An accessible method to standardize polyethylene microsphere (<100 µm) concentrations for zooplankton ingestion experiments.

The ubiquity of microplastics has caused alarm as to the impact of these materials on aquatic life, leading to experimental studies to understand these effects. In zooplankton bioassays, microspheres (Ms) are often used as a proxy to represent aquatic microplastic contamination due to their homogeneity and small sizes (<100 µm). The present study proposes an accessible protocol that does not require highly specialized equipment for the creation of Ms stock solutions and environmentally realistic experimental concentrations and describes some common issues. Adult females of the calanoid copepod Centropages furcatus underwent treatments of two Ms sizes at experimental concentrations of 10 Ms/mL. They consumed on average 0.9 ± 2.6 Ms/mL of 45-53 µm Ms, and 2.4 ± 1.1 Ms/mL of 38-45 µm Ms. The results are not directly comparable with other studies due to the wide variety of methods used but successfully demonstrate the reproducibility of the proposed protocol.

In situ microplastic ingestion by neritic zooplankton of the central Mexican Pacific.

Microplastics (MPs) are present across the global ocean and can be encountered by many species, including zooplankton. Although they fall within the size range of zooplankton prey, there are few studies on MPs ingestion carried out in situ. In this study, we analyzed MPs ingestion during two seasons (rainy and dry) of organisms from 5 taxonomic groups of zooplankton from two bays of the Mexican central Pacific: Manzanillo and Navidad. In total, 2643 individuals were analyzed, and of those 23 individuals contained MPs. The ingestion rate by taxonomic group was 1 MP/36 copepods (0.02), 1 MP/30 decapods-mysis (0.03), 1 MP/29 decapods-megalopa (0.03), and 1 MP/200 fish larvae (0.005). No plastics were found in chaetognaths, amphipods, or decapods-zoea. The average length of the ingested particles was 468.1 ± 113.8 µm, with a minimum of 15.6 and a maximum of 647.6 µm. All MPs >300 µm were fibers, with diameters <50 µm. Fragments were the most abundant MPs (54.2%), followed by fibers (34.2%) and spheres (11.4%). Statistical analyses showed no significant differences (p > 0.05) between the bays or seasons. Using RAMAN spectroscopy, it was possible to identify 6 different types of polymers, with poly (ethylene:propylene) being the most abundant (42.8%). This polymer is commonly used to manufacture plastic bags, ropes and fishing nets. The results confirm that certain zooplankton groups are consuming MPs and suggest that omnivorous species are more likely to ingest MPs, possibly due to their capacity for foraging flexibility and opportunistic feeding strategies. However, the ingestion of MPs cannot be attributed to a single factor; it is necessary to consider variables such as the sampling area, feeding strategy, size, and seasonality to understand the dynamics of MPs ingestion by zooplankton groups.

Identification of microplastics and associated contaminants using ultra high resolution microscopic and spectroscopic techniques.

The present study establishes a new procedure to characterize micro(nano)plastics (MNPs) and identify contaminants adhered to the plastic particles in aquatic environments by applying ultra-high resolution microscopy and spectroscopy techniques. Naturally fragmented microplastics (MPs) were collected from Manzanillo and Santiago Bays, Mexico and analyzed using: Confocal Laser Scanning Microscopy (CLSM), Fourier-Transform Infrared Spectroscopy (FTIR), µ-RAMAN, Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Environmental Electron Scanning Microscopy (ESEM). The information obtained from each of these techniques was integrated to produce a comprehensive profile of each particle. Sample preparation was tested by applying three different rinses (unrinsed, distilled water and alcohol) to untreated MPs collected from Manzanillo Bay, finding that when large impurities are present an alcohol rinse makes it easier to examine the associated contaminants. Based on this emerging methodology, polyethylene and polypropylene MPs were identified with associated contaminants such as arsenic, cadmium, aluminum, and benzene. This study demonstrates the presence of pollutants that may be linked to MNPs in aquatic ecosystems and proposes an accurate relatively fast procedure for their analysis that does not require chemical extraction.

Surface layer microplastic pollution in four bays of the central Mexican Pacific.

Surface microplastics were sampled monthly in four tropical bays (Manzanillo, Santiago, Navidad and Cuastecomates) of the central Mexican Pacific during March 2017 to February 2018. Microplastic concentrations ranged between 0.01 and 1.05 particles/m2 with a median per bay ranging between 0.26 and 0.40 particles/m2. Raman spectroscopy registered polypropylene (40%), polyethylene (40%) and polyester (20%) polymers. Fibers dominated all samples, except for Manzanillo where fragments numerically dominated during the rainy season (Jun-Oct). Fiber concentration was not significantly different among bays or seasons, likely associated with continuous wastewater discharge. Fragment concentrations were significantly higher in Bahía Manzanillo and Santiago than the other two bays. Non-metric multidimensional scaling showed distinct distribution of Manzanillo samples (which has important port activities) as compared to Santiago, Navidad, Cuastecomates (where tourism economic activities predominate). This first direct comparison of sea surface microplastic concentration among four bays in Mexico provides a baseline to study impacts on marine zooplankton in this tropical ecosystem.

Seasonal variability of copepod community structure and abundance modified by the El Niño-La Niña transition (2010), Pacific, Mexico / Variabilidad estacional de la estructura comunitaria y abundancia de copépodos, modificada por la transición El Niño-La Niña (2010) en el Pacífico, México

Abstract Copepods are an important planktonic group, and account for most of the total biomass and species diversity in pelagic marine ecosystems. Seasonal variability of the community structure of copepods in the Eastern tropical Pacific off central Mexico was studied during three distinct hydrodynamic periods in 2010 using statistical and multivariate analyses. The survey period included the second half of the 2009-2010 El Niño (January), the neutral transition period (May-June), and the first half of the 2010-2011 La Niña (October). Seventy-eight copepod species were identified; richness ranged from 11 to 47 species per station, with seasonal averages from 25 species in May to 35 species in January. Cluster analysis indicated that there were four principal groups present across the surveyed periods, defined by January (El Niño), October (La Niña), May offshore stations, and May upwelling stations (cyclonic eddy and coastal stations). There were no significant differences in abundance, but the January (El Niño) cluster was most diverse with 32 species, May offshore and October (La Niña) clusters each had 25 species, and the May upwelling was the least diverse cluster with 18 species. Mesoscale processes were strongest during May, which was the only period with a significant inshore-offshore gradient of species richness and diversity. Canonical correspondence analysis (CCA) revealed that variability was primarily driven by subsurface (75-200 m) ammonium, and surface (0-50 m) temperature, nitrates+nitrites, salinity and phosphorus. Copepodites and adults of the primarily herbivorous Eucalanidae dominated the stations of the upwelling cluster, while copepodites and adults of the carnivorous Euchaetidae dominated the January (El Niño) station cluster. The higher Chl a levels during the less productive (reduced upwelling) El Niño period were probably due to reduced grazing activities and increased ammonium availability through increased zooplankton metabolism. The horizontal distribution of copepods in the Eastern Tropical Pacific off Mexico appears to be principally defined by mesoscale eddy processes (offshore) and upwelling (coastal). These mesoscale processes were affected by El Niño - La Niña transitions, which subsequently disrupted the inshore-offshore gradient and in the case of El Niño likely caused reductions in copepod abundance across the entire region which persisted for the entire study period, and possibly longer.(AU)

Resumen Los copépodos son un importante grupo planctónico y representan la mayor parte de la biomasa total y la diversidad de especies en los ecosistemas marinos pelágicos. La variabilidad estacional de la estructura de la comunidad de copépodos se analizó en el Pacífico central mexicano durante tres períodos hidrodinámicos durante el 2010, mediante análisis estadísticos y multivariados. El período de estudio incluyó la segunda mitad del Niño 2009-2010 (enero), el período de transicional (mayo) y la primera mitad del La Niña 2010-2011 (octubre). Setenta y ocho especies de copépodos fueron identificadas; la riqueza varió de 11 a 47 especies por estación, con promedios estacionales de 25 especies en mayo a 35 especies en enero. El análisis de clúster indicó la presencia de cuatro grupos principales en los períodos estudiados: enero (El Niño), octubre (La Niña), un grupo de estaciones oceánicas en mayo, y un grupo de estaciones de afloramientos en mayo (remolino ciclónico y estaciones costeras). No hubo diferencias significativas en la abundancia entre grupos, pero el grupo de enero (El Niño) fue más diverso con 32 especies. Los grupos de mayo (oceánico) y octubre (La Niña) tenían 25 especies cada uno, y el grupo de mayo (afloramientos) fue el menos diverso con 18 especies. Los procesos de mesoescala fueron más intensos durante mayo, que fue el único período con un gradiente significativo costeroocéano de riqueza de especies y diversidad. El análisis de correspondencias canónicas explicó que la variabilidad se debe principalmente a la concentración de amonio en la capa profunda (75-200), y la temperatura, nitratos + nitritos, salinidad y fósforo presente en la capa superficial (0-50 m) de la columna de agua. Los copepoditos y adultos herbívoros de la familia Eucalanidae, dominaron las estaciones de surgencia, mientras que los copepoditos y adultos carnívoros de Euchaetidae dominaron las estaciones de enero (El Niño). Las concentraciones más altas de Clorofila a durante El Niño, que fue el periodo menos productivo (surgencia reducida), se deben probablemente a la reducción de actividades de pastoreo. La distribución horizontal de copépodos en el Pacífico central mexicano parece estar definida principalmente por la influencia de remolinos de mesoescala (mar adentro) y surgencias (costera). Estos procesos oceanográficos fueron afectados por la transición de El Niño a La Niña, que posteriormente interrumpieron el gradiente costero-oceánico y en el caso de El Niño probablemente causó una disminución en la abundancia de copépodos en toda la región durante todo el período de estudio, que posiblemente persistió en los meses posteriores.(AU)