Los arrecifes mesofóticos se encuentran en una capa del océano definida por la cantidad de luz incidente (1%–10% con respecto a la superficie). Estos ecosistemas permanecen inexplorados en algunas regiones, como el Pacífico a lo largo de la costa mexicana, debido al difícil acceso mediante métodos tradicionales como el buceo autónomo. Se utilizó un vehículo operado remotamente para caracterizar los ensamblajes de peces de arrecifes rocosos y zonas arenosas en profundidades mesofóticas alrededor de islas continentales del golfo de California e islas oceánicas del archipiélago de Revillagigedo (México). Se realizaron 78 video-transectos y se identificaron los peces observados al mínimo taxón posible. Con base en la presencia de especies por video-transecto, se calcularon índices de diversidad tradicionales (riqueza de especies, diferenciación taxonómica y nivel trófico) e índices funcionales (número de entidades funcionales, riqueza funcional y volumen funcional) para cada conjunto insular y tipo de hábitat. Los modelos aplicados señalaron que el tipo de hábitat es el factor con mayor efecto en la diversidad de peces mesofóticos. Los índices funcionales presentaron mayores valores para los arrecifes rocosos de islas oceánicas que para los hábitats arenosos, lo que se asocia con la presencia de elasmobranquios y especies transpacíficas de importancia comercial. Aunque los valores de diferenciación taxonómica y diversidad funcional podrían indicar que los arrecifes mesofóticos del conjunto oceánico se encuentran en mejor estado de conservación que los del conjunto continental, se requiere mayor exploración para determinar si esta condición perdura en el tiempo y si estos ecosistemas pueden ser un refugio para especies comerciales ante el creciente impacto de disturbios en arrecifes someros.

Differences in fish assemblages’ structures and their relations with environmental variables (due to the variations in sampled seasons, habitats, and zones) were analyzed in two adjacent estuaries on the north Pacific coast of Mexico. Environmental variables and fish catches were registered monthly between August 2018 and October 2020. Multivariate analyses were conducted to define habitats and zones based on their environmental characteristics, and the effect of this variability on fish assemblages’ composition, biomass, and diversity (α and β) was evaluated. A total of 12,008 fish individuals of 143 species were collected using different fishing nets. Multivariate analyses indicated that fish assemblages’ structures were different between zones due to the presence, height, and coverage of distinct mangrove species. Additionally, depth and salinity showed effects on fish assemblages’ diversity (α and β-nestedness), which presented higher values in the ocean and remained similar in the rest of the analyzed zones and habitats. These results and the differences in species replacement (β-turnover) indicate the singularity of fish assemblages at estuaries (even in areas close to the ocean) and the necessity to establish local management strategies for these ecosystems.

The deep reef refugia hypothesis suggests that the effects of disturbance decrease as depth increases; thus, reefs in the mesophotic zone potentially serve as refuges for communities in shallower zones. This study challenged this hypothesis by evaluating fish diversity in shallow and mesophotic reefs in a marine protected area in the Gulf of California. During 2021–2022, we conducted 189 5‐min video transects using remotely operated vehicles to document species richness and abundance. We evaluated six biological traits for each species (length, mobility, position, gregariousness, diet, and activity period) to estimate four functional indices (number of entities, richness, originality, and divergence), one phylogenetic index (Δ*), and Hill's numbers for taxonomic and functional indices. Benthic organisms were analyzed to explore relationships with ichthyofauna, while monthly water turbidity satellite data products were transformed into a light attenuation coefficient to identify the mesophotic zone (area between 10% and 0.1% of the incident light at the surface). At the study site, the mesophotic zone was identified to extend to 21 m under optimal conditions, which is shallower than what is typically observed in oligotrophic regions. Generalized linear models revealed significant variations in reef fish composition across spatial (site and zone) and temporal (season and year) dimensions. Additionally, generalized linear mixed models of functional richness and taxonomic Hill's numbers exhibited significantly higher values in the shallow zone. However, functional and phylogenetic indices showed similarities in fish assemblages. Despite differences in fish taxonomic diversity among zones that could be related to less environmental variation and resource availability in deep strata, mesophotic reef fish assemblages presented similar functions. Functions were maintained in mesophotic reefs, which suggests that the two zones are connected and that mesophotic reefs have the potential to act as partial refugia in the face of current and near‐future climate change‐related disturbances that could affect shallow zones.

Differences in fish assemblages’ composition and their relationship with the environmental variables were analyzed in the Urías estuarine system, Mexican North Pacific. Environmental variables and fish catches were recorded bimonthly between June 2018 and November 2021, including a period before and during the COVID-19 pandemic. Multivariate analyses were performed in the studied area to define zones based on their environmental, biotic, and abiotic characteristics and the effect of these on the fish assemblages. Two zones were identified, an estuarine with mangrove forest and a surf zone in the coastal area outside the estuarine system. Fish composition, biomass, and diversity (α and β) were evaluated among the factors of the period (before–during COVID-19), climatic seasons, and zones. A total of 5947 fish individuals of 41 species were collected using beach seines as fishing gear. The structure of the fish assemblages was different between zones and periods. Abiotic (temperature, salinity, and total matter suspended), biotic (mangrove area), and temporal (season and period before–during COVID-19) variables had an effect on fish biomass and α diversity, while the results of the β diversity only indicate changes in the nestedness component before–during the lockdown. These results indicate a change in fish assemblages’ structure and composition between periods, which might be a consequence of the limitation of human activities derived from the pandemic, climatic changes, or a combination of both effects. Our results show that fish assemblages in the estuarine systems of the Tropical Eastern Pacific are unique, and there is a need to establish local management strategies for these ecosystems.

Taxonomic and functional diversity patterns of fish in temperate reefs in the Mexican Pacific have not been analyzed in integrative biodiversity studies. Thus, this study compared the taxonomic, phylogenetic, and functional diversity of reef fish in 4 biogeographic provinces: Californian, Cortez, Panamic, and Oceanic Islands. Species checklists were compiled from the literature, museum collections, and monitoring data from 21 sites in marine protected areas (MPAs) and 45 non-protected sites. Based on this data and 6 biological traits (size, mobility, period of activity, gregariousness, position in the water column, and diet), we calculated species richness (S), average taxonomic distinctness (Δ+), number of functional entities (FE), functional redundancy (RED), functional vulnerability (FV), and functional volume (FVol). We registered 1,045 species; the dominant categories were benthic, highly site-attached, diurnal, solitary, medium-sized, and invertivores. The Cortez province showed the highest S and FE values, whereas the Californian province presented the lowest values. Notably, FVol was >70% across the 4 biogeographic provinces, suggesting that the range of ecological functions and processes was maintained across provinces despite their contrasting biodiversity levels, environmental conditions, and evolutionary histories. A “regional backbone” was identified, consisting of 74 species and 58 FE (the fundamental species and shared ecological roles across provinces). At the regional level, low RED (55% of FEs represented by a single species) were observed. All provinces presented high values of Δ+ (>80%), reflecting the broad range of taxonomic lineages within the region. The MPAs presented higher S and RED than non-protected sites; however, further research is needed to elucidate the positive effects of protection.