The Portuguese war (Physalia physalis), also known as the man-of-war or bluebottle, is a marine hydrozoan found in the Atlantic, Indian, and Pacific oceans. While it is typically considered the only species in its genus, Physalia, and family, Physaliidae, genetic evidence suggests there may be more.
Although it superficially resembles a jellyfish, the Portuguese man o' war is in fact a siphonophore. Like all siphonophores, it is a colonial organism, made up of many smaller units called zooids. Although they are morphologically quite different, all of the zooids in a single specimen are genetically identical. These different types of zooids fulfill specialized functions, such as hunting, digestion, and reproduction, and together they allow the colony to operate as a single individual.
The man o' war is part of the neuston, organisms that live on the surface of the water. A gas-filled bladder called the pneumatophore provides buoyancy that lets the animal stay afloat on the surface of the water while its tentacles, which can be up to long, hang below the surface, containing venomous cnidocytes that help capture prey. The cnidocytes can deliver a sting powerful enough to kill fish, crustaceans, and in some cases, humans. A sail on the pneumatophore propels it about the sea, sometimes in groups as large as 1,000 individuals. The sail may be left or right-handed, being so assigned on the basis of the direction in which the wind catches it.
Etymology
The name man o' war comes from the man-of-war, a sailing warship, and the animal's resemblance to the Portuguese version (the caravel) at full sail. and species name physalis are both derived from the Greek word physalis, meaning "bubble" or "bladder".
Taxonomy
The Portuguese man o' war was first described by Carl Linnaeus in the 10th edition of his Systema Naturae under the name Holothuria physalis. and family Physaliidae by Brandt in 1835.
Although siphonophore systematists have often treated Physalia as monotypic (with Physalia physalis as the only species), both morphological and genetic studies have suggested that Physalia includes multiple distinct lineages and may comprise more than one species. Historically, proposed splits within Physalia were often based on morphology; for example, P. utriculus, identified by a smaller float and a single long fishing tentacle, is often considered a separate species. These characteristics however are also present in juvenile specimens of P. physalis.
Phylogeny
Physaliidae is one of two families, the other being Rhizophysidae, in the siphonophore suborder Cystonectae. Cystonectae was the earliest group of siphonophores to diverge, and as such maintain many ancestral characteristics, such as dioecy and the presence of palpons. The below cladogram is based on Munro and colleagues (2018). i.e. the two basic body plans of cnidarians. Both of these body plans comprise entire individuals in non-colonial cnidarians (for example, a jellyfish is a medusa, while a sea anemone is a polyp). All zooids in a man o' war develop from the same single fertilized egg and are therefore genetically identical. They remain physiologically connected throughout life, and essentially function as organs in a shared body. Hence, a Portuguese man o' war constitutes a single organism from an ecological perspective, but is made up of many individuals from an embryological perspective. In the event of a surface attack, the pneumatophore can be deflated, allowing the animal to temporarily submerge.
The colony hunts and feeds through the cooperation of two types of zooids: the "tentacular palpons" from which the tentacles grow, and the gastrozooids. Each tentacle bears tiny, coiled, thread-like structures called nematocysts. Nematocysts trigger and inject venom on contact, stinging, paralyzing, and killing molluscs and fishes. The gastrozooids surround and digest the food by secreting digestive enzymes. Large groups of Portuguese man o' war, sometimes over 1,000 individuals, may reduce fishery populations. As neither fertilization nor early development has been directly observed in the wild, it is not yet known at what depth these occur. The gas-filled bladder, or pneumatophore, remains at the surface, while the remainder is submerged. The animal has no means of propulsion; it moves passively, driven by the winds, currents, and tides. Winds can drive them into bays or onto beaches.
Predators and prey
thumb|The [[Janthina janthina|violet sea snail, which uses a raft of bubbles, as shown here, to float at the ocean surface, feeds on men o' war.]]
The Portuguese man o' war is a carnivore. The turtle's skin, including that of its tongue and throat, is too thick for the stings to penetrate. The blue sea slug (aka blue dragon) also specializes in feeding on the Portuguese man o' war, as does the violet sea snail. The ocean sunfish's diet, once thought to consist mainly of jellyfish, has been found to include many species, including the Portuguese man o' war.
Commensalism and symbiosis
thumb|[[Man-of-war fish]]
The Portuguese man o' war is often found with a variety of other marine fish, including yellow jack. These fish benefit from the shelter from predators provided by the stinging tentacles, and for the Portuguese , the presence of these species may attract other fish to eat.
The blanket octopus is immune to the venom of the Portuguese man o' war. Individuals have been observed to carry broken man o' war tentacles, which males and immature females rip off and use for offensive and defensive purposes.
The man-of-war fish is known to be able to live surrounded by the tentacles of the Portuguese man o' war, having at least one antigen to the man o' war's toxin, although still avoids being stung by swimming around them. The fish feeds on the tentacles and gonads of the man o' war, and may incentivize other fish to approach it, facilitating a quick and easy meal for the siphonophore, making the relationship potentially mutualistic.
Blooms
Cnidarians go through periods of large bursts in population growth called jellyfish blooms. These bloom events cause adverse affects to the food web. Men o' war in large populations can disturb the prey of fish, such as smaller larval fish, or compete for the same resources as them, resulting in the ripple effect disrupting the food web. Future bloom events are expected to multiply as the climate changes, further affecting the oceanic wildlife in areas the man o' war occupies.
Venom
thumb|Man o' war warning sign in Hawaii
The stinging, venom-filled nematocysts in the tentacles of the Portuguese man o' war can paralyze small fish and other prey. Detached tentacles and dead specimens (including those that wash up on shore) can sting just as painfully as those of the live organism in the water and may remain potent for hours or even days after the death of the organism or the detachment of the tentacle.
Stings usually cause severe pain to humans, lasting one to three hours. Red, whip-like welts appear on the skin that last two or three days after the sting. In some cases, the venom may travel to the lymph nodes and may cause symptoms that mimic an allergic reaction, including swelling of the larynx, airway blockage, cardiac distress and shortness of breath. Other symptoms may include fever, circulatory shock and, in extreme cases, even death, although this is extremely rare. Medical attention for those exposed to large numbers of tentacles may become necessary to relieve pain or open airways if the pain becomes excruciating or lasts for more than three hours, or if breathing becomes difficult. Instances in which the stings completely surround the trunk of a young child are among those that may be fatal.
The species is responsible for up to 10,000 human stings in Australia each summer, particularly on the east coast, with some others occurring off the coast of South Australia and Western Australia.
Treatment
Stings from a Portuguese man o' war can result in severe dermatitis characterized by long, thin, open wounds that resemble those caused by a whip. These are not caused by any impact or cutting action, but by irritating urticariogenic substances in the tentacles.
Treatment for sting pain is immersion in water for 20 minutes. Vinegar use is highly supported as the primary rinse solution for Portuguese man o' war stings, as they irreversibly inhibit cnidae discharge. Diluting the vinegar reduces its protective effects.
Drifting dynamics
thumb|The bluebottle course at zero angle of attack is dependent on the sail camber.
The man o' war uses a float filled with carbon monoxide and air as a sail to travel by wind for thousands of miles, dragging behind long tentacles that deliver a deadly venomous sting to fish. This sailing ability, combined with a painful sting and a life cycle with seasonal blooms, results in periodic mass beach strandings and occasional human envenomations, making the man o' war the most well-known of the siphonophores. Despite being a common occurrence, the origin of the man o' war or bluebottle before reaching the coastline is not well understood, and neither is the way it drifts at the surface of the ocean. Because of their long tentacles, these currents can overtake the wind drift and wash them ashore. In strong winds, it drifts with its float oriented in the same direction of the wind. Regional populations can have substantial differences in float size and the number of tentacles used for hunting. The regional form previously known as P. utriculus has a bladder rarely exceeding in length and has one long hunting tentacle that is less than long. In comparison, the typical man o' war has a float of around , and several hunting tentacles that can reach in mature colonies when fully extended. In 2015 Prieto et al. included both the effect of the surface currents and wind to predict the initial colony position prior to major beaching events in the Mediterranean.