A deep-sea isopod that consumes Sargassum sinking from the ocean's surface

Most deep-ocean life relies on organic carbon from the surface ocean. While settling primary production rapidly attenuates in the water column, pulses of organic material can be quickly transported to depth in the form of food falls. One example of fresh material that can reach great depths across the tropical Atlantic Ocean and Caribbean Sea is the pelagic macroalgae Sargassum. However, little is known about the deep-ocean organisms able to use this food source. Here, we encountered the isopod Bathyopsurus nybelini at depths 5002-6288 m in the Puerto Rico Trench and Mid-Cayman Spreading Center using the Deep Submergence Vehicle Alvin. In most of the 32 observations, the isopods carried fronds of Sargassum. Through an integrative suite of morphological, DNA sequencing, and microbiological approaches, we show that this species is adapted to feed on Sargassum by using a specialized swimming stroke, having serrated and grinding mouthparts, and containing a gut microbiome that provides a dietary contribution through the degradation of macroalgal polysaccharides and fixing nitrogen. The isopod's physiological, morphological, and ecological adaptations demonstrate that vertical deposition of Sargassum is a direct trophic link between the surface and deep ocean and that some deep-sea organisms are poised to use this material.

Scientific and technological progress in the microbial exploration of the hadal zone

The hadal zone is the deepest point in the ocean with a depth that exceeds 6000 m. Exploration of the biological communities in hadal zone began in the 1950s (the first wave of hadal exploration) and substantial advances have been made since the turn of the twenty-first century (the second wave of hadal exploration), resulting in a focus on the hadal sphere as a research hotspot because of its unique physical and chemical conditions. A variety of prokaryotes are found in the hadal zone. The mechanisms used by these prokaryotes to manage the high hydrostatic pressures and acquire energy from the environment are of substantial interest. Moreover, the symbioses between microbes and hadal animals have barely been studied. In addition, equipment has been developed that can now mimic hadal environments in the laboratory and allow cultivation of microbes under simulated in situ pressure. This review provides a brief summary of recent progress in the mechanisms by which microbes adapt to high hydrostatic pressures, manage limited energy resources and coexist with animals in the hadal zone, as well as technical developments in the exploration of hadal microbial life.

Exploration of the Puerto Rico Trench in the mid-twentieth century: Today's significance and relevance

The Puerto Rico Trench is a deep oceanic subduction zone that runs parallel with the northern coasts of Puerto Rico and the Dominican Republic. It is the deepest place in the Atlantic Ocean with a maximum depth of approximately 8400 m. Discovered by the HMS Challenger Expedition in 1875, the depth of the trench increased multiple times in the ensuing 100 years with the onset of sonar usage. It is perhaps unique among the world's deep trenches in that a series of unrelated but equally pioneering expeditions captured the true biological and geological characteristics of one of the deepest places in the world, observations that are still highly relevant today. Multiple deep water trawling campaigns and surveys using drop cameras and exploratory dives in a deep diving submersible provided great insight into the morphology of the trench, the types of habitat within the trench, the substrate, the food supply, and the diversity of species that inhabit these extraordinary depths. Many of these accounts are obscure and disparate, yet combined bear a remarkable similarity to recent work in other trenches. These unique and insightful accounts are collated and retold here alongside recent and comparable findings to contextualise these discoveries, prevent them from being forgotten, and keep the efforts of those involved to remain relevant as we continue to explore the deepest places of the world's oceans.