The Puquios of the Salar de Llamara in the Atacama Desert, northern Chile, is a system of small lakes that is characterized by evaporitic mineral deposition and that commonly hosts microbial communities. This region is known for its extreme aridity, solar irradiance, and temperature fluctuations. The Puquios are a highly diverse ecosystem with a variety of sedimentary bottom types. Our previous results identified electrical conductivity (EC) as a first-order environmental control on bottom types. In the present paper, we extend our analysis to examine the effects of additional environmental parameters on bottom types and to consider reasons for the importance of EC as a control of sedimentology. Our results identify microbially produced extracellular polymeric substances (EPS) as a major player in the determination of bottom types. The relative amounts and properties of EPS are determined by EC. EPS, in turn, determines the consistency of bottom types, exchange of bottom substrate with the overlying water column, and mineral precipitation within the substrate. Low-EC ponds in the Puquios system have flocculent to semi-cohesive bottom types, with low-viscosity EPS that allows for high-exchange with the surrounding waters and mineral precipitation of granular gypsum, carbonate, and Mg–Si clay in close association with microbes. Ponds with elevated EC have bottom types that are laminated and highly cohesive with high-viscosity EPS that restricts the exchange between sediments and the surrounding waters; mineral precipitation in these high-EC ponds includes granular to laminated gypsum, carbonate and Mg–Si, which also form in close association with microbes. Bottom types in ponds with EC above the threshold for thriving benthic microbial communities have insufficient EPS accumulations to affect mineral precipitation, and the dominant mineral is gypsum (selenite). The variations in EPS production throughout the Puquios, associated with heterogeneity in environmental conditions, make the Puquios region an ideal location for understanding the controls of sedimentary bottom types in evaporative extreme environments that may be similar to those that existed on early Earth and beyond.

This study identified and quantified in the field the natural predators of juvenile spiny lobster Jasus frontalis, an endemic, ecologically relevant species, and the most valuable local commercial catch of Robinson Crusoe Island. It also assessed the predation pressure that these predators exerted on juveniles lobsters and whether they showed preferences for particular body sizes within the juvenile size range. A series of tethering experiments were performed in three coastal sites of Robinson Crusoe Island (Juan Fernández archipelago. Chile). In overnight experiments, survival of juveniles decreased over time in all three sites, reaching ∼50% at the end of the experiment. The evidence suggests that fish were relevant predators since mortality of lobsters was proportional to their abundance. Although video surveillances depicted numerous octopus attacks, their abundance did not exhibit a statistically significant relationship with lobster mortality. Predatory events were not selective of juvenile sizes. These results are fundamental to understand one of the key factor (i.e., predation) that affects the juvenile (and more vulnerable) benthic phase of J. frontalis.

The Juan Fernández Archipelago (JFA) is a unique ecosystem due to its diversity and high endemism. In recent years, there has been an increase in the populations of the endemic sea urchin Centrostephanus sylviae, generating negative impacts on the ecological and socio-economic systems of the Archipelago. Here, we describe the establishment of C. sylviae and the consequences of its overabundance on the subtidal communities, specifically around Robinson Crusoe and Santa Clara islands. Also, we describe the variation in SST (°C) around both islands during the last 40 years. The increase in abundance of C. sylviae and its community-level impacts (i.e. sessile benthic, macroinvertebrates, and fishes) were documented by visual surveys using scuba diving at various sites during January 2014 (12 sites), March 2017 (12 sites), March 2020 (4 sites), and January 2024 (7 sites). Over this period, the increase of C. sylviae abundance (∼400%) was associated with a significant decrease in sessile biotic benthic cover and an increase in the percentage of barren grounds (40%–84%). Additionally, there was a significant decrease in the abundance of the sea star Patiriella calcarata (100%) and the sea cucumber Mertensiothuria platei (70%). In terms of fish, a decrease in the abundance of the endemic wrasse Malapterus reticulatus (95%), and an increase of the chilean sweeper Scorpis chilensis (40%) were observed. Both species evidenced a decrease in biomass (90% and 84%, respectively). In general, the abundance of C. sylviae could be attributed to the synergistic effects of both top-down and bottom-up processes, including the low presence of predators (Astrotole platei and Jasus frontalis), by the increase in nutrient concentrations, and by the influence of climate change. These results could serve as a baseline for exploring ongoing community changes in subtidal environments.