The ocean plays a crucial role in the functioning of the Earth System and in the provision of vital goods and services. The United Nations (UN) declared 2021–2030 as the UN Decade of Ocean Science for Sustainable Development. The Roadmap for the Ocean Decade aims to achieve six critical societal outcomes (SOs) by 2030, through the pursuit of four objectives (Os). It specifically recognizes the scarcity of biological data for deep-sea biomes, and challenges the global scientific community to conduct research to advance understanding of deep-sea ecosystems to inform sustainable management. In this paper, we map four key scientific questions identified by the academic community to the Ocean Decade SOs: (i) What is the diversity of life in the deep ocean? (ii) How are populations and habitats connected? (iii) What is the role of living organisms in ecosystem function and service provision? and (iv) How do species, communities, and ecosystems respond to disturbance? We then consider the design of a global-scale program to address these questions by reviewing key drivers of ecological pattern and process. We recommend using the following criteria to stratify a global survey design: biogeographic region, depth, horizontal distance, substrate type, high and low climate hazard, fished/unfished, near/far from sources of pollution, licensed/protected from industry activities. We consider both spatial and temporal surveys, and emphasize new biological data collection that prioritizes southern and polar latitudes, deeper (> 2000 m) depths, and midwater environments. We provide guidance on observational, experimental, and monitoring needs for different benthic and pelagic ecosystems. We then review recent efforts to standardize biological data and specimen collection and archiving, making “sampling design to knowledge application” recommendations in the context of a new global program. We also review and comment on needs, and recommend actions, to develop capacity in deep-sea research; and the role of inclusivity - from accessing indigenous and local knowledge to the sharing of technologies - as part of such a global program. We discuss the concept of a new global deep-sea biological research program ‘Challenger 150,’ highlighting what it could deliver for the Ocean Decade and UN Sustainable Development Goal 14.

The UN Decade of Ocean Science for Sustainable Development represents a once in a generation opportunity to effect positive change in ocean use. We outline what is required of the deep-sea research community in order to achieve the ambitious objectives of the Ocean Decade and call for the development of a new ten-year research programme.The health of the global ocean, on which society is dependent, is in decline. The importance of sustainable use to ocean health has long been recognized 1 . The First World Ocean Assessment 2 highlighted increasing ocean pressures from accelerated expansion of human activities, including climate change, affecting all ocean regions, from the coast to the deep sea 3 . In response to this concern, and in keeping with several international policy commitments, the UN General Assembly proclaimed 2021-2030 the Decade of Ocean Science for Sustainable Development 4 . The Ocean Decade Roadmap recognizes the deep sea as a frontier of science and discovery, calling for research to advance understanding of deep-sea ecosystems, their functions, vulnerabilities, and services to society. Published in March 2020, the draft Implementation Plan for the Ocean Decade describes a framework to guide the design and implementation of 'Actions' throughout the Decade. These Actions underpin the move from the 'ocean we have' to the 'ocean we want'. Different levels of Actions are identified, and include programmes, projects, activities and contributions. The draft plan calls upon the scientific community to develop Actions to help deliver on four key objectives (see Fig. 1).The deep-sea biology community responded to this call through working groups of the Deep-Ocean Stewardship Initiative (DOSI) and the Scientific Committee on Oceanic Research. In keeping with the Ocean Decade's focus on fair and equitable partnerships, these groups gather experts from developed and developing nations, representing diverse ethnic backgrounds, different genders and career stages. Together, these groups considered each of the Ocean Decade objectives in a deep-sea biology context, and the associated research needs. Here we present a series of recommendations under each objective to inform the development of deep-sea focused Ocean Decade Actions. Figure 1: The Ocean Decade through a deep-sea biology lens, and our recommendations to support the development of Actions focused on achieving the Ocean Decade objectives.

The Galician rias are singular and complex estuarine systems of great economic importance. Seagrasses are key elements of the ecosystem and favor the maintenance of high species diversity in benthic communities. Nevertheless, the ecological role of seagrass meadows in the Galician rias has been only partially assessed. Peracarid crustaceans are an important component of soft-bottom faunas and have great importance for the structure of benthic assemblages. In this work, species diversity, patterns of distribution and seasonal fluctuations of peracarids (Crustacea, Peracarida) are studied in estuarine sediments colonized by two species of Zostera (Z. marina and Z. noltii) at the O Grove inlet (Ría de Arousa, Galicia, NW Iberian Peninsula). The spatial distribution of peracarid assemblages was characterized by high numerical dominances due to a few species, particularly tanaidaceans. The temporal study at a Z. marina meadow showed a strongly seasonal pattern defined by great fluctuations of the amphipod population, the latter being the dominant group in abundance and number of species. The highest numbers of species and individuals were observed in September, with minimum values in March. Analyses pointed out a high correlation among the granulometric features of the studied bottoms and the faunistic attributes. Nevertheless, the presence of the seagrasses should influence in a major way the hydrodynamic and sedimentary features of the habitat and utterly the spatial and temporal patterns observed in the peracarid assemblage in the O Grove inlet.

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