Effects of ammonia on zoea I of the Southern King Crab, Lithodes santolla (Decapoda, Lithodidae) were analyzed through acute (96 h) and chronic (29 days in total) assays (seven total ammonia nitrogen (TAN) concentrations: 9, 15, 25, 41, 67, 110, and 182 mg L⁻¹, plus control). The estimated LC₅₀-96 h was 107.97 mg TAN L⁻¹ (1.93 mg NH₃-N L⁻¹), while the safe level of ammonia was 10.79 mg TAN L⁻¹ (0.19 mg NH₃-N L⁻¹). Survival was highest in the three lowest ammonia concentrations throughout 96 h (93.3%, 90% and 93.3% in 9, 15 and 25 mg TAN L⁻¹, respectively). In chronic assays, the percentage of survival decreased along with the exposure time and the ammonia concentration. Zoeae´s mean life time tended to increase almost gradually with the increment of ammonia concentration. Mean molting time from zoea I to II was 4.06 days, while it increased from zoea II to III, and zoea III to the post-larval stage (6.00 and 8.39 more days, respectively) with ammonia concentration. The percentage of individuals that have molted in every molt stage tended to decrease while ammonia concentration increased. Therefore, the results obtained in the present study bring new information about ammonia toxicity in early stages of development of crab Lithodes santolla, an important commercial species of the Beagle Channel.

The Beagle Channel, located south of Tierra del Fuego (~54° S), is South America’s southernmost intracoastal ecosystem. Here, we applied environmental DNA metabarcoding using a partial sequence of the 12sRNA mitochondrial gene to evaluate the seasonal and spatial dynamics of marine vertebrate communities along the longitudinal gradient of the Beagle Channel. Water samples were collected across seasons and sites spanning the central and eastern sectors of the channel. Vertebrate DNA was amplified and analyzed against a custom reference database enriched with locally generated sequences. A total of 43 vertebrate taxa were detected, including 25 fish, 13 mammals, and 5 seabirds. Vertebrate assemblages were spatially structured along the longitudinal gradient of the Beagle Channel, with the central sector characterized by higher relative abundances of Fuegian sprat (Sprattus fuegensis), Southern elephant seal (Mirounga leonina), South American fur seal (Arctocephalus australis), and domestic species, whereas the eastern sector showed higher relative abundances of fish species including silversides (Odontesthes spp.), Magellanic rockcod (Paranotothenia magellanica), and striped rockcod (Trematomus hansoni), as well as mammals including southern sea lion (Otaria flavescens), North American beaver (Castor canadensis), and native grass mice (Abrothrix spp.). This spatial differentiation was associated with contrasting environmental conditions. No significant seasonal effect was detected. This study provides the first environmental DNA-based baseline of marine vertebrates on the Beagle Channel and validates this approach for ecosystem-scale biodiversity monitoring in subantarctic coastal environments.