High Nutrient Input Research Articles

Trophic Web Structure and Ecosystem Attributes of a Coastal Lagoon System in the Southwest Atlantic

A comparative study of the lagoons that form the coastal lagoon system of Maricá-Guarapina (Southeast Atlantic, Brazil) was carried out based on the results of trophic models that describe the structure and functioning of each system. Two models were constructed using ECOPATH program to differentiate the main biomass fluxes in the systems. The model developed for Guarapina Lagoon considered 32 functional groups while that of Maricá Lagoon was developed with 29 that included primary producers to top predators, in addition to artisanal lagoon fisheries. The results indicated that biomass and production are concentrated at trophic levels 2 and 3 and the detritivore is more relevant than the grazing chain in both lagoons. This highlights the bottom-up control of our food webs despite the high trophic level of key groups. Otherwise, the increasing detritus could also reduce oxygen and influence most fish species, including mortality mass events reducing the fishery and the water quality. Ecosystem attributes suggest that both lagoons are in the intermediate stages of development. The low value of the Finn cycling index shows that Maricá Lagoon cannot recycle the organic matter, mainly because of the high input of nutrients. The importance of an ecosystem-based assessment, as presented here, constitutes an important tool for anticipating possible impacts from environmental disturbances on ecosystem functions, including the associated socio-economic challenges.

Characterization of coral communities in the shallow hydrothermal vents of Mabini, Batangas, Philippines

The existence of shallow hydrothermal vents in Mabini, Batangas, Philippines, has been recognized to contribute to CO2-rich submarine groundwater discharges. However, little is known about the existing coral community structure in the area which provides valuable ecosystem goods and ecological services. We characterized the reef community in this unique microenvironment falls within the predicted future reef condition with low pH and aragonite saturation using coral recruitment tiles, examined coral life-history strategies and size frequency distribution, and measured calcification of transplanted fragments from the genus Goniopora sp., Pectinia sp., and Porites sp. The availability of larval supply has proven that corals can still settle (45–73 recruits m−2) due to the presence of hard substrate and settlement cues such as the crustose coralline algae. The existing coral colonies were mostly dominated by stress-tolerant groups and sizes ranging from 5 to 20 cm. Deployed coral fragments showed growth via extension, and calcification was negatively affected by local conditions, such as Porites sp. fragments. Higher nutrient input may have promoted coral growth, but combined with low carbonate chemistry, it likely made the corals more susceptible to physical damage, as seen on the fragments. This study highlights the importance of naturally occurring extreme environments to determine climate-resilient corals that can adapt to changing conditions and recover from disturbances over time.

Chronic hypoxia drives the occurrence of ferroptosis in liver of fat greening (Hexagrammos otakii) by activating HIF-1α and promoting iron production

BackgroundHypoxia caused by global climate change and human activities has become a growing concern eliciting serious effect and damages to aquatic animals. Hexagrammos otakii is usually a victim of hypoxia which caused by high density aquaculture and high nutrient input. The mechanism underlying ferroptosis regulation after hypoxia-stress in liver of H. otakii, however, remains elusive. MethodsFor a duration of 15 days, expose the H. otakii to low concentrations of dissolved oxygen (3.4 ± 0.2 mg/L). Detecting alterations in the H. otakii liver tissue by chemical staining, immunohistochemistry, and electron microscopy. The expression variations of relevant genes in the liver of the H. otakii were simultaneously detected using Western blot and qPCR. A correlation analysis was performed between HIF-1α and iron ion expression in the liver of H. otakii following hypoxic stress. ResultsIn this study, we conducted the whole ferroptosis integrated analysis of H. otakii under chronic hypoxic condition. Reactive oxygen species (ROS) are highly accumulated under the hypoxia treatment (Superoxide Dismutase, SOD; Catalase, CAT), and which results in a significantly enhanced of lipid peroxidation (Lipid Peroxidation, LPO; Malondialdehyde, MDA; Aminotransferase, AST; Alanine aminotransferase, ALT) in liver tissue. The HIF-1α signaling is activated to cope with the hypoxia stress through strategies including changing iron ion concentration (Fe3+ and TFR1) to breaking the oxidation balance (GSH and GSH-Px), and enhancing ferroptosis gene expression (GPX4). The expression of genes related to ferroptosis pathway (DMT1, FTH1, STEAP3, ACSL4, γ-GCS, SLC7A11) is significantly upregulated and associated to the expression of iron and HIF-1α. ConclusionsIt is demonstrated that the HIF-1α/Fe3+/ROS/GPX4 axis is involved in promoting ferroptosis in fat greening hepatocytes following hypoxia-stress. Ultimately, our findings unveil a process by which hypoxic stress strongly encourages ferroptosis by triggering HIF-1α and boosting iron synthesis.

A newly formed lagoon under eutrophication on the coast of Kumlubent-Gelibolu, Çanakkale Strait (Dardanelles), Sea of Marmara

Lagoons are semi-enclosed and dynamic water bodies that are highly vulnerable to coastal dynamics and environmental stressors associated with anthropogenic activities and climate change. We investigated a pristine lagoon, hereafter referred to as Kumlubent Lagoon, located on the coast of Gelibolu in the Çanakkale Strait in the Sea of Marmara. The evolution of coastal morphology and Kumlubent Lagoon’s formation was investigated by using satellite images collected between 2006 and 2020. In addition, water samples were collected from the lagoon and the shore on April 15 and 16, 2022 for nutrient (NO3, NO2, NH4, PO4, and Si), chlorophyll-a (chl-a) and total organic carbon (TOC) analyses in order to determine the trophic status of the lagoon. Our results showed that the nearshore deposition of coastal sediments gradually formed a sand barrier that isolated the lagoon from the sea in the year 2013. The nutrient analyses showed a clear indication of eutrophication of the lagoon. Accordingly, 29.784 µm/L of NH4, 1.168 µm/L of PO4, 34.15 (±1.54) µg/L of chl-a and 40.50 mg/L of TOC were measured in the water samples from the Kumlubent Lagoon. Our study suggests that the deposition of longshore drifted sediments in a southwesterly direction along the Çanakkale Strait plays a dramatic role in the development of coastal morphology in the Gelibolu-Kumlubent region. The rapid eutrophication of the Kumlubent Lagoon may be related to the high nutrient input from agricultural activities in the region.

Unravelling the genetic mechanisms and paleoenvironmental controls of early Cretaceous Oyster Mass occurrences (OMOs), Neuquén Basin, west-central Argentina

Lower Valanginian oyster mass occurrences (OMOs) from the Neuquén Basin of Argentina are analyzed using a multidisciplinary approach, including the description of their sedimentological signature and stratigraphic contacts, assessment of taphonomical attributes, and paleontological and paleoecological characteristics. These OMOs present a wide distribution in the study area, with lateral continuity for at least 2.5 km and up to 12 m thick. They occur within a single stratigraphic interval, constrained in terms of sequence stratigraphy and biostratigraphy. Three stacked tabular OMOs separated by mudstone levels were recorded in all the studied localities. The associated lithofacies point to a mainly outer ramp paleoenvironment, below storm wave base and occasionally disturbed by exceptional, distal storm flows. Internally, the OMOs share a common vertical trend characterized, from base to top, by a gradual increase in oyster abundance and a transition from mainly reclining, disarticulated oysters to articulated, cementing oysters conforming build-ups. Hence, a mainly biogenic origin is proposed, with autobiostromes grading vertically to bioherms. This vertical trend was interpreted in terms of development stages, namely, colonization, expansion, climax and extinction, which were in turn related to specific paleoenvironmental controls. Particularly, the OMOs establishment and development were associated to low sedimentation rates, salinity fluctuations and high nutrient input as a result of high primary productivity. At a larger scale, the overall paleoenvironmental conditions and subtropical geographical position of the basin were detrimental for most reef builders typical of the Cretaceous period (e.g., corals, sponges, rudists), and could have favored oyster proliferation and OMOs development instead.

Submerged macrophyte root oxygen release reduces sediment oxygen demand: A positive feedback loop in shallow lakes

Shallow lakes have two stable ecological states, macrophyte dominated or algal dominated. The macrophyte dominated state is the more desired state as it generally has clearer water that is safe for contact recreation. Whereas the algal dominated state is considered degraded, resulting from high anthropogenic nutrient inputs, with turbid water that is often unsafe for contact recreation. These ecological states are somewhat resilient due to in-lake feedback loops that maintain or enhance conditions for the dominate primary producer. For the macrophyte dominated state, many of these feedback loops are theoretically plant density dependent, but rarely has the plant density required to initiate these feedback loops been identified. Here we illustrate the plant density dependence of a previously unstudied feedback loop present in the macrophyte dominated state. Increased densities of Isoëtes kirkii were able to reduce sediment oxygen demand through their root oxygen releases. This reduction in sediment oxygen demand occurred at 32 plants m−2 in a garden soil and 63 plants m−2 in the sediment of a hypo-eutrophic lake, a disparity likely due to the higher initial sediment oxygen demand present in the lake sediments. In a shallow lake, plants present in the hypolimnion will reduce sediment oxygen demand, increasing the amount of time required before anoxic conditions are created and the resulting release of dissolved reactive phosphorus. This will likely decrease the potential for subsequent algal blooms and the associated shading of submerged macrophytes, thus maintaining in-lake conditions that favour macrophytes.

Assessing long-term diatom changes in sub-Arctic ponds receiving high fluxes of seabird nutrients.

Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate-related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub-Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck-affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine-derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird-free Arctic ponds-these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird-derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice-free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub-Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required.

Nutrients and Contaminants in Soils of Current and Former Oil Palm Production Systems from Indonesia

Palm oil production in Southeast Asia often occurs on nutrient-poor, acidic soils converted from primary forest. Both the agricultural conversion and the production of oil palm are subsidised in Indonesia. As well as depleting soil organic C and plant nutrients, agricultural production on these soils can result in the accumulation of trace elements (TEs)—including micronutrients and non-essential trace elements—from the use of TE-containing agrichemicals including phosphate fertilisers and Cu fungicides. We tested the hypothesis that palm soils will have lower C concentrations than forest soils, as well as accumulation of TEs including Cu, Zn and Cd. Soil samples from active and abandoned oil palm plantations in Sumatra, Indonesia, were analysed for general soil properties as well as TE concentrations. Soils were acidic and low in key nutrients, with production likely to be limited by deficiencies of N, P, K, Mg and Mo, present at some sites in mean concentrations as low as 0.021%, 118 mg kg−1, 778 mg kg−1, 1023 mg kg−1 and 0.095 mg kg−1, respectively. Mean organic C was lower (2.0–3.3%) than reported values in nearby forest soils (7.7%). Soils under palm production contained elevated levels of Cu, Zn, As and Pb up to 38, 91, 9.0 and 28 mg kg−1, respectively, likely due to agrichemical use. The correction of nutrient deficiencies in palm production would require significant fertiliser inputs, which would exacerbate TE accumulation and reduce the net economic revenue from oil production. Our data have shown that in the plantations we have sampled, soils have become degraded. These tropical, weathered, and naturally nutrient-poor soils are ill suited to intensive production that requires high ongoing nutrient inputs. These findings have implications for the sustainability of a regionally significant production system across Southeast Asia.

Long-term warming and human-induced plankton shifts at a coastal Eastern Mediterranean site

Plankton are key ecological indicators for assessing the impacts of human-induced pressures like climate change and waste-water discharge. Here, 26 years (1988–2015) of biweekly in-situ chlorophyll-a concentration, mesozooplankton biomass and remotely-sensed sea surface temperature (SST) data are utilized to investigate long-term changes of plankton biomass and timing of growth (phenology) in relation to warming, in a coastal region of the Saronikos Gulf (Aegean Sea). A Waste-Water Treatment Plant (WWTP) was established in 1995, leading to decreased nutrient concentrations circa 2004. Overall, the results indicate an interplay between warming and changes in ecological status. During higher nutrient input (1989–2004), a temporal mismatch between zooplankton and phytoplankton, and a positive zooplankton growth—SST association, are evident. Conversely, in the warmer, less mesotrophic period 2005–2015, an earlier timing of zooplankton growth (related to copepod abundance) synchronizes with phytoplankton growth, including a secondary autumn growth period. Concurrently, an abrupt negative interannual relationship between SST and mesozooplankton, and a summer biomass decrease (linked with cladoceran abundance) are observed. This work provides evidence that current warming could alter plankton abundance and phenology in nearshore Eastern Mediterranean ecosystems, suggesting shifts in plankton community composition that could trigger potential cascading effects on higher trophic levels.

Newly discovered Botryococcus-rich source rocks in the western Qaidam Basin, NW China and their implications for shale oil exploration in saline lacustrine basins

Owing to the high hydrocarbon content and photosynthetic efficiency of phytoplankton, planktonic microalgae account for the main source of petroleum hydrocarbons in marine and continental petroliferous basins. Therefore, the presence of algal residues in such basins is considered an important indicator of high-quality hydrocarbon source rocks. The southwestern region of the Qaidam Basin, characterized by lacustrine deposits from the Paleogene, has substantial petroleum resources. However, studies on the development of source rocks and the mechanisms involved in their organic matter enrichment are insufficient, thus hampering ongoing shale oil exploration efforts. Herein, abundant Botryococcus fossils were discovered in the main source rocks of the upper member of Xiaganchaigou Formation of Paleogene in Southwest Qaidam, accounting for >50 % of the total organic matter content. The palynofacies assemblages reflected relatively distal and oxygen-rich sedimentary environments. The algae-rich rocks usually exhibited distinctive laminated structures alternately composed of quartz-feldspathic, clay and carbonate laminae, indicating periodic climate fluctuations. The Botryococcus, which was mainly preserved in the coarse-grain quartz-feldspathic laminae, probably reflected heavy precipitation conditions and subsequently high nutrient inputs. Finally, the oxygen-rich, low salinity and eutrophic water was likely taking form which benefit the growth of these hydrobiontic algae. These algal-rich shales exhibited typically high hydrogen index (IH) and total organic carbon (TOC) values, indicating their high hydrocarbon-generation potential. Thus, they are important marker beds for high-quality source rocks in petroliferous basins. Concurrently, the coarse-grained detrital mineral laminae displayed excellent reservoir physical properties, probably providing sufficient reservoir space for planktonic algae-derived liquid hydrocarbon. Therefore, these Botryococcus-rich source rocks might represent important targets for ongoing shale oil exploration.

Environmental controls on the distribution of GDGT molecules in Lake Höglwörth, Southern Germany

Tetraether lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), are an increasingly used proxy for reconstructing paleoclimatic and paleoenvironmental dynamics. On a global scale, environmental drivers controlling the distribution of GDGTs in lake systems have been described extensively. However, the drivers that control down-core sedimentary GDGT composition within single lake systems are still poorly constrained. Here, we analysed GDGTs in a sediment core collected from Lake Höglwörth (Bavaria, Germany) covering the last ∼1100 years. The increase in ratio ΣIIIa/ΣIIa values (a ratio which captures the variation of 3 structural isomers of penta- and hexamethylated brGDGTs respectively) reflects a higher contribution of branched (br) GDGTs from aquatic sources after 1800 CE. This is synchronous with a high nutrient input as a result of increased local anthropogenic activities. The climate proxy methylation of branched tetraethers (MBT'5ME) reveals a pattern that deviates from the anticipated temperature changes during the last millennium. Instead, high MBT'5ME values from ∼880 to 1120 CE coincide with a period of increased soil input, resulting from lake damming and/or construction of the Höglwörth monastery. Decreased values after 1800 CE until present date correspond to a higher contribution of aquatic brGDGTs, with changes in the dependency between Ia and IIa suggesting a direct influence of bacterial community changes on the MBT'5ME. The proxy cyclisation of branched tetraethers (CBT') shows a linear increase with time, and a stepwise increase at 1700 CE, when a creek stream inflow channel was rerouted. Over time, MBT’5ME decreases gradually, while CBT’ and ΣIIIa/ΣIIa increase. This is hypothesized to be potentially caused by decreasing water depth over time and/or post- or syn-sedimentary production of GDGTs. The degree of cyclization (DC') shows variations on shorter timescales, possibly driven by the lake mixing regime and water column redox conditions. Our results indicate that caution must be taken when interpreting GDGTs for paleoclimate and paleoenvironmental reconstruction considering the possible influence of shifts in the provenance of brGDGTs. Further studies focusing on both sedimentary and intact polar lipids are highly recommended to constrain the source (water column, or sedimentary production) of GDGTs in lake sediments.

Sea star wasting syndrome reaches the high Antarctic: Two recent outbreaks in McMurdo Sound.

Sea star wasting syndrome (SSWS) can cause widespread mortality in starfish populations as well as long-lasting changes to benthic community structure and dynamics. SSWS symptoms have been documented in numerous species and locations around the world, but to date there is only one record of SSWS from the Antarctic and this outbreak was associated with volcanically-driven high temperature anomalies. Here we report outbreaks of SSWS-like symptoms that affected ~30% of individuals of Odontaster validus at two different sites in McMurdo Sound, Antarctica in 2019 and 2022. Unlike many SSWS events in other parts of the world, these outbreaks were not associated with anomalously warm temperatures. Instead, we suggest they may have been triggered by high nutrient input events on a local scale. Although the exact cause of these outbreaks is not known, these findings are of great concern because of the keystone role of O. validus and the slow recovery rate of Antarctic benthic ecosystems to environmental stressors.

Detection of secondary cyanobacterial metabolites using LC-HRMS in Lake Karaoun

Harmful algal blooms events have been reported worldwide and during the last decades are occurred with increasing frequency and intensity due to the climate change and the high inputs of nutrients in freshwaters from anthropogenic activities. During blooms cyanobacteria release in water their toxic secondary metabolites, known as cyanotoxins, along with other bioactive metabolites. Due to the negative impacts of these compounds on aquatic ecosystems and public health, there is an urgent need to detect and identify known and unknown cyanobacterial metabolites in surface waters. In the frame of the present study, a method based on liquid chromatography - high resolution mass spectrometry (LC-HRMS) was developed to investigate the presence of cyanometabolites in bloom samples from Lake Karaoun, Lebanon. Data analysis was performed using Compound Discoverer software with related tools and databases in combination to the CyanoMetDB mass list for detection, identification and structural elucidation of the cyanobacterial metabolites. In the course of this study, 92 cyanometabolites were annotated including 51 cyanotoxins belonging to microcystins, 15 microginins, 10 aeruginosins, 6 cyclamides, 5 anabaenopeptins, a cyanopeptolin, the dipeptides radiosumin B and dehydroradiosumin, the planktoncyclin and a mycosporine–like amino acid. Out of them, 7 new cyanobacterial metabolites, the chlorinated MC-ClYR, [epoxyAdda5]MC-YR, MC-LI, aeruginosin 638, aeruginosin 588, microginin 755C and microginin 727 were discovered. Moreover, the presence of anthropogenic contaminants was recorded indicating the pollution of the lake and emphasizing the need for assessment of the co-occurrence of cyanotoxins, other cyanobacterial metabolites and other compounds hazardous to the environment. Overall, results prove the suitability of the proposed approach for the detection of cyanobacterial metabolites in environmental samples but also highlight the necessity of spectral libraries for these compounds, considering the absence of their reference standards.

Effect of pre-chlorination on Microcystis aeruginosa cell integrity and microcystins removal

ABSTRACT High nutrient input into waterbodies increases potentially toxic cyanobacteria blooms. Pre-chlorination treatment is excellent for cyanobacterial cell inactivation and dissolved cyanotoxins removal in water supply sources. This study aims to evaluate the pre-chlorination effect treatment on Microcystis aeruginosa cell integrity and its hepatotoxins (microcystins, MC) release and degradation on a laboratory scale. Loss of cell integrity is observed with increasing chlorine concentration. The maximum cell permeability without cell disintegration occurs at 2.5 mg Cl2 L−1. Degradations up to 70% and chlorophyll-a reductions over 70% are observed after 60 min exposure, with complete degradation at 2.5 and 3 mg Cl2 L−1. However, chlorine (Cl2) exposure over 40.66 mg min L−1 is required for microcystins MC-LR (i.e. radicals: leucine (L) and arginine (R)) and MC-RR (i.e. radicals: arginine and arginine) oxidation oxidation to concentrations below the legislation value for water potability.

Spatial and temporal variability of greenhouse gas ebullition from temperate freshwater fish ponds

Fish ponds with their typically high carbon and nutrient inputs are relevant sources of greenhouse gases. However, not much is known about gas bubble emissions (ebullition) and their high spatiotemporal variability. This is the first study which quantified diffusive and ebullitive greenhouse gas emissions from temperate fish ponds. To improve greenhouse gas estimates, we investigated the diurnal and spatial variability of diffusive and ebullitive fluxes in 12 extensively to semi-intensively managed fish ponds near Bautzen, Germany. Emissions differed greatly between the different ponds but methane was consistently the predominant greenhouse gas. The feeding sites were hotspots with one order of magnitude higher ebullition rates compared to other parts of the ponds. At these hotspots, ebullitive fluxes of up to 38 L/m2d were measured with a mean bubble methane content of 79%, corresponding to a methane flux of 1.24 mol/m2d. Methane accounted for 90% of the global warming potential in one fish pond but carbon dioxide emissions of up to 242 mmol/m2d at the feeding sites were also significant. Nitrous oxide fluxes, in contrast, were low with 5 ± 9 μmol/m2d. Greenhouse gas ebullition decreased exponentially along a transect from the feeding site into the pond and showed some diurnal fluctuations. While diffusion was higher during night, ebullition rates increased in the morning, presumably caused by higher benthivorous fish activity. Our results highlight the potential of temperate fish ponds as significant greenhouse gas sources and ebullition as a significant pathway. For robust quantification, both small scale spatial and temporal variability as well as the hotspot of the feeding area must be considered.

Winter picoplankton composition, abundance, and vertical distribution in the Midriff islands and central regions of the Gulf of California

This study provides the first quantitative comparison of the composition and distribution of picoplankton components in the Gulf of California central region, including the Midriff islands Archipelago, in February 2014. Autotrophic picoplankton and heterotrophic bacterial abundances, estimated using flow cytometry were quantified at 5 m depth, at the peak of maximum fluorescence (FMax), and 30 m below FMax. Temperature and dissolved oxygen concentrations were lower in the northern Midriff islands Archipelago (MiA) than in the southern deep central gulf with a bathymetric sill toward the San Pedro Martir basin, where a more stratified water column prevailed (up to 40 m of the mixed layer). Gulf of California Water in the upper 150–200 m​ and Subtropical Subsurface Water below 200 m depth were observed. Heterotrophic bacteria (mean 3.59 × 105 cells mL−1) dominated numerically the picoplankton composition, followed by Synechococcus (mean 1.36 × 104 cells mL−1), Prochlorococcus (mean 7.15 × 103 cells mL−1), picoeukaryotes (mean 6.11 × 103 cells mL−1) and phycoerythrin-containing eukaryotes (mean 3.21 × 102 cells mL−1). Heterotrophic bacteria contributed 70.6 ± 16.7% to the total picoplankton carbon biomass. Total picoeukaryotes averaged 24 ± 2.85%, and Synechococcus accounted for 5.10 ± 4.83%. Prochlorococcus showed the lowest biomass of all picoplankton taxonomic groups (0.29 ± 0.50%). The canonical correspondence analysis showed that temperature was the main driver of Prochlorococcus and picoeukaryotes abundances, whereas picoeukaryotes were related to sigma-Θ and Synechococcus to dissolved oxygen concentration. The sharp differences in the spatial distribution of the picoplankton community in the surface layer (0–60 m) were closely associated with the oceanographic dynamics of the MiA and the central region of the Gulf of California. They provided evidence that heterotrophic bacteria and picoeukaryotes dominate the picoplankton biomass during the cold period of the 2014-year with a typically high nutrient input.

Short-term effect of filamentous macroalgae Chaetomorpha linum on Cymodocea nodosa: Does clonal integration alleviate macroalgae impacts?

Seagrasses are clonal plants that can form meadows in shallow coastal water. Under natural conditions, drift macroalgae can be found associated with seagrass but when facilitated by high nutrient input, opportunistic macroalgae can grow excessively and form mats that impose stressful and highly competitive conditions for seagrasses. In this study, we experimentally investigate the ecological significance of clonal integration in the ability of Cymodocea nodosa to tolerate biotic stress triggered by interactions with the drift macroalgae Chaeotomorpha linum. Our findings provide little support for the hypothesis that clonal integration can influence C. nodosa response to stress, as disconnected plants did not show significant differences in structural and morphological characteristics compared to intact plants. However, the physiological analysis suggests that C. nodosa may still benefit from shared resources with neighbouring plants to mitigate stress caused by C. linum. Moreover, the results indicate that C. nodosa adapts to the presence of the filamentous drift macroalgae C. linum by increasing leaf photosynthetic content, reducing growth rate, and modulating its morphology, regardless of its integration status.

Direction of Alliaria petiolata (garlic mustard) leachate's effect on early litter mass loss is dependent upon saprotrophic community composition

Differences between fungal and bacterial decomposition trajectories can be related to differences in sensitivity to nutrient input and to plant secondary metabolites. The invasive plant Alliaria petiolata (Beib. Cavara and Grande; garlic mustard) produces unique secondary metabolites (glucosinolates) capable of altering the functioning of root-associated communities. However, few studies explore whether these compounds can alter litter decomposition— a route for ecosystem-level impacts of garlic mustard invasion. This preliminary study investigated the potential for aqueous garlic mustard leachate to alter mass loss from tea litterbags in artificially fungal-dominant compared to intact soils (fungal and bacterial components) in laboratory microcosm incubations. Garlic mustard and native Acer saccharum (Marsh.; sugar maple) leachates stimulated fungal decomposition indistinguishably. In intact soils, garlic mustard suppressed mass loss relative to a water control and native leachate, though this later effect was only marginally significant. These results suggest the energetic benefit of labile carbon in garlic mustard leachate may exceed any negative effect of glucosinolates for fungal decomposers, but that bacteria were more sensitive to leachate toxicity and the inhibitory effects of high nutrient input. Overall, our results imply the direction of garlic mustard's effect on decomposition may depend on saprotrophic community composition and therefore the consequences for litter decay in garlic mustard invaded soils may be context-dependent.

An Early Cretaceous sponge meadow from the Neuquén Basin, west-central Argentina: unsuspected hosts of a dynamic sclerobiont community

ABSTRACTSponges, especially Calcarea, are minor components of benthic associations, especially during the Mesozoic. In the Lower Cretaceous of the Neuquén Basin, small calcareous sponges have been found building a small monospecific meadow. It is restricted to a marlstone lens-shaped bed in a quiet outer-ramp setting in the Cerro Marucho Locality (Picún Leufú depocentre), above a shell bed of small exogyrid oysters; oysters and sponges were the only preserved macrobenthic faunal elements. Individual sponges were small, under 4 cm high, and presented a sub-cylindrical morphology with one or more rounded, apical osculi, many inhalant openings and triactine spicules. Specimens studied here were assigned to Endostoma sp. aff. Endostoma nodosa. These sponges are quite commonly encrusted by exogyrid oysters, serpulids, sabellids, agglutinating foraminifers and cyclostome bryozoans. Overgrowths among sclerobionts were common, though no undoubtedly in vivo interaction has been recorded. Disarticulated left oyster valves were frequently bioclaustrated by the sponges, showing that in vivo settlement upon sponges was common. Many oysters settled in the periphery of the osculum suggesting a commensal relationship. The study of this sponge meadow and its sclerobiont community allowed the identification of different stages of ecological succession. The pioneer stage was characterised by sponge settlement on oyster valves, within an otherwise soft consistency bottom. High sedimentation or high nutrient inputs, either individually or in combination, could explain the great abundance of oysters. During the climax stage, sponges thrived and harboured several sclerobiont taxa, developing a relatively dynamic palaeocommunity. Finally, an intensification in either sedimentation rates or nutrient input (or both) past the tolerable threshold for sponges may have been the cause(s) of the meadow's demise. Endostoma and similar forms were up to now reported mostly from the Jurassic and Cretaceous of Europe as accessory builders, or as accompanying fauna in reefal settings. This new record shows that in rare occasions they could form low-relief meadows on their own.

Rise of toxic cyanobacterial blooms is promoted by agricultural intensification in the basin of a large subtropical river of South America.

Toxic cyanobacterial blooms are globally increasing with negative effects on aquatic ecosystems, water use and human health. Blooms' main driving forces are eutrophication, dam construction, urban waste, replacement of natural vegetation with croplands and climate change and variability. The relative effects of each driver have not still been properly addressed, particularly in large river basins. Here, we performed a historical analysis of cyanobacterial abundance in a large and important ecosystem of South America (Uruguay river, ca 1900 km long, 365,000 km2 basin). We evaluated the interannual relationships between cyanobacterial abundance and land use change, river flow, urban sewage, temperature and precipitation from 1963 to the present. Our results indicated an exponential increase in cyanobacterial abundance during the last two decades, congruent with an increase in phosphorus concentration. A sharp shift in the cyanobacterial abundance rate of increase after the year 2000 was identified, resulting in abundance levels above public health alert since 2010. Path analyses showed a strong positive correlation between cyanobacteria and cropland area at the entire catchment level, while precipitation, temperature and water flow effects were negligible. Present results help to identify high nutrient input agricultural practices and nutrient enrichment as the main factors driving toxic bloom formation. These practices are already exerting severe effects on both aquatic ecosystems and human health and projections suggest these trends will be intensified in the future. To avoid further water degradation and health risk for future generations, a large-scale (transboundary) change in agricultural management towards agroecological practices will be required.