Introduction to the Essential Ocean Variables Framework
Essential Ocean Variables are defined by the Global Ocean Observing System (GOOS) as the minimum set of ocean variables that are needed to assess ocean state and variability for important global ocean phenomena, and to provide essential data for applications that support societal benefit. They are derived from sustained individual measurements, or combinations of measurements, that can be undertaken at global scale and in a cost-effective manner.
The EOV framework has also been for the first time comprehensively described in a peer-reviewed publication "GOOS Essential Ocean Variables: the backbone of a sustained and evolving global ocean observing system" (Martín Míguez B., Heslop E., et al., 2026) with strong contribution from the project.
BioEcoOcean contribution to the BioEco EOVs
From the beginning of the project we have been working hand in hand with the Global Ocean Observing System (GOOS) Biology & Ecosystems Panel of Experts who are acting as stewards of the BioEco EOVs. Close synergy between our activities are ensured by convening two joint in-person meetings (February 2025 and September 2026) as well as by the fact that several BioEcoOcean project members are serving on the Panel. Together, we have provided expert input into the revision of, or development of new, BioEco EOV Specification Sheets, helped launch the first ever public review of EOVs, and subsequently published new versions of the BioEco EOV Spec Sheets (see below) and a corresponding Guide to EOVs.
Key Project Results
- Advanced Biology & Ecosystems Essential Ocean Variable Specification Sheets to support global assessments and foster the development of ocean climate monitoring and reporting
- Pilot demonstrations and roadmaps towards new data and data synthesis products for Biology & Ecosystems EOVs to enhance the value of in situ and remote sensing observing capacity in the coastal and open ocean
Phytoplankton Biomass and Diversity EOV
Biomass and diversity are basic characteristics of the phytoplankton, the photosynthetic microorganisms found in all aquatic habitats that receive sunlight. The phytoplankton can be planktonic, benthic, or grow as symbionts on or within other organisms. Phytoplankton are at the base of most marine food webs (except those fuelled by chemosynthesis). Phytoplankton support important ecosystem services in coastal, estuarine, and offshore pelagic areas and, thus, are part of “Nature Contributions to People”. They are also often sensitive indicators of water quality and ecosystem health. They are fundamental in the function of most food webs and ecosystems, not just as sources of food and energy, but for their role in the cycling of nitrogen and many micronutrients and metals, carbon fixation and emission, as well as in production and consumption of oxygen and other gases.Zooplankton Biomass and Diversity EOV
Zooplankton (drifting animals in the world’s oceans) are foundational to marine ecosystems worldwide, linking primary producers (phytoplankton) to higher trophic levels (including marine mammals, seabirds, fish, and invertebrates), directly sustaining fisheries critical for global food security and livelihoods, and supporting endangered and vulnerable marine megafauna. Zooplankton play a pivotal role in regulating the global carbon cycle, contributing to the biological pump that sequesters carbon in the deep ocean, thereby contributing to the mitigation of climate change. They are also critical for nutrient cycling, recycling key elements like nitrogen and phosphorus, which maintain ocean productivity and sustain marine food webs. Their biomass and diversity are sensitive indicators of ocean health, reflecting responses to stressors such as warming, acidification, and deoxygenation, making them essential for tracking ecosystem health and resilience. Zooplankton underpin marine biodiversity and ecosystem services, and monitoring zooplankton is essential for meeting international goals such as SDG 13 (Climate Action) and SDG 14 (Life Below Water).Fish Abundance and Distribution EOV
Monitoring fish abundance and distribution is essential to sustaining marine ecosystems, global food security, and economic stability. Fish are integral to ecosystem health maintaining the balance by playing a critical role as predators and prey in almost all marine ecosystems. Fish are a vital food source, improve livelihoods and wellbeing for millions of people, and hold cultural significance across diverse societies. Sea Turtles Abundance and Distribution EOV
Sea turtles are a key endangered marine organisms that are charismatic, keystone species. They occupy the top of the food web, help maintain the health of seagrass and coral habitats, and facilitate the energy flow between ocean basins as well as between the ocean-land interface. Sea turtles also support human societies by helping sequester carbon in seagrasses, benefiting the fishing industry by controlling jellyfish populations and other nuisance species. They are a key part of socio-ecological systems, particularly within the 'Blue Economy,' and hold important cultural and recreational significance across diverse societies.Seabirds Abundance and Distribution EOV
Seabirds are vital indicators of ocean health due to their mobility and reliance on diverse marine ecosystems. As top predators, most seabirds integrate information across large spatial and temporal scales, making them essential for monitoring changes in ocean conditions, such as shifts in prey availability or habitat degradation caused by pressures like overfishing, climate change, and pollution. Seabird population dynamics, breeding success, and foraging behavior reflect the health of marine environments, providing early warnings about broader ecosystem disruptions. This makes seabirds a critical Essential Ocean Variable (EOV), helping assess the impacts of human activities on marine biodiversity, fisheries, and coastal communities.Marine Mammal Abundance and Distribution EOV
As wide-ranging, relatively long-lived and large-bodied animals, marine mammals play a crucial role in maintaining the health of their ecosystems. These charismatic megafauna interact with and influence population dynamics and distribution of numerous prey species. To evaluate these interactions and their variability, an understanding of marine mammal abundance and distribution is essential. Stock assessment analyses require accurate, up-to-date information on abundance and distribution in order to inform appropriate management and/or conservation measures. This EOV will facilitate evaluation of the potential impacts of several pressures on upper trophic levels of marine food webs.Coral Cover and Composition EOV
Corals span shallow tropical waters to deep-sea environments, forming biodiverse reefs of immense ecological and economic importance. As ecosystem engineers, hard corals (Scleractinia, Stylasteridae), soft corals (Octocorallia), and sponges create biogenic habitats that support 25% of marine species while sustaining fisheries worth 6.8 billion annually (Souster et al., 2021). These ecosystems provide coastal protection, novel pharmaceuticals, and contribute 375 billion yearly to the global economy, including 36 billion from reef tourism.Seagrass Cover and Composition EOV
Seagrass cover and composition is recognized as an Essential Ocean Variable (EOV) because it provides vital insights into ocean health, biodiversity, and climate resilience. These ecosystems are important habitats and play a key role in supporting marine biodiversity, sustaining fisheries, stabilising coastlines, and filtering pollutants, delivering critical benefits to coastal communities around the world (Nordlund et al 2016). Moreover, their noteworthy capacity for "blue carbon" sequestration and storage significantly contributes to climate change mitigation efforts (UNEP, 2020). Monitoring and assessing seagrass cover and composition allow for tracking environmental quality and ecosystem dynamics at global to local scales (Duffy et al. 2019). These insights inform conservation strategies, promote sustainable fisheries, and guide policy development aimed at fostering resilient coastal ecosystems.Macroalgal Canopy Cover and Composition EOV
Macroalgae forms the foundation of coastal ecosystems around the world, providing essential services for ocean ecosystems and humanity. Macroalgal forests and intertidal provide habitat, food, shoreline protection, nurseries, food for many global communities, and more. Kelp forests alone provide $500 billion USD in services per year (Eger et al. 2023). Intertidal algal canopies are valued roughly $5 million USD per mile of intertidal habitat (Hall et al. 2008). Macroalgal habitats face serious threats from global, regional, and local stressors. Ocean warming, pollution, habitat degradation, the spread of invasive species, release of grazers due to overfishing, and more all weaken macroalgal systems and can lead to shifts and population collapse.Mangrove Cover and Composition EOV
Mangroves are intertidal, tree-dominated wetlands distributed along tropical and subtropical coastlines and estuaries around the world influenced by ocean tides. Mangroves mediate key biogeochemical fluxes (Kristensen et al. 2008), are highly productive (Zhang et al. 2024), and support rich biological communities (Sievers et al. 2023; zu Ermgassen et al. 2025). They protect coastal communities from erosion and flood damage from storm surges (Menéndez et al. 2020), filter errestrial un-off (Ewel et al. 1998), supply timber, and generate significant revenue through ecotourism and biodiversity conservation (Costanza et al. 1997). The global value of mangrove ecosystems is estimated at nearly US$32 billion annually, which underscores their importance in combating climate change and supporting local economies (Costanza et al. 2014). Mangroves provide critical nursery habitat for marine species around the world (Sheaves et al. 2015).Microbe Biomass and Diversity EOV [*pilot]
Microbes, or microorganisms, are unseen but essential for life on Earth, inhabiting every environment on the planet. They constitute the majority of the world’s biodiversity, representing nearly 80% of all life. Marine microbes play pivotal roles in ocean health, underpinning food webs, producing essential vitamins, mediating global biogeochemical cycles and carbon sequestration, sustaining symbioses, coastal and oceanic health including coral reefs, fisheries, and nurseries. Their metabolisms and thereby their roles in ocean biogeochemistry are diverse. They fix nitrogen, thus supplying limiting nutrients to fuel primary production, cycle greenhouse gases, and they respire organic carbon, contributing to the creation of oxygen minimum zones. They are key to the improvement of water quality after eutrophication events or oil spills (Dombrowski et al., 2016), the defense of disease in coral reefs (Rosenberg, et al., 2007), and many other ecosystem services.Benthic Invertebrate Abundance and Distribution [*pilot]
Benthic invertebrates live on, near or beneath seafloors across the world, from polar seas to tropical reefs, and from intertidal mudflats to abyssal plains. They represent a huge number of taxa (27 phyla) and a large range of sizes (nanograms to kilograms). Benthic invertebrates make up a significant proportion of global biodiversity across the ocean's most extreme gradients of temperature, oxygen availability, food supply, and pH. They play critical roles in ecosystem function, including food webs, carbon cycling, and habitat provision. Additionally, many species are of economic, social and cultural benefit, supporting food security, tourism, and indigenous values. Many taxa and habitats within this group are also protected under conservation frameworks.
