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Laguna Larga (Cayo Coco, Cuba) is a eutrophic coastal lagoon due to tourism development. As part of long-term monitoring of Laguna Larga, we were able to follow the lagoon's water quality from 2015 to 2018 and could assess the impacts of Hurricane Irma (September 8–9, 2017) by intensifying our sampling frequency. Physicochemical parameters (salinity, pH, dissolved oxygen, dissolved inorganic nitrogen, dissolved reactive silicate and total nitrogen) exhibited significant variations associated with Hurricane Irma. Salinity decreased due to the extraordinary rainfall of the hurricane (339.8 mm/24 h, a new record for Cayo Coco). The water level in the lagoon rose 0.85 m. Strong hurricane winds and intense runoff drove organic matter and sediment resuspension. Anoxia and an increase of nutrients occurred throughout the lagoon. The main biogeochemical impact was that it boosted these eutrophic conditions of the lagoon, to levels that lasted for several months. A significant correlation among nutrients, salinity and dissolved oxygen was found. After 6 months, water quality in the lagoon had recovered to conditions similar to those before the hurricane. The case of Laguna Larga shows that those coastal systems under anthropic pressure can take longer to recover after extreme climatic events, and highlights the need for long-term monitoring of tropical coastal ecosystems.

Cadmium is a toxic element and its effects are well understood for human health, but its biogeochemical behaviour is still poorly studied and understood in natural ecosystems. This work addresses knowledge gaps concerning its presence, biogeochemical behaviour and impacts in mangrove ecosystems. Through geochemical data and multivariate analysis (i.e., factor and cluster analysis) of data from mangroves of Isla del Carmen, one of the largest extents in Mexico we explored the biogeochemical behaviour of Cd, a potentially toxic element, to identify its anthropogenic sources and interactions with sediments. Pollution indices, including enrichment factor (EF), geo-accumulation index (Igeo), sediment quality guidelines (SQG) and toxicological studies were used to assess the biological impacts of Cd and infer the natural levels tolerated by mangrove trees that form the basis of this natural ecosystem. Our results highlighted that Cd accumulation is driven by interactions between organic matter (OM), sulphur and fine particles; whereas enrichment factor showed values of 6.9 (EF) and 3.5 (EF) associated with point sources and ranged between 2 and 2.9 (EF) in relation to non-point sources. Finally, our geochemical approach revealed that Cd enrichment originates from urban activities and from the poor management of urban residuals.

The marine N cycle is driven mainly by microorganisms whose distribution can be shaped by mesoscale eddies. Recently, eddies containing oxygen minimum zones (OMZs) have been recognised as N-loss hotspots, complicating even more the calculations of the marine N budgets. As a contribution to this understanding, we investigated the effect of a cyclonic eddy confined in an oxygen-depleted basin on the distribution of the N-cycling communities. We measured hydrographic properties of the water column, nutrient concentrations, and the abundance of key genes involved in the processes of nitrification (archaeal and bacterial amoA), denitrification (nirS and nirK), dissimilatory nitrate reduction to ammonia (DNRA; nrfA) and anammox (hzo) within the eddy. Our results indicated that the cyclonic circulation affected the distribution of nutrients and the abundance of amoA and nirS genes, whereas oxygen influenced the distribution of nirK, nrfA, and hzo genes. Additionally, the aerobic ammonium oxidation by archaea seems to be an important source of nitrite, which might fuel denitrifier, DNRA, and anammox communities in this basin. These findings along with the high N deficit in the OMZ suggest the existence of an active N cycling that might enhance the N-loss in this oxygen-depleted basin.

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but information is needed on the variability of their biogeochemical dynamics, especially for tropical systems. A long-term N and P mass balance (2003-2018) in a small tropical eutrophic reservoir lake, Valle de Bravo (VB), Mexico, showed it is a net sink of N (-41.7 g N m-2 y-1), and P (-2.7 g P m-2 y-1), mainly through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m-2 y-1 and 4.2 g P m-2 y-1). N mass balance showed that VB has a high net N atmospheric influx (31.6 g N m-2 y-1), which was 1.3 times the external load, and likely dominated by N2 fixation. During a period of high water level fluctuations (WLF), the net N atmospheric flux decreased by half compared to high level years. WLF can be a useful management tool to improve the trophic status of water bodies by decreasing anoxic conditions and net atmospheric fluxes, possibly through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load.

Coastal lagoons are highly sensitive ecosystems from the ecological point of view. Water samples to assess physicochemical parameters, as well as sediments to measure trace metals (Cd, Cr, Cu, Ni, ...

[EN] Wetlands act as nutrient sinks or sources playing a key role in downstream water quality and ecosystem productivity. Despite their importance, wetlands are highly threatened ecosystems and biogeochemical processes are changing in response to several external and internal constrains; however, these functional alterations have not been evaluated in the long term. In this paper we assess the nutrient dynamics (TOC, TN and TP) in Las Tablas de Daimiel in the long-term, through an input-output study using nutrient concentrations and flows measured monthly in the wetland from October 1980 to December 2018. Considering the entire period, on an annual basis Las Tablas de Daimiel was a net source of TOC (467 % of TOC inputs were exported) and net sink of TN and TP (83 % of TN and 92 % of phosphorus were retained and transformed in the wetland). For the longer period of records, mean export loading of TOC was 2177 g C/m2/y, while retention of TN and TP were 62.8 g N/m2/y and 5.7 g P/m2/y, respectively. However, since the 1980s nutrient concentration and nutrient import and export trends have changed dramatically as has their seasonality. High TOC export in Las Tablas are probably related to the short circuit existing in the hydrological functioning of the wetland after the 1980s in which outflows are usually disrupted to extend the wetland inundation for longer. TN and TP retentions begin to show signs of exhaustion but currently it is not possible to conclude if the wetland sediments have reached nutrient saturation. During the last 38 years the wetland has undergone similar environmental scenarios several times but the biogeochemical response of the system has never been repeated. This means the time scale of the environmental interactions and the ecosystem responses are unpredictable, and therefore long-term observations are key to understanding how nature will respond to upcoming global change., [ES] Los humedales actúan como sumideros o fuentes de nutrientes y desempeñan un papel clave en la calidad del agua y la produc-tividad de los ecosistemas ubicados aguas abajo. En estos ecosistemas tan amenazados los procesos biogeoquímicos están en continuo cambio como respuesta los impactos externos e internos. Sin embargo, estas alteraciones funcionales no se han evaluado a largo plazo. En este trabajo hemos estudiado la dinámica de los nutrientes (TOC, TN y TP) en Las Tablas Daimiel a largo plazo, mediante un balance de entradas y salidas que utiliza concentraciones de nutrientes y caudales medidos mensualmente en el humedal desde octubre de 1980 hasta diciembre de 2018. Teniendo en cuenta todo el período, a escala anual Las Tablas fueron una fuente neta de TOC (se exportó el 467 % de las entradas) y un sumidero neto de TN y TP (el 83 % del nitrógeno y el 92 % del fósforo). En este período, la carga de exportación media de TOC fue de 2177 g C/m2/año, mientras que la retención de TN y TP fue de 62.8 g N/m2/ año y 5.7 g P/m2/ año, respectivamente. Sin embargo, las tendencias en la concentración de nutrientes y en su importación y exportación cambiaron drásticamente desde 1980, haciéndolo también su estacionalidad. La elevadísima exportación de TOC en Las tablas probablemente esté relacionada con el cortocircuito en el funcionamiento hidrológico que sufre el humedal desde la década de 1980, pues las salidas se han interrumpido para expan-dir la inundación del humedal por más tiempo. Las retenciones de TN y TP comienzan a mostrar signos de agotamiento, pero actualmente no es posible concluir si los sedimentos del humedal están ya saturados de nutrientes. Durante los últimos 38 años, el humedal ha experimentado escenarios ambientales similares varias veces, pero la respuesta biogeoquímica del sistema nunca ha sido la misma. Debido a que la escala temporal de las interacciones ambientales y las respuestas de los ecosistemas son impredecibles aún, las observaciones a largo plazo son claves para comprender cómo la naturaleza responde a las próximas nuevas condiciones globales., Several projects funded by the Agency for National Parks from 1992 supported this study.

High mountain lakes and their catchments are remote ecosystems in areas with low anthropogenic disturbance. High mountain lakes integrate changes in the atmosphere and catchment areas (e.g., acid rain, airborne pollutants, climate change). The present research analyses long-term datasets of meteorological and limnological variables representing two tropical high mountain lakes, El Sol and La Luna, in Central Mexico to identify the impacts of anthropogenic disturbance (i.e., sentinels of global/climate change). The 54-year meteorological analysis showed marked interannual variability with no statistically significant air temperature or rainfall trends. However, from 2000 to 2018, the air temperature increased by 0.5 °C. Accordingly, the lake water temperature increased (Lake El Sol: 0.8 °C, Lake La Luna: 0.6 °C). Although the rainfall displayed no change, the water level decreased in both lakes (1.5 m), most likely associated with increased evapotranspiration. Unexpectedly, the dissolved inorganic nitrogen (DIN) concentration in the lakes decreased. The initial acid pH rose to close neutrality in Lake La Luna and to alkaline values in Lake El Sol. The latter may be a consequence of the lowered SOx and NOx emissions from governmental regulations promulgated to control atmospheric pollution beginning in 2000 and probably resulting in less acidic deposition. An additional explanation for the lakes' deacidification is the increased deposition of alkaline ions derived from activities at the volcano slopes. Since the atmospheric supply is the primary nitrogen source to high mountain lakes, the DIN concentration decline could reflect the reduction in atmospheric HNO

This study was conducted in the Jardines de la Reina National Park, Cuba. The health of the communities of corals and crustose coralline algae was studied in the years 2001, 2012 and 2017. The probable effect of hurricanes and sea surface temperature on these communities was also assessed. The area was only affected by three hurricanes and a tropical storm from 2000 to 2017. Sea surface temperature showed an increasing trend (by 0.03°C). The highest percentage of old mortality was recorded in 2001 (74% on the fore reef and 53% on reef crests) and the lowest of recent mortality in 2012 (0.03% on the fore reef and 0.17% on reef crests). Coral cover increased on the fore reef by between 3% and 2% in 2017 in comparison with 2001 and 2012. On the reef crests, the highest cover percentage was in 2001 (14.8%). Unlike local stressors, it was determined that hurricanes and sea surface temperature have likely negatively affected the coral reefs, particularly on reef crests. Both habitats have shown resistance and/or recovery capacity from the impacts suffered after 2001, which suggests some level of resilience. Este estudio se realizó en el Parque Nacional Jardines de la Reina, Cuba. Se estudió la salud de las comunidades de corales y algas coralinas costrosas en los años 2001, 2012 y 2017. También se evaluó el probable efecto de los huracanes y la temperatura superficial del mar sobre dichas comunidades. La zona solo ha sido afectada por tres huracanes y una tormenta tropical en este siglo (desde 2000 hasta 2017). La temperatura de la superficie del mar mostró una tendencia creciente (en 0.03°C). El mayor porcentaje de Mortalidad Antigua se registró en 2001 (74% en arrecife frontal y 53% en crestas del arrecife) y el más bajo de Mortalidad Reciente en 2012 (0.03% en arrecife frontal y 0.17% en crestas del arrecife). La cobertura de coral aumentó en el arrecife frontal en 2017, entre 3% y 2%, respecto de 2001 y 2012. En las crestas del arrecife, el mayor porcentaje de cobertura se registró en 2001 (14.8%). A diferencia de los factores de estrés locales, se determinó que los huracanes y la temperatura de la superficie del mar probablemente hayan afectado negativamente a los arrecifes de coral, particularmente a las crestas del arrecife. Ambos hábitats han mostrado resistencia y/o capacidad de recuperación de los impactos sufridos después de 2001, lo que sugiere cierto nivel de resiliencia.

Inland aquatic ecosystems are valuable sentinels of anthropic-associated changes (e.g., agriculture and tourism). Eutrophication has become of primary importance in altering aquatic ecosystem functioning. Quantifying the CO2 emissions by inland aquatic ecosystems of different trophic statuses may provide helpful information about the role of eutrophication on greenhouse gas emissions. This study investigated diel and seasonal carbon dioxide (CO2) concentrations and emissions in three tropical karst lakes with different trophic statuses. We measured CO2 emissions using static floating chambers twice daily during the rainy/warm and dry/cold seasons while the lakes were thermally stratified and mixed, respectively. The CO2 concentration was estimated by gas chromatography and photoacoustic spectroscopy. The results showed a significant seasonal variation in the dissolved CO2 concentration (CCO2) and the CO2 flux (FCO2), with the largest values in the rainy/warm season but not along the diel cycle. The CCO2 values ranged from 13.3 to 168.6 µmol L−1 averaging 41.9 ± 35.3 µmol L−1 over the rainy/warm season and from 12.9 to 38.0 µmol L−1 with an average of 21.0 ± 7.2 µmol L−1 over the dry/cold season. The FCO2 values ranged from 0.2 to 12.1 g CO2 m−2 d −1 averaging 4.9 ± 4.0 g CO2 m−2 d −1 over the rainy/warm season and from 0.1 to 1.7 g CO2 m−2 d −1 with an average of 0.8 ± 0.5 g CO2 m−2 d −1 over the dry/cold season. During the rainy/warm season the emission was higher in the eutrophic lake San Lorenzo (9.1 ± 1.2 g CO2 m−2 d−1), and during the dry/cold the highest emission was recorded in the mesotrophic lake San José (1.42 ± 0.2 g CO2 m−2 d−1). Our results indicated that eutrophication in tropical karst lakes increased CO2 evasion rates to the atmosphere mainly due to the persistence of anoxia in most of the lake’s water column, which maintained high rates of anaerobic respiration coupled with the anaerobic oxidation of methane. Contrarily, groundwater inflows that provide richdissolved inorganic carbon waters sustain emissions in meso and oligotrophic karstic tropical lakes., This research was supported with public funds from the National Research Programs of Mexico (DGAPA/UNAM through the Projects PAPIIT-IN219215, PAPIIT-IV200319, and PAPIITIV200122, PINCC/UNAM through Projects PINCC 2020 and PINCC 2021), and Spain (PID2020-116147GB-C21 funded by MCIN/AEI/ 10.13039/501100011033 as well COOPA20433 funded by CSIC within the i-COOP + 2020 Program).

Globally, nutrient river discharges drive water quality of coastal ecosystems, and excess nutrients can cause eutrophication impacts. The Grijalva-Usumacinta River System (GURS) discharges in the southern Gulf of Mexico (SGoM) and it is the second largest riverine input to the Gulf. To study how contrasting GURS freshwater flow between rainy and dry seasons affects nutrients concentrations in the receiving coastal ecosystem, we evaluated nutrient variability in the water column during both seasons. High inorganic nutrients and total phosphate outline the rivers discharge plumes during rainy season, and were significantly higher than during the dry season throughout the study area, suggesting contrasting seasonal nutrient discharge of the GURS to coastal waters. On average the GURS discharged 141,123 t N yr

The pelagic / anoxic hypolimnion population of Spirostomum teres was investigated as a part of the long-term ciliates’ monitoring (2003–2016) in an oligo- to mesotrophic monomictic hyposaline crater lake Alchichica (Puebla / Veracruz, Mexico), including an analysis of picoplankton (both heterotrophic, HPP and autotrophic, APP) and inorganic compounds of nitrogen (ammonium, nitrite, nitrate), phosphorus (dissolved reactive phosphorus, DRP) and silicon. Additionally, detailed studies of the ciliate vertical distribution and feeding activity measured upon fluorescently labelled APP (picocyanobacteria) were carried out. The results were compared with those from a neighbour freshwater crater lake La Preciosa and with a meromictic karstic lake La Cruz (Cuenca, Spain). The ciliate vertical distribution within the water column was very well defined: During the first decade, the benthic population was frequently found throughout a developing stratification of the lake. The established stratification of the lake turned the conditions favourable for the formation of an oxycline / hypolimnion population, typically, several meters below the deep chlorophyll maximum (formed basically by diatoms); the population preferred the layers without detectable dissolved oxygen. However, an observed gradient of light (PAR) could support both oxygenic and anoxygenic photosynthesis. Late stratification after deepening of the thermocline reduced the layers with S. teres population to a minimum apparently due to the drastic change in physicochemical conditions within a metalimnion, coupled with an oxycline, and limited to 1 to 2 meters; microstratification was found. Last years, the very bottom population disappeared or it was reduced and the late stratification S. teres peaks were smaller or did not appeared. Generally, S. teres oxycline / anoxic hypolimnion population was observed from June through November. Optimum picoplankton numbers in conditions that supported the ciliate growth were found: The ciliate was peaking at APP of 0.6 to 1 × 105 cells mL–1; the optimum of HPP was observed round 1.4 × 106 cells mL–1. S. teres was efficiently feeding upon picocyanobacteria in numbers of 105 cells mL–1 reaching the clearance rate of 2000 nL cell–1h–1, which represented in average 130 to 210 cells cell–1h–1 ingested. Feeding upon purple sulphur bacteria was observed but only during the end of the lake stable stratification when the ciliate population was already dropping. On the other hand, the volume specific clearance of S. teres upon picocyanobacteria (103 h–1) did not support the hypothesis that they could serve as a sole prey. Feeding upon eukaryote phytoplankton (chlorophytes Monoraphidium minutum, diatoms Cyclotella choc tawhatcheeana) could be of higher importance that previously supposed. Additionally, a use of ingested and retained photosynthetic prokaryotes is hypothesized.

Antarctic microorganisms are characterized for living under extreme conditions such as low temperatures, and high UV-radiation, including and freeze-thaw stress derived from annual environmental changes. Microbial mats are successful microbial consortia in these extreme environments, yet much is unknown regarding their diversity and functional role in terrestrial polar regions. The bacterial diversity in microbial mats from Fildes Peninsula in Maritime Antarctica and their genetic potential for nitrogen acquisition has been explored in our laboratory. The results showed that microbial mats were clustered within two main groups according to their 16S rRNA genetic diversity, separating those collected nearby scientific stations from those in coastal plains. The later showed a lower relative proportion of Proteobacteria and a higher proportion of Cyanobacteria, Planctomycetes, and Thaumarchaeota, possibly due to physicochemical and biological factors associated with sea-land interactions. All microbial mats had a strong nifH genetic signal, mainly associated with Cyanobacteria and Proteobacteria, suggesting the relevance of both oxygenic and anoxygenic bacteria potentially involved in N-fixation. The capacity of Oscillatoriales and Acaryochloris marina to assimilate Nitrogen was also evidenced. This study showed the diversity and structure of microbial mats in the Fildes Peninsula and the importance of cyanobacteria in microbial mats based on their role for N2 fixation and N- assimilation.

Mesoscale eddies are ubiquitous oceanic structures that play pivotal roles in planktonic ecosystems. In this paper, we present observational evidence of the impact of a mesoscale cyclonic eddy on the phytoplankton biomass, measured by chlorophyll-a concentration, in the Bay of La Paz, Gulf of California, using information gathered during a multidisciplinary research cruise in the summer (August) of 2017. A CTD rosette system was used to record high-resolution hydrographic readings and to take water samples for nutrients and spectrophotometric determination of chlorophyll-a concentrations, throughout a grid of stations covering the whole area. The results showed that a mesoscale cyclonic eddy, with a diameter of ∼20 km and a maximum velocity of 0.95 m s–1 at its periphery, had established from the surface to a depth of 100 m, inducing differences in the hydrographic properties of the water column. The phytoplankton biomass distribution was closely related to the circulation pattern, with the highest chlorophyll-a concentration (>3 mg m–3) observed in the center of the eddy, in a layer between 20 and 30 m depth, with absolute maximum values located at 20 m depth as a consequence of nutrient pumping. The presence of mesoscale eddies in the Bay of La Paz has been described previously, but their impact on the phytoplankton biomass and its three-dimensional variability has not been quantified systematically. Therefore, further studies that document the effects of these eddies on phytoplankton biomass are needed to better understand highly productive marine areas, such as the Bay of La Paz, and to propose conservation and management strategies.

The Ring of Cenotes (RC) extends along the edge of the Chicxulub crater, in the limestone platform of the Yucatan Peninsula (YP), where groundwater shows two preferential flow paths toward the coast near Celestun and Dzilam Bravo towns. The objectives of this study were to describe the regional hydrogeochemical evolution of the groundwater in the RC, and its association with the dissolution/precipitation of the minerals present along its pathway to the ocean. These objectives results were obtained by: a) characterizing groundwater hydrogeochemistry, b) calculating calcite, dolomite, and gypsum saturation indexes in the study area, and c) developing a hydrogeochemical model using PHREEQC (U. S. Geological Survey) inverse modelling approach. The model predictions confirmed that there are two evolution pathways of the groundwater consistent with the preferential flow paths suggested in a previous regionalization of the RC. On the western path, where groundwater flows towards Celestun, marine intrusion influences the hydrogeochemical processes and represents a risk for the freshwater. On the eastern path, where groundwater flows toward Dzilam Bravo, rainfall has an important effect on the hydrogeochemical processes, evidenced by a higher concentration in sulfates during droughts than during rainy periods. Then, monitoring of marine intrusion and phases dissolution in the RC is highly recommended

Coralline algae are worldwide carbonate builders, considered to be foundational species and biodiversity hotspots. Coralline habitats face increasing pressure from human activities and effects related to Global Change, yet their ecological properties and adaptive responses remain poorly understood. The relationships of the algal microbiota with the mineral bioconstructions, as well as plasticity and resilience of coralline holobionts in a changing environment, are of particular interest. In the Gulf of California, Neogoniolithon trichotomum (Rhodophyta) is the main carbonate builder in tidal pools. We performed a multi-disciplinary assessment of the N. trichotomum microstructure using XRD, SEM microscopy and SR-FTIR spectromicroscopy. In the algal perithallus, magnesium-calcite and aragonite were spatially segregated and embedded in a polysaccharide matrix (rich in sulfated polysaccharides). Mg-calcites (18-19mol%Mg) were the main mineral components of the thallus overall, followed by iron carbonates related to dolomite (ankerite) and siderite. Minerals of late evaporitic sequences (sylvite and bischofite) were also present, suggesting potential halophilic microenvironments within the algal thalli. The diverse set of abundant halophilic, halotolerant and oligotrophic taxa, whose abundance increase in the summer, further suggests this condition. We created an integrated model, based on environmental parameters and the microbiota distribution, that identified temperature and nutrient availability (particularly nitrate and silicate) as the main parameters related to specific taxa patterns. Among these, Hahella, Granulossicoccus, Ferrimonas, Spongiibacteraceae and cyanobacterial Xenococcaceae and Nostocaceae change significantly between seasons. These bacterial components might play relevant roles in algal plasticity and adaptive responses to a changing environment. This study contributes to the understanding of the interplay of the prokaryotic microbiota with the mineral microenvironments of coralline algae. Because of their carbonates with potential resistance to dissolution in a higher pCO2 world and their seasonally dynamic bacteria, coralline algae are relevant targets to study coastal resilience and carbonated systems responses to changing environments.

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but the variability of their biogeochemical dynamics is still poorly documented, particularly in tropical systems. To contribute to the extending of information on tropical reservoirs and to increase the insight on the factors affecting N and P cycling in aquatic ecosystems, we here report on a long-term N and P mass balance (2003–2018) in Valle de Bravo, Mexico, which showed that this tropical eutrophic reservoir lake acts as a net sink of N (−41.7 g N m y) and P (−2.7 g P m y), mainly occurring through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m y and 4.2 g P m y). The N mass balance also showed that the Valle de Bravo reservoir has a high net N atmospheric influx (31.6 g N m y), which was 1.3 times the external load and likely dominated by N fixation. P flux was driven mainly by external load, while in the case of N, net fixation also contributed. During a period of high water level fluctuations, the net N atmospheric flux decreased by 50% compared to high level years. Our results outlining water regulation can be used as a useful management tool of water bodies, by decreasing anoxic conditions and net atmospheric fluxes, either through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load. These findings also sustain the usefulness of long-term mass balances to assess biogeochemical dynamics and its variability., This research was funded by UNAM, PAPIIT-IN207702 and CONACYT-SEMARNAT, C01-1125 projects to M.M-I

Dissolved and particulate organic matter are the energy source for secondary production in forested streams. Cycling of or¬ganic matter and stream ecosystem functioning are linked to organic matter input and storage capacity and timing. This study assessed the seasonal variation (dry and rainy seasons) of environmental parameters, organic matter stock and input, and stream metabolism in two first-order tropical streams in the Selva Lacandona, Mexico. We also aimed to identify the drivers of organic matter and stream metabolism seasonality. We found seasonal variation in organic matter stock and input correlated with trop¬ical seasonality. Dissolved organic matter and seston increased in the rainy season, while benthic primary producers and leaf litter stock and input increased in the dry season correlated with lower water discharge. Gross primary production increased in the dry season, while ecosystem respiration did not differ between seasons. Seasonality defined by the rainfall pattern and its effect on stream hydrology is the main driver of organic matter dynamics in tropical streams. However, environmental parameters and organic matter stock and input were not good predictors of stream metabolism.

Karst aquifers show dissolution/precipitation processes of the minerals present in the carbonate rocks. The Ring of Cenotes (RC) extends along the edge of the Chicxulub crater, in the limestone platform of the Yucatan Peninsula (YP), where groundwater shows preferential flow paths toward the coast near Celestun and Dzilam Bravo towns. This study aimed to describe the regional hydrogeochemical evolution of groundwater of the RC, and its association with the dissolution/precipitation of the minerals present along its path to the ocean. To achieve this aim, we: a) characterized groundwater's hydrogeochemistry; b) determined the calcite, dolomite, and gypsum saturation indexes (reaction phases with the groundwater) in the study area; c) proposed a hydrogeochemical model developed through PHREEQC using an inverse modelling approach. The model predictions confirmed that there are two evolution pathways of the groundwater consistent with the preferential flow paths suggested in a previous regionalization of the RC. On the western path, where groundwater flows towards Celestun, an important marine intrusion influences the hydrogeochemical processes and represents a risk for the prevalence of freshwater. On the eastern path, where groundwater flows toward Dzilam Bravo, the hydrogeochemistry in the sinkholes correlates well with rainfall, suggesting a higher vulnerability during droughts than during rainy periods.

Considerable variability in methane production and emissions has been reported in mangroves, explained by methane inhibition and oxidation. In this study, soil pore waters were collected from mangrove forests located in the Gulf of California (Mexico) exposed to shrimp farm disturbance. The δ13C of dissolved inorganic carbon (DIC) and CH4 were analyzed along with the δ13C of the soil organic matter to assess the proportion of CO2 derived from methanogenesis, its main pathway, and the fraction of methane oxidized. We performed slurry incubation experiments to fit the isotope–mass balance approach. Very low stoichiometric ratios of CH4/CO2 were measured in pore waters, but isotope mass balances revealed that 30–70% of the total CO2 measured was produced by methanogenesis. Mangrove soils receiving effluent discharges shifted the main methanogenesis pathway to CO2 reduction because of an increase in refractory organic matter. Isotope–mass balances of incubations indicated that methane was mainly oxidized by anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and the increase in recalcitrant organic matter should fuel AOM as humus serves as a terminal electron acceptor. Since methanogenesis in mangrove soils is strongly controlled by the oxygen supply provided by mangrove roots, conservation of the forest plays a crucial role in mitigating greenhouse gas emissions., CONACyT: PROFAPI, Spanish Ministry of Science and Innovation (Grant: CGL2014-54502) and CSIC (Grant: I-COOP+2020–COOPA20433) funded this research.

Isla del Carmen lies within a natural protected area in the southern Gulf of Mexico and supports many plants and animal species of ecological conservation concern. However, rapid urbanization threatens its biodiversity. Although many animal groups here are relatively well studied, there is a lack of monitoring of the bird communities at least during the last 15 years. To contribute to the knowledge and to update the information on the birdlife in this area, we evaluated the inter-annual variation of the abundance and species richness of birds along the coastline of Isla del Carmen from 2012 to 2016 using survey transects on the shore and nearby urban areas. We recorded 137 bird species, from which more than half (56%) are considered migratory species, and 3% are exotics. Some of the recorded bird species, considered winter visitors, showed signs of reproductive activity, as evident reproductive plumage was observed during the local breeding season for more than one year, including seven species considered winter visitors. There was significant inter-annual variation in bird diversity and abundance, which may be linked to human activities and or coastal erosion processes. Twenty-three out of the 137 avian species recorded are first time reports in this area. The results presented here contribute to updating the knowledge on the resident and migratory avian community in the southern Gulf of Mexico, as well as on the distribution of bird species of international concern.

Antecedentes: Cambios en los patrones hidrológicos degradan la estructura forestal y afectan la productividad primaria. Con acciones de restauración hidrológica, se pretende restablecer condiciones biogeoquímicas para facilitar el establecimiento, sobrevivencia y crecimiento de la vegetación del manglar que permitan la recuperación de la estructura forestal y la productividad de raíces subterráneas (< 20 mm).Pregunta: ¿Pueden los cambios ambientales inducidos por la restauración hidrológica reactivar la productividad de raíces?Especie en estudio: Los cambios en biomasa y productividad de raíces subterráneas de Avicennia germinans fueron usadas como indicador de éxito de la restauración.Sitio de estudio y fechas: Isla del Carmen, Laguna de Términos, Campeche, agosto de 2013 a febrero de 2015.Métodos: Se seleccionaron tres sitios de manglar en restauración y uno natural como referencia. En ellos se evaluó la concentración de algunos nutrientes (nitratos, nitritos, amonio y fosfatos) y reguladores como la salinidad y el hidroperíodo. Se evaluó entre sitios la biomasa y productividad de raíces en núcleos de crecimiento enterrados a 30 cm de profundidad durante 18 meses.Resultados: La productividad de raíces < 20 mm de diámetro fue menor en los sitios en restauración (17 a 233 g m2 año-1) que en el sitio de referencia (414 g m2 año-1). La productividad de raíces estuvo asociada con la estructura forestal y las condiciones hidrológicas.Conclusiones: La proporción de raíces >2 mm de diámetro fue mayor en el sitio de referencia y decreció hacia los sitios restaurados, indicando que la estructura forestal (regeneración natural) y el tiempo (años) después de la restauración fue importante para la recuperación funcional del ecosistema de manglar.

The identification and quantification of global change, including climate change, requires long time series of key variables. In this work, the fundamentals and operation of low-cost long-term coastal observatories are described, and preliminary data are shown. The vision is to offer a scientific platform of physicochemical data for at least the next 100 years, what requires establishing sustainable strategies, training human resources, strong institutional support, and long-term funding sources. The network formally operates since 2013 and has generated more than 6 million data points, continuously growing, of which >1.5 million data points are permanently stored and available through a public access web platform. The strategies and methodologies are described and, in the Mazatlan observatory, data recovery and basic statistics of eight environmental variables are presented. During 2015, an extreme El Nino year, marine temperatures increased from the bay to the middle Urias coastal lagoon, were h...

Sea level rise, one of the most evident effects of recent climate change, is already impacting coastal ecosystems. Because of its low relief, population increase and economic development during the last century, the Celestun lagoon is highly vulnerable to global change, including sea level rise. Here, we study a sediment core from a tropical saltmarsh to evaluate the impact of sea level rise on sediment accretion and carbon fluxes. Some geochemical indicators in a 210Pb dated sediment core showed clear signals of marine influence. This was reflected on increased accretion rates, from 0.3 ± 0.1 mm yr− 1 in ≈ 1941 to 2.9 ± 1.2 mm yr− 1 in 2012. These accretion rates were similar to eustatic sea level rise, and mean acceleration ranged from 0.037–0.22 mm yr− 2, implying a SLR by 2100 ranging from 14 to 86 cm. The one-century (1917–2013) organic carbon stock in sediments was calculated to be 10.1 ± 0.2 Mg C ha− 1. During the same period, the organic carbon flux, corrected for organic carbon degradation, increased from 7 ± 3 g C m− 2 yr− 1 to 73 ± 26 g C m− 2 yr− 1, attributed to the impact of sea level rise in this ecosystem. This work shows that tropical saltmarshes may provide useful information on sea level rise, and the presented methodology may be used where instrumental records do not exist or they are too short.

The present study explores the impact of different land uses on water quality in a Mexican basin and addresses key mitigation measures, with key measurements made by citizen scientists. The Amanalco-Valle de Bravo Basin reservoir is the major freshwater supply for Mexico City. By measuring physical-chemical and bacteriological parameters in creeks over 21 months and correlating them to land use areas, it was possible to understand the impacts of different land uses (urban, forest, riparian forests, and different agricultural systems) in water quality. The results show that the concentration of E. coli, nitrates, nitrites, total phosphorus, total nitrogen, and total suspended solids were higher than the recommended reference levels, and that average oxygen saturation and alkalinity were lower than the recommended reference levels in most sites. The analysis of the Pearson correlation coefficient showed a strong relationship between water pollution and urban and agricultural land uses, specifically a higher impact of potato cultivation, due to its intensive use of agrochemicals and downhill tilling. There was a clear positive relationship between total forest area and riparian vegetation cover with improved water quality, validating their potential as nature-based solutions for the regulation of water quality. The results of the present study indicate the opportunities that better land management practices generate to ensure communities’ and water ecosystems’ health. This study also highlights the benefits of citizen science as a tool for raising awareness with regard to water quality and nature-based solutions, and as an appropriate tool for participative watershed management.

Nutrient and chlorophyll-a distributions in the Bay of La Paz, Gulf of California, Mexico were analyzed during the late spring of 2004 to assess their relations to hydrography and circulation patterns. The results show the presence of both Gulf of California Water and Subtropical Subsurface Water. Water circulation was dominated by wind stress driven cyclonic circulation along f / H contours ( f is planetary vorticity and H is depth), and upwelling resulting from the divergence shows a vertical velocity of ∼0.4 m d−1. Nutrient concentrations were higher in the center of the cyclonic pattern, where a rise in the nutricline contributed nutrients to the euphotic layer as a result of Ekman pumping. The vertical section showed the presence of a chlorophyll-a maximum at the thermocline shoaling to a depth of only 12 m. Along the surface, two peaks of chlorophyll-a were observed, one at Boca Grande and another off San Juan de la Costa, associated with upwelling and mixing derived from current interactions with abrupt topographies. The chlorophyll-a maximum increased from 0.8 mg m−3 in the external part of the cyclonic pattern to 2.0 mg m−3 in its center. The vertically integrated chlorophyll-a concentrations followed a similar pattern, rising from 10 to 20 mg m−2 and reaching their highest values in the center of the cyclonic circulation pattern. A schematic model was developed to describe processes that occur in late spring: the wind stress driven cyclonic structure promotes upward nutrient flux, which in turn drives an enhancement of chlorophyll-a. Upwelling was found to be the main mechanism of fertilization responsible for the enhancement of productivity levels by means of nutrient transport into the euphotic zone during spring. Other chlorophyll enhancement areas point to the occurrence of additional fertilization processes that may derive from interactions between cyclonic circulation patterns and the topography off of San Juan de la Costa, where phosphate mining occurs.

The nitrogen (N) cycle is highly dependent on microbial processes. Distribution of these communities is one of the most important factors in the variation of the N cycling in warm‐monomictic lakes. However, the effects of the alternation of water stratification and mixing periods on the ecology of microbial communities involved in these processes are rarely studied in this type of aquatic ecosystem. We explored vertical and seasonal patterns of picoplankton and the genetic potential for ammonium oxidation (amoA gene for bacteria and archaea), denitrification (nirS and nirK), anammox (hzsA), and DNRA (nrfA) and their relationships with the main limnological variables in Lake Alchichica (Central Mexican Plateau) to provide insight into the distribution and importance of these planktonic communities in warm‐monomictic tropical lakes. Ten depths were sampled during late stratification (November 2015) and mixing (February 2016) periods, covering the epilimnion, metalimnion (oxycline), and hypolimnion layers in the first case. We showed that temperature and oxygen stratification shaped the distribution of picoplankton and functional N genes in this lake. These communities also varied in relation to nutrient availability and underwent temporal changes throughout the water column. The amoA genes, along with autotrophic picoplankton, were more abundant during the stratification, indicating that nitrification could be potentially more important during this period, mainly at the oxycline layer. Denitrifying genes showed strong variations during the stratification period, with highest gene copy numbers at the oxycline and hypolimnion layers. Anoxic conditions were characterised by a relative increase in the abundance of the nrfA gene with depth, which was positively correlated with NH₄ ⁺ concentration. On the other hand, the hzsA gene was not detected in any sample. Our findings highlight the importance of thermal stratification as one of the main factors influencing the genetic potential for N transformations within the water column in warm‐monomictic tropical lakes.

The restoration of mangroves has gained prominence in recent decades. Hydrological rehabilitation has been undertaken to connect impaired mangroves with the sea, lagoons or estuaries. Because mangrove hydrodynamics occurs on the surface and interstitial spaces in the sediment, we propose to determine the hydrological flow paths to restore the hydrological regimes of the impaired mangroves. The hydrological flow paths were determined through a micro basin analysis based on microtopographic data to generate a digital elevation model. Applying this methodological approach, the hydrology of an impaired area on a barrier island in the Gulf of Mexico was restored by excavating, desilting or clearing the channels on the identified hydrological flow paths. This area was compared to one in which impaired mangroves were reconnected to the marine lagoon but disregarding the flow paths. Data collected in both areas were evaluated by flood level analysis, using two methods: (i) a simple linear regression model (SLRM) and (ii) spectral analysis (SA), also known as dominant frequency analysis. The results suggest that restoration based on the hydrological flow paths was more effective than the direct opening to the nearest main water body without accounting for the microtopography. In both areas, soil salinity and sulfides decreased after hydrological reconnection. However, a greater efficiency in the investment of time and human resources was achieved when preferential flow paths were identified and taken into account. The methodological procedures described in this study are of universal application to other mangrove restoration programs.

Microbial communities play a central role in the N cycle of oceanic oxygen minimum zones (OMZs), such as in the Eastern Tropical North Pacific (ETNP). We explored the spatial distribution of the genetic potential for ammonia oxidation (amoA gene for bacteria and archaea), denitrification (nirS and nirK), anaerobic ammonium oxidation (anammox) (hzo) and dissimilarity nitrate reduction to ammonia (DNRA) (nrfA) and their relationships with the hydrological variables and isotopic composition of nitrate in the ETNP off Mexico. Oxygen concentration, the availability of N chemical forms and the upwelling shaped the distribution of N cycling genes along the water column. The high abundance of N genes and the isotopic composition of nitrate suggest the N cycling is very dynamic in the OMZ core. The accumulation of nitrite, the high abundance of archaeal amoA genes, and the deviation of the N and O isotopes of nitrate from the expected 1:1 ratio for nitrate reduction in the upper portion of this OMZ indicate that nitrification is a relevant process that fuels the denitrifier community. Conversely, the high abundances of nitrate, ammonium and nrfA genes in the deeper layer indicate that DNRA is a crucial process enhancing anammox there. These results show the need for more detailed studies of the N processes in OMZs.

Los manglares de Laguna de Términos, Campeche han sido afectados por la pérdida de la conexión hidrológica durante el paso de tormentas y huracanes. El objetivo de este trabajo fue evaluar la regeneración natural del manglar en un área degradada, después de haber implementado acciones de restauración hidrológica. Se establecieron tres sitios de muestreo con diferentes tiempos de restauración (1 año - 3 años) y un sitio de manglar natural conservado como referencia. El muestreo se realizó en los años 2014 a 2015. Se evaluó densidad, altura, sobrevivencia y tasa de crecimiento de las plántulas, así como las características ambientales. La relación entre la vegetación y las características ambientales se realizaron mediante regresiones lineales simples y un análisis de escalamiento multidimensional. Para determinar la dispersión de propágulos respecto a los manglares naturales, se generó un modelo lineal mixto de la densidad de propágulos vs. la distancia y el tiempo de restauración. Los resultados demostraron que la distancia respecto a los manglares naturales afectó la densidad de los propágulos. La concentración de fosfato se relacionó con la sobrevivencia de las plántulas; mientras que la concentración de amonioy la concentración de sulfuro se relacionaron negativamente con la densidad de las plántulas. Las acciones de restauración hidrológica influyeron en el establecimiento y desarrollo de la vegetación de manglar; por lo tanto, las zonas de manglar natural y la restauración hidrológica facilitaron la dispersión de los propágulos hacia las zonas degradadas, resaltando la importancia de contemplar estas áreas naturales dentro de los proyectos de restauración.

Marine zooplankton play a pivotal position in the pelagic ecosystem and, as one of their principal members, copepods represent by far the most significant direct link between phytoplankton and the higher trophic levels. In this study, observational evidence of the effect of a mesoscale cyclonic eddy on the abundance of copepods (adult calanoids, adult cyclopoids and all copepodite stages) in the Bay of La Paz, southern Gulf of California, a region recognized as exhibiting high biodiversity, is presented. During a multidisciplinary research cruise in February 2006, high-resolution hydrographic profiles were obtained from a grid of stations throughout the bay, and oblique zooplankton hauls were made in its north-central portion. The results showed the presence of a mature mesoscale cyclonic eddy, which extended to 110 m depth and 30 km diameter, reaching a surface azimuthal velocity of 20 cm s–1 at its periphery. Below the mixed layer at 50 m depth this eddy induced a cold-core water dome (~16.25 °C) at its center. Within this cold water dome, nutrients concentrations were much higher than outside the eddy. Nitrate reached up to 15 μM, soluble reactive phosphorous (SRP) up to 1.6 μM, and soluble reactive silicate (SRSi) up to 30 μM within the eddy. The total abundance of the organisms analyzed varied according to group: the calanoid copepods reached values of 8112 ind 100 m–3, the cyclopoid copepods of 4281 ind 100 m–3, and the highest abundance was recorded by all copepodite stages, of 32,076 ind 100 m–3. The influence of the cyclonic structure on copepod abundance was to induce the formation of a circular shape around the eddy periphery, which could be called a ‘copepod belt shape’. We suggest that several mechanisms induce this aggregation, including: 1) the affinity of these organisms for waters with a favorable temperature, and 2) the availability of food (phytoplankton) generated by the presence of the cyclonic eddy and the sub-mesoscale processes there, as well as by the presence of a bathymetric sill. These results represent the first observational report on the influence of a mesoscale cyclonic eddy in the Bay of La Paz on zooplankton organisms in winter, which should contribute to a better understanding of the dynamics of this highly productive area.

For decades, La Redonda lagoon was an excellent location for fishing the largemouth bass (Micopterus salmoides, Lacepède) in Cuba. There are indications that the species disappeared from the lagoon in 2009. Three water surveys were carried out in 2013 and 2014. Physicochemical parameters, including nutrients, were measured in all surveys. Chlorophyllaand water transparency were only measured in November 2013. Results showed that this lagoon is a fresh to brackish water system, with common salinization episodes. There were some hypoxic conditions, but mean dissolved oxygen value was above 5.0 ± 2.8 mg L−1for the entire survey period. The trophic state was evaluated as oligotrophic and Nitrogen and Phosphorus were limiting in most of the survey sites. The Habitat Suitability Index model (HSI) for largemouth bass had a mean value of 0.63 ± 0.02 (moderate degree of suitability). All results showed that bass recovery could be possible in La Redonda lagoon, but management criteria are necessary. The largemouth bass recovery could help to increase visitations of American anglers to this place and a portion of the revenue could be used to conduct environmental monitoring and studies of the largemouth bass ecology in Cuba.

Stable isotopes of nitrogen ( δ 15 N) have been widely used around the world to evaluate the impact of anthropogenic activities on marine ecosystems; however, in the Caribbean Sea countries, such as Mexico and Cuba, they are rarely used. Inputs of nutrients related to urban development and tourist activities along the coasts of the Caribbean Sea have the potential to deteriorate their fragile marine ecosystems. The use of isotopic tools and elemental analysis in sentinel organisms would be useful to provide evidence of the impact generated by anthropogenic nutrients. Measurements of δ 15 N ( ‰ ), carbon and nitrogen content, and C:N ratios, were conducted in different sentinel groups (macroalgae, seagrasses, gorgonians, and corals) collected in five marine ecosystems with different nearby coastal development pressure in both countries. The selected ecosystems, ordered according to the level of coastal areas development (low to high), were: Jardines de la Reina (JR), Gulf of Ana Maria (GAM), Cayo Coco (CC), and Laguna Larga (LL) in Cuba, and Puerto Morelos (PM) in Mexico. Results evidenced that the majority of sentinels inhabiting near the most developed coastal areas, in terms of population and tourism, showed higher N contents, lower C:N ratios and higher values of δ 15 N (e.g., PM and LL) than those near less developed coastal ecosystems (e.g., GAM and JR). Land-based nutrients from municipal wastewater constitute the primary source of N pollution. Because eutrophication represents a significant threat to the integrity of valuable coastal ecosystems, there is an urgent need to accelerate progress in wastewater treatment systems, in terms of capacity and efficiency, to significantly reduce nutrient inputs to coastal ecosystems. Otherwise, more negative changes and deteriorations to the health of coastal ecosystems, including coral reefs, are expected along the Mexican Caribbean and numerous key points of Cuba and other Caribbean countries.

The petrochemical industry and urban activities are widely recognized worldwide as a source of pollution to mangrove environments. They can supply pollutants such as trace elements that can modify the ecosystem structure and associated services, as well as human populations. Through geochemical data, multivariate statistical analysis and pollution indices such as the enrichment factor (EF), geo-accumulation index (Igeo), adverse effect index (AEI) and the pollution load index (PLI), we evaluated the factors that control trace element distribution, punctual sources and determined the pollution level of sediments and their potential biological impact in the mangrove ecosystem of Isla del Carmen, Mexico. The factor and cluster analysis highlighted that the distribution of trace elements is influenced by the mineralogy, texture as well as urban derived sources. The pollution indices showed values in the punctual sources from the urban area of EF > 10, Igeo > 3, AEI > 3, PLI > 1 by Cu, Zn and Pb. Finally, the results revealed that mangroves from Isla del Carmen has a major influence from urban activities and natural sources rather than oil industry and also indicate a degraded environment as a result of anthropogenic activities that could have knock-on effect for human health if polluted marine organisms derived from the urban mangroves are consumed. Capsule abstract Surface sediments show the influence of point sources on selected trace element concentrations correlated with human activities within the mangroves of Isla del Carmen, Mexico.

Recientemente se ha revalorado la relevancia de los sistemas acuaticos epicontinentales en el ciclo global del carbono, ya que estos tienen una gran capacidad de ser tanto sumideros de carbono, hacia sus sedimentos, como fuentes de carbono atmosferico. Sin embargo, la informacion acerca de los sistemas tropicales es aun heterogenea y escasa, situacion particularmente critica, dado que estos sistemas enfrentan problemas crecientes en el panorama del cambio global, contaminacion y eutrofizacion incluidas, particularmente esta ultima, asi como impactos de las estrategias de manejo (e.g., cambios en el nivel de agua). El estudio de la dinamica del oxigeno, criticado en el pasado, ha sido retomado y hoy es nuevamente utilizado ampliamente para estimar la produccion primaria y la respiracion ecosistemica ante la urgencia por estimar los flujos de carbono asociados a los sistemas acuaticos. Se revisan aqui, por ello, los aspectos metodologico-conceptuales asociados a la implementacion moderna del metodo de evolucion del oxigeno y se discuten las ventajas y los problemas asociados a esta metodologia, para facilitar y extender su aplicacion a los sistemas tropicales, donde su implementacion es muy conveniente. Se propone tambien una secuencia metodologica unificadora para hacer posible la comparacion entre estudios, y el escalamiento de los flujos de carbono, tanto espacial como temporalmente. Los inventarios de carbono en diferentes escalas (espaciales y temporales) son necesarios para entender la participacion y las respuestas de los sistemas acuaticos y regiones tropicales (en particular su papel como fuentes o sumideros de carbono) frente al cambio global.

Maritime Antarctica has shown the highest increase in temperature in the Southern Hemisphere. Under this scenario, biogeochemical cycles may be altered, resulting in rapid environmental change for Antarctic biota. Microbes that drive biogeochemical cycles often form biofilms or microbial mats in continental meltwater environments. Limnetic microbial mats from the Fildes Peninsula were studied using high-throughput 16S rRNA gene sequencing. Mat samples were collected from 15 meltwater stream sites, comprising a natural gradient from ultraoligotrophic glacier flows to meltwater streams exposed to anthropogenic activities. Our analyses show that microbial community structure differences between mats are explained by environmental NH4+, NO3-, DIN, soluble reactive silicon and conductivity. Microbial mats living under ultraoligotrophic meltwater conditions did not exhibit a dominance of cyanobacterial photoautotrophs, as has been documented for other Antarctic limnetic microbial mats. Instead, ultraoligotrophic mat communities were characterized by the presence of microbes recognized as heterotrophs and photoheterotrophs. This suggests that microbial capabilities for recycling organic matter may be a key factor to dwell in ultra-low nutrient conditions. Our analyses show that phylotype level assemblages exhibit coupled distribution patterns in environmental oligotrophic inland waters. The evaluation of these microbes suggests the relevance of reproductive and structural strategies to pioneer these psychrophilic ultraoligotrophic environments.

Marine picophytoplankton has become an important issue to understand the global ecology of phototrophic forms, due to its wide distribution and contribution to biomass and productivity. We studied the abundance, distribution and signature pigments of the prokaryote picophytoplankters Prochlorococcus and Synechococcus during an oceanographic cruise (26 April to 7 May, 2011) in the central Mexican Pacific, a relatively poorly-known oxygen minimum zone (OMZ), and the effect of three environmental gradients. Prochlorococcus and Synechococcus abundances were comparable with those found in other tropical areas (0.17 to 30.37 X 104 cells mL-1, and 0.9 to 30.97 X 104 cells mL-1, respectively). Prochlorococcus abundances reached highest numbers in deeper waters, often coinciding with the second deep in situ fluorescence (and chlorophyll α) maxima, at oceanic stations, below the nitratecline, whereas Synechococcus abundances were higher at subsurface waters and its concentration maxima usually coincided with the subsurface in situ fluorescence maxima, with slightly higher abundances in coastal stations. Statistical analyses support significantly these results. Distribution of divinyl-chlorophyll α was erratic along the water column and occasionally coincided with the deep in situ fluorescence maxima, whereas the distribution of zeaxanthin usually followed that of chlorophyll α and the abundances of Synechococcus, and peaked together. These results are similar to those previously found in the study area and in more temperate zones, and also to the general trend in OMZ, but confirm that the second deep chlorophyll α maxima are attributed to high Prochlorococcus densities. We additionally found the abundance and distribution of Prochlorococcus and Synechococcus strongly driven by the environmental gradients observed. Resumo O picophytoplankton marinho tornou-se uma questão importante para compreender a ecologia global das formas fototróficas, devido à sua ampla distribuição e contribuição para a biomassa e a produtividade. Estudamos os pigmentos de abundância, distribuição e assinatura do picofitoplâncton procarionte Prochlorococcus e Synechococcus durante um cruzeiro oceanográfico no Pacífico central mexicano, uma zona mínima de oxigênio relativamente poco conhecida (OMZ) e o efeito de três gradientes ambientais. As abundâncias de Prochlorococcus e Synechococcus foram comparáveis às encontradas em outras áreas tropicais (0.17 to 30.37 X 104 células mL-1, e 0.9 to 30.97 X 104 células mL-1, respectivamente). As abundâncias de Prochlorococcus atingiram o maior número em águas mais profundas, coincidindo frequentemente com a segunda intensidade de fluorescência in situ profunda (e clorofila a), em estações oceânicas, abaixo da nitratoclina, enquanto as abundâncias de Synechococcus foram maiores nas águas de subsuperficie e sua concentração máxima geralmente coincidiu com os máximos de subsuperficie de fluorescência in situ, com abundâncias ligeiramente mais altas nas estações costeiras. As análises estatísticas suportam significativamente esses resultados. A distribuição da divinil-clorofila a foi errática ao longo da coluna de água e coincidiu ocasionalmente com os máximos de fluorescência in situ profundos, enquanto que a distribuição da zeaxantina seguiu geralmente a da clorofila a e as abundâncias de Synechococcus e atingiu o pico. Estes resultados são semelhantes aos encontrados anteriormente na área de estudo e em zonas mais temperadas, e também à tendência geral na OMZ, mas confirmam que a clorofila profunda a maxima é atribuída a altas densidades de Prochlorococcus. Além disso, encontramos a abundância e distribuição de Prochlorococcus e Synechococcus fortemente conduzida pelos gradientes ambientais observados.

Microbes can modulate ecosystem function since they harbor a vast genetic potential for biogeochemical cycling. The spatial and temporal dynamics of this genetic diversity should be acknowledged to establish a link between ecosystem function and community structure. In this study, we analyzed the genetic diversity of bacterial phosphorus utilization genes in two microbial assemblages, microbialites and bacterioplankton of Lake Alchichica, a semiclosed (i.e., endorheic) system with marked seasonality that varies in nutrient conditions, temperature, dissolved oxygen, and water column stability. We focused on dissolved organic phosphorus (DOP) utilization gene dynamics during contrasting mixing and stratification periods. Bacterial alkaline phosphatases (phoX and phoD) and alkaline beta-propeller phytases (bpp) were surveyed. DOP utilization genes showed different dynamics evidenced by a marked change within an intra-annual period and a differential circadian pattern of expression. Although Lake Alchichica is a semiclosed system, this dynamic turnover of phylotypes (from lake circulation to stratification) points to a different potential of DOP utilization by the microbial communities within periods. DOP utilization gene dynamics was different among genetic markers and among assemblages (microbialite vs. bacterioplankton). As estimated by the system's P mass balance, P inputs and outputs were similar in magnitude (difference was