marine environment

Celebrating Deep Day with Incredible Deep-Sea Research

Protecting the deep sea, the largest and least explored habitat on Earth, requires collaborative effort.

May 7th marks Deep Day, a global day of awareness and action dedicated to the deep sea. Founded by the Deep Sea Conservation Coalition, it aims to raise awareness of the deep sea’s immense ecological importance and call for its protection against threats like deep-sea mining and destructive fishing.

To celebrate the wonders of our oceans and raise awareness of the incredible biodiversity of the deep sea, we at Pensoft Publishers would like to highlight some of the remarkable marine studies that have recently been published in our scientific journals.

A Global Collaboration to Uncover Deep-Sea Amphipods

24 deep-sea amphipods — The 24 newly described deep-sea amphipod species. Image credit to: Eleanor Frost, National Oceanography Centre

Demonstrating the power of global teamwork, an international group of experts recently discovered 24 new deep-sea amphipod species in the central Pacific Ocean’s Clarion-Clipperton Zone (CCZ). Researchers from institutions worldwide, including the University of Lodz and the National Oceanography Centre, came together for a coordinated taxonomy workshop to achieve this. Their work revealed a completely new evolutionary branch with the discovery of a new superfamily, Mirabestioidea.

Crucially, their findings form part of the International Seabed Authority’s Sustainable Seabed Knowledge Initiative (SSKI) and its ‘One Thousand Reasons’ project, which aims to formally describe 1,000 new species by the end of the decade.

Highlighting the importance of this joint effort, Dr. Anna Jażdżewska from the University of Lodz shared:

This was a truly collaborative process that allowed us to achieve the ambitious goal of describing more than 20 species new to science within a year – something that would not have been possible if each of us worked independently. The team’s findings provide information that is crucial for future conservation and policy decisions.

Learn more in the Special Issue: New deep-sea Amphipoda from Clarion-Clipperton Zone

What lives 10 km below the surface?

@pensoft.publishers
😯Fascinating new #study recorded 108 morphotaxa from 4,500m down to the #hadal depths of 9,775m, revealing the hidden life of the NW Pacific trenches. 🎥They analyzed 460 hours of video from landers & submersibles across the Japan, Ryukyu, and Izu-Ogasawara trenches. 👇Full study here: https://doi.org/10.3897 /BDJ.14.e182172 📗You can read all about it on Pensoft’s blog 👇 https://blog.pensoft.net/2026/04/06/what-lives-10-km-below-the-surface-a-new-look-at-life-in-japans-deepest-ocean-trenches/ Research center: Minderoo-UWA Deep-Sea Research Centre. Main funders of the expedition: Inkfish, Caladan Oceanic #deepsea #sciencetok #research
♬ THE MOON – Camargguinho

Photo and video credit to Minderoo-UWA Deep-Sea Research Centre, Inkfish, Caladan Oceanic, Jamieson et al., 2026

Another recent expedition provided a profound look at life up to nearly 10 kilometers below the surface in the Japan, Ryukyu, and Izu-Ogasawara trenches, cataloging at least 108 distinct organism groups. The research captured rare footage of species interactions at extreme depths – and one baffling, unidentified animal that has left taxonomists worldwide perplexed.

The unknown organism or Animalia incerta sedis. Credit to Jamieson et al., 2026, o Minderoo-UWA Deep-Sea Research Centre, Inkfish and Caladan Oceanic.

Rather than using traditional trawls that can damage fragile organisms, the team utilized crewed submersibles and free-fall baited landers. Explaining the value of this non-destructive method, the research team noted:

This combination enabled us to build the most comprehensive visual baseline yet for abyssal and hadal megafauna in the Northwest Pacific to date.

They added that the study aims to establish a foundation for the future, emphasizing that:

More than anything, the hadal zone remains one of Earth’s least-explored and most intriguing frontiers.

Learn more: Jamieson AJ, Swanborn DJB, Bond T, Cundy MC, Fujiwara Y, Lindsay D, Stott MS, Kitazato H (2026) Faunal biodiversity of the lower abyssal and hadal zones of the Japan, Ryukyu and Izu-Ogasawara trenches (NW Pacific Ocean; 4534-9775 m). Biodiversity Data Journal 14: e182172. https://doi.org/10.3897/BDJ.14.e182172

The Internet Names a New Deep-Sea Chiton

Finally, highlighting a unique way the public can engage with science and taxonomy, a recently found deep-sea chiton was named by the internet after science YouTuber Ze Frank featured it in an episode of his “True Facts” series. Originally discovered in 2024 within the Izu-Ogasawara Trench at a depth of 5,500 meters, this new species belongs to the genus Ferreiraella, a rare and specialized group of mollusks that live exclusively on sunken wood in the deep sea.

From over 8,000 suggestions submitted across social media, the research team selected the name Ferreiraella populi. The epithet populi is a Latin singular noun in the genitive case meaning “of the people”.

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Prof. Dr. Julia Sigwart, co-chair of the Senckenberg Ocean Species Alliance (SOSA), emphasized the broader significance of this public discovery:

Ferreiraella populi exemplifies the overwhelming biodiversity of the oceans, the vast majority of which remains unexplored. Many species go extinct before we even know they exist – this is especially true for marine invertebrates.

Learn more: (SOSA) SOSA, Chen C, Frank H, Kraniotis L, Nakadera Y, Schwabe E, Sigwart JD, Trautwein B, Vončina K (2026) Ocean Species Discoveries 28–30 — new species of chitons (Mollusca, Polyplacophora) and a public naming competition. Biodiversity Data Journal 14: e180491. https://doi.org/10.3897/BDJ.14.e180491

@pensoft.publishers
Happy #DeepDay ! Started by Deep Sea Conservation Coalition, this annual day is aimed at raising awareness to the incredible diversity in our deep seas. Today, we’re sharing with you three remarkable studies from our journals – each one a window into a fascinating world, hoping to raise awareness and inspire action to #DefendtheDeep . 👇𝐎𝐮𝐫 𝐛𝐥𝐨𝐠: https://blog.pensoft.net/…/celebrating-deep-day-with…/ 🔎By analysing 460 hours of video from landers and submersibles across the Japan, Ryukyu, and Izu-Ogasawara trenches, researchers found something extraordinary: a mysterious organism so unusual it was classified as Animalia incerta sedis! 📗𝐑𝐞𝐚𝐝 𝐭𝐡𝐞 𝐟𝐮𝐥𝐥 𝐬𝐭𝐮𝐝𝐲 𝐩𝐮𝐛𝐥𝐢𝐬𝐡𝐞𝐝 𝐢𝐧 Biodiversity Data Journal (𝐁𝐃𝐉) 𝐡𝐞𝐫𝐞: https://doi.org/10.3897/BDJ.14.e182172 Cc: Minderoo-UWA Deep-Sea Research Centre at The The University of Western Australia, JAMSTEC: Japan Agency for Marine-Earth Science and Technology, Inkfish, Caladan Oceanic LLC 🎥Footage credit: Minderoo-UWA Deep-Sea Research Centre, Inkfish, Caladan Oceanic, Jamieson et al., 2026 After thousands of name suggestions from the public, the “chiton of the people” has been officially described in Biodiversity Data Journal. 🙌A huge thank you to everyone who voted and participated! Cc: True Facts Senckenberg Senckenberg Ocean Species Alliance – SOSA 🎥Footage credit: ©ChongChen/JAMSTEC 𝐅𝐮𝐥𝐥 𝐚𝐫𝐭𝐢𝐜𝐥𝐞 𝐢𝐧 𝐁𝐃𝐉: https://doi.org/10.3897/BDJ.14.e180491 🦐24 new deep-sea amphipods discovered in the Clarion Clipperton Zone. Through an international collaboration – with key momentum from a 2024 taxonomic workshop at Uniwersytet Łódzki – researchers described 24 new species of amphipods from the central Pacific abyss. 𝐀𝐜𝐜𝐞𝐬𝐬 𝐚𝐥𝐥 𝐭𝐡𝐞 𝐩𝐮𝐛𝐥𝐢𝐜𝐚𝐭𝐢𝐨𝐧𝐬 𝐢𝐧 ZooKeys: https://zookeys.pensoft.net/issue/4856/ See less #deepsea #deepocean #sciencetok
♬ Fantasy in an Immersive World – Ernesto P. Neto

These studies highlight the vastness of the unexplored frontier that our deep seas and oceans offer. Revealing this hidden life – from entirely new evolutionary branches of amphipods to records of unknown organisms – requires global collaboration, cutting-edge exploration technologies, and the involvement of the general public.

Ultimately, this shared pursuit of discovery provides the fundamental knowledge crucial for conservation and policy decisions. As Deep Day reminds us of the encroaching threats from deep-sea mining, human-derived debris, and destructive fishing, we must work together to understand these fragile habitats so that we can effectively protect them and #DefendtheDeep.

For more curious research follow Pensoft Publishers’ socials: Facebook, Bluesky, Instagram, TikTok, LinkedIn and X.

A Simple Filter Swap Could Advance Marine eDNA Biomonitoring

A simple adjustment to water filtration methods can dramatically improve the detection of marine animal DNA when using advanced, PCR-free sequencing.

Over the past two decades, environmental DNA (eDNA) analysis has become a crucial tool for monitoring aquatic ecosystems. The most common method, metabarcoding, relies on PCR amplification of a smaller genetic region to identify specific taxa. However, PCR can lead to “significant taxonomic bias” because it often amplifies the DNA of different organisms unequally, making quantitative estimates difficult.

To avoid this, scientists have increasingly explored “shotgun sequencing“- an approach that sequences the DNA in a sample much more broadly – across the entire tree of life and across the genome. Unfortunately, in marine environments, shotgun sequencing is typically overwhelmed by microbial DNA, burying the genetic traces of less abundant macro-organisms such as animals.

Bigger Pores, Better Animal DNA Capture?

In a new study published in Metabarcoding and Metagenomics, researchers investigated if they could capture a higher proportion of eukaryotic (animal and plant) DNA simply by using filters with larger pore sizes.

Filter pore sizes are expected to influence results, since eDNA may be present in many different states, including but not limited to complete organisms, sloughed tissue, feces, free DNA, or gametes.
commented Dr. Adrián Gómez-Repollés, the lead author of the study.

To test this, the team collected 15 seawater samples from Skovshoved Harbour in Denmark and filtered them using pore sizes ranging from 0.2 µm to 8.0 µm. The results showed a stark contrast in the type of DNA captured based on the filter size.

Filters with smaller pore sizes (0.2 µm and 1.2 µm) retained a significantly greater proportion of bacterial reads than eukaryotic reads (63% vs. 28%); conversely, filters with larger pore sizes (5.0 µm and 8.0 µm) retained a significantly greater proportion of eukaryotic reads than bacterial reads (49% vs. 31%).

By switching to 5.0 µm or 8.0 µm filters, the researchers successfully reduced the dominance of bacteria. Of the 19 metazoan (animal) phyla detected using shotgun sequencing, all but one were found to be more abundant when using the larger pore sizes.

Looking to the Future of Biomonitoring

Taxonomic comparison at the kingdom and phylum levels of eukaryotes detected with shotgun sequencing and metabarcoding. A. Number and relative abundance (percentages) of taxonomically classified reads after rarefaction per sample and kingdom for shotgun sequencing; B. Number and relative abundance of taxonomically classified reads after rarefaction per sample and kingdom for metabarcoding. For both heatmaps, sample replicates are ordered along the y-axis by increasing pore size, starting with the enclosed filter type (EN) and continuing with the open pore filter type (OP). Pore sizes are in µm; C. Cladogram of the full set of eukaryotic phyla identified by shotgun sequencing and metabarcoding. Branch colors represent kingdoms (blue, Metazoa; red, Fungi; green, Viridiplantae; pink, other eukaryotes). Three surrounding rings indicate phyla shared between shotgun sequencing and metabarcoding (gray), phyla uniquely detected with metabarcoding (yellow), and phyla uniquely detected with shotgun sequencing (blue). Information in the rings is summarized in a Venn diagram in the upper left corner. Taxa marked with an asterisk are no longer categorized as a phylum. Credit to Gómez-Repollés et al., 2026

When compared alongside traditional 18S rDNA metabarcoding, the shotgun sequencing method successfully shared 39 of the 54 detected eukaryotic phyla, indicating a similar performance in detecting the presence of high-level taxonomic groups.

To test the potential of shotgun sequencing in applied biomonitoring even further, the researchers examined the results at genus-level for a number of well known marine animals such as fish, mussels, crustaceans and bristle worms. Here, they found both DNA matches to native Danish species but also to exotic taxa that were highly unlikely and probably due to the low level of resolution in shotgun sequencing, where genetic regions of low variation and coverage are sequenced.

Water sample collection. Photo by David Stanciu.

But, when they looked further into the results they observed that the local taxa consistently comprised a higher number of reads. The number of reads could thus be a simple way to initially separate authentic taxa from erroneous matches in eDNA studies based on shotgun sequencing, although the approach needs further testing.

However, the authors note current limitations with the technology, primarily driven by incomplete public DNA reference databases. In the study, only 0.78% of the total shotgun reads could be definitively assigned to a superkingdom level. Another drawback was the lack of field controls to rule out cross-contamination or input from airborne DNA, coupled with a limited spatiotemporal design involving only a single sampling location.

Despite these hurdles, shotgun sequencing and filters with larger pore sizes could potentially be a significant step forward for eDNA in marine biology. As global genomic databases continue to expand, “the taxonomic coverage and resolution of shotgun sequencing should improve, likely enhancing the potential of shotgun sequencing for future eDNA research“, says Philip Francis Thomsen, professor and senior author on the study.

Original study:

Gómez-Repollés A, Sigsgaard EE, Jensen MR, Thomsen PF (2026) Filter pore size influences taxonomic composition of retained eDNA from seawater samples—evidence from shotgun sequencing. Metabarcoding and Metagenomics 10: e164232. https://doi.org/10.3897/mbmg.10.164232

New Way of Conservation: An Acoustic Device Helps Reduce Bycatch of Endangered Black Sea Porpoises

A new study published in Nature Conservation shows that not all acoustic deterrent devices may be effective in protecting the Black Sea porpoise, Europe’s smallest marine mammal.

Guest blog post by Dr. Dimitar Popov

The endangered Black Sea harbour porpoise (Phocoena phocoena relicta) is facing a critical fight for survival. As Europe’s smallest marine mammal, this isolated population is being pushed toward extinction by bycatch – the unintentional entanglement in fishing gear. The crisis is most acute in the Black Sea turbot fishery, where recent estimates reveal that more than 10,000 porpoises die annually.

Led by a strong motivation to address threats to this iconic species, a team of Bulgarian researchers has carried out a four-year trial study of 57 hauls seeking effective solutions to reduce porpoise mortality. The study, now published in Nature Conservation, found bycatch in 61% of all hauls, accounting for 189 cetaceans: 182 harbour porpoises, five bottlenose dolphins, and two common dolphins.

Bycaught Black Sea harbour porpoises. Photo credit to Dimitar Popov.

The trials did not begin promisingly, as the first two models of acoustic deterrent devices (pingers) tested, proved ineffective at reducing bycatch.
the researchers noted

This initial setback prompted the team to search for an alternative solution, eventually leading to a breakthrough with the PAL Wideband pinger, an acoustic deterrent device developed in Germany.

PAL Wideband pinger attached to a fishing net. Photo credit to Dimitar Popov.

Field trials demonstrated that this device can reduce harbour porpoise bycatch in the Black Sea by approximately 74%. Researchers believe the specific acoustic signals, namely the wider frequency band (between 10 and 150 kHz) emitted by the PAL Wideband model, contributed to its effectiveness, as it was the only one of the three pingers tested, that successfully deterred porpoises from approaching fishing nets.

Map of the conducted trials involving PAL Wideband pingers in 2020 and 2021. Credit to Popov et al., 2026

“Other recent studies have highlighted significant shortcomings in the conservation of harbour porpoise populations in European waters,” the researchers stated. This underscores the urgent need for effective strategies to reduce bycatch, the leading human-induced cause of mortality for the species.

Mitigation measures could include spatio-temporal closures of high-risk fisheries in areas where harbour porpoises are most abundant, as well as the adoption of alternative or modified fishing gear, including the use of acoustic deterrent devices.
the experts noted

black sea harbour porpoise in a net — Bycaught Black Sea harbour porpoise. Photo credit to Dimitar Popov.

Among the available options, the use of effective pingers, supported by appropriate financing mechanisms, is increasingly seen as one of the most practical and widely accepted approaches to reducing bycatch while maintaining profitable fishing operations.

Not all acoustic deterrent devices are equally effective in reducing the bycatch of the harbour porpoise in the Black Sea.
the researchers concluded

Their findings demonstrate that certain pinger models fail to mitigate porpoise bycatch in the bottom-set gillnets specifically used to target turbot.

The study underscores the importance of careful selection and testing of deterrent devices and emphasizes that this distinction must be explicitly taken into account in the development of targeted and effective strategies to reduce bycatch in Black Sea fisheries.

If you are interested in other marine research from Bulgaria, take a look at the topical collection “Black Sea ecosystem in the spotlight” which includes this study.

Original source:

Popov D, Meshkova G, Dimitrov H, Panayotova M (2026) Can pingers mitigate the bycatch of the endangered Black Sea Harbour Porpoise? Nature Conservation 63: 1-15. https://doi.org/10.3897/natureconservation.63.183768