products as Emerging Pollutants to Coastal Waters

A growing awareness of the risks associated with skin exposure to ultraviolet (UV) radiation over the past decades has led to increased use of sunscreen cosmetic products leading the introduction of new chemical compounds in the marine environment. Although coastal tourism and recreation are the largest and most rapidly growing activities in the world, the evaluation of sunscreen as source of chemicals to the coastal marine system has not been addressed. Concentrations of chemical UV filters included in the formulation of sunscreens, such as benzophehone 3 (BZ-3), 4-methylbenzylidene camphor (4-MBC), TiO2 and ZnO, are detected in nearshore waters with variable concentrations along the day and mainly concentrated in the surface microlayer (i.e. 53.6–577.5 ng L-1 BZ-3; 51.4–113.4 ng L-1 4-MBC; 6.9–37.6 µg L-1 Ti; 1.0–3.3 µg L-1 Zn). The presence of these compounds in seawater suggests relevant effects on phytoplankton. Indeed, we provide evidences of the negative effect of sunblocks on the growth of the commonly found marine diatom Chaetoceros gracilis (mean EC50 = 125±71 mg L-1). Dissolution of sunscreens in seawater also releases inorganic nutrients (N, P and Si forms) that can fuel algal growth. In particular, PO4 3− is released by these products in notable amounts (up to 17 µmol PO4 3− g−1). We conservatively estimate an increase of up to 100% background PO4 3− concentrations (0.12 µmol L-1 over a background level of 0.06 µmol L-1) in nearshore waters during low water renewal conditions in a populated beach in Majorca island. Our results show that sunscreen products are a significant source of organic and inorganic chemicals that reach the sea with potential ecological consequences on the coastal marine ecosystem.

The significance of the episodic nature of atmospheric deposition to Low Nutrient Low Chlorophyll regions

In the vast Low Nutrient Low-Chlorophyll (LNLC) Ocean, the vertical nutrient supply from the subsurface to the sunlit surface waters is low, and atmospheric contribution of nutrients may be one order of magnitude greater over short timescales. The short turnover time of atmospheric Fe and N supply (<1 month for nitrate) further supports deposition being an important source of nutrients in LNLC regions. Yet, the extent to which atmospheric inputs are impacting biological activity and modifying the carbon balance in oligotrophic environments has not been constrained. Here, we quantify and compare the biogeochemical impacts of atmospheric deposition in LNLC regions using both a compilation of experimental data and model outputs. A metadata-analysis of recently conducted field and laboratory bioassay experiments reveals complex responses, and the overall impact is not a simple “fertilization effect of increasing phytoplankton biomass” as observed in HNLC regions. Although phytoplankton growth may be enhanced, increases in bacterial activity and respiration result in weakening of biological carbon sequestration. The application of models using climatological or time-averaged non-synoptic deposition rates produced responses that were generally much lower than observed in the bioassay experiments. We demonstrate that experimental data and model outputs show better agreement on short timescale (days to weeks) when strong synoptic pulse of aerosols deposition, similar in magnitude to those observed in the field and introduced in bioassay experiments, is superimposed over the mean atmospheric deposition fields. These results suggest that atmospheric impacts in LNLC regions have been underestimated by models, at least at daily to weekly timescales, as they typically overlook large synoptic variations in atmospheric deposition and associated nutrient and particle inputs. Inclusion of the large synoptic variability of atmospheric input, and improved representation and parameterization of key processes that respond to atmospheric deposition, is required to better constrain impacts in ocean biogeochemical models. This is critical for understanding and prediction of current and future functioning of LNLC regions and their contribution to the global carbon cycle.

Copper aerosols inhibit phytoplankton growth in the Mediterranean Sea

Aerosol deposition plays an important role in climate and biogeochemical cycles by supplying nutrients to the open ocean, in turn stimulating ocean productivity and carbon sequestration. Aerosol particles also contain elements such as copper (Cu) that are essential in trace amounts for phytoplankton physiology but that can be toxic at high concentrations. Although the toxicity of Cu associated with aerosols has been demonstrated in bioassay experiments, extrapolation of these laboratory results to natural conditions is not straightforward. This study provides observational evidence of the negative effect of aerosols containing high Cu concentrations on marine phytoplankton over a vast region of the western Mediterranean Sea. Direct aerosol measurements were combined with satellite observations, resulting in the detection of significant declines in phytoplankton biomass after atmospheric aerosol events characterized by high Cu concentrations. The declines were more evident during summer, when nanoflagellates predominate in the phytoplankton population and stratification and oligotrophic conditions prevail in the study region. Together with previous findings concerning atmospheric Cu deposition, these results demonstrate that the toxicity of Cu-rich aerosols can involve large areas of the world’s oceans. Moreover, they highlight the present vulnerability of oceanic ecosystems to Cu-rich aerosols of anthropogenic origins. Because anthropogenic emissions are increasing, large-scale negative effects on marine ecosystems can be anticipated.

B vitamins as regulators of phytoplankton dynamics

Without an adequate supply of dissolved vitamins, many species of phytoplankton do not grow. Additions of inorganic nutrients like phosphorus and nitrogen, and trace metals like iron, are not alone adequate to sustain life—a practical lesson learned quickly by experimental biologists when they try to keep eukaryotic phytoplankton cultures alive in their labs. The reason is that coenzymes such as B vitamins are also required for many metabolic pathways. For example, vitamin B, serves as a cofactor for a large number of enzymatic systems, including the pyruvate dehydrogenase complex required for the metabolism of carbohydrates (glycolysis) and amino acid synthesis [Vandamme, 1989]. Vitamin B 12 is used primarily to assist two enzymes: methionine synthase, which is involved in DNA synthesis, and methylmalonyl CoA mutase, which is required for inorganic carbon assimilation [Lindemans and Abels, 1985].

Determination of UV filters in both soluble and particulate fractions of seawaters by dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

An analytical method to determine the total content (i.e., not only in the soluble fraction but also in the particulate one) of eight commonly used UV filters in seawater samples is presented for the first time. Dispersive liquid-liquid microextraction (DLLME) is used as microextraction technique to pre-concentrate the target analytes before their determination by gas chromatography-mass spectrometry (GC-MS). In order to release the UV filters from the suspended particles an ultrasound treatment is performed before DLLME. The ultrasound treatment time was studied in order to achieve a quantitative lixiviation of the target analytes. The type and volume of both disperser and extraction solvent, the sample volume, the pH and the ionic strength involved in the DLLME have been optimized to provide the best enrichment factors. Under the optimized conditions, the method was successfully validated showing good linearity, enrichment factors between 112 and 263 depending on the analyte, limits of detection and quantification in the low ng L(-1) range (10-30 ng L(-1) and 33-99 ng L(-1), respectively) and good intra- and inter-day repeatability (RSD <15%). No significant matrix effects were found. Finally, the method was satisfactorily applied to the analysis of three seawater samples from different origin. Results showed significant amounts of UV filters in the particulate fraction that would have been ignored if only the soluble fraction had been considered. This fact shows that the UV filters are also accumulated in the suspended particles contained in water, what should be taken into account from an environmental standpoint.

Response of sulfate-reducing bacteria to an artificial oil-spill in a coastal marine sediment

In situ mesocosm experiments using a calcareous sand flat from a coastal area of the island of Mallorca in the Mediterranean Sea were performed in order to study the response of sulfate-reducing bacteria (SRB) to controlled crude oil contamination, or heavy contamination with naphthalene. Changes in the microbial community caused by the contamination were monitored by a combination of comparative sequence analysis of 16S rRNA genes, fluorescence in situ hybridization, cultivation approaches and metabolic activity rates. Our results showed that crude oil and naphthalene negatively influenced the total microbial community as the natural increase in cell numbers due to the seasonal dynamics was attenuated. However, both contaminants enhanced the sulfate reduction rates, as well as the culturability of SRB. Our results suggested the presence of autochthonous deltaproteobacterial SRBs that were able to degrade crude oil or polycyclic aromatic hydrocarbons such as naphthalene in anaerobic sediment layers.

Are sunscreens a new environmental risk associated with coastal tourism

The world coastal-zone population and coastal tourism are expected to grow during this century. Associated with that, there will be an increase in the use of sunscreens and cosmetics with UV-filters in their formulation, which will make coastal regions worldwide susceptible to the impact of these cosmetics. Recent investigations indicate that organic and inorganic UV-filters, as well as many other components that are constituents of the sunscreens, reach the marine environment--directly as a consequence of water recreational activities and/or indirectly from wastewater treatment plants (WWTP) effluents. Toxicity of organic and inorganic UV filters has been demonstrated in aquatic organism. UV-filters inhibit growth in marine phytoplankton and tend to bioaccumulate in the food webs. These findings together with coastal tourism data records highlight the potential risk that the increasing use of these cosmetics would have in coastal marine areas. Nevertheless, future investigations into distribution, residence time, aging, partitioning and speciation of their main components and by-products in the water column, persistence, accumulation and toxicity in the trophic chain, are needed to understand the magnitude and real impact of these emerging pollutants in the marine system.