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Sea pen
Temporal range: Cambrian–Recent
"Pennatulida" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Cnidaria
Subphylum: Anthozoa
Class: Octocorallia
Order: Scleralcyonacea
Superfamily: Pennatuloidea
Ehrenberg, 1834
Families

see text

Sea pens are marine cnidarians belonging to the superfamily Pennatuloidea,[1] which are colony-forming benthic filter feeders within the order Scleralcyonacea.[1][2] The order comprises 16 families and 44 extant genera, with around 235 accepted species.[3]

Sea pens have a cosmopolitan distribution, being found in tropical and temperate waters worldwide, from intertidal shallow waters to deep seas of more than 6,100 m (20,000 ft).[2]

The earliest accepted sea pen fossils are known from the Cambrian-aged Burgess Shale (Thaumaptilon). Similar fossils from the Ediacaran may show the dawn of sea pens.[4] Precisely what these early fossils are, however, is not decided.[5]

Taxonomy

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The superfamily Pennatulacea consists of the following families:[1]

Biology

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Due to their wide geographic distribution and long evolutionary history, genetic variation within the different species of sea pen is quite large. Throughout evolution, most sea pens have kept their original mitochondrial gene order, but a certain clade of sea pens shown unique rearrangements through ancestral state reconstruction. There are many populations of sea pens found in mainly Indian waters. It is their polyps that are affected genetically, as they have dispersed within the different waters and islands, and how they use their polyps (tentacles) to protect themselves and other species.[6]

Uprooted sea pen with the bulbous peduncle in view
Pierre's armina feeding on purple sea pen
Sea pen at Vancouver Aquarium

As octocorals, sea pens are colonial animals with multiple polyps (which look somewhat like miniature sea anemones), each with eight tentacles. Unlike other octocorals, however, a sea pen's polyps are specialized to specific functions: a single polyp develops into a rigid, erect stalk (the rachis) and loses its tentacles, forming a bulbous "root" or peduncle at its base.[7] The other polyps branch out from this central stalk, forming water intake structures (siphonozooids), feeding structures (autozooids) with nematocysts, and reproductive structures. The entire colony is fortified by calcium carbonate in the form of spicules and a central axial rod.[citation needed]

Using their root-like peduncles to anchor themselves in sandy or muddy substrate, the exposed portion of sea pens may rise up to 2 metres (6.6 ft) in some species, such as the tall sea pen (Funiculina quadrangularis). Sea pens are sometimes brightly coloured; the orange sea pen (Ptilosarcus gurneyi) is a notable example. Rarely found above depths of 10 metres (33 ft), sea pens prefer deeper waters where turbulence is less likely to uproot them. Some species may inhabit depths of 2,000 metres (6,600 ft) or more.[citation needed]

While generally sessile animals, sea pens are able to relocate and re-anchor themselves if need be.[7] They position themselves favourably in the path of currents, ensuring a steady flow of plankton, the sea pens' chief source of food. Their primary predators are nudibranchs and sea stars, some of which feed exclusively on sea pens. The sea pens' ability to be clumped together and spatially unpredictable hinders sea stars' predation abilities.[8] When touched, some sea pens emit a bright greenish light; this is known as bioluminescence. They may also force water out of their bodies for defence, rapidly deflating and retreating into their peduncle.[citation needed]

Like other anthozoans, sea pens reproduce by coordinating a release of sperm and eggs into the water column; this may occur seasonally or throughout the year. Fertilized eggs develop into larvae called planulae which drift freely for about a week before settling on the substrate. Mature sea pens provide shelter for other animals, such as juvenile fish. Analysis of rachis growth rings indicates sea pens may live for 100 years or more, if the rings are indeed annual in nature.[citation needed]

Some sea pens exhibit glide reflection symmetry,[9] rare among extant animals.

Aquarium trade

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Sea pens are sometimes sold in the aquarium trade. However, they are generally hard to care for because they need a very deep substrate and have special food requirements.[citation needed]

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References

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Sea pen

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Sea pens are colonial belonging to the order Pennatulacea within the subclass of the phylum , characterized by feather-like or whip-shaped colonies that anchor into soft seafloor sediments. Each colony originates from a single primary polyp, known as the oozooid, which elongates to form a central rachis supporting secondary polyps specialized for different functions: autozooids with eight tentacles for capturing prey, siphonozooids for pumping water through the colony, and in some cases, polyps dedicated to reproduction. The colony is supported by a muscular peduncle at the base for burrowing and an internal axis often reinforced with , while sclerites in the form of smooth spindles or ovals provide additional structure. Comprising approximately 220 valid species across 41 genera and 16 families, sea pens exhibit remarkable morphological diversity, ranging from plumose forms to umbellate or club-shaped structures, and are found in virtually all marine environments worldwide. Their distribution spans polar to equatorial latitudes and depths from the to over 6,100 meters in hadal trenches, inhabiting substrates such as mud flats, reefs, continental slopes, and abyssal plains. As benthic suspension feeders, sea pens orient perpendicular to currents to capture , , and organic particles using nematocyst-armed tentacles on their autozooids, with siphonozozooids facilitating water flow for oxygenation and nutrient distribution. Many display , likely as a defense mechanism against predators, and some form symbiotic associations, such as with that seek refuge among their branches. Reproduction in sea pens is primarily sexual, with colonies being dioecious—each either or —and involving the coordinated release of gametes into the water column for , often seasonally. Eggs are typically large (e.g., 500–600 micrometers in some species), developing into larvae that may remain planktonic for extended periods or be brooded within the colony; via also occurs to expand the colony. Despite their ancient lineage, with fossil spicules dating back to the , sea pens remain understudied, particularly in deep-sea habitats, where ongoing discoveries highlight their ecological importance in benthic communities.

Description and Anatomy

Physical Structure

Sea pens are colonial marine cnidarians in the order Pennatulacea, exhibiting an elongated, feather-like or quill-shaped morphology that distinguishes them from other octocorals. The colony originates from a single primary polyp, or oozooid, which elongates to form a central axis comprising the upper rachis and lower peduncle. The rachis extends upward, bearing rows of secondary polyps arranged along leaf-like branches that give the colony its pinnate appearance, while the peduncle forms the basal portion for attachment to the substrate. Colonies display considerable variation in size and shape, ranging from a few centimeters to over 2 meters in height; for example, Funiculina quadrangularis can attain heights of up to 2 meters, forming tall, narrow structures. The central axis may exhibit a square or round cross-section across species, with F. quadrangularis featuring a distinctive square, box-like axis that contributes to its structural rigidity. These adaptations allow sea pens to thrive in diverse benthic environments, from shallow coastal waters to deep-sea floors. Anchoring is achieved through the basal peduncle, a smooth, muscular extension that burrows into soft sediments such as mud or sand, often terminating in a bulbous holdfast or caudal bulb for enhanced stability against currents. This mechanism enables the colony to remain upright and exposed for filter feeding. Internally, the axis contains a calcareous skeleton composed primarily of high-magnesium calcite ((Ca, Mg)CO₃), which provides essential support and contrasts with the surrounding soft, fleshy outer tissues divided by mesenteric septa into canals for water flow. Additionally, the soft tissues contain sclerites, microscopic calcareous spicules typically shaped as smooth spindles, rods, ovals, or plates, which embed in the coenenchyme and polyp walls to provide further rigidity and defense against predators. This mineralized core, often brittle and white in color, runs continuously from the peduncle through the rachis, underscoring the colony's balance between flexibility and durability.

Polyp Organization and Functions

Sea pens, members of the order Pennatulacea, exhibit a highly specialized colonial derived from a single primary polyp known as the oozooid. This initial polyp undergoes significant modification during colony development, losing its tentacles and elongating to form the rigid central axis, which comprises the peduncle and rachis. The peduncle, a bulbous basal structure, anchors the into soft sediments, while the rachis serves as the upright stalk supporting secondary polyps. This transformation provides structural support for the entire , enabling it to maintain an erect posture in benthic environments. Secondary polyps bud laterally from the body wall of the primary polyp along the rachis and are polymorphic, with distinct types adapted to specific roles. Autozooids are the larger, tentacled polyps primarily responsible for feeding and prey capture, emerging from the rachis surface to extend their eight tentacles for capturing planktonic particles. These polyps are typically arranged in whorls or rows, often concentrated on the ventral side of the rachis in many . In contrast, siphonozooids are smaller polyps lacking tentacles, equipped with cilia that facilitate circulation through the colony's internal canal system. They function to draw in for oxygenation, distribution, and expulsion, pumping fluids via the coenenchyme—a thin linking all polyps. Some genera, such as , may also feature intermediate mesozooids, but autozooids and siphonozooids predominate across most taxa. The polyps coordinate through a shared , with the primary axis acting as a central conduit for and waste removal. When disturbed, such as by predators or currents, autozooids and siphonozooids retract rapidly into the protective coenenchyme of the rachis, a behavior mediated by muscular contractions and nerve nets, allowing the colony to collapse or into for defense, as observed in species like Virgularia mirabilis. This response ensures colony survival by minimizing exposure while maintaining internal circulation.

Taxonomy and Classification

Evolutionary History

Sea pens, or pennatulaceans, are classified within the phylum , class , subclass , order Pennatulacea, and the superfamily Pennatuloidea. This placement situates them among the octocorals, a group characterized by eight-fold symmetry in their polyps and colonial growth forms, distinct from the hexacorallian anthozoans like sea anemones and stony corals. The evolutionary history of sea pens is marked by a sparse fossil record, with the earliest potential evidence appearing in the middle Cambrian period. Fossils such as Thaumaptilon walcotti from the , dated to approximately 508 million years ago, exhibit a frond-like structure with a central axis and lateral branches, suggesting affinities to early pennatulaceans. Possible Ediacaran precursors, including frondose forms like Charnia, have been proposed due to superficial morphological similarities, but phylogenetic analyses indicate these are unrelated and likely represent distinct lineages such as rangeomorphs. More definitive sea pen fossils, including spicules and colony impressions, emerge in the period, around 144 million years ago, aligning with molecular divergence estimates for the order. Key evolutionary adaptations in sea pens include the transition from solitary or less specialized colonial anthozoans to highly polymorphic colonies optimized for benthic environments. This shift involved the development of the pennatacean axis—a central, chitinous that provides rigidity and anchorage in soft sediments—allowing upright orientation for filter feeding. Pennatulaceans are thought to have diverged from soft (alcyonacean) ancestors, with the axis and polyp dimorphism evolving to enhance stability and division of labor among autozooids, siphonozooids, and other specialized forms.

Diversity and Species

Sea pens, belonging to the order Pennatulacea within the class , exhibit significant taxonomic diversity, comprising approximately 16 families, 44 genera, and 235 accepted species according to the (WoRMS) database. This diversity reflects their adaptation to various marine environments, though ongoing molecular studies continue to refine classifications. Among the key families, Pennatulidae stands out for its widespread representation, including the genus with species such as Pennatula phosphorea, known for its phosphorescent properties in temperate waters. Funiculinidae includes robust forms like Funiculina quadrangularis, characterized by quadrangular cross-sections in its primary polyp, often found in colder regions. Anthoptilidae encompasses more delicate, feather-like structures, with genera such as Anthoptilum featuring autozooids arranged in bilateral . Notable species illustrate the range of adaptations within this order; for instance, Ptilosarcus gurneyi represents shallow-water forms, inhabiting subtidal sandy or muddy substrates from to depths of about 135 meters along the northeastern Pacific coast. In contrast, Halipteris africana exemplifies deep-sea variants, occurring at depths of 459–659 meters in amphi-Atlantic regions with autozooids in oblique rows. Recent taxonomic updates, particularly within the order Scleralcyonacea, have highlighted non-monophyly in many sea pen families based on genomic analyses, necessitating reclassifications to better align with phylogenetic relationships as of 2025.

Habitat and Distribution

Environmental Requirements

Sea pens require soft, unconsolidated sediments such as or to anchor their root-like peduncles, enabling burrowing and stability while avoiding rocky or hard bottoms that prevent attachment. These substrates facilitate the embedding of the basal structure, with preferences for muddy sands or high mud-to-sand ratios observed in like Virgularia mirabilis and Funiculina quadrangularis. Dense aggregations often form in fine-grained sediments where the peduncle can penetrate deeply without resistance. Depth preferences vary across species but predominantly favor deeper waters greater than 10 m, extending to hadal zones beyond 6,000 m, though some like Ptilosarcus gurneyi occur in shallow subtidal zones from 5 to 30 m. In the Mediterranean, for instance, Funiculina quadrangularis thrives between 40 and 270 m, while Pennatula species are common up to 100 m, reflecting adaptations to low-light conditions inherent to these depths. Overall, most sea pens inhabit sublittoral to bathyal environments, with rare intertidal occurrences limited to tolerant species. Water conditions must be stable and cold, typically with temperatures ranging from 3 to 15°C in deep-sea habitats, supporting metabolic processes in low-oxygen, aphotic settings. Moderate currents, around 0.25 m/s, are essential for suspending sediments and delivering without causing erosion of the fragile colony or smothering the base. levels above 30 psu are generally required, with minimum thresholds influencing distribution in variable coastal areas. Due to their delicate, elongated structures, sea pens exhibit high sensitivity to disturbances, including physical impacts from or anchoring that can uproot colonies, and smothering that clogs polyps and inhibits feeding. Macrofaunal communities associated with sea pen fields show reduced resilience, amplifying in areas prone to bottom-contact or natural shifts. Such sensitivities underscore the need for stable, undisturbed soft-bottom environments to maintain population integrity.

Global Occurrence

Sea pens (order Pennatulacea) exhibit a , inhabiting all major ocean basins from the to the regions. This widespread occurrence spans the Atlantic, , Indian, and , with adapted to diverse environments across global latitudes. In the , several of the genus , such as P. phosphorea and P. rubra, are commonly found on soft substrates along continental shelves. Off Argentine waters in the southwestern Atlantic, Anthoptilum grandiflorum has been documented in deep-sea habitats, contributing to the regional diversity of pennatulaceans. In the North Atlantic, deep-sea populations thrive in bathyal zones, while Indo- shallows host certain on sandy or muddy bottoms; further south, the supports dense aggregations in cold, stable environments. The majority of sea pen species occupy bathyal (200–4,000 m) and abyssal (4,000–6,000 m) zones, where they anchor into soft sediments. Occurrences in shallower waters are less common, particularly in polar regions, though some species appear in coastal shallows of temperate and tropical areas. Studies have documented inflata in slope habitats off , expanding the known range in Argentine waters.

Ecology and Behavior

Feeding and Nutrition

Sea pens are passive suspension feeders that depend on ambient currents to deliver food particles to their . The autozooids, which are the primary feeding polyps, extend pinnate to form a semi-cylindrical filter on the downstream side of the colony, capturing suspended particles through direct and nematocyst action. secreted by the tentacles traps and , while ciliary movements along the tentacle surfaces transport the adhered material toward the polyp's for . This mechanism allows efficient particle collection without active pursuit of prey. Their diet consists mainly of small planktonic organisms and , including such as copepods, like dinoflagellates, and . Analysis of profiles in deep-sea octocorals, including pennatulaceans, indicates a mixed intake where contributes significantly alongside microbial and algal sources, adapted to the variable flux of particles in benthic environments. Sea pens do not engage in active , relying instead on the passive delivery of these resources by currents. Captured are processed in the individual polyp's gastrovascular cavity and then distributed throughout the via interconnected canals in the coenosarc, enabling resource sharing among polyps and supporting the non-feeding siphonozooids. This colonial integration, observed in gorgonian octocorals and applicable to pennatulaceans, facilitates and circulation, with peristaltic contractions aiding nutrient transport over distances up to several centimeters. To cope with the sparse and intermittent food supply in deep-sea habitats, sea pens maintain low metabolic rates, typically below 1 μmol O₂ g⁻¹ h⁻¹, which minimizes energy expenditure while maximizing the efficiency of captured resources. This adaptation aligns with their slow growth and long lifespans, ensuring survival in oligotrophic conditions where food particles may arrive irregularly.

Bioluminescence and Predation

Sea pens possess the ability to produce bioluminescence through a chemical reaction involving the oxidation of coelenterazine, a luciferin substrate, catalyzed by luciferase enzymes, often facilitated by calcium-dependent binding proteins and green fluorescent proteins that shift the emission to green wavelengths peaking around 485–513 nm. This light emission, typically triggered by mechanical disturbance, catecholamines such as adrenaline, or calcium ions, serves primarily as a defensive mechanism to deter predators by startling them or acting as an aposematic signal. For instance, species like Pennatula phosphorea, Anthoptilum murrayi, and Funiculina quadrangularis generate colony-wide green flashes upon stimulation, enhancing survival in low-light benthic environments. Predators of sea pens include specialized nudibranchs, such as Armina species, and various sea stars, including the leather star (Dermasterias imbricata), sunflower star (Pycnopodia helianthoides), and firebrick star (Hippasteria phrygiana). These predators target the polyps, with sea stars using to grasp and evert stomachs over colonies, while nudibranchs consume tissues directly; annual predation rates can remove up to 3.1% of adult sea pen populations in some areas. Sea pens detect threats via chemical receptors on polyp tentacles, distinguishing dangerous predators like D. imbricata from less harmful ones through waterborne cues and physical contact, though responses are primarily elicited by direct touch rather than odors alone. In response to predation threats, sea pens employ defensive retraction, rapidly withdrawing the entire colony into the by deflating and burrowing, a process that can occur in seconds and is modulated by predator type—stronger against specialists like D. imbricata (up to 73% burrowing rate) than generalists. This behavior, combined with bioluminescent flashes, allows temporary evasion until conditions stabilize. Ecologically, sea pens act as indicators of healthy benthic communities in soft s, where their erect structures provide biogenic that enhances by sheltering macrofauna, including polychaetes, crustaceans, and small anemones, while influencing local sedimentary processes.

Reproduction and Life Cycle

Sexual Reproduction

Most sea pens (order Pennatulacea) are gonochoric, with colonies exhibiting separate sexes at the individual level and typically maintaining a 1:1 across populations where applicable. However, some in the superfamily Pennatuloidea, particularly in families Umbellulidae and Pseudumbellulidae, exhibit hermaphroditism or even (presence of male, female, and hermaphroditic colonies). Gonads develop within the autozooids, the feeding polyps along the rachis, where oocytes in females and spermatocysts in males mature asynchronously over extended periods, often exceeding 12 months in some . Reproduction occurs through broadcast spawning, where mature gametes are released into the water column for . Females produce large eggs, typically 500–600 micrometers in diameter in species like Ptilosarcus gurneyi, while males release in bundles; this strategy relies on sufficient population densities to ensure successful union of gametes. Spawning is often seasonal, peaking in March–April for temperate species such as P. gurneyi, though timing varies by location and depth, with some deep-sea forms like Anthoptilum murrayi showing more continuous activity. Recent studies as of 2025 have highlighted variations in reproductive modes and environmental influences; for instance, sea pens near sites show signs of stress affecting reproductive structures, such as polyp contraction and overproduction. Following fertilization, zygotes develop into lecithotrophic larvae, which are non-feeding and free-swimming for a brief period before settling onto soft substrates to initiate into primary polyps. This larval stage facilitates dispersal but is short-lived, emphasizing the importance of nearby suitable habitats. Environmental cues, particularly rising water temperatures and seasonal changes in food availability, synchronize spawning in many , as observed in phosphorea where events align with summer warming. While lunar cycles influence spawning in some anthozoans, evidence for sea pens points more strongly to thermal triggers, though endogenous rhythms may also contribute to annual synchrony.

Development and Growth

Sea pen larvae, known as planulae, are free-swimming and typically settle on soft sediments such as or coarse within days to weeks after spawning, where they metamorphose into a primary polyp called the oozooid. This settlement process is crucial for establishing the in stable, low-energy benthic environments, with the planula attaching via its aboral end and undergoing morphological changes to form the initial polyp structure, including tentacles for feeding. Once settled, the primary polyp initiates colony development by secondary polyps laterally from its body wall, forming specialized types such as gastrozooids for feeding and siphonozooids for water circulation. This iterative process expands the 's rachis and leaves, with growth rates varying by depth; in deep-water species like Halipteris finmarchica, radial extension is notably slow at approximately 0.067 mm per year, reflecting to low temperatures and limited food availability. Sea pens exhibit long lifespans in stable environments, often spanning decades, with some deep-water species reaching ages of 70 years or more as determined by annual growth rings in the axis. These rings, visible through cross-sections, allow for age estimation similar to tree rings, highlighting slow but persistent growth over time. Recent analyses as of 2025 on species like Pennatula aculeata and Ptilella grandis indicate that conditions can influence age structures and growth, with denser populations showing potentially faster development. Asexual reproduction is uncommon in sea pens but occurs rarely through fragmentation or in certain , primarily serving colony repair rather than . Such mechanisms enable damaged to regenerate polyps, though they are less prevalent compared to .

Human Interactions and Conservation

Aquarium Trade and Captivity

Sea pens, belonging to the order Pennatulacea within the class , are occasionally available in the marine aquarium trade, where they are valued for their elegant, feather-like structure and ability to display when disturbed. These organisms are primarily sourced through wild collection from soft habitats, with such as Cavernularia obesa being among the more commonly imported for hobbyist and public displays. Maintaining sea pens in captivity presents significant challenges due to their specialized requirements mimicking deep-sea conditions. They necessitate a deep substrate of fine or , typically at least 20 cm thick, to allow the central axis to and retract properly; shallower or coarser beds often lead to stress and . As non-photosynthetic organisms, they tolerate low light levels but require gentle, consistent water flow to simulate natural currents without causing tissue damage. Feeding is particularly demanding, relying on frequent doses of live microplankton such as rotifers, copepods, or , as larger foods like nauplii are unsuitable and can result in . High mortality rates are common, often stemming from mishandling during shipping, inadequate substrate preparation, excessive turbulence, or insufficient nutrition, with many specimens perishing before reaching retailers or shortly thereafter. Successful long-term captivity has been achieved in public aquariums with controlled environments replicating subtidal conditions. For instance, Ptilosarcus gurneyi, the orange sea pen, is exhibited at institutions like the , where it is maintained in sandy-bottom displays and fed drifting plankton to support its filter-feeding habits. Similarly, west coast facilities such as the and Aquarium have sustained populations of this species, highlighting the feasibility of professional setups with simulated deep-water parameters. The aquarium raises ethical concerns regarding overcollection, as harvesting pressures can deplete local populations in vulnerable soft-sediment ecosystems, exacerbating declines observed in areas like . Poor in further amplifies the impact, with most collected sea pens dying en route or in , contributing to unnecessary wild removals without successful .

Threats and Protection Status

Sea pens, as fragile benthic organisms, face significant anthropogenic threats that compromise their populations and the ecosystems they inhabit. Bottom trawling represents the primary danger, physically disrupting the soft sediments where sea pens anchor and often leading to direct mortality or displacement of colonies. For instance, studies in the Central have shown marked declines in the abundance of the tall sea pen Funiculina quadrangularis in areas subject to intensive trawling, with densities dropping significantly compared to protected zones. Similarly, demersal fishing activities across the OSPAR maritime regions have been documented to reduce and shift community structures, exacerbating habitat degradation for sea pens. Ocean , driven by rising atmospheric CO₂ levels, further imperils sea pens by hindering the processes essential for their calcareous axes and internal structures. Studies on octocorals, including sea pens such as Malacobelemnon daytoni, indicate reduced survival, growth, and rates under elevated CO₂ conditions, potentially leading to weakened structural integrity and increased vulnerability to environmental stressors. , particularly from organic enrichment and smothering associated with and coastal runoff, adds to these pressures by causing localized oxygen depletion and burial of polyps, which disrupts feeding and respiration in sediment-dependent species. In OSPAR regions, projected increases in output are expected to intensify these contamination risks, threatening sea pen fields in circalittoral fine mud habitats, though recent actions like the January 2025 permanent ban on net-pen in Washington's aim to mitigate such threats locally. Many sea pen species are classified as vulnerable or near threatened on the , reflecting widespread population declines due to these cumulative impacts. For example, in the first comprehensive assessment of North Atlantic cold-water anthozoans conducted in 2025, 41% of evaluated species, including F. quadrangularis, were deemed threatened or near threatened, with data deficiencies hindering full risk evaluations for others. Sea pens are recognized as key indicators of Vulnerable Marine Ecosystems (VMEs) under resolutions and FAO criteria, due to their role in providing structural complexity and habitat for associated fauna in deep-sea soft sediments. Protection measures focus on mitigating fishing pressures in deep-sea habitats, with OSPAR designating marine protected areas (MPAs) and implementing trawl bans in regions such as the , , and to safeguard sea pen communities. In October 2025, the announced prohibitions on fishing with mobile bottom-contacting gears in specific areas of the starting November 18, 2025, to protect sensitive habitats including sea pen communities. FAO guidelines promote encounter protocols and move-on rules for fisheries interacting with VMEs, encouraging the identification and avoidance of sea pen aggregations to prevent irreversible damage. Recent studies from Argentine waters, including new distributional records for species like Anthoptilum grandiflorum and Pennatula inflata, underscore the fragility of these populations in the South Atlantic, highlighting the need for expanded regional protections amid ongoing habitat pressures. Ongoing research emphasizes the urgency of monitoring effects on sea pen distributions, as warming and acidification may drive poleward shifts or range contractions, further stressing vulnerable populations. Ecological niche modeling predicts significant loss for species like the slender sea pen Virgularia mirabilis under future scenarios, necessitating enhanced surveillance to inform . gaps in pressure thresholds and long-term trends remain critical barriers, calling for standardized surveys to support effective conservation.

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