Mexican Pacific Coast Research Articles

U-Pb Ages of Zircon Grains in the Playa Azul Beach Sediments, Guerrero State, Mexican Pacific

ABSTRACT The mineralogy of bulk sediments, U-Pb ages and chemistry of 195 detrital zircon grains recovered in the Playa Azul beach, Mexican Pacific coast were performed to infer their provenance. The bulk sediments were composed of minerals like quartz, feldspar, titanite, plagioclase, zircon, and magnetite. The average Th/U ratio in zircon grains was ~ > 0.2, indicated an igneous origin. The chondrite normalized rare earth element (REE) patterns of zircons were depleted in low REE (LREE) and enriched in heavy REE (HREE), with positive cerium and negative europium anomalies, indicating a granitoid source. U-Pb ages of zircon grains revealed the predominance of Cenozoic and Mesozoic ages in samples PAC2 (~ 33.8 - 61.8 Ma, n = 90 and ~ 67 - 132 Ma, n = 10, respectively) and PAC19 (~ 0.1 -39.6 Ma, n = 55 and ~ 67 - 251 Ma, n = 20, respectively). Minor peaks were represented by Palaeozoic (n = 9) and Precambrian (n = 11) ages in PAC19. Zircon ages and their morphology indicated that they were mostly derived from the nearby terranes. The source terranes, which supplied Cenozoic zircons to the beach area were the coastal Cenozoic plutons and Cuicateco terrane. The Mesozoic zircons in the Playa Azul coastal sediments were derived from the Mixteca (Acatlan Complex), Guerrero, and Xolapa terranes, located along the Mexican Pacific coastal zone. The Proterozoic zircons were represented by the coastal Oaxacan Complex. In addition, the Arteaga Complex in the Guerrero State, adjacent to the playa Azul beach was the potential source for the Eocene zircons.

Sediment composition and U–Pb ages of detrital zircons in the Salina Cruz and Puerto Ángel beaches along the Gulf of Tehuantepec, Mexican Pacific

The Salina Cruz and Puerto Ángel beach areas in the Gulf of Tehuantepec, Mexican Pacific coast represent an important economic sector of the region. In this study, the mineralogy and geochemistry of bulk sediments, and geochronology of 400 detrital zircons recovered from the beach sediments were analysed to investigate their origin. The sediments are abundant in quartz, feldspar, ilmenite, cordierite, aragonite and anorthite. The chemical index of weathering revealed a moderate to intense weathering in the source area. The chondrite normalized REE patterns of bulk sediments are similar to the found in the Upper Continental Crust, suggesting the derivation of sediments from felsic igneous rocks. The REE patterns of zircons and the trace elemental ratios reveal a continental crust origin. Zircon U–Pb ages in the Salina Cruz beach were represented by Proterozoic (~545.1–1314.1 Ma; n = 170) and Cenozoic (~0.01–66 Ma; n = 20). The Puerto Ángel beach was abundant in Proterozoic zircon grains (~600.9–1171.4 Ma; n = 109) and followed by Mesozoic grains (~73.78–246.9 Ma; n = 40). The comparison of zircon U–Pb ages of this study with probable source rocks reveals that the Oaxaquia Terrane and Chiapas Massif Complex were the major contributors of Proterozoic zircons to the coastal areas. Similarly, the results indicate that the Cenozoic zircons were contributed by the Chiapas Massif Complex, coastal batholith and Cuicateco Terrane. The Mesozoic zircons are very few, derived from the nearby Xolapa Complex and the Chuacús Terrane.

TEMPERATURE AND PRECIPITATION TRENDS DUE TO CLIMATE CHANGE IN THE HUIXTLA RIVER BASIN IN CHIAPAS, MEXICO

The objective of this work was to analyze whether there is a trend in climate change in the Huixtla River basin on the Mexican Pacific coast in the State of Chiapas. To detect this, temperature and precipitation trends were analyzed using data for the 1960–2014 period and the 27 indices proposed by the Expert Team on Climate Change Detection and Indices (ETCCDI) at Despoblado, Escuintla, Finca Chicharras, Huehuetán, Huixtla, and Motozintla weather stations of the National Meteorological Service (SMN). Missing data were collected where necessary for precipitation using the U.S. National Wheater Service method and for temperatures using the Climate Engine platform. The indices were obtained with RClimDex by conducting the proposed data quality controls and classified on the basis of their statistical significance (0.05) and their increasing or decreasing trend. Among the changes found, higher temperatures were detected in the middle and lower western parts of the basin (TX90p), as well as a longer period of hot days (WSDI). The upper and lower eastern parts of the basin presented a shorter period of hot days. The upper and lower parts of the basin showed a cooling trend, with colder days (TX10p) over longer periods (CSDI). Across the basin, precipitation has increased by one and five days (RX1day and RX5day) as well as in total amount (PRCPTOT). In general, there were shorter dry periods (CDD) and longer wet periods (CWD). Rainfall above the R5mm, R10mm, R20mm, R70mm, and R150mm thresholds across the basin showed an increasing trend.

Monthly Occurrence of Endoparasites of Chaetognaths in a Coastal System of the Mexican Central Pacific

The prevalence of endoparasites associated with chaetognath abundance in the coastal waters of the Mexican Central Pacific was studied fortnightly from November 2010 to December 2011. A total of 35 (0.21%) out of 16,407 chaetognaths were found to be parasitized. Five out of twelve chaetognath species (Flaccisagitta enflata, F. hexaptera, Parasagitta euneritica, Serratosagitta pacifica, Zonosagitta bedoti) were found to be parasitized by nine endoparasitic taxa: Protists (two morphotypes), digenean metacercariae [Didymozoidae, Hemiuridae, Parahemiurus sp., Lepocreadiidae, Prosorhynchus sp. (Bucephalidae)], and cestodes (metacestodes) [Tetraphyllidea (two morphotypes)]. Parasagitta. euneritica and Z. bedoti were the most abundant chaetognath species, and Protist sp. 2 and Tetraphyllidea sp. 1 were the most abundant parasites. The highest prevalence for most of the endoparasite species occurred in June, and the values varied according to three hydroclimatic periods: stratified (S), semi-mixed (SM), and mixed (M). Eight non-infected chaetognath species, two parasitized chaetognaths (F. enflata and S. pacifica), and two parasites (Protist sp. 1 and Tetraphyllidea sp. 2) were associated with warm temperatures (S and SM periods); in contrast, P. euneritica, Z. bedoti, parasitized F. hexaptera, and the parasite Tetraphyllidea sp. 1 showed a strong local preference for cooler temperatures, high productivity, and high biomass conditions (M periods). We discovered the occurrence of the digenean Prosorhynchus sp. (Bucephalidae) parasitizing the chaetognath P. euneritica, and this is the first report of Prosorhynchus parasitizing chaetognaths worldwide. We also confirmed the presence of Lepocrediidae (metacercariae larval stage) infecting F. hexaptera, a parasite that had only been recorded infecting other chaetognaths of the Atlantic Ocean. The parasite diversity affecting the chaetognath populations of the Central Mexican Pacific coast likely differs between the offshore, outer slope areas, and the surveyed coastal system.

CHARACTERIZATION OF MICROPLASTICS IN MARINE SEDIMENTS FROM THE GULF OF TEHUANTEPEC, MEXICAN PACIFIC

Microplastics (MPs), a universal pollutant is widely distributed in sediments, which attracted the environmental researchers worldwide. MPs are harmful may adsorb toxic compounds present in the environment, which can be ingested by benthic organisms and easily transfer to humans. We investigated the distribution of MPs and its types in beach sediments from the Tehuantepec River mouth, Gulf of Tehuantepec, Mexican Pacific coast. MPs are categorized by their size, shape, color, and polymer types. 73 % of MPs detected are < 5 mm in size. Fiber and colorless are mostly dominated in all samples. The fibers are weathered and degraded with adhered particles on their surfaces. The polymer types detected are polyacrylamide (PAM) and poly(methyl acrylate) (PMA), which are rarely reported in Mexico beach sediments. The prevalence of colorless MPs at the Gulf of Tehuantepec beach needs further attention.

New records and five new species of sipunculans (Sipuncula) from the central and northwestern Mexican Pacific

Sipuncula are marine unsegmented worms that can be found in benthic habitats, from shallow to deep-sea waters. In Mexico these worms have been scarcely studied. Among nine studies in the entire Mexican Pacific coasts, seven are from the central and northwestern Mexican Pacific. For over 80 years, only 24 species have been recorded. To improve the knowledge of the sipunculans from the central and northwestern Mexican Pacific, 501 specimens from three scientific collections of Mexico were revised. The specimens were collected by diverse methods from intertidal, subtidal, and bathyal depths (~1000 m), from 27 locations along the central and northwestern Mexican Pacific. Sixteen taxa belonging to nine genera and five families were identified. One species is recorded for the first time in the Mexican Pacific and five new species are described, one from intertidal and shallow subtidal depths: Phascolosoma (Phascolosoma) azteca sp. nov.; two from subtidal depths: Phascolion (Lesenka) salgadoi sp. nov. and Sipunculus (Sipunculus) bastidai sp. nov.; and two from bathyal depths: Apionsoma (Apionsoma) silviae sp. nov. and Apionsoma (Edmondsius) hendrickxi sp. nov.

Habitat fragmentation erodes taxonomic and functional diversity of waterbird communities of the South Pacific coast of Mexico

We characterize the taxonomic and functional diversity of waterbird communities in mangrove forests of 23 coastal lagoons in the southern Mexican Pacific coast, to evaluate the hypothesis of decline of taxonomic and functional richness of waterbird communities in the face of loss of natural habitat cover and increased fragmentation. We quantified patterns of land use cover, considering the heterogeneity of natural and anthropized vegetation cover as a proxy for human-caused fragmentation, and used generalized linear models to explore the relationship between these two covers with the taxonomic richness and functional richness of bird communities. Results show that both aspects of biodiversity positively relate to larger natural habitat areas, while higher fragmentation values have a negative effect on them. Our results suggest that habitat loss and fragmentation of vegetation cover negatively affect the diversity of waterbird communities and can compromise their link to ecosystem functioning processes in coastal lagoons, by decreasing their functional diversity.

Seasonal variation of organic carbon in the urban tropical mangrove estuary El Salado, in Jalisco, Mexico

ABSTRACT In the El Salado estuary in the Mexican Pacific coast, we examined the seasonal variation of organic carbon (OC) in sediments, pore water and litterfall in three areas dominated by common mangrove species (Avicennia germinans, Laguncularia racemosa, and Rhizophora. mangle), as well as in the water and sediments in the main channel of the estuary. Mangrove sediment OC varied from 3.70% in the R. mangle area to 12.58% in the L. racemosa area, whereas variations in sediment pore water OC varied from 285.6 to 22.6 mg·L−1. OC from mangrove litterfall varied from 151.2 to 0.6 g·m−2 in the different mangrove species areas. OC values were higher in the dry season and lower in the rainy season. The observed OC among the different species in the dominated areas indicates that mangroves are able to release a considerable amount of OC through litterfall, with part of it sequestered in sediments.

Improved eDNA assay evidences further refugia for critically endangered smalltooth sawfish (Pristis pectinata) in Mexico

Sawfishes are considered one of the most threatened marine fish taxa globally, with major contractions in their geographic range documented over the last 50 years across all oceans. Two sawfish species used to be found in Mexico, but a historical lack of research and first-hand baseline information recently raised concerns about the fate of both species there. Recent Local Ecological Knowledge (LEK) and environmental DNA (eDNA) research has shown that: a) Pristis pectinata and P. pristis were formerly abundant and widely distributed in the Mexican Atlantic coast, and the latter also in the Mexican Pacific coast, and b) sawfishes (at least P. pectinata) are still found in some coastal refugia in central Veracruz state and Campeche state on the Atlantic coast. In the present research we developed improved primers that allow for better species ID resolution for Pristis pectinata and P. pristis through successful sequencing of eDNA samples by amplifying a 270 bp fragment of the CO1 gene. Our results based on the analysis of 305 eDNA samples showed an improved positive species identification rate through sequencing, demonstrate that P. pectinata occurs in other coastal refugia along the Yucatán Peninsula in the Mexican Caribbean, and suggest this species might be extirpated from southern Veracruz, while no P. pristis eDNA has been found along the Atlantic coast.

Thelephora pacifica (Basidiomycota: Thelephorales), a new species of the tropical forests in the Mexican Pacific coast

Thelephora is a genus of ectomycorrhizal fungi distributed in angiosperm and gymnosperm forests around the world. In this study, we describe Thelephora pacifica, a new species associated with tropical oak forests in Mexico. Phylogenetically, it is the sister group of T. pseudoganbajun from China. Morphologically, it corresponds to T. vialis previously reported in Mexico. Thelephora pacifica has a flabelliform basidiocarp with a hymenophore of grayish-brown color with pinkish tinges contrasting with the yellowish-olive margin. It is distributed in the Pacific forests of Mexico, an area with a high potential for endemism.

Fish assemblage structure related to habitat heterogeneity in rocky reefs in the Mexican Pacific coast

Abstract One of the major paradigms in ecology is the understanding of processes and patterns related to the structure of biological communities. Reef ecosystems, with their high productivity, habitat heterogeneity, and fish diversity provide a model for studying these processes. We sampled four sites three times during the season associated with the California Current and two times associated with the North Equatorial Current using video-transects on the coast of Zihuatanejo, Guerrero, Mexico to determine the relationship between the habitat characteristics and the structure of the fish assemblage. We recorded a total of 26 families and 54 species and estimated fish richness and abundance. In addition to measuring local water variables such as temperature (°C), salinity (PPT), pH and dissolved oxygen (O2%), we determined habitat heterogeneity by processing photographs of the substrate and calculated rugosity using the tape chain. Oxygen and temperature were the variables associated to sea water conditions that differentiated the sampled sites. The fish community structure presented high correlations with temperature, salinity, and dissolved oxygen, followed by the heterogeneity components such as rugosity and substrate diversity. Our results showed that seasonal changes in water conditions and physical components in the coast of Zihuatanejo promotes changes in the fish community.

Distribution, eco-climatic characterization and modelling of suitable soursop cultivation zones in Mexico

Soursop (Annona muricata L.) is a tropical fruit tree highly valued for its organoleptic characteristics, and is the most important Annonaceae species in Mexico. This study aimed to generate maps of the natural geographic and eco-climatic distribution where soursop grows in Mexico, and to model potential zones according to climate change scenarios estimated for 2050. The natural distribution model showed that this species is found in most tropical and some subtropical areas of Mexico. This fruit tree grows in three different eco-climatic regions (two tropical and one temperate): Aw1 (found on the edges of the Balsas basin, and in the south, southeast and central north of the Veracruz region, as well as in the center of the Mexican Pacific coast), Am (north and central south of the Veracruz region, and the Yucatán peninsula) and C(w0) (east of the Trans-Mexican Volcanic Belt). Modelling of suitable climate adaptation zones showed that the Pacific coast of Mexico and Veracruz, as well as some areas of the Balsas basin and the Yucatán peninsula, have potential for soursop cultivation. Likewise, in the scenario of global climate change, beneficial effects on the adaptation of this species are predicted.

Bird Watching Tourism in Sustainable and Accessible Destinations: The Case of the Entrepreneurial Venture Explora Caloccita in the Mexican Pacific Coast

Summary Bird watching is an activity that may prompt sustainable tourism development in remote communities. This case study lays out some lessons learned from the entrepreneurship case Explora Caloccita, a young venture offering bird watching to tourists in the Mexican Pacific coast. This case is based on descriptive research, laying out the practitioners’ insights and analysing the supply of experiences related to bird watching. The innovative vision of the entrepreneurs, the financial and logistical backing by the local hotel La Quinta, and the support of residents and local tour operators allow for the conclusion that bird-watching tourism has been, in this particular case, a sustainable economic alternative. Furthermore, the entrepreneurship Explora Caloccita is embedded in a destination that strongly supports accessible tourism, sustainable local development and nature preservation. The venture and the place’s sustainability are both possible thanks to the strong connections among all stakeholders and residents in the area, as locals also support the bird-watching routes and thus contribute to the conservation of the native and migrant bird species. Information © The Authors 2023

Spiny but photogenic: Amateur sightings complement herbarium specimens to reveal the bioregions of cacti.

Cacti are characteristic elements of the Neotropical flora and of major interest for biogeographic, evolutionary, and ecological studies. We tested global biogeographic boundaries for Neotropical Cactaceae using specimen-based occurrences, coupled with data from visual observations, as a means to tackle the known collection biases in the family. Species richness and record density were assessed for preserved specimens and human observations, and a bioregional scheme tailored to Cactaceae was produced using the interactive web application Infomap Bioregions, based on data from 261,272 point records cleaned through automated and manual steps. We found that areas in Mexico and southwestern USA, in eastern Brazil, and along the Andean region have the greatest density of records and the highest species richness. Human observations complement information from preserved specimens substantially, especially along the Andes. We propose 24 cactus bioregions, among which the most species-rich are northern Mexico/southwestern USA, central Mexico, southern central Mexico, Central America, Mexican Pacific coast, central and southern Andes, northwestern Mexico/extreme southwestern USA, southwestern Bolivia, northeastern Brazil, and Mexico/Baja California. The bioregionalization proposed shows biogeographic boundaries specific to cacti and can thereby aid further evolutionary, biogeographic, and ecological studies by providing a validated framework for further analyses. This classification builds upon, and is distinctive from, other expert-derived regionalization schemes for other taxa. Our results showcase how observation data, including citizen-science records, can complement traditional specimen-based data for biogeographic research, particularly for taxa with specific specimen collection and preservation challenges and those that are threatened or internationally protected.

Stratigraphic evidence of relative sea level changes produced by megathrust earthquakes in the Jalisco subduction zone, Mexico. The signature of the 1995 Colima-Jalisco earthquake (Mw 8) as a modern analogue

Geological evidence of megathrust earthquakes along the Mexican Pacific coast relies predominantly on tsunami deposits. Records of coseismic relative sea-level changes are scarce even though such evidence can complement and constrain tsunami records, providing information to reconstruct past earthquake rupture dimensions to improve the earthquake hazard assessment of the region. This paper provides the first diatom-based quantitative reconstruction of coastal subsidence along the Mexican subduction zone through the analysis of coastal wetland sediments. We use the stratigraphic signature of the 1995 Colima-Jalisco earthquake (Mw 8.0) as this earthquake is instrumentally well-constrained, allowing us to evaluate our findings and establish approaches to investigate earlier earthquakes. Deposits beneath the wetland Estero Potrero Grande reveal a stratigraphic sequence, < 28 cm beneath the wetland surface, that resembles a signature of rapid submergence. This sequence consists of a horizontal bed of silt with highly humified organic matter abruptly overlain by a horizontal bed of grey silt. The abrupt stratigraphic contact between the two units extends across >1 km of the wetland. Using 14C ages and 137Cs chronohorizons to build an age-depth model, we estimate the age range (1985–2003 CE) and mean age (1995 CE) of this abrupt stratigraphic contact, coincident with the year of the earthquake. Three elemental log-ratios (S/Zn, Br/Zn and Ca/Zn) indicate an abrupt increase of salinity across the stratigraphic contact, which we interpret as marsh submergence recording coseismic coastal subsidence, reflected as relative sea-level rise. Fossil diatom assemblages confirm this trend, and through quantitative approaches we estimate its magnitude (−0.06 ± 0.08 m and − 0.11 ± 0.23 m), which is comparable with coastal subsidence measured by geodetic instruments. Our records reveal a millimetric spike of sand, which we interpret as a signature of the tsunami that accompanied this great earthquake. These findings demonstrate that coastal wetland sediments from the Mexican Pacific coast can record tectonic induced relative sea-level changes. This approach can allow us to better understand the long-term spatial and temporal behavior of this subduction zone.

Benthic Characterization of Mesophotic Communities Based on Optical Depths in the Southern Mexican Pacific Coast (Oaxaca)

The distinction between shallow coral reefs and mesophotic coral ecosystems (MCEs) has not been fully clarified yet. The original definition of MCEs, by depths of 30–150 m, fixes their bathymetrical limits and fails to accommodate environmental and biological variation. Recent studies have indicated that water transparency and light availability may explain why MCEs do not occur at fixed depths but vary among localities. This study aimed to evaluate the presence and distribution of MCEs, along the central coast of Oaxaca, through optical depths and the associated benthic community. Using MODIS-Aqua satellite data (Kd490), we estimated the mesophotic optical depths monthly (z10%, z1%, z0.1%), over the last four years. In addition, to characterize benthic community structure, we conducted underwater photo quadrat surveys at two locations on the southern Mexican Pacific coast from 10 to 55 m depth. Significant differences between depths and locations were found in benthic communities. Furthermore, the lower distribution of photosynthetic taxa was different between the two locations but indicative to the z10% and z1% in both cases. Those differences were associated with the upwelling season, which reduces, drastically and differentially, the light availability for benthic communities between the two locations and limits the development of MCEs on the central coast of Oaxaca.

Reproductive Ecology of the Chilean Round Ray (Urotrygon chilensis, Günther, 1872) in the Southern Gulf of California

The Chilean round ray (Urotrygon chilensis, Günther, 1872) is commonly caught as bycatch in the Mexican Pacific, but changes in its reproductive ecology as a consequence of fishery effects have never been investigated. In this work, the reproductive ecology of this species was determined in the Southern Gulf of California (SGC). Total length (TL) ranged from 11.4 to 51.6 cm, and females were larger than males. Size at maturity (TL50) was estimated at 27.5 cm for females and 25.3 cm for males. The seasonal variation of mature individuals, the presence of pregnant females, the mean oocyte size, the size of embryos and the smallest free-living specimens along the year suggest the existence of two reproductive periods during the year in the SGC, and the size of birth was estimated to be 11.2 to 15.6 cm TL. The average fecundity was 2.14 embryos. Spatial variations detected in size at maturity, fecundity, and reproductive cycle along the Mexican Pacific coast suggest the presence of separated populations. Some of these differences could be related to differences in maximum size attained in each region, though fishing pressure and environmental factors could have an important role, too.

Seabed morphodynamics of a coastal lagoon of the Gulf of California

A two-dimensional, vertically integrated, non-linear numerical model was applied to investigate the Urias coastal lagoon’s (URCOL) tide-driven currents, bed load sediment transport, and seabed morphodynamics. The coastal body of water, located on the eastern side of the Gulf of California, includes the Mazatlán harbour, the most important port on the Pacific Mexican coast due to the relevant activities like the heavy vessel traffic. URCOL also includes an extensive aquaculture infrastructure at the lagoon head. The tidal hydrodynamic modelling revealed the mixed character of tides predominantly semidiurnal in the lagoon. The numerical computation at the harbour entrance showed an ebb-dominant tidal distortion. The distribution patterns of the erosion and accretion rates are consistent with the convergent and divergent character of the vectors of sediment transport rates. The sediment accretion has been predicted mainly in the middle part of the channel, right where the channel starts curving, changing the alignment of the lagoon. The tidal hydrodynamics, sharp topographic gradient, and geometric features of the lagoon seem to determine the location of accretion and erosion areas.

Anthropogenic drivers of increasing sediment accumulation in contrasting Mexican mangrove ecosystems

Mangrove sediments are valuable records to reconstruct the impacts of human-induced changes on the coastal zone. Seven lead-210 dated sediment cores were used to evaluate temporal trends of sedimentation rates over the past century in Mexican mangrove areas at Términos Lagoon (TL; southern Gulf of Mexico) and El Verde Camacho Lagoon (EV; northern Mexican Pacific coast). We hypothesized that the contrasting characteristics (e.g., meteorological, demographic, and land-use change) would lead to significant differences in sedimentation rates between the study sites. Sediment accumulation rates (SAR) in both sites (TL 0.03–2.1 cm yr−1; EV 0.04–4 cm yr−1) were comparable to the global SAR range for mangrove forests. Mass accumulation rates (MAR) in the TL cores (0.03–0.47 g cm−2 yr−1) were consistent with previous studies of the region. Excluding conspicuous MAR maxima, attributed to meteorological events, MAR values in the EV cores (0.04–0.9 g cm−2 yr−1) were higher than in other mangrove areas of the Mexican Pacific coast, but comparable to other sites in the world. Similar exponentially increasing MAR values towards present in both sites were attributed to general factors driving sediment accumulation in mangroves, mainly continental erosion promoted by land-use changes, which has accelerated since the 1950s, associated with (i) population growth and the consequent expansion of human activities and (ii) sea-level rise, similar in the studied regions and from which mangrove ecosystems seem to adapt. Intensifying population growth and land-use change are already reducing the extent of mangrove coverage in some parts of the study areas. Adaptation to an accelerating sea-level rise depends on maintaining conditions that allow mangroves to accrete vertically. However, both global change pressures may pose future threats to these ecosystems. Efforts to monitor sediment accretion and adapt the management of mangrove conservation areas are required to understand better mangrove response to global change impacts.

Ultrastructural characterization of Minutocellus polymorphus (Cymatosiraceae, Bacillariophyta) and first record from the Eastern Pacific

Abstract The diatom Minutocellus polymorphus is a widely studied species because it is an ideal model for toxicity tests since it grows rapidly. Although the gross morphology has been extensively described, the ultrastructural characters associated with its importance, are unknown. It is also the only species in the genus that has been documented in the North American Atlantic, but unknown on the Eastern Pacific coasts. In a collection made in Acapulco Bay, Guerrero, Mexico, cells morphologically identical to M. polymorphus were isolated. From cultures and observations in transmission electron microscope, a first description of the ultrastructure of the genus is provided, and from sequences of 18S, we confirmed its taxonomic identity as M. polymorphus. However, more detailed studies are needed to continue increasing the knowledge about the ultrastructure of diatoms on the Mexican Pacific coasts, where they are previously unknown.