Palaemon (crustacean)

Palaemon is a genus of caridean shrimps belonging to the family Palaemonidae, encompassing around 90 recognized species (though counts vary between 63 and 95 across taxonomic authorities due to ongoing revisions), of small, decapod crustaceans characterized by a well-developed rostrum typically armed with 5–12 dorsal teeth, asymmetrical chelipeds on the second pereopods, and a translucent to semi-opaque body usually measuring 2–8 cm in length.^[1][2][3] These shrimps inhabit a wide range of aquatic environments, from marine and estuarine waters to brackish marshes and freshwater wetlands, with a global distribution spanning tropical and temperate regions.^[1][4][2] First described by Friedrich Weber in 1795, the genus has undergone significant taxonomic revisions, including the synonymization of subfamilies within Palaemonidae and the incorporation of former genera like Palaemonetes as junior synonyms, reflecting its polyphyletic nature and ongoing debates in classification based on morphological and molecular data. Recent discoveries, such as Palaemon parvibrachium in 2024, highlight continued taxonomic activity.^[1][5][6] Species diversity is highest in coastal and wetland ecosystems, where Palaemon shrimps serve crucial ecological functions, such as facilitating organic matter decomposition, nutrient cycling, and energy transfer between primary producers and higher trophic levels, with biomass productivities reaching 9–16 g dry weight per square meter per year in some habitats.^[1][2] Certain species, including P. serratus and P. elegans, hold commercial value in fisheries and aquaculture due to their abundance and palatability, while others like P. pugio are model organisms for studies in ecology, genetics, and invasion biology.^[4][7]

Taxonomy

Etymology and history

The genus name Palaemon is derived from the Greek "palaemōn" (Παλαίμων), meaning "wrestler," a reference to the mythological sea god Palaemon and evoking the agile, combative locomotion of these shrimps through water using their powerful appendages.^[8] This etymology underscores the genus's association with dynamic aquatic environments, where species exhibit rapid, grappling-like movements.^[9] The genus Palaemon was formally established by Friedrich Heinrich Weber in 1795 through his publication Nomenclator Entomologicus secundum Entomologiam systematicum ill. Fabricii, which provided an early systematic nomenclature for entomological and crustacean taxa.^[10] The type species, Palaemon adspersus (described by Henrik Rathke in 1836), was later designated to anchor the genus's definition, reflecting its focus on caridean shrimps with specific rostral and appendage characteristics.^[11] In the early 19th century, the genus rapidly expanded as naturalists like Rathke incorporated diverse shrimp forms from European waters, describing multiple species such as P. adspersus and P. elegans based on morphological observations from Baltic and North Sea collections.^[12] Throughout the 19th century, over 100 species were proposed for inclusion in Palaemon as explorations revealed varied shrimp morphologies worldwide, though many descriptions lacked rigorous comparative analysis, leading to nomenclatural instability.^[5] Taxonomic refinements accelerated in the 20th century, with Rathke's foundational work supplemented by later systematists who clarified distinctions within Palaemonidae. A pivotal 20th- and 21st-century contribution came from De Grave and Fransen (2011), whose Carideorum Catalogus compiled a global inventory of caridean shrimps, recognizing approximately 26 valid species in Palaemon at the time while noting numerous synonyms. Further revisions by De Grave and Ashelby (2013) integrated molecular and morphological data to synonymize Palaemonetes, Exopalaemon, and Coutierella under Palaemon, reducing overall synonymy and elevating the genus to 83 valid species by absorbing previously separate taxa.^[13] As of 2024, ongoing descriptions and phylogenetic studies have increased the recognized valid species in Palaemon to 95, reflecting refined boundaries within Palaemonidae while continuing to resolve historical misclassifications from the 1800s.^[1] This evolution from broad 19th-century inclusions to a more precise modern delineation highlights the genus's central role in understanding caridean diversity.

Classification and phylogeny

The genus Palaemon is classified within the kingdom Animalia, phylum Arthropoda, subphylum Crustacea, class Malacostraca, order Decapoda, suborder Pleocyemata, infraorder Caridea, superfamily Palaemonoidea, family Palaemonidae, and genus Palaemon.^[2] This hierarchical placement positions Palaemon among the caridean shrimps, a diverse group characterized by their pleocyemate development and adapted to a range of aquatic environments. Phylogenetically, the family Palaemonidae, which includes Palaemon, diverged during the Late Cretaceous approximately 92 million years ago in the Indo-West Pacific region, based on Bayesian relaxed clock analyses calibrated with fossil records.^[14] The genus Palaemon forms a distinct clade within the Palaemoninae subfamily of Caridea, supported as monophyletic in molecular phylogenies utilizing multi-gene datasets including 18S rRNA and cytochrome c oxidase subunit I (COI) sequences from studies spanning 2011 to 2022.^[14] These analyses reveal high bootstrap support for the clade, highlighting evolutionary adaptations such as ambulatory pereiopods suited for diverse habitats.^[4] Close relatives of Palaemon include the genera Macrobrachium (freshwater prawns) and Exopalaemon, which form sister clades within Palaemonidae based on shared ancestral traits and phylogenetic reconstructions.^[15] Distinctions among these genera are primarily morphological: Palaemon species typically exhibit a mandibular palp, a rostrum with 6–10 dorsal and 2–5 ventral teeth, and chelate second pereiopods that are subequal in males, contrasting with Macrobrachium's elongate, spiniform rostrum, absence of a mandibular palp in some species, and markedly unequal second pereiopods in males adapted for freshwater locomotion.^[16] Exopalaemon differs subtly in rostral dentition (often fewer ventral teeth) and pereiopod setation, though some taxa have been synonymized with Palaemon in recent revisions.^[17] Recent molecular studies have illuminated genetic diversity within Palaemon, particularly in European species like P. elegans, resolving cryptic species complexes through mitogenome phylogenetics and COI analyses.^[4] For instance, P. elegans populations show divergence into distinct haplogroups dating to the Messinian Salinity Crisis (approximately 5.3–5.9 million years ago), with further splits in Atlantic-Mediterranean lineages around 0.7 million years ago linked to Pleistocene glaciations, indicating hidden biodiversity and potential taxonomic revisions.^[4] These insights, drawn from mitochondrial protein-coding genes, underscore the role of historical barriers in shaping palaemonid evolution.^[18]

Description

Morphology

The body of species in the genus Palaemon is bilaterally symmetrical and elongated, divided into two main regions: the cephalothorax and the abdomen. The cephalothorax results from the fusion of the head and thorax, covered dorsally and laterally by a rigid carapace that extends as a branchiostegite to enclose the branchial chamber. A prominent rostrum projects anteriorly from the carapace, typically bearing 6–10 dorsal teeth (including a post-orbital tooth) and fewer ventral teeth, aiding in protection and sensory functions.^[19][20][21] The appendages of Palaemon are highly specialized for locomotion, feeding, and swimming. The thorax bears five pairs of pereiopods: the first pair is chelate, forming robust pincers for grasping prey and manipulation; the second pair is also chelate but asymmetrical and more slender; and the third to fifth pairs are ambulatory, lacking chelae, for walking along substrates. The abdomen features five pairs of biramous pleopods (swimmerets), which facilitate swimming and, in females, brood protection; the sixth abdominal segment bears uropods and a telson, together forming a fan-like tail for rapid backward escape propulsion.^[19][20][22] Sensory structures in Palaemon enable detection of chemical, mechanical, and gravitational stimuli. Compound eyes are mounted on movable stalks, providing wide visual fields for detecting light and motion. The antennules (first antennae) are biramous, with the inner flagellum specialized for chemoreception and the outer for mechanoreception, while the longer antennae serve primarily for tactile exploration. Statocysts, located in the precoxal segment of each antennule, function as balance organs, containing statoliths that stimulate hair cells in response to gravity and acceleration.^[23][20] The exoskeleton of Palaemon is composed primarily of chitin, impregnated with calcium carbonate for rigidity, and periodically molted to allow growth. Respiration occurs via phyllobranchiate gills housed within the branchial chamber beneath the carapace, where water is circulated by the scaphognathite of the second maxilla to facilitate oxygen uptake.^[24][20]

Size and variation

Adult individuals in the genus Palaemon typically attain total lengths ranging from 2 to 8 cm, with considerable interspecific variation influenced by habitat and regional factors. For instance, in P. elegans, females can reach up to 6 cm, while males are generally smaller at around 4 cm maximum.^[25][26] Species within Palaemon exhibit a translucent body coloration, often accented by transverse dark bands across the abdomen for camouflage in aquatic environments. Live specimens may display subtle red or green hues that intensify in vegetated or rocky habitats but fade rapidly after death, reflecting adaptive pigmentation patterns.^[27][28] Sexual dimorphism is pronounced in Palaemon, with females generally achieving larger body sizes than males to support reproductive demands. Males possess elongated second pleopods bearing an appendix masculina for spermatophore transfer, whereas females feature a broader, rounded abdomen suited for brooding eggs beneath the tail.^[26][29] Intraspecific variation occurs across life stages and environmental gradients in Palaemon. Juveniles often lack the full complement of rostral teeth present in adults, with dentition developing progressively with growth.^[30]

Habitat and distribution

Environmental preferences

Species of the genus Palaemon are predominantly euryhaline, exhibiting a broad salinity tolerance that enables them to inhabit environments ranging from freshwater (near 0 ppt) to fully marine conditions (up to 35 ppt), with many species particularly thriving in brackish estuarine waters of 5-20 ppt.^[31][32] For instance, P. elegans demonstrates high survival (80-100%) across salinities from 0.6 to 35 ppt, while P. adspersus tolerates 1-35 ppt under similar conditions.^[31] Optimal salinities for development and survival in species like P. serratus fall between 21-29 ppt, though juveniles show greater low-salinity resilience, with critical thresholds around 5.5-12 ppt depending on life stage.^[33] Temperature preferences in Palaemon species generally center on a moderate range of 10-25°C for optimal physiological performance, though tolerances extend to extremes influenced by acclimation and habitat.^[32] Both P. adspersus and P. elegans exhibit 80-100% survival across 2-22°C, with osmoregulation weakening at higher temperatures and low salinities.^[31] In Baltic Sea populations, P. adspersus persists through near-freezing winters (around 2°C), reflecting adaptations to cool, brackish environments.^[34] For P. serratus, larval development accelerates with rising temperatures up to 19°C, but survival declines below 10°C or above 19°C at suboptimal salinities.^[33] Palaemon species favor structured microhabitats providing cover, such as vegetated substrates with algae, seagrasses, or rocks, which offer refuge from predators and support foraging.^[35] They are commonly associated with dense beds of submerged aquatic vegetation or fouling communities on submerged structures, showing a strong preference for such habitats over exposed sandy or open bottoms.^[36][37] This selection for vegetated areas enhances their abundance in shallow, estuarine zones.^[38] These shrimps require well-oxygenated waters, with oxygen consumption remaining stable down to approximately 1.8 mg/L before increasing under hypoxia, though they perform best above 4-6 mg/L in natural settings.^[39][40] Regarding pH, Palaemon species tolerate a neutral to slightly alkaline range of 7-8.5, aligning with typical estuarine conditions, with stress emerging below 7.6 or above 8.5 in acidification studies.^[41][42]

Global range

The genus Palaemon exhibits a native distribution primarily in the Northern Hemisphere but also including African coastal waters, with species inhabiting coastal and estuarine environments across Europe, Asia, North America, and parts of Africa. In Europe, P. elegans is widespread from the Mediterranean Sea and Black Sea northward to the Baltic Sea and along the Atlantic coast from Norway to the Iberian Peninsula. In Asia, P. paucidens occurs in freshwater and brackish systems of East Asia, including rivers and lakes in Japan, Korea, and China. In North America, P. paludosus is native to Atlantic and Gulf Coast estuaries from New Jersey southward to Florida and Texas, favoring vegetated shallows in low-salinity environments. In Africa, species such as P. concinnus are found in southern coastal estuaries. Several Palaemon species have established introduced ranges outside their native areas, often through human activities. P. macrodactylus, originating from the Northwest Pacific coasts of Asia (Russia to northern China and Japan), was first detected as invasive in San Francisco Bay, California, in 1957, likely transported via ballast water from Asian shipping routes; it has since spread to other Pacific Coast estuaries including Oregon and Washington (with first reports in the Salish Sea as of 2025), as well as to the Atlantic Coast since 2001 (e.g., New York, Connecticut, Rhode Island, Virginia, Maryland), and to South America and Australia. Similarly, P. elegans has expanded into North American waters since the early 2000s, with initial records in Salem Harbor, Massachusetts, in 2010, followed by detections in Rhode Island, Maine, and other northeastern Atlantic sites, attributed to transatlantic shipping vectors. P. adspersus, native to European waters, was introduced to northeastern North America around 2011, with established populations in coastal areas, likely via shipping. These introductions have also occurred in the southern hemisphere for species like P. macrodactylus. Biogeographically, Palaemon species are primarily confined to temperate and subtropical zones, with a concentration in coastal regions where seasonal temperature fluctuations support their euryhaline lifestyles. Their presence is limited in tropical regions, where competition from more diverse palaemonid genera, such as Macrobrachium, restricts niche availability in warm, stable waters. Dispersal in Palaemon is facilitated by a planktonic larval stage, which enables passive oceanic transport over moderate distances via currents, allowing colonization of new estuarine habitats. Human-mediated factors, including ballast water discharge from international shipping and unintentional releases from aquaculture operations, have significantly accelerated range expansions, particularly for invasive populations.

Ecology and behavior

Diet and feeding habits

Species of the genus Palaemon exhibit an omnivorous diet, functioning primarily as detritivores and micropredators in aquatic ecosystems. They consume a variety of organic matter, including algae, detritus, and small invertebrates such as amphipods, copepods, ostracods, chironomid larvae, and polychaetes like Hediste diversicolor. Plant material, such as fragments of Cladophora spp., Enteromorpha spp., and other macroalgae, forms a significant portion of their intake, alongside occasional molluscs and potential fish eggs depending on availability.^[43][44][45] Feeding mechanisms in Palaemon involve both scavenging and active predation, facilitated by their chelipeds (chelae) for grasping and manipulating food items. They employ antennular flicking to detect chemical cues from prey or detritus, enhancing foraging efficiency in low-visibility environments. Foraging activity peaks nocturnally, aligning with reduced predation risk and increased prey availability in many habitats.^[46][47][48] As opportunistic mid-level consumers, Palaemon species occupy a flexible trophic position, with gut content analyses revealing substantial plant-derived matter; for instance, detritus and plant fragments constitute over 80% by frequency in P. elegans. Seasonal variations influence diet composition, with increased consumption of protein-rich animal matter during reproductive periods to support energy demands. In high-density environments such as aquaculture ponds, intensified competition for shared resources like algae and invertebrates can alter foraging patterns and nutritional intake.^{[49][43][44][50][51]}

Interactions with other organisms

Palaemon species serve as important prey in coastal and estuarine ecosystems, facing predation from a variety of organisms including fishes such as perch and gobies, birds like herons, and crabs.^[52][53][54] For instance, gobies (Gobiidae) frequently consume Palaemon serratus, while herons and other wading birds target smaller individuals in shallow waters.^[52][53] Crabs, including shore crabs (Carcinus maenas), also prey on juvenile Palaemon, contributing to high mortality rates in dense populations.^[55] To evade these predators, Palaemon shrimp employ rapid tail-flip swimming, a burst escape response triggered by visual or mechanosensory stimuli that propels them backward at high speeds.^[56][57] This mechanism is particularly effective against gape-limited fish predators, allowing larger individuals like Palaemon elegans to increase survival by directing escapes away from the threat.^[56] Competition among Palaemon species and with other shrimp occurs primarily for food and space in shared estuarine habitats. In crowded estuaries, intraspecific aggression is common, with dominant individuals establishing linear hierarchies to secure resources, as observed in Palaemon pugio where females display aggressive behaviors to defend territories.^[58][59] Interspecific competition arises with sympatric species like Crangon septemspinosa, where co-occurrence in polyhaline zones leads to overlap in foraging areas and shelter use, potentially limiting recruitment of subordinate Palaemon populations.^[59][60] Symbiotic relationships involving Palaemon include commensal interactions where species like Palaemon elegans and Palaemon adspersus act as cleaners in temperate waters, removing ectoparasites from client fishes at informal stations and gaining nutritional benefits without harming the hosts.^[61] Some Palaemon individuals host epibionts such as balanid barnacles, which attach to the exoskeleton in low densities, potentially providing camouflage while relying on the shrimp's mobility for dispersal.^[62] Additionally, Palaemon elegans associates closely with eelgrass (Zostera marina) beds, where it interacts with algal grazers like Gammarus locusta, facilitating trophic dynamics in these seagrass systems through shared habitat use.^[63] Invasive interactions are exemplified by Palaemon macrodactylus, which outcompetes native shrimp in introduced regions by exhibiting higher aggression and prolonged time at food sources, displacing species like Palaemon elegans and altering local food webs.^[64] This competitive dominance can reduce native shrimp abundance, impacting higher trophic levels such as fish populations that rely on them as prey, leading to broader ecosystem disruptions in estuaries like those in the northwestern Atlantic, with new establishments reported in Washington state as of 2025.^{[65][66][67][68]} Recent studies (as of 2024) have shown that invasive populations of P. elegans in the Baltic Sea exhibit greater risk-taking behavior than native P. adspersus, potentially enhancing their competitive success.^[69]

Reproduction and life cycle

Mating and reproduction

Palaemon species exhibit gonochorism, with distinct male and female sexes, and no hermaphroditism reported in the genus.^[70] Sexual dimorphism is evident, particularly in the larger chelae of males, which are used in agonistic interactions.^[71] Males detect receptive females primarily through contact pheromones released during the female's parturial molt, sensed via antennules; these pheromones elicit searching and mounting behaviors in males.^[72] Courtship typically involves male-male combat, where dominant males use their chelae to fend off rivals and secure access to females, often leading to precopulatory mate guarding in which the male carries the female ventrally until her molt and subsequent copulation.^[70] Copulation is brief, lasting 5-10 seconds, and occurs immediately after the female's molt when her exoskeleton is soft, facilitating spermatophore transfer to the ventral sternum.^[72][73] Following fertilization, females extrude eggs and attach them to the pleopods on their ventral abdomen using a glue-like adhesive secreted from the oostegites, forming a brood mass that is aerated by pleopod beating.^[74] Fecundity varies by species and female size, with representative clutches ranging from 200 to 3,700 eggs; for instance, Palaemon elegans females carry 222-2,628 eggs, while Palaemon adspersus produce up to 3,710.^[37][75] Reproductive strategies differ across species, with some like Palaemon paucidens being largely semelparous (one breeding season) and others like Palaemon serratus iteroparous, producing multiple clutches annually.^[72][76] Embryonic development within the brood mass is temperature-dependent, with hatching occurring after 36-56 days at 15-18°C in Palaemon serratus; higher temperatures accelerate development but may reduce viability if exceeding optimal ranges.^[77] Recent studies indicate that climate-driven temperature increases can shorten embryonic development but lower larval survival rates in species like P. serratus.^[78] Females actively brood the eggs, fanning them to maintain oxygenation and prevent fungal growth, until larvae hatch as free-swimming zoeae.^[74]

Development stages

The development of Palaemon species begins with the egg stage, where berried females carry fertilized embryos attached to their pleopods. Embryonic incubation typically lasts 20-60 days, depending on species and environmental conditions; for instance, in P. serratus, development lasts approximately 37 days at 18°C and 56 days at 15°C, extending to ~126 days at 10°C.^[77] In some freshwater-adapted species, such as P. sinensis, direct development occurs without a free-living larval phase, allowing embryos to hatch as miniature adults directly in low-salinity habitats.^[79] Following hatching, most marine and brackish Palaemon species undergo a planktonic larval phase consisting of 5-10 zoeal stages, characterized by elongated bodies and spines that aid in buoyancy and dispersal in coastal waters.^[80] These zoeae feed on plankton and progress through molts, with species like P. serratus typically exhibiting 8-9 stages before transitioning.^[80] The larval period culminates in metamorphosis to a post-larval stage, often termed mysis or decapodid, which resembles a scaled-down adult with developing appendages and reduced spines, enabling settlement into benthic habitats.^[81] Juveniles emerge from the post-larval stage and grow through frequent molting, typically every 1-2 weeks in optimal conditions, as seen in P. varians where the molt cycle averages 8.7 days at ambient temperatures.^[82] Growth involves iterative exoskeleton shedding and regeneration, with individuals reaching sexual maturity in 3-6 months; for example, P. gravieri yearlings mature and produce their first brood within the initial year post-settlement.^[83] Environmental factors significantly influence these stages, particularly salinity and temperature. Larval survival in P. serratus is highest at 21-29‰ salinity, with lower levels reducing viability and development success, while freshwater species tolerate near-zero salinity due to abbreviated ontogeny.^[80] Temperature accelerates development via a Q10 effect, where rates approximately double for every 10°C increase; in P. elegans, incubation shortens from 11 days at 19°C to 9 days at 27°C, and larval progression follows similar thermal acceleration.^[84]

Diversity and species

List of recognized species

The genus Palaemon Weber, 1795, encompasses 63 accepted species according to the World Register of Marine Species (WoRMS), reflecting ongoing taxonomic refinements that incorporate molecular and morphological data.^[2] Recent revisions have synonymized several junior names and transferred certain tropical and freshwater forms to related genera, such as Macrobrachium and Nematopalaemon, to better align with phylogenetic relationships.^[2] The accepted species are listed alphabetically below, with authorities and years of description.

Notable species profiles

Palaemon elegans, commonly known as the rockpool shrimp, is a euryhaline species native to European coastal waters, including the Mediterranean, Black Sea, and Atlantic shores from Norway to the Canary Islands.^[53] It has established invasive populations in North America, first detected in Salem Sound, Massachusetts, in 2010, and subsequently in [Rhode Island](/page/Rhode Island), with potential for further spread along the Atlantic coast due to its broad environmental tolerances.^[85] This shrimp exhibits remarkable salinity tolerance, surviving from 0.6 to 35 PSU with 80-100% survival rates between 1 and 35 PSU, enabling it to thrive in diverse habitats from full marine to nearly freshwater conditions.^[31] Adults typically reach a total length of up to 6 cm, featuring a distinctive rostrum with 7-9 dorsal teeth and translucent bodies marked by reddish-brown bands.^[86] Palaemon macrodactylus, the oriental shrimp, originates from estuarine and coastal waters along the Northwest Pacific, spanning Russia, Japan, Korea, and China.^[51] It has become invasive on Pacific coasts of North America, first recorded in San Francisco Bay in the 1950s, and has since spread to estuaries in California, Oregon, and Washington, competing aggressively with native species for resources.^[87] In aquaculture settings, particularly fish and prawn ponds in Asia, it acts as a significant pest due to its rapid reproduction and competition for food and space with cultured stocks.^[88] The species supports multiple generations annually, with 3-4 cohorts possible in favorable conditions during its extended spawning season from mid-April to October, facilitated by a lifespan of about two years and high fecundity.^[89] Palaemon adspersus, referred to as the Baltic prawn, is adapted to cold, low-salinity environments in brackish and freshwater-influenced waters of the Baltic Sea and adjacent regions, from southern Norway to the Mediterranean.^[90] It plays a key role in regional fisheries, targeted for its abundance in coastal lagoons and estuaries.^[91] Genetic analyses reveal distinct population structuring in the Baltic, with a pronounced break from North Sea lineages, indicating local adaptation and potential endemicity shaped by the area's environmental gradient and historical isolation.^[92] This cold-tolerant species maintains osmoregulatory efficiency across salinities of 1-35 PSU, though it shows lower resilience to extreme lows (below 1 PSU) compared to congeners like P. elegans.^[31] Palaemon pacificus, an Asian representative often associated with freshwater and brackish forms in the genus, inhabits estuarine and littoral zones across East Asia, including rocky shores, tidal pools, and seagrass beds in regions like Japan and the eastern Cape estuaries.^[93] It exhibits a versatile biology suited to variable conditions, with adults foraging on small invertebrates in shallow waters and demonstrating backward swimming for predator evasion.^[94] This species tolerates temperatures from 10 to 28°C and salinities typical of estuarine gradients, supporting its presence in both marine and landward-directed habitats.^[95]

Significance

Economic importance

Species of the genus Palaemon hold economic significance primarily through small-scale fisheries in Europe, where they are harvested for human consumption and as bait in recreational angling. For instance, P. serratus supports a notable fishery in Ireland, with annual landings ranging from 150 to 550 tonnes between 1990 and 2006, generating values of €2.25 to €8.25 million at approximately €15 per kg.^[96] This fishery involves around 300 vessels using static traps, contributing to coastal employment, particularly in regions like the southwest and west of Ireland.^[96] Similarly, P. adspersus is targeted in Denmark and, to a lesser extent, Sweden and Norway, often via small-scale methods in the Baltic Sea.^[97] Palaemon species are also valued as bait in angling, with P. longirostris noted for this use in estuarine fisheries.^[98] In aquaculture, certain Palaemon species pose challenges as invasives that can disrupt operations. P. macrodactylus, an introduced species in European and North American estuaries, exhibits aggressive behavior and dominates food resources over native congeners like P. elegans, potentially reducing availability for cultured fish in extensive pond systems.^[64] This competition alters food webs in coastal aquaculture wetlands, where increased water flow can facilitate its colonization and impact overall productivity.^[99] Control measures, such as netting, are difficult due to the species' mobility and pelagic larvae, though monitoring in aquaculture sites helps mitigate establishment.^[100] Invasive Palaemon species incur economic costs through monitoring and management in affected regions, while offering some benefits. P. elegans, first detected in U.S. estuaries like those in New England in 2010, requires ongoing surveillance as the first invasive palaemonid in North America, contributing to broader invasive species management expenses estimated in the billions annually across the U.S.^[66][101] However, it provides positive economic value by serving as prey for commercial fish species in introduced ranges.^[37] Similarly, P. macrodactylus invasions in U.S. Pacific estuaries, such as San Francisco Bay, necessitate tracking efforts, though specific localized costs remain part of wider invasive crustacean impacts totaling hundreds of millions globally.^[68][101] Palaemon species serve as valuable model organisms in research, particularly for studies on euryhalinity and osmoregulation, with investigations dating back to the 1980s. P. longirostris has been used to examine water permeability changes under varying salinities, highlighting adaptive mechanisms in estuarine crustaceans.^[102] Research on P. macrodactylus and other congeners explores osmotic stress responses and salinity tolerance across life stages, informing broader understanding of environmental adaptability in aquaculture and invasion biology.^[103][104] These studies underscore the genus's role in advancing physiological ecology without direct commercial breeding applications.^[105]

Ecological role and conservation

Palaemon species play crucial roles in aquatic ecosystems, particularly in coastal, estuarine, and wetland environments, where they serve as intermediate links in food webs. As omnivorous consumers, they feed on detritus, algae, and small invertebrates, facilitating nutrient cycling and the decomposition of organic matter, which enhances water quality and supports primary productivity.^[1] These shrimps are also vital prey for predatory fish, birds, and larger crustaceans, thereby transferring energy across trophic levels and maintaining ecosystem balance.^[106] In some cases, such as with Palaemon gravieri in marine systems, they help regulate populations of jellyfish, preventing blooms that could otherwise disrupt plankton communities.^[107] Invasive Palaemon species, notably Palaemon macrodactylus, pose risks to biodiversity by outcompeting native invertebrates and altering community structures in invaded estuaries. This non-native shrimp preys on local grazers and small crustaceans, potentially reducing the abundance and diversity of indigenous shrimp and benthic organisms, which can cascade through food webs to affect higher trophic levels.^[51] In March 2025, P. macrodactylus was first reported in the Washington portion of the Salish Sea, expanding its invasive range in U.S. Pacific waters.^[68] Such disruptions highlight Palaemon's dual role as both ecosystem engineers and potential threats when introduced outside their native ranges. Most Palaemon species are assessed as Least Concern or Not Evaluated on the IUCN Red List, reflecting their widespread distributions and adaptability to varied habitats.^[108] Broader threats include habitat degradation from estuarine pollution and wetland loss, which diminish suitable brackish environments essential for larval development. Conservation efforts emphasize habitat protection and invasive species management. In the European Union, brackish-water Palaemon species benefit from designations under wetland protection directives, safeguarding critical estuarine sites from development.^[109] Monitoring programs, increasingly utilizing environmental DNA (eDNA) techniques since around 2020, enable early detection of invasive Palaemon populations, facilitating targeted interventions to preserve native biodiversity.^[110]