Abstract. Seamounts are abundant and prominent features on the deep-sea floor and intersperse with the nodule fields of the Clarion-Clipperton Fracture Zone (CCZ). There is a particular interest in characterising the fauna inhabiting seamounts in the CCZ because they are the only other ecosystem in the region to provide hard substrata besides the abundant nodules on the soft-sediment abyssal plains. It has been hypothesised that seamounts could provide refuge for organisms during deep-sea mining actions or that they could play a role in the (re-)colonisation of the disturbed nodule fields. This hypothesis is tested by analysing video transects in both ecosystems, assessing megafauna composition and abundance. Nine video transects (ROV dives) from two different license areas and one Area of Particular Environmental Interest in the eastern CCZ were analysed. Four of these transects were carried out as exploratory dives on four different seamounts in order to gain first insights into megafauna composition. The five other dives were carried out in the neighbouring nodule fields in the same areas. Variation in community composition observed among and along the video transects was high, with little morphospecies overlap along intra-ecosystem transects. Despite the observation of considerable faunal variations within each ecosystem, differences between seamounts and nodule fields prevailed, showing significantly different species associations characterising them, thus calling into question their use as a possible refuge area.

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.

a b s t r a c tThe Nazaré Canyon on the Portuguese Margin (NE Atlantic) was sampled during spring-summer for three consecutive years (2005)(2006)(2007), permitting the first inter-annual study of the meiofaunal communities at the Iberian Margin at two abyssal depths ( 3500 m and 4400 m). Using new and already published data, the meiofauna standing stocks (abundance and biomass) and nematode structural and functional diversity were investigated in relation to the sediment biogeochemistry (e.g. organic carbon, nitrogen, chlorophyll a, phaeopigments) and grain size. A conspicuous increase in sand content from 2005 to 2006 and decrease of phytodetritus at both sites, suggested the occurrence of one or more physical disturbance events. Nematode standing stocks and trophic diversity decreased after these events, seemingly followed by a recovery/recolonisation period in 2007, which was strongly correlated with an increase in the quantity and bioavailability of phytodetrital organic matter supplied. Changes in meiofauna assemblages, however, also differed between stations, likely because of the contrasting hydrodynamic and food supply conditions. Higher meiofauna and nematode abundances, biomass and trophic complexity were found at the shallowest canyon station, where the quantity, quality and bioavailability of food material were higher than at the deeper site. The present results suggest that even though inter-annual variations in the sedimentary environment can regulate the meiofauna in the abyssal Nazaré Canyon, heterogeneity between sampling locations in the canyon were more pronounced.