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Current information on the status and trends of ocean change is needed to support effective and responsive management, particularly for the deep ocean. Creating consistent, collaborative and actionable mechanisms is a key component of the Deep Ocean Observing Strategy, a program of the United Nations Decade of Ocean Science for Sustainable Development. Here, we share an iterative, agile, and human-centred approach to co-designing datastreams for deep-sea indicators that serves stakeholders, including US National Marine Sanctuaries, presented as a four-phase project roadmap initially focused on the Monterey Bay National Marine Sanctuary, and then generalized to other areas such as the US West Coast, offshore wind development areas, and managed marine spaces globally. Ongoing efforts to provide key physical, biogeochemical, biological, and ecosystem variables for California's Marine Protected Areas are informing this co-design process. We share lessons learned so far and present co-design as a useful tool for (1) assessing the availability of information from deep ecosystems, (2) ensuring interoperability, and (3) providing essential information on the status and trends of indicators. Documenting and sharing this co-design strategy and scalable four-phase roadmap will further the aims of DOOS and other initiatives, including the Deep Ocean Stewardship Initiative and Challenger 150.

Climate change is altering the intensity and variability of environmental stress that organisms and ecosystems experience, but effects of changing stress regimes are not well understood. We examined impacts of constant and variable sublethal hypoxia exposures on multiple biological processes in the sea urchinStrongylocentrotus purpuratus, a key grazer in California Current kelp forests, which experience high variability in physical conditions. We quantified metabolic rates, grazing, growth, calcification, spine regeneration, and gonad production under constant, 3-hour variable, and 6-hour variable exposures to sublethal hypoxia, and compared responses for each hypoxia regime to normoxic conditions. Sea urchins in constant hypoxia maintained baseline metabolic rates, but had lower grazing, gonad development, and calcification rates than those in ambient conditions. The sublethal impacts of variable hypoxia differed among biological processes. Spine regrowth was reduced under all hypoxia treatments, calcification rates under variable hypoxia were intermediate between normoxia and constant hypoxia, and gonad production correlated negatively with continuous time under hypoxia. Therefore, exposure variability can differentially modulate the impacts of sublethal hypoxia, and may impact sea urchin populations and ecosystems via reduced feeding and reproduction. Addressing realistic, multifaceted stressor exposures and multiple biological responses is crucial for understanding climate change impacts on species and ecosystems.

Declining oxygen is one of the most drastic changes in the ocean, and this trend is expected to worsen under future climate change scenarios. Spatial variability in dissolved oxygen dynamics and hypoxia exposures can drive differences in vulnerabilities of coastal ecosystems and resources, but documentation of variability at regional scales is rare in open-coast systems. Using a regional collaborative network of dissolved oxygen and temperature sensors maintained by scientists and fishing cooperatives from California, USA, and Baja California, Mexico, we characterize spatial and temporal variability in dissolved oxygen and seawater temperature dynamics in kelp forest ecosystems across 13° of latitude in the productive California Current upwelling system. We find distinct latitudinal patterns of hypoxia exposure and evidence for upwelling and respiration as regional drivers of oxygen dynamics, as well as more localized effects. This regional and small-scale spatial variability in dissolved oxygen dynamics supports the use of adaptive management at local scales, and highlights the value of collaborative, large-scale coastal monitoring networks for informing effective adaptation strategies for coastal communities and fisheries in a changing climate.

Marine organisms and ecosystems face multiple, temporally variable stressors in a rapidly changing world. Realistic experiments that incorporate these aspects of physiological stress are important for advancing our ability to understand, predict, and manage their ecological impacts. However, the experimental systems needed to conduct such experiments can be costly. Here, we describe a low‐cost, modular control system that can be used with seawater sensors and actuators to dynamically manipulate multiple seawater variables. It enables researchers to run a variety of realistic multiple‐stressor, variable exposure experiments with a range of marine organisms. This tank controller system is based on the open‐source Arduino prototyping platform and features a custom‐made circuit board with a 16‐bit analog‐to‐digital converter, a real‐time clock, a MicroSD memory card reader, a high‐voltage transistor array, and solderless screw terminal connectors for easy connection of sensors, actuators, and power supplies. The assembly and use of this controller system does not require extensive electronics engineering or programming experience, and each module can be assembled for under 80 USD in parts. To demonstrate the system's capabilities, we present seawater manipulations from experiments involving (1) simultaneous manipulations of dissolved oxygen and pH; (2) fluctuating dissolved oxygen levels; and (3) a controlled stepwise decrease in dissolved oxygen at different temperatures. The low cost and high customizability of this Arduino‐based control system can contribute to expanding capacities for running global change experiments for researchers and students worldwide.