Dynamic change in an ocean desert: Microbial diversity and trophic transfer along the 110 °E meridional in the Indian Ocean

The eastern Indian Ocean is among the most oligotrophic regions in the world and has been described as an ocean desert. Limited information exists on microbial community profiles from marker gene data, and an open question in this system is how energy is transported from the base of the food web to higher trophic levels. Here we show that, along a 3300 km long transect in the ultra-oligotrophic eastern Indian Ocean, both alpha and beta diversity metrics for prokaryotic and eukaryotic trophic groups revealed remarkably strong latitudinal trends. The latitudinal Shannon diversity pattern for autotrophic eukaryotes furthermore aligned with the isotopic δ13C ratios of particulate organic carbon, fractionated zooplankton and hand-picked fish larvae, suggesting a close trophic linkage between autotrophic eukaryotes and higher trophic levels. Our data also showed an increasing contribution of eukaryotic mixotrophs and a high contribution of heterotrophic eukaryotes towards warmer waters. These findings highlight that not only the recycling of organic matter via bacterial regeneration is important in this system but that mixo- and heterotrophic eukaryotes play a major role in redistributing energy within the marine food web of these oligotrophic waters. Our data provide a baseline to understand how environmental changes such as warming surface waters might impact the open-ocean food web in this oligotrophic basin

Dynamic change in an ocean desert: Microbial diversity and trophic transfer along the 110 °E meridional in the Indian Ocean

The eastern Indian Ocean is among the most oligotrophic regions in the world and has been described as an ocean desert. Limited information exists on microbial community profiles from marker gene data, and an open question in this system is how energy is transported from the base of the food web to higher trophic levels. Here we show that, along a 3300 km long transect in the ultra-oligotrophic eastern Indian Ocean, both alpha and beta diversity metrics for prokaryotic and eukaryotic trophic groups revealed remarkably strong latitudinal trends. The latitudinal Shannon diversity pattern for autotrophic eukaryotes furthermore aligned with the isotopic δ13C ratios of particulate organic carbon, fractionated zooplankton and hand-picked fish larvae, suggesting a close trophic linkage between autotrophic eukaryotes and higher trophic levels. Our data also showed an increasing contribution of eukaryotic mixotrophs and a high contribution of heterotrophic eukaryotes towards warmer waters. These findings highlight that not only the recycling of organic matter via bacterial regeneration is important in this system but that mixo- and heterotrophic eukaryotes play a major role in redistributing energy within the marine food web of these oligotrophic waters. Our data provide a baseline to understand how environmental changes such as warming surface waters might impact the open-ocean food web in this oligotrophic basin

Diazotrophy in the Indian Ocean: Current understanding and future perspectives

Abstract Dinitrogen (N2) fixation provides the major source of reactive nitrogen in the open ocean, sustaining biological productivity. The Indian Ocean (IO) covers 22% of the ocean surface, while it only represents 1% of the global diazotroph database. Hence, constraining the sources of nitrogen in the IO is crucial. Here, we compile three decades of N2 fixation and diazotroph DNA data in the IO. Our analysis reveals basin‐scale yearly rates between ~ 7 and 13 Tg N yr−1. These rates are in the range of previous modeling‐based estimates but may represent a lower bound estimate due to the lack of data in this basin. Diazotroph variability among sub‐basins may suggest endemicity but needs to be taken with caution due to biased sampling toward certain seasons and uneven spatial coverage. We provide recommendations for a more accurate representation of the IO in the global nitrogen budget and our knowledge of diazotroph biogeography

EuroSea Strategic vision

This report provides recommendations to foster collaboration and cooperation between technologies and disciplines and for implementing truly integrated ocean observing systems. Based on an intensive literature review and a careful examination of different examples of integration in different fields, this work identifies the issues and barriers that must be addressed, and proposes a vision for a real implementation of this ocean integration ambition. This work is a contribution to the implementation of EOOS, a much-needed step forward in Europe, following the international guidance of GOOS

Ocean integration : The needs and challenges of effective coordination within the ocean observing system

Understanding and sustainably managing complex environments such as marine ecosystems benefits from an integrated approach to ensure that information about all relevant components and their interactions at multiple and nested spatiotemporal scales are considered. This information is based on a wide range of ocean observations using different systems and approaches. An integrated approach thus requires effective collaboration between areas of expertise in order to improve coordination at each step of the ocean observing value chain, from the design and deployment of multi-platform observations to their analysis and the delivery of products, sometimes through data assimilation in numerical models. Despite significant advances over the last two decades in more cooperation across the ocean observing activities, this integrated approach has not yet been fully realized. The ocean observing system still suffers from organizational silos due to independent and often disconnected initiatives, the strong and sometimes destructive competition across disciplines and among scientists, and the absence of a well-established overall governance framework. Here, we address the need for enhanced organizational integration among all the actors of ocean observing, focusing on the occidental systems. We advocate for a major evolution in the way we collaborate, calling for transformative scientific, cultural, behavioral, and management changes. This is timely because we now have the scientific and technical capabilities as well as urgent societal and political drivers. The ambition of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) and the various efforts to grow a sustainable ocean economy and effective ocean protection efforts all require a more integrated approach to ocean observing. After analyzing the barriers that currently prevent this full integration within the occidental systems, we suggest nine approaches for breaking down the silos and promoting better coordination and sharing. These recommendations are related to the organizational framework, the ocean science culture, the system of recognition and rewards, the data management system, the ocean governance structure, and the ocean observing drivers and funding. These reflections are intended to provide food for thought for further dialogue between all parties involved and trigger concrete actions to foster a real transformational change in ocean observing