Elva Escobar-Briones

Invertebrate communities at depths greater than 200 m in the Gulf of California are less well known than those inhabiting shallow waters. This study analyzes imagery recorded by the ROV Doc Ricketts to characterize the taxonomic composition and richness of epibenthic megafauna in soft-sediment habitats at the upper boundary of the Oxygen Minimum Zone in a previously unexplored bathyal area of the Delfín Basin in the northern Gulf of California. Observations based on morphology and color patterns allowed the identification of twelve species belong to six Phyla: Cnidaria (1), Mollusca (2), Annelida (1), Echinodermata (1), Bryozoa (1) and Chordata (6). The mean Chao2 estimator was 11.25 ± 2.9. A total of 119 individuals were accounted for, with the dominance of the colonial ascidian Didemnum sp. (39.5%), the cephalopod Octopus rubescens (21.9 %), and Sea pens (Pennatula phosphorea) (10.9 %). For the 12 species, the overall density was estimated at 7.9 x 103 orgs. ha-1. Our results provide information on the extents of the distribution to the North of Derepodichthys alepidotus, Sebastes cortezi, Coelorinchus scaphopsis, Eptatretus sinus, P. phosphorea, and Strongylocentrotus fragilis within the Gulf, and reports a deeper occurrence of O. rubescens in the bathyal zone. Here, we document that three-dimensional structures generated by P. phosphorea, Didemnum sp. and colonial bryozoans (Gymnolaemata) enhance the structural complexity of soft sediment habitat, with demersal fish, cephalopods, and sea urchins occurring in the surroundings of these biogenic structures. This study provides valuable datasets and advances knowledge of epibenthic megafauna at the upper OMZ boundary, a habitat that remains underexplored and poorly known both in the GoC and globally. Our findings contribute essential baseline knowledge for the planning and design of deep-sea protected areas in the GoC.

The intricate relationship between prokaryotic vitamin B₁₂ (cobalamin) producers and metazoans in deep-sea ecosystems, particularly within ferromanganese crusts and polymetallic nodules, is critical for understanding oceanic biogeochemical cycling of cobalt. Microbial communities are key regulators of essential biogeochemical cycles, with cobalt serving as a vital component in the synthesis of cobalamin, a metallocofactor indispensable for numerous metabolic processes. We analyzed the significance of cobalamin biosynthetic pathways confined to prokaryotes and emphasized the ecological importance of auxotrophic organisms that rely on exogenous sources of vitamin B₁₂. Additionally, we recognize recent research regarding the spatial distribution of dissolved cobalt and its consequential effects on cobalamin production and bioavailability, indicating the scarcity of cobalt and cobalamin in marine environments. We propose that cobalt-rich environments may foster unique interactions between prokaryotic and eukaryotic organisms, potentially altering the food web dynamics owing to the localized abundance of this element. By investigating the roles of cobalt and cobalamin in nutrient cycling and interspecies interactions, we outlined key criteria for future research on deep-sea microbial communities and their contributions to the cobalt biogeochemical cycle.

The Chapopote Knoll at 3200 m depth, in the southern Gulf of Mexico harbors highly diverse benthic habitats, including massive asphalt flows and surficial gas hydrates with gas seepage. Its associated benthic megafauna includes endemic cold-seep species and background species. This study describes the benthic habitat preferences, distribution patterns and diets of three crustacean species, the caridean shrimp Alvinocaris muricola and the galatheids Munidopsis geyeri and M. exuta. High-resolution imaging recorded eight habitats and helped depict their spatial distributions. A. muricola aggregates on Siboglinidae clusters and in gas seepage sites. M. geyeri and M. exuta are less selective and occur in almost all habitats. The carbon (δ¹³C) and nitrogen (δ¹⁵N) values of A. muricola show a nutritional preference of bacteria from mats and water column detritus retained among the Sibolindiae, whereas the two Munidopsis species have wider spectrum diets. Gut content analysis in all three species, validate the stable isotope values, food sources and confirm the secondary consumer’s trophic level. This study recognizes coexistence of A. muricola and the two Munidopsis species in the benthic habitats while using different resources. Compound specific isotope analyses of galatheid guts revealed females to have more ¹³C-depleted lipids (-35‰) compared to males (-28‰), calling for more detailed analyses to clarify this trophic segregation.

The history of colonization and dispersal of fauna among deep-sea chemosynthetic ecosystems remains enigmatic and poorly understood. The distribution of squat lobsters of the genus Munidopsis Whiteaves, 1874 can be influenced by the rich organic matter and associated organism communities of chemosynthetic ecosystems. The present work analyzed the molecular relationships and morphology of individuals from different populations of Munidopsis exuta Macpherson & Segonzac, 2005 and M. geyeri Pequegnat & Pequegnat, 1970 in such ecosystems along the Atlantic Equatorial Belt, including the Chapopote Knoll, in the southern Gulf of Mexico. Munidopsis geyeri is re-described based on the present findings and reference to the literature. This analysis documented the genetic distances, as well as range of variation in the diagnostic characters that support the separation of M. exuta and M. geyeri. Our results confirm that the two species coexist in seep ecosystems and have an amphi-Atlantic distribution.

The establishment of thresholds is integral to environmental management. This paper introduces the use of thresholds in the context of deep-seabed mining, a nascent industry for which an exploitation regime of regulations, standards and guidelines is still in the process of being developed, and for which the roles and values of thresholds have yet to be finalised. There are several options for integrating thresholds into the International Seabed Authority’s regulatory regime, from being stipulated in regulations to being part of a mining contract, each option having its own advantages and disadvantages. Here we explore the range of ways that thresholds can be derived, set out the challenges in translating ecological and management data into thresholds, highlight factors for acceptance and operationalisation of thresholds in deep-seabed mining, and explain the necessity of refining thresholds as knowledge on impacts to features improves. Some comparable marine industries already use thresholds and these could potentially be used as starting points for the development of thresholds for deep-seabed mining. In order to be acceptable to the wide range of deep-seabed mining stakeholders, thresholds need to strike a balance among levels of harm acceptable by society, levels of environmental precaution justifiable by governments, scientific robustness, and operational practicality.

This study collates and reviews the state of the art in the phenomenon of atypical pelagic Sargassum influxes in the coastline of the Mexican Caribbean, focusing on projects, studies and initiatives that have been conducted in the country for a decade. We integrated multisectoral and multidisciplinary knowledge and identified gaps and strengths in current knowledge. Initiatives and projects conducted in Mexico are numerous, diverse and valuable. However, interdisciplinary and transdisciplinary research and interinstitutional coordinated actions in the medium- and long-term are still lacking. Because of this, there is an imbalance of actions in different knowledge areas that prevents this phenomenon from being addressed in a comprehensive way. Furthermore, the funding opportunities for Sargassum research projects and other initiatives seem to respond to the events of massive influxes, without continuity or long-term planning. Attention is mainly focused on urban and touristic areas, so impacts to rural or uninhabited zones are unknown. This review represents a stepping-stone towards an integrated multisectoral effort to shift the perspective from Sargassum being a “national problem” to a “national resource,” considering and fully understanding the ecological importance of this macroalgae as a floating ecosystem and its potential as an economic resource once it massively arrives in Mexican coastal areas.