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)

Changes in parasite-chaetognath species assemblages in the Mexican Central Pacific before and during El Niño 1997-1998.

We investigated the seasonal and interannual changes in diversity, abundance, and prevalence of chaetognaths and their parasites collected monthly during 1996-1998 in the Mexican Central Pacific. We tested the hypothesis of a positive relationship between abundance and species richness of chaetognaths and their parasites, and investigated the influence of the 1997-1998 El Niño event on this host-parasite interaction. Of the 9 chaetognath species collected in the present study, only 7 were found to be parasitized. Of 78154 chaetognath specimens collected, 790 were parasitized (1% prevalence) with at least 1 type of epibiont (cysts, perhaps protists) and 6 types of endoparasites: protists (apicomplexans, dinoflagellates, and ciliates), digeneans, cestodes, acanthocephalans, nematodes, and other unidentified endoparasites. Cysts, digeneans, and cestodes were the most abundant parasites. Mean intensity ranged from 1-4 endoparasites and from 1-21 epibionts host-1. Zonosagitta bedoti and Flaccisagitta enflata were the most abundant chaetognath species and had the highest parasite diversity. Mesosagitta minima and Parasagitta euneritica had the highest parasite prevalence (>2%). A 2-way cluster analysis defined sampling month groups as before, during, and after the 1997-1998 El Niño. The highest abundances of chaetognaths and parasites were associated with a high thermal stratification index, salinity, and mixed layer depth. We conclude that there is a positive, non-linear correlation between the abundance of chaetognaths and their parasites. Although El Niño decreased the abundance and diversity of chaetognaths throughout the time series, the abundance and diversity of their parasites were not significantly different among hydro-climatic periods, suggesting that host abundance must decrease orders of magnitude to influence host availability for parasites.

The discovery of acanthocephalans parasitizing chaetognaths.

A comprehensive literature review shows that 12 types of pathogens, micropredators and parasites are reported to interact with chaetognaths, mostly digenean trematodes, cestodes and nematodes larval stages. Through analysis of 78,152 chaetognaths from a monthly zooplankton time series (Jan 1996-Dec 1998) collected in the Mexican Central Pacific twelve acanthocephalan larvae parasitizing chaetognaths were discovered. This is the first record of an acanthocephalan parasitizing chaetognaths, raising to 13 the types of symbionts known to interact with them (excluding predators). Cystacanth larval specimens of Corynosoma sp. (Polymorphidae) were observed parasitizing the head, trunk and caudal cavities of three of the eight chaetognath species inhabiting this tropical coastal region (Flaccisagitta enflata, Flaccisagitta hexaptera and Zonosagitta bedoti). Because Corynosoma sp. parasitized chaetognaths during different months and years (Jan-Feb 1996, Mar and Jul 1997, Jan, Jun, Aug-Sep 1998) and because the total length of these cystacanths varied between 165-480 µm, suggesting growth inside the hosts, we conclude that chaetognaths are intermediate hosts of Corynosoma sp. The twelve parasitized chaetognaths were juveniles (without gonads) or immature adults (none in reproductively mature stage IV); therefore Corynosoma may have a negative influence on host reproduction. Marine crustaceans (amphipods, decapods, copepods, mysids and euphausiids) and fishes are common intermediate or paratenic hosts of acanthocephalans. Fish, sea birds and marine mammals are definitive hosts for marine Corynosoma species. The present discovery implies that acanthocephalans are transmitted trophically through different intermediate hosts (crustaceans, chaetognaths and/or fish); thus chaetognaths can also be part of the marine acanthocephalan life cycle.