Changes in the community structure of stony corals in the southern Mexican Caribbean.

The Mexican Caribbean coral reef ecosystem has endured the effects of global and regional stressors and, recently, the massive arrivals of the free-living, floating brown algae Sargassum spp. This study aimed to evaluate spatiotemporal changes in the stony coral community structure in the southern Mexican Caribbean by a temporal comparison of live coral cover and colony density using a data set collected in 2008-2009 and a recent survey in 2021 within a Protected Natural Area. A multivariate analysis approach was used to reveal spatiotemporal changes in coral cover and colony densities. Coral cover ranged from 6.9 to 8.9% in 2008-2009 to 6.5% in 2021, the lowest values recorded for the area. Coral colony density ranged from 0.68 to 0.78 colonies m-1 in 2008-2009 to 0.68 colonies m-1 in 2021. The present results appear to represent subtle changes during the last decade.

Synthesis of a New Co Metal-Organic Framework Assembled from 5,10,15,20-Tetrakis((pyridin-4-yl) phenyl)porphyrin "Co-MTPhPyP" and Its Application to the Removal of Heavy Metal Ions.

The synthesis of a Co metal-organic framework assembled from 5,10,15,20-tetrakis((pyridin-4-yl)phenyl)porphyrin; TPhPyP) "Co-MTPhPyP" is reported. The TPhPyP ligand was synthesized via aldehyde condensation in 28% yield and characterized by 1H nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FTIR), high-resolution mass spectrometry (HRMS), and UV-visible spectroscopy (UV-vis). Co-MTPhPyP was prepared by the solvothermal method from TPhPyP and CoCl2·H2O in 55% yield and characterized by X-ray powder diffraction (XRD), FTIR, thermogravimetric analysis (TGA), field-emission scanning electron microscopy with energy-dispersive X-ray (FESEM-EDS), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS), showing a particle size distribution of 418 ± 58 nm. The sorption properties of the Co-MTPhPyP for the effective removal of Pb(II) and Cu(II) were evaluated in an aqueous medium and Cthe results showed uptake capacities of 383.4 and 168 mg of the metal g-1 after 2 h, respectively. Kinetic studies of Pb(II) adsorption by Co-MTPhPyP were adjusted to the pseudo-second-order model with a maximum adsorption capacity of 458.8 mg g-1 at 30 min of exposition.

Predicting the Simultaneous Oxidation of Ammonia, Nitrite, and m-cresol and Microbial Growth in a Sequencing Batch Reactor with a Kinetic Model Using Inhibition and Inactivation Effects.

The kinetic model derived in this study was able to adequately predict the simultaneous oxidation of ammonia, nitrite, and m-cresol and microbial growth using nitrifying sludge in a sequencing batch reactor. Time-varying inhibition and inactivation effects were successfully incorporated in the process kinetics to account for the past cell exposure history to m-cresol increasing concentrations (up to 150 mg C L-1). The initial concentration of the microbial species (ammonia and nitrite oxidizers, heterotrophs) was evaluated using pyrosequencing of DNA samples of the consortium. These measurements allowed to establish a model that explicitly handles specific reaction rates and to enhance the practical identifiability of the model parameters. A single simulation run was used to adequately predict the kinetic behavior of the main variables throughout the 242 cycles using a single set of initial conditions in the first cycle. This kind of dynamic model may be used as a helpful predictive tool to improve nitrification by avoiding the occurrence of severely repetitive inhibitive conditions due to the presence of inhibitive/toxic aromatic compounds.

Leachate effects of pelagic Sargassum spp. on larval swimming behavior of the coral Acropora palmata.

An emerging disturbance for Caribbean reefs is the massive arrival of pelagic Sargassum, which deteriorates water quality due to the production of leachates. The highest arrivals of Sargassum took place when broadcasting corals spawned. We experimentally determined the effect of Sargassum leachates on swimming behavior of Acropora palmata larvae through five treatments (control, stain (simulating 100% leachate color), and 25%, 50% and 100% Sargassum leachate concentrations) during 30 min (10 min of videos and 20 min of post-observations). In the videos, larvae with leachates reduced swimming speed, were positively geotactic, the percentage of individuals that swam in a spiral pattern increased, and most behavioral displacements occurred at lower frequencies than larvae without leachates. Moreover, symptomatic spiral behavior was higher in the presence of leachates, suggesting that this behavior may be an effect of pollution. During post-observations, most larvae with leachates were motionless. This is the first time that Sargassum leachates have been documented modifying larval swimming behavior, which may reduce larval dispersion and genetic diversity. We suggest that a future evaluation of the effects of leachates at lower concentrations and over longer periods of exposure is needed. The resilience of corals may be compromised if Sargassum arrivals become frequent events.

Microencapsulation of Red Sorghum Phenolic Compounds with Esterified Sorghum Starch as Encapsulant Materials by Spray Drying.

Phenolic compounds with antioxidant properties are highly sensitive molecules, which limits their application. In response, extruded esterified starch has been proposed as efficient encapsulating material. In this work, we aim to describe the encapsulation of red sorghum phenolic compounds by spray drying using extruded phosphorylated, acetylated and double esterified sorghum starch as wall material. Their respective encapsulation yields were 77.4, 67.4 and 56.8%, and encapsulation efficiency 91.4, 89.7 and 84.6%. Degree of substitution confirmed esterification of the sorghum starch and Fourier transform infrared spectroscopy showed the significant chemical and structural changes in the extruded esterified starch loaded with phenolic compounds. Microcapsules from phosphorylated sorghum starch showed the highest endothermic transition (173.89 °C) and provided a greater protection of the phenolic compounds during storage at 60 °C for 35 days than the other wall materials. Extruded esterified sorghum starch proved to be effective material for the protection of phenolic compounds due to its high encapsulation efficiency and stability during storage.

Synthesis and succinylation of starch nanoparticles by means of a single step using sonochemical energy.

In the present research work, esterified nanoparticles with 2-octen-1-ylsuccinic anhydride were synthesized from waxy corn starch, to our knowledge for the first time, in a single step of ultrasonic treatment. First, the ultrasound time to produce non-esterified nanoparticles was studied. The results showed that non-esterified nanoparticles had sizes ranging from 63 to 48 nm, as well as polydispersity indexes (PDI) ranging from 0.458 to 0.224 and ζ-potential values ranging from -16 to -24 mV in ultrasonication times ranging from 20 to 100 min. Succinylated nanoparticles were obtained at 80 min with two degrees of substitution i.e., 0.003 and 0.01, hydrodynamic sizes of 57 and 83 nm, PDI of 0.479 and 0.91, and ζ-potential values of -6.27 and -14.03 mV, respectively. The succinylation of nanoparticles was confirmed by FTIR spectroscopy, and it was possible to elucidate the conversion of amylopectin molecules into amylose blocks. The nanoparticles showed stability during storage in aqueous suspension at 4 °C. By means of the ultrasonic technology, destructuring of the waxy corn starch and, at the same time, the succinylation of the nanoparticles in a total time of 120 min was effectively achieved.

Severe impacts of brown tides caused by Sargassum spp. on near-shore Caribbean seagrass communities.

From mid-2014 until the end of 2015, the Mexican Caribbean coast experienced a massive influx of drifting Sargassum spp. that accumulated on the shores, resulting in build-up of decaying beach-cast material and near-shore murky brown waters (Sargassum-brown-tides, Sbt). The effects of Sbt on four near-shore waters included reduction in light, oxygen (hypoxia or anoxia) and pH. The monthly influx of nitrogen, and phosphorus by drifting Sargassum spp. was estimated at 6150 and 61kgkm-1 respectively, resulting in eutrophication. Near-shore seagrass meadows dominated by Thalassia testudinum were replaced by a community dominated by calcareous rhizophytic algae and drifting algae and/or epiphytes, resulting in 61.6-99.5% loss of below-ground biomass. Near-shore corals suffered total or partial mortality. Recovery of affected seagrass meadows may take years or even decades, or changes could be permanent if massive influxes of Sargassum spp. recur.

Respirometric response and microbial succession of nitrifying sludge to m-cresol pulses in a sequencing batch reactor.

A nitrifying consortium was kinetically, stoichiometrically and molecularly characterized via the in situ pulse respirometric method and pyrosequencing analysis before and after the addition of m-cresol (25 mg C L-1) in a sequencing batch reactor (SBR). Five important kinetic and stoichiometric parameters were determined: the maximum oxygen uptake rate, the maximum nitrification rate, the oxidation yield, the biomass growth yield, and the substrate affinity constant. An inhibitory effect was observed in the nitrification process with a recovery of this by up to eight SBR cycles after m-cresol was added to the system. However, full recovery of the nitrification process was not observed, as the maximum oxygen uptake rate was 25% lower than that of the previous operation without m-cresol addition. Furthermore, the pyrosequencing analyses of the nitrifying consortium after the addition of only two pulses of 25 mg C L-1 m-cresol showed an important microbial community change represented by a decrease in the nitrifying populations and an increase in the populations degrading phenolic compounds.