Tropical reefs are among the most threatened ecosystems on Earth. In the Caribbean, dominance has shifted from coral to macroalgae, due to several proximal and distal causes, such as the decline in the population of herbivorous fish, eutrophication, pollution, and climate change. Macroalgae are essential components of reefs, although their overgrowth results in phase shifts, disrupting the reef community balance. Over the course of a year, we examined the seasonal relationship between environmental factors and changes in macroalgal dominance in a western Caribbean reef lagoon. Sampling yielded 5160 macroalgae thalli, spanning 40 species. From these, 3663 thalli (71%) and eleven species corresponded to Ochrophyta (Brown algae), 816 thalli (15.8%) and 12 species to Rhodophyta (Red algae), and 681 thalli (13.2%) and 17 species to Chlorophyta (Green algae). Results showed that macroalgae cover was significantly related to water temperature, nutrient concentration, and photosynthetically active radiation (PAR). Brown algae cover increased during the wet season when water temperature was high, and PAR was low. The cover of the three macroalgae groups was lower during the dry season, concurrently with high PAR values. Nutrient concentrations were found to be within normal ranges, with no signs of eutrophication. The seasonal variations in the environmental conditions, together with the rare occurrence of herbivore fish and sea urchins, support the assumption that these factors are the underlying drivers of the dominance recorded. These findings provide evidence of the relative importance of driving factors and mechanisms ruling the coral-algal phase shift phenomenon in tropical reefs.

Zooplankton are crucial for marine productivity, supporting commercially valuable species and contributing to fisheries. This study identifies major zooplankton groups (MZG) in the neritic zone of the eastern Campeche Bank, focusing on Octopoda paralarvae (PL). Octopoda includes at least five species, only some of which support commercial fisheries. We analyzed MZG, taxa diversity, PL abundance, and horizontal distribution relative to sea surface temperature (SST) and chlorophyll-a (Chl-a). PL abundance peaked in May–June during high SST, with a second peak in December during low SST. Paralarvae were recorded across a wide range of Chl-a concentrations, occurring under both high (>0.25 mg m⁻³) and low (<0.25 mg m⁻³) productivity conditions, consistent with GAM results indicating broad environmental tolerance, probably driven by taxa-specific seasonal variability. The association of PL with fish larvae and decapods in warmer months, and with copepods in colder months, suggests that optimal SST and food availability favor spawning, hatching, and growth. These variation trends support the view of the Campeche Bank as a larval nursery for octopus.

Meiofauna in marine ecosystems is little known, although interest in its study has increased recently. Meiofauna, an integral part of the benthic community, represents a set of organisms that actively participate in the biogeochemical processes and trophic web of sedimentary environments. This paper explains the ecological relevance of this group of organisms and the interest in using the knowledge generated about it for environmental diagnosis purposes. The information collected comes from bibliographic portals such as Web of Science, Scopus, and TESIUNAM, emphasizingits composition, abundance, geographical distribution, and use as ecological stress indicators, particularly in Mexico. The design ofenvironmental diagnostic tools constitutes valuable support for decision-makingon the ecological status of the seabed.

A new species of the sphaeromatid isopod genus Ancinus is described and illustrated. It comes from the Cinvestav Merida research project, Invertebrate Benthic Diversity of the Yucatan Intertidal and Shallow Subtidal Zones. This genus is easily recognized by having an oval and flattened body; in males, the first two pereonal appendages are subchelate, while in females, only the first one is subchelate, the pleotelson is triangular, and the first pleopods and uropods are uniramous. This new species of Ancinus differs from all others by body surface smooth and unpigmented; eyes not elevated; suture between head and pereonite 1 complete, straight; mandible lacinia mobilis lateral margins parallel; 3 irregular teeth, 1 long, 2 short blunt sclerotized cusps; mandible palp third article inner margin with 12 blunt robust distal setae; 2 maxilliped coupling setae; coxae 5-7 visible in dorsal view; pleopod 2 endopod margin with 20 short setae; male appendix styliform, fluted, and shorter than endopod; curved tip. This is the third known species of Ancinus in the Gulf of Mexico and the tenth worldwide. A table with the main differences among the three known species in the gulf is also given.

La meiofauna en los ecosistemas marinos es poco conocida, aunque el interés por su estudio se ha incrementado en los últimos años. La meiofauna, parte de la comunidad bentónica, representa un conjunto de organismos que participan en los procesos biogeoquímicos y en las redes tróficas de los ambientes sedimentarios. Se explica la relevancia ecológica de este grupo de organismos, así como el interés en utilizar el conocimiento generado sobre él con fines de diagnóstico ambiental. La información recopilada proviene de portales bibliográficos como Web of Science, Scopus y TESIUNAM y pone énfasis en la composición, abundancia, distribución geográfica y uso de la meiofauna como indicadores ecológicos de estrés, particularmente en México. El diseño de herramientas de diagnóstico ambiental ayuda a la toma de decisiones sobre el estado ecológico de los fondos marinos.

Background: The importance of the port of Dos Bocas, Tabasco, for the oil industry in the southern Gulf of Mexico, contrasts with the scarce information on the zooplankton community in its surroundings. Objectives: Generate baseline information on the spatial distribution of richness, abundance and holoplankton/meroplankton (H/M) ratio of zooplankton groups (ZG) along the salinity gradient. Methods: In October 2016, one sampling was conducted at 17 sites in the coastal area adjacent to the Dos Bocas port and the Mecoacan Lagoon. The biological samples were obtained using a plankton net with a 300 mu m filtering mesh, recording water salinity and temperature. Results: The richness, abundance, and H/M ratio decreased with salinity. The coastal zone was characterized as a euhaline environment, where 26 ZG were recorded, with a mean abundance of 3,880 ind 100 m-3 and H/M ratio = 11.3, with copepods being the dominant group, which is indicative of the secondary productivity associated with the coastal environment. In the Mecoacan Lagoon, a meso-polyhaline environment predominated, where 17 ZG were recorded, with a mean abundance of 409 ind 100 m(-3 )and H/M ratio = 1.8, with fish eggs being the dominant group, which is indicative of the importance of the Mecoacan Lagoon for species with commercial or ecological importance, before their adult stage. Conclusions: The changes in the richness and abundance of zooplankton taxa along the salinity gradient provide baseline information on the differential use of the Mecoacan Lagoon and the adjacent coast by ZG with distinct life cycles, representing the first contribution to the knowledge of zooplankton in the study area.

Meiofauna is a good pollution indicator that reflects the ecological status of sediments and their linkages with overlying communities. However, long-term monitoring of this fauna is a developing research activity in most marine ecosystems. This study assessed seasonal spatial and temporal changes in meiofauna composition, abundance, and biological traits in the southern Gulf of Mexico sublittoral zone. We examined two questions: How do the meiofauna attributes vary spatially and seasonally? Which contaminants correlate with the distribution of meiofauna biological traits? We analysed sediment characteristics, metals, hydrocarbons, and meiofauna data collected at shallow coastal sites (<10m) during eight annual surveys (2005-2020). Organic contamination increased when natural disturbances occurred, mainly in the dry season, decreasing the number of nematode taxa and increasing their abundance. During the eight yearly sampling events, nematodes, harpacticoid copepods, and polychaetes varied according to the sedimentary gradient. Chronic contamination (aromatic compounds, Cr, V, Cd, Cr) covaried with meiofauna biological traits. Our results point out meiofauna taxa (e.g., Anoplostoma, Halalaimus, Monhystera, harpacticoid copepods, saccocirrid polychaetes) as bioindicators of resilient and disturbed sites for terrigenous and transitional sediments, while in carbonate sediments dominated sensitive species. Resilient sites were exposed to the Grijalva-Usumacinta river discharges and the oil industry. Tolerant and opportunistic taxa such as the nematodes Anoplostoma and Xyala were classified as colonisers and non-selective deposit feeders. Conversely, sensitive taxa such as Halalaimus and harpacticoid copepods were semelparous, carnivorous, and persisters.

In the western Atlantic, the presence of the invasive tiger shrimp Penaeus monodon has been recorded since 1987. Established and incipient populations are reported from North Carolina, USA, to Sergipe, Brazil. In the Yucatán Peninsula, in the south-southeast Gulf of Mexico, the first sightings of P . monodon were reported in 2014. To date, the sparse records suggest an ongoing incipient invasion, providing a time-critical opportunity for early biological assessment. In the present study, two wild adults of P . monodon are reported for Río Lagartos Lagoon, Yucatán, situated in the innermost part of the southeast Gulf of Mexico, close to the Caribbean Sea. Penaeus monodon identification was initially assessed based on macroscopic morphological features. Molecular analyses were used to corroborate morphological identification. A BLAST search was conducted by comparing partial sequences (510 bp) of the mtDNA control region (CR) of tiger shrimps from Yucatán (used as queries) with sequences deposited in the GenBank database. A Maximum Likelihood phylogenetic tree, generated from BLAST top hits (E-value cutoff = 0), revealed that sequences from Yucatán were most closely related to native sequences submitted from Indonesia. This accurate species identification has implications since this invasive shrimp threatens native biodiversity. The probable regional routes of the spread of P . monodon to the south- southeast Gulf of Mexico are discussed.

In ecosystems, natural radionuclides are present in the environment and living organisms. The 238 U natural decay chain produces multiple radioactive elements, such as 234 U, 226 Ra, 210 Pb, and 210 Po. These radionuclides can be found in air, water, rocks, soil, and other biotic and abiotic components, mainly derived from minerals, such as zircon and apatite. In this study, we determined the activity concentration of radionuclides from the 238 U decay chain in the sediment of a coastal ecosystem on the southern Mexican coast in the western Caribbean, an ecosystem minimally affected by industrial activities. Methods included high-resolution gamma-ray spectrometry and alpha-particle spectrometry. Results showed that the sediment samples had an activity concentration range of 18.2 -36.6 Bq/kg for 238 U, 25.0 -41.4 Bq/kg for 234 U, 10.1 -37.3 Bq/kg for 210 Pb, and 29.9 -46.0 Bq/kg for 210 Po. Water samples ranged between 17.9 and 36.3 mBq/L and 27.9 -66.0 mBq/L for 238 U and 234 U, respectively. The activity concentration of these radionuclides in the sediment and water of this area is compared with that of other coral reefs worldwide, providing a radiometric baseline for comparison purposes.

The tropical Octopus insularis is a shallow-water species widely distributed in the western Atlantic. Recent studies of niche models have identified suitable habitats for its settlement also on the east coast of the Atlantic. Considering the pelagic larval period and the high tolerance of this species to environmental variations, this study aimed to analyze the possibility of O. insularis occurrence in the West Atlantic (Sao Tome Island) through molecular analyses, dispersion, and niche models. The molecular analyses were performed using fragments of 481 bp of the mitochondrial gene (cox1) from three muscle samples collected in Sao Tome Island. The O. insularis long-range connectivity between South America and Western Africa was analyzed using a Lagrangian particle tracking model. Additionally, O. insularis records across its entire known distribution were applied to run the ecological niche model (ENM) using the Maxent algorithm. The Bayesian phylogenetic reconstruction showed that two of the three octopus sequences from Sao Tome island (Central-Western Africa) belong to a monophyletic and well-supported O. insularis clade. The third octopus sample revealed a new species related to the clade with the Octopus vulgaris species complex. The dispersal models pointed out that passive particles could potentially reach the seamounts region at Africa coast via oceanic currents (mainly the North Equatorial Countercurrent) from Sao Pedro and Sao Paulo archipelago (Central-Western Region of the Atlantic) in a period of similar to 30-60 days. This suggests that Sao Pedro and Sao Paulo archipelago could act as a potential source of paralarvae to Western Africa, although we hypothesize that this connection was more common during the Pleistocene, when sea level was around 120 m lower. In addition to the already known areas of O. insularis occurrence, the ENM pointed suitable habitats to the octopus settlement from Guinea-Bissau down to Equatorial Guinea and Gabon, and African Islands, such as Sao Tome and Principe. The new record of O. insularis in Africa raises important questions regarding regional fisheries management. Considering that O. insularis is highly tolerant to environmental variations and very adapted to warm shallow waters, there is a possibility that octopus fisheries stocks on the African coast have a mixed composition (O. vulgaris, O. insularis, and Octopus sp.) and therefore the fisheries must follow management measures suitable for each species. In addition, further studies should be carried out in order to characterize and describe the potential new octopus species found only in Sao Tome Island according to our genetic survey.

Monitoring benthic fauna in the Gulf of Mexico is needed to assess its ecological status under multiple human pressures and natural variability. The knowledge about the large-scale and long-term variability of the benthic ecological status still needs to be improved. Here, AZTI's Marine Biotic Index (AMBI) and multivariate AMBI (M-AMBI) assess benthic ecological status under human pressures and natural disturbances. The total number of samples analyzed was 1123 (from the coast to the deep sea), obtained during a relatively long period (nine yearly sampling events) and a wide area (the southern Gulf of Mexico -436,000 km2), in which benthic fauna, environmental and contaminant data were obtained. AMBI and M-AMBI were able to identify the effects on the benthic communities from natural and human disturbance: 1) benthic assemblages responded to climate pat-terns, such as El Nin similar to o events and other natural disturbances (i.e. dry and windy seasons); 2) these natural dis-turbances were associated to an exacerbation of contamination, mainly metals, hydrocarbons, and potential redox that exceeded the sediment quality guidelines; 3) the contamination can be related to human pressures, such as pollutant discharges from land-based activities and the oil industry. AMBI and M-AMBI provide baseline guidelines for determining the benthic ecological status of each sedimentary environment identified within the area since the entire region is affected by chronic and sublethal pollution, harmful in the long term to the benthic biota.

A new species of pardaliscid amphipod is described and illustrated from a single male specimen collected from bathyal sediments (2125 m depth) in the southern Gulf of Mexico. The new species is morphologically closest to Pardaliscoides fictotelson Barnard, 1966, previously documented from Southern California, at 218 m depth. The new pardaliscid differs from other species in the genus in having antenna 1 with a 10-articulate accessory flagellum; maxilliped palp very long; pereopods 5-7 elongate, slender; basis pereopod 7 expanded; telson with a short U-shaped cleft and pointed lobes; uropods 1-2 outer ramus curved, peduncle flat, longer than rami; uropod 3 rami flat, fleshy-lined, with marginal distal short robust setae. An identification key for all known species in the Pardaliscoides genus is also provided. The new species increase the number of Pardaliscoides species documented to six worldwide.

The eastern Campeche Bank is a region where the composition, distribution and abundance of one of its most promising resources, the teuthid cephalopods (squids), need to be better documented, particularly at the paralarval stage. To contribute to its knowledge, we obtained paralarvae from zooplankton samples collected from May 2016 to November 2017, relating and modeling their distribution to sea surface temperature, salinity, dissolved oxygen (DO), chlorophyll-a (Chl-a), zooplankton biomass and depth. The results showed that most paralarvae measured <2.0 mm mantle length. Higher abundances were found during upwelling months. Spatiotemporal segregation of teuthid species was observed, with oceanic paralarvae occurring offshore in May-July, and neritic ones appearing nearshore in September-November, Abralia redfieldi and Doryteuthis plei being the most abundant. Statistical generalized additive model for location, scale and shape showed that A. redfieldi was present in the north (offshore), related to warm Caribbean waters, and increased Chl-a and DO concentration. In contrast, D. plei was present in the south (nearshore), related to Yucatan shelf waters and low Chl-a.

Due to anthropogenic pressures, the global loss of biodiversity has increased the interest in understanding the relationship between species and their environment. However, there is still a gap in knowing this relationship for most species, more evident in small non-commercial species. The present study is the first specific effort to document the environmental variables influencing the abundance of rare frog crab species (Superfamily Raninoidea) in the continental shelf of the southwest Gulf of Mexico. The relative abundance of frog crabs, depth, bottom water (water salinity, water temperature, and dissolved oxygen), and sediment (calcium carbonate, organic matter, total organic carbon, and texture) were determined in 143 sampling sites during four research cruises conducted from 2012 to 2015. Five hundred and fourteen frog crabs were collected (90% in the Campeche Sound), belonging to Lysirude nitidus (A. Milne-edwards, 1880), Raninoides laevis (Latreille, 1825), R. lamarcki A. Milne-edwards and bouvier, 1923, and R. louisianensis Rathbun, 1933. R. louisianensis was the most abundant (441 individuals) and frequent species (collected in 37 sites). A Multivariate Generalized Linear Model (GLM) - using a negative binomial regression model -was performed to assess which environmental variables best explain the abundance of frog crab species. The GLM results showed that depth, salinity, temperature, and sand content in sediment were the most explanatory variables influencing the abundance of the frog crab species. R. louisianensis was significantly related with salinity and depth-salinity-sand interactions, R. lamarcki with depth-temperature and depth-salinity interactions, L. nitidus with depth, and R. laevis with temperature. These results suggest that spatial environmental variability in the southwest Gulf of Mexico (mainly related to the depth) influenced distinctly the abundance of each studied raninoid species promoting interspecific spatial segregation. Environmental optimal range, tolerance range, and tolerance limits are provided for each species, representing important baseline references for ecosystem and resources management. Regional terms: Atlantic Ocean, Gulf of Mexico, Mexico.

Macroalgae depend on specific substrata for their growth and propagation. This relationship is essential to understand the functioning of coral reefs. In Mexico, however, studies on this subject are scarce. Therefore, in the present study, the diversity of macroalgae species in the Xcalak Reefs National Park (PNAX) was determined in relation to the substrata they colonize. In July 2012, 10 sampling sites were selected in 4 zones of the PNAX: Zaragoza Canal (C), Lagoon Reef 1 (LA1), Lagoon Reef 2 (LA2), and Fore Reef (AF). With the help of transects and quadrants, specimens of 61 taxa of macroalgae (among them a morphotype) were collected manually, mainly Rhodophyta, on 3 abiotic and 18 biotic substrata. Of these taxa, 17 species were new records for the PNAX and 1 for the Quintana Roo's coast. The diversity was higher in LA (3.89), followed by AF (3.71), observing common species between both zones. The families Halimedaceae, Udoteaceae, and Anadyomenaceae were observed growing on abiotic substrata, while the families Halimedaceae and Dictyotaceae constituted substrata for other Rhodophyta. The number of macroalgae registered in the PNAX represents 10.4% of the total registered for Quintana Roo's coast.

Las macroalgas dependen de sustratos específicos para su crecimiento y propagación. Esta relación es importante para comprender el funcionamiento de los arrecifes de coral. En México, sin embargo, los estudios sobre este tema son escasos. Así, en el presente estudio se determinó la diversidad de especies de macroalgas en el Parque Nacional Arrecifes de Xcalak (PNAX), en relación con el sustrato que colonizan. En julio del 2012, se seleccionaron 10 sitios de muestreo en 4 zonas del PNAX: canal de Zaragoza (C), laguna arrecifal 1 (LA1), laguna arrecifal 2 (LA2), y arrecife frontal (AF). Con ayuda de transectos y cuadrantes se recolectaron manualmente especímenes de 61 taxones de macroalgas (entre ellos un morfotipo), principalmente rodofitas, sobre 3 sustratos abióticos y 18 bióticos. De estos taxones, 17 especies constituyeron nuevos registros para el PNAX y 1 para la costa de Quintana Roo. La diversidad fue mayor en LA (3.89), seguido de AF (3.71), observando especies comunes entre ambas zonas. Las familias Halimedaceae, Udoteaceae y Anadyomenaceae se observaron sobre sustrato abiótico, mientras que las familias Halimedaceae y Dictyotaceae constituyeron sustrato para otras rodofitas. El número de macroalgas registrado en el PNAX representa 10.4% del total registrado para la costa de Quintana Roo.

Microplastics (MPs) are emerging pollutants of widespread concern in aquatic environments. The aim of this study was to evaluate the negative impact of pristine MPs of polystyrene of 100 μm on embryo and larvae of Danio rerio exposed to three environmentally relevant concentrations of polystyrene (3.84 × 10− 6, 3.84 × 10− 7, and 3.84 × 10− 8 g/mL). The exposure effect was evaluated through the general morphology score, biometrics, and integrated biomarker response version 2 index. No mortality was observed but the anatomical structure of fishes was affected showing pigmentation deficiency and alterations in the head region as the main affected endpoints. The general morphology score and the integrated biomarker response values were highly sensitive to address the effect of the three concentrations of MPs used here. Our results provide solid evidence of the negative impact of 100 μm pristine polystyrene MPs exposure on early stages of zebrafish.

A new monotypic genus of eriopisid amphipod Bathypisella gen. nov. is described and illustrated. The specimens were collected on sediments from the southern Gulf of Mexico, at 884 m depth, aboard the RN Justo Sierra. The new eriopisid herein described differs from other genera mainly by bearing coxae 1-7 with a posteroventral notch; pleonal and urosomal segments dorsally toothed, and without setae; pereopod 7 basis narrow; and telson with 2 robust setae dorsally. The new genus and species increase the number of eriopisid genera recorded to 19 worldwide, and the deep-sea benthic amphipods (below 200 m) from the Gulf of Mexico to 20.

The activity concentration of polonium-210 in the soft tissue of several species of mollusks of coastal areas from Tabasco, Mexico, has been determined. Polonium-210 is a natural radionuclide that may be bioaccumulated by flora and fauna, particularly by mollusks. Radioecological evaluation of polonium-210 in mollusks is of particular interest for environmental radioactivity surveillance and to understand the mechanisms of migration of this radionuclide from the environment to humans. In this work, an analysis of the levels of polonium-210 in mollusks from Mexico is presented. Methods include the use of alpha-particle spectrometry to measure polonium-210 in the soft tissue of the studied mollusks. Results show an average value of 158 Bq/kg in mollusks from Tabasco, Mexico. Mollusks from the taxonomic class Bivalvia bioaccumulate more polonium-210 than Gastropods. The activity concentration values of polonium-210 in mollusks from Mexico are of the same order as those reported internationally. A further work on the mechanisms of migration and bioaccumulation of polonium in these organisms is necessary.