Understanding and safeguarding marine biodiversity is essential for sustaining life on Earth
Context
Our oceans regulate our climate, provide food and oxygen, and support intricate ecological networks vital to planetary systems. Yet, most of our oceans remain biologically unexplored, particularly in offshore and remote regions, due to the high cost and logistical constraints of traditional research expeditions. Environmental DNA (eDNA) technologies are transforming our ability to monitor biodiversity by offering a non-invasive, scalable and cost-effective alternative to conventional methods. All marine organisms – from microbes to whales – shed DNA into their surrounding environment through skin cells, waste products and secretions. By filtering small volumes of seawater and sequencing short, taxonomically informative regions of this DNA, scientists can detect a wide array of organisms without the need for direct observation or collection. This approach not only minimises disturbance to ecosystems, but it also captures biodiversity signals across multiple trophic levels and time frames, enabling large-scale ecological assessments with unprecedented resolution.
The Citizens of the Sea programme addresses one of the most pressing challenges in ocean science: how to collect high-quality biological data at scale, especially in data-poor regions of the open ocean. Citizens of the Sea equips ocean cruisers and offshore yachts with a user-friendly, towable eDNA sampler known as TorpeDNA (developed by Cawthron Institute), which enables the efficient collection of eDNA using in-water DNA capture technology while the vessel is underway at cruising speeds. This innovation eliminates the need for specialised research vessels or laborious onboard filtration, thereby dramatically reducing the cost and complexity of offshore sampling.
These efforts aim to create a spatio-temporal catalogue of biodiversity and ocean health indicators accessible to scientists, conservationists and policymakers alike. A key focus of the organisation is fostering collaboration across diverse stakeholders, including sailors, government agencies, NGOs, scientific researchers and indigenous communities.
Analysis from our first year of sampling in 2024 demonstrated the ability of citizen-driven science to conduct biodiversity monitoring at an ocean basin scale. The dataset produced in this first campaign is unique, meeting high-quality standards and providing the first high-resolution biodiversity assessment of a vast and understudied ocean region. By leveraging existing sailing networks, user-friendly molecular tools and rigorous analytical protocols, Citizens of the Sea is helping to expand participation in ocean science and contribute to distributed, open ocean biodiversity monitoring networks. This approach provides valuable data for informing adaptive management and conservation strategies.
Results
The Citizens of the Sea partnership achieved extensive spatial coverage compared to traditional scientific expeditions, which are normally constrained by complex logistics and high costs. Similarly, we show that the data gathered by seafarers meets high standards of scientific quality and probably provides the highest-resolution ‘picture’ at a basin scale of this part of the Pacific Ocean to date. This dataset therefore represents the one of the first eDNA baseline assessment of marine biodiversity in this region, and as such, will be a cornerstone for monitoring biodiversity changes in the southwest Pacific Ocean in the coming years.
Twenty-six yachts participated in the Pacific Rally 2024, collectively sampling more than 1.5 million km2 of open ocean between Aotearoa New Zealand, Tonga and Fiji from May to July 2024. Applying high-throughput metabarcoding of eDNA, we sequenced 745 samples using four genetic markers (bacterial 16S, eukaryotic 18S, mitochondrial COI and vertebrate-specific mitochondrial 16S). This resulted in nearly 2 billion raw sequence reads. Following rigorous bioinformatic filtering, the final dataset included 466 million high-quality reads and 212,191 unique amplicon sequence variants (ASVs) across 708 samples.
Our analyses revealed variation linked to field and laboratory procedures, including a positive correlation between ASV richness and vessel speed. After accounting for this source of variation, we also found a clear biogeographic gradient in the community structure of bacterial (16S), eukaryotic (18S) and metazoan (COI) communities [plankton?], all of which displayed a strong and significant correlation with sea surface temperature, and to a lesser extent, with chlorophyll-a concentration. Our results also indicate that in this dataset, the ASV richness asymptote is reached with approximately 500 samples for the 16S, 18S and COI markers, providing a landmark in terms of the sampling effort required to characterise planktonic communities at an ocean basin scale. Additionally, we demonstrate the usefulness of this dataset to explore the spatial distribution of putative pathogenic bacteria and microalgae responsible for harmful algal blooms.
Plankton is the basis of the ocean’s food chain and is the canary in the coal mine—if it disappears, everything else will follow. It is of vital importance we measure plankton and any changes over time, likewise the spread of invasive species. Detections of marine vertebrates, including marine mammals, pave the way for improving distribution mapping of International Union for Conservation of Nature (IUCN) Red List species across open ocean settings.
These results suggest that our sampling strategy was sufficient to obtain a comprehensive characterisation of the biodiversity of surface waters that is detectable using these markers. However, results from the mt16S marker also revealed that this method does not work as well for some taxonomic groups such as vertebrates. Nevertheless, in general, the results reinforce the notion that only citizen science approaches will yield sampling designs that are comprehensive at open ocean spatial scales at affordable costs.
Fish detections generally reflected known geographic species distributions, with seven tropical coral reef fish species detected predominantly in tropical waters. We also documented high diversity among lantern fishes (14 species), which aligns with their status as the most abundant and diverse fish groups in open oceans and their dominance in our dataset. Additionally, we detected five different cetacean species, including the Endangered sei whale (as per the latest update of the IUCN Red List). While our vertebrate detections were limited, these results provide valuable data to global conservation initiatives such as those led by the IUCN, enhancing knowledge of species that are typically elusive and difficult to observe directly.
Implementation challenges and operational lessons
The Pacific Rally 2024 campaign provided major operational lessons and technical challenges. The success of this ambitious endeavour depended not only on developing robust, easy-to-use sampling tools, but also on the careful orchestration of human networks, training, logistics and downstream processing. A central enabler of this programme was the TorpeDNA device – a lightweight, towable eDNA sampler capable of collecting high-quality DNA material from surface waters while the vessel is underway at sailing speeds of up to 12 knots. The device, developed by Cawthron Institute, significantly reduced the complexity and cost of offshore molecular sampling. In practice, the hardware proved resilient and effective across a range of vessel types, weather conditions and user skill levels, and the sampling protocol was successfully executed in the vast majority of cases. This high sample quality rate corroborates the effectiveness of adopting this easy-to-use technology and simplified sampling protocols for citizen science sampling.
Another key component of the success of this pilot campaign was the alliance with the Island Cruising network, which facilitated the recruitment of 26 vessels. The network’s established communication channels and trust with offshore sailors proved essential. That said, aligning scientific needs with cruising schedules was not without difficulty. Sampling instructions had to accommodate diverse sailing conditions and priorities. To this end, sampling was opportunistic rather than spatially predesignated, emphasising safety, flexibility and simplicity. Participants were instructed to collect triplicate samples in good weather and daylight, ideally between 10am and 2pm, using standardised protocols provided through detailed video tutorials,1 manuals and remote training sessions, strategies successfully used in other eDNA citizen science initiatives. Despite these safeguards, we did see some variability in metadata capture (e.g. sample scanning, GPS logging) and variation in data output linked to vessel identity and speed. Nonetheless, the integration of field metadata via ArcGIS Survey123 forms was generally successful, simplified data input by sailors and minimised data entry errors, offering a scalable solution for future deployments.
It is also worth mentioning that we piloted logistical solutions for refrigerated sample consolidation in Savusavu and Viseisei (Fiji) and Nuku’alofa (Tonga), followed by cold-chain shipping to Cawthron Institute in Aotearoa New Zealand. This system functioned reliably, as can be seen by the high quality of data obtained from the vast majority of samples, and can serve as a model for regional sample relay in future programmes.
In summary, this first full-scale deployment confirms that a well-designed citizen science programme can collect molecular-quality biodiversity data across thousands of kilometres of ocean at a fraction of the cost of traditional expeditions. The lessons learnt have already been translated into protocol refinements and field upgrades, and they provide a foundation for scaling up sampling in 2026 and beyond.
Looking forward: the value of our data
The strategic value of the Citizens of the Sea dataset lies not only in its spatial coverage, but also in its long-term accessibility and utility. Unlocking this value will require a coordinated approach to data management, ethical sharing and platform development that aligns with both international open science frameworks and Pacific regional priorities. From the outset, the Citizens of the Sea programme has committed to operating under the FAIR (findable, accessible, interoperable, reusable) and CARE (collective benefit, authority to control, responsibility, ethics) data principles, while ensuring respect for national data sovereignty, especially for data collected within the EEZs of Pacific Island nations. This balance requires both technological and diplomatic solutions. The project team has actively consulted with local ministries and research institutions in Tonga, Fiji and New Caledonia to co-develop permit requests and processing and data-sharing protocols. In return, partners will receive access to sample data collected within their jurisdictions, and will be offered dashboards and training resources to support local use of the information.
There is a distinct lack of historical and current baseline surveys of non-indigenous species (NIS) across most Pacific Island nations, and no cohesion in marine biosecurity management systems between countries. However, there have been calls to develop a national or territorial invasive species strategy and action plans for the region (SPREP 2022). Given the high-resolution, large spatio-temporal sampling afforded by Citizens of the Sea, our approach has the potential to fill significant gaps in knowledge about the transport, adaptation, distribution and long-term impacts of NIS, HABs and pathogens in the Pacific Ocean, and therefore will constitute a powerful new platform that is set to revolutionise marine biosecurity systems in the region and beyond. This, of course, will require effort, logistics and coordination with different nations that are part of the future objectives of the programme.
To maximise scientific and conservation impacts, the data must be linked back to global targets – such as tracking progress toward the 30×30 biodiversity goal or detecting climate-induced species range shifts. With nearly 2 billion DNA sequences already processed and 1,300-plus samples collected across multiple campaigns, Citizens of the Sea has laid the foundation for the world’s largest eDNA-based ocean biodiversity observatory. However, realising its full potential will depend on continued investment in data infrastructure, Pacific partnerships, and a shift towards automated, equitable and impactful data dissemination.