A decade of submersible observations revealed temporal trends in elasmobranchs in a remote island of the Eastern Tropical Pacific Ocean.

No-take marine protected areas (MPAs) can mitigate the effects of overfishing, climate change and habitat degradation, which are leading causes of an unprecedented global biodiversity crisis. However, assessing the effectiveness of MPAs, especially in remote oceanic islands, can be logistically challenging and often restricted to relatively shallow and accessible environments. Here, we used a long-term dataset (2010-2019) collected by the DeepSee submersible of the Undersea Hunter Group that operates in Isla del Coco National Park, Costa Rica, to (1) determine the frequency of occurrence of elasmobranch species at two depth intervals (50-100 m; 300-400 m), and (2) investigate temporal trends in the occurrence of common elasmobranch species between 2010 and 2019, as well as potential drivers of the observed changes. Overall, we observed 17 elasmobranch species, 15 of which were recorded on shallow dives (50-100 m) and 11 on deep dives (300-400 m). We found a decreasing trend in the probability of occurrence of Carcharhinus falciformis over time (2010-2019), while other species (e.g. Taeniurops meyeni, Sphyrna lewini, Carcharhinus galapagensis, Triaenodon obesus, and Galeocerdo cuvier) showed an increasing trend. Our study suggests that some species like S. lewini may be shifting their distributions towards deeper waters in response to ocean warming but may also be sensitive to low oxygen levels at greater depths. These findings highlight the need for regional 3D environmental information and long-term deepwater surveys to understand the extent of shark and ray population declines in the ETP and other regions, as most fishery-independent surveys from data-poor countries have been limited to relatively shallow waters.

Variation of bacterial communities along the vertical gradient in Lake Issyk Kul, Kyrgyzstan.

We explored the diversity and community composition of bacteria along a vertical gradient in Lake Issyk Kul, Kyrgyzstan, one of the world's largest and deepest brackish lakes. We identified 4904 bacterial amplicon sequence variants based on the 16S rRNA gene analysis and determined significant changes in the composition, responding mainly to depth and salinity. A higher abundance of Proteobacteria and Bacteroidetes was observed in the surface waters and lake tributaries. Cyanobacteria were more abundant in the deep chlorophyll maximum from 28.5 to 128 m, while Planctomycetes and Chloroflexi were dominant in the deepest layers, from 128 to 600 m. According to our machine learning analyses, depth and temperature were the most critical environmental factors, with strong effects on Proteobacteria, Planctomycetes and Chloroflexi, while oxygen was associated with the variations in Cyanobacteria. We also observed that with increasing depth, the alpha diversity values increased. The dominance of Planctomycetes and Chloroflexi in the deepest layers can only be seen in a few lakes of the world. However, the lake is facing increasing anthropogenic and climatic pressure. There is an urgent need to understand better the ecological role and function of these unique deep-water microbial communities.