For instance, in recent years ecologists have realised the critical importance of wetlands, mangroves, seagrass beds and coral reefs, often operating as a single unit which supports the recovery of entire ecosystems and their services,31 and even traps marine plastics.32 Similarly, the scale of ecosystem services provided by plankton continues to expand under examination.33
Increasing exploration of the deep-sea water column and seafloor substrate — by submersibles, robotic vehicles and other methods — is revealing complex ecosystems unlike anything at the surface. Hydrothermal vents are emerging as major contributors to the overall marine ecosystem.34 Researchers are finally able to explore the microbes living in oceanic crust,35 revealing hidden ecosystems shaped by magmatism and water-rock interactions.36 Some marine microbes perform metabolic processes such as degrading petrochemicals,37 and genetic information from deep-sea microbes and from sponges has aided the development of antiviral drugs and rapid testing for COVID-19.38 Marine genetic resources represent a large, and mostly untapped, source of potentially useful substances.39 However, the open-water pelagic zone (including the dark ecosystem), the largest habitat on Earth, remains under-explored.
A key challenge is to determine the fluxes of carbon and other nutrients through marine ecosystems, enabling us to track the carbon budget of the oceans,40 including the deep ocean,41 and the oceans’ ability to remove carbon from the atmosphere.42 Autonomous platforms can help monitor these biogeochemical processes.43 Behaviours such as deep diving by large predators like sperm whales are crucial to these fluxes.44
Available data on ecosystem function covers less than the past 25 years. Attention has mostly focused on a handful of charismatic groups, notably shallow-water corals, the decline of which is fairly well-documented.45 Expanding this longitudinal tracking to other species, including in the deep sea, will be crucial for tracking ecosystem responses to climate-driven changes such as ice-shelf collapses.46 It will also be key for planning how we use and conserve marine ecosystems.47
