BBSR
Marine Invertebrates of Bermuda

Portuguese Man-of-war (Physalia physalis)

By Miranda Hoover

Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 


Portuguese man-of-war(<i>Physalia physalis</i>)
Taxononmy


Phylum: Cnidaria
  Class: Hydrozoa
    Order: Siphonophora
       Family: Physaliidae


The Portuguese man-of-war (Physalia physalis) is the only genus in the family Physaliidae (Kirkpatrick & Pugh 1984). The man-of war is often mistaken for a jellyfish. However, this animal is a floating hydrozoan colony, made up of four polyp types: pneumatophore (float), dactylozooids (tentacles for defense and prey capture), gastrozooids (feeding), and gonozooids (reproduction) (Kurlansky 2004). They are recognized by the bluish pneumatophore, or float, which can be up to 30 cm in length (Kirkpatrick & Pugh 1984). This float is an overgrown polyp that is oblong-shaped and filled with gas (Kurlansky 2004). In most siphonophorans the gas is similar to the surrounding air composition, but in Physalia there is a greater concentration of carbon monoxide (Brusca & Brusca 2003). The floats include a mechanism that controls the gas to regulate the depth of the organism, which in the case of men-of-war keeps them on the surface of the water (Brusca & Brusca 2003). The tentacles, which can appear blue to purple, may reach lengths of up to 50 m (Sterrer 1992). A defining characteristic of the phylum Cnidaria is nematocysts, or stinging cells. Men-of-war have two different sizes of nematocysts (small and large) for stunning or killing prey (Kurlansky 2004). The fossil records for this species go back 600 million years (Parks 2000).

Habitat


The Portuguese man-of-war is a pelagic marine animal, blown about by the winds and pushed around by the currents (Sterrer 1992). They also fall under the classification of macro-holoplankton. The pneumatophore stays at the surface of the ocean, dipping into the water only to keep from drying out (Sterrer 1992). The transparent blue and purple coloration camouflages the animal against the backdrop of ocean waves. Although they are most common in the open ocean, waves may direct them into shallow waters or wash them up on beaches. The float of each individual is either right or left-sided, which causes the man-of-war to drift 45 degrees to the right or left of the wind direction (Kurlansky 2004). This adaptation allows the species to populate oceans throughout the world (Kurlansky 2004). Also, if one half of the population floats into predators or a current that washes them up on shore, the other half can survive. Sometimes they end up floating into groups of thousands of organisms (Lee 2003).

Men-of-war are most often found in warm, tropical and subtropical waters of the world’s oceans (Kurlanksky 2004 & Kirkpatrick & Pugh 1984). However, there have been hundreds of reports of them washing up on beaches in England, Wales, and Ireland (Kirkpatrick & Pugh 1984). In general, they can be found in the Atlantic Ocean, Pacific Ocean, Indian Ocean, and the Caribbean (Kurlansky 2004). They are especially common in the Sargasso Sea (Kurlansky 2004).

Ecology


Prey

Portuguese men-of-war feed on a wide variety of prey, including fish, fish larvae, cephalopods, chaetognaths, and leptocephalus (eel) larvae (Purcell 1989). All of this prey has the common theme of being soft-bodied. The structure of man-of-war nematocysts may prevent the capture of hard-bodied prey (Purcell 1989). In a study conducted by Purcell (1989), the stomach contents of men-of-war were found to be 70-90% larval fish. Each man-of-war consumed about 120 fish larva daily. Of the larvae ingested, 60% was available in the water column at 0 to 5 m depth.

Men-of-war do not have the elements of speed or surprise to attack prey, since their movements are greatly restricted by winds and waves. They must rely on other adaptations to survive. While hunting, they stretch out the stinging tentacles to full length to act as a floating net (Johnsen 2000). Although they are mostly transparent, their tentacles have pigmented regions that resemble larval fish, copepods, and small shrimp to lure prey into their stinging net (Johnsen 2000 & 2001). In the absence of jaws or brute strength, the tentacles serve to stun and entangle prey. Once prey is trapped, men-of-war can contract their tentacles to bring the prey into contact with polyps that secrete digestive enzymes to liquefy their catch (Lee 2003).

Predators

In Hawaii, the Pacific sand crab, Emerita pacifica, is known to grab men-of-war that have drifted into shallow waters (Bonnet 1946). Although this predator tries to drag the man-of-war into the sand, often the float can get pushed onto shore by the waves (Bonnet 1946). The crab rolls up on to the beach hanging onto the man-of-war. Once washed ashore, more crabs gather around the man-of-war (Bonnet 1946). The observational evidence that crabs feed on men-of-war was confirmed by testing gut contents of these crabs (Bonnet 1946). The macroscopic evidence of blue tissue and microscopic evidence of Physalia physalis nematocysts shows that the men-of-war are a food source for sand crabs (Bonnet 1946). These crabs apparently are unaffected by the stinging cells (Bonnet 1946).

Other predators of men-of-war are nudibranch mollusks of the planktonic family Glaucidae (Thompson & Bennett 1969). After ingesting the men-of-war, the nudibranchs take the nematocysts and use them in their own bodies for defense (Thompson & Bennett 1969). The nudibranchs select Physalia physalis nematocysts over those of their other prey: Velella (By-the-Wind-Sailor) and Porpita (Blue Button) (Thompson & Bennett 1969). This phenomenon has been reported in Australia and Japan (Thompson & Bennett 1969). Thus, Physalia physalis is important to nudibranchs not only as a food source, but for defensive adaptations.

Loggerhead sea turtles, Caretta carette, and leatherback sea turtles, Dermochelys coriacea, also feed on man-of wars (Lee 2003). This is of environmental importance when it comes to proper trash disposal. If sea turtles come across plastic bags floating in the ocean, they look like men-of war or jellyfish and will be ingested by the turtle. Plastic bags cannot be digested, and sea turtles can get sick and die.

Parasitic flukes can also bring about the demise of the Portuguese man-of-war (Parks 2000).

Symbiosis

Some Portuguese men-of-war have commensal relationships with fish species, including: Cavanx bartholomaei (yellow jack), Naucrates ductor (pilot fish), Mupus maculatus (spotted ruff), Macrorhamphosus scolopax (long snipefish), and Nomeus gronorii (man-of-war fish) (Jenkins 1983). Nomeus gronorii feed on the man-of-war’s tentacles while avoiding the dactylozooids, which contain the stinging cells (Jenkins 1983). The fish is not completely immune to the stings, but it can tolerate venom ten times the strength of other fish (Jenkins 1983). The fish relies on its speed and agility to avoid being stung (Jenkins 1983). The fish receives protection amongst the tentacles from other predators, and the tentacles, as well as leftover bits from man-of-war meals, are a food source. Since the man-of-war can regenerate the tentacles, it is not harmed, and it benefits from using the fish as a lure to attract other fish to the tentacle net.

Reproduction

Spawning most often takes place in the fall (Kurlansky 2004). The reproductive parts of the man-of-war are either male or female (Kurlansky 2004). The gametes are formed by the gonozooids and shed into the water. The sperm of one colony joins with the egg of another colony (Lee 2003). Physalia physalis also reproduce by asexual, mitotic division or budding (Lee 2003).

Recent Research


Edwards and Hessinger (2000) conducted to a study to determine if the venom of Physalia physalis could cause calcium influxes into different cell types. Previous research had determined that cells of the cardiovascular system were affected, as evidenced by studies done with embryonic chick heart cells. Postmortem specimens were envenomated to observe the effects on other cell types. In addition, cultured cells were exposed to man-of-war venom. Rat pituitary cells, fetal rat lung cells, and fibroblasts all experienced increased influx of calcium. This study aids in understanding the effects of man-of-war venom on cell types.

Edwards et al. (2002) studied membrane pore-formation due to Physalia physalis venom to continue their research on calcium influxes. The results of the study show that the venom creates membranes pores, causing osmotic swelling, and eventual cell lysis. The membrane pores, or lesions, were observed to be larger with greater surface density as the venom concentration increased. The researchers believe that physalitoxin is the man-of-war venom most likely responsible for formation of the membrane lesions. Once the lesions have developed, ionic fluxes lead to colloid osmosis causing cell swelling to the point of lysis. The experiment was done with cultured cells and evaluated using electron microscopy. This experiment builds on the knowledge of cellular response to Physalia physalis venom.

Bullard and Hay (2002) conducted a study to determine selectivity of macro-holoplankton species by predator fish. The experiment used generalist fishes and tested to see their feeding response to fresh tissues, freeze-dried homogenate, and chemical extracts from different prey types. The study found that fish ingested salp and chaetognath fresh tissues, but avoided the fresh tissues of all cnidarians (including Physalia physalis), ctenophores, and cyanobacteria. The nematocysts of the cnidarians tissues were deactivated and the tissues were retested. The tentacles without nematocysts were accepted as food, designating nematocysts as a defense mechanism. Higher quality macro-holoplankton was selected for by the fish. The researchers took note that the species higher in protein content had adapted the defensive traits. Researchers were determining the motivation behind palatability of different types of macro-holoplankton.

Johnsen (2001) compiled the current knowledge on the aspects of biological transparency: distribution, ecology, and physical basis. Transparency is unique because it is the only camouflage that involves the entire organism, internal and external, and because it is one of the few forms of camouflage that will be effective in the open sea, blending in with water and no substrate. Thus, transparency is mainly a pelagic animal characteristic. Physalia physalis was included in the phylogeny of transparent species. Johnsen also looked at the relationship with the optical environment, visual predation, and applying optical principles to anatomical and ultrastructural modifications. The purpose was to combine known information about biological transparency and address the need for future research in the area.

Haddad et al. (2002) considered the incidents of jellyfish (Cnidaria) stings over a period of five years on the southeastern coast of Brazil. The forty-nine accidents recorded, including four stings from Physalia physalis. The report laid out the identification of different species of jellyfish. Details about the statistics on the cases such as the sex of the victims and the location of the stings on the body were presented. There was also a description of effects of the stings on the body. The importance of this study is in the direct connection of Cnidaria to the human population.

Commercial Importance


Negative

Portuguese men-of-war can harm the tourism industry (Kurlansky 2004). People will not pay to visit beaches that are covered with jellyfish or swim in waters where they are floating. People do not want to chance being stung or put their children at risk for stings. In addition, money is spent to treat swimmers who are stung (Kurlansky 2004). Most swimmers know they have been stung by a man-of-war because the purple or blue float is visibly floating on the water (Haddad et al. 2002). The result of a sting is long, linear red marks and intense pain (Haddad et al. 2002). The most common perscribed treatment is to remove any remaining tentacles with gloves and ice the stings. In severe cases, the stings can cause heart and lung problems, even anaphylactic shock (Lee 2003). The first human fatality from Physalia physalis occurred in 1987 on the Atlantic coast of Florida (Stein et al. 1989).

Men-of-war have the potential to impact the fishing industry. Fish harvests could be influenced by man-of-war feeding on larval fish populations, especially in areas with major commercial fisheries, such as the Gulf of Mexico (Purcell 1989). If there is a boom in the man-of-war population, there could be a dramatic decrease in the amount of larval fish. If the fish are consumed in the larval stages by man-of wars, they cannot grow to become a food source for human beings.

Positive

Portuguese Men-of-war do benefit the economy as well. They are eaten by some fish and crustaceans of commercial value (Kurlansky 2004). In addition, the man-of-war could fill an important ecological role that has not yet been studied that keeps the ecosystem in balance.

Bermuda Laws


None

Personal Interest


When starting this project, I wanted to choose a species that I had actually come into contact with while in Bermuda. Little did I know I would have such close contact with the Portuguese man-of-war. My first glimpse of a Portuguese man-of-war was while out for a boat ride with two other students and two Bermudian guys. We pulled into a cove to wade and found many men-of-war that had washed in by the currents. My second view of them was on my first visit to a Bermudian beach. Horseshoe Bay has a gorgeous view, gentle waves, and soft sand, but it also had many Portuguese men-of-war washed up on shore. However, I spent my day at the beach without incident. A few weeks later I went to Warwick Long Bay for an afternoon at the beach with a Canadian guy I had met while in Bermuda. The water was cold, but we were getting our feet wet in the surf. As we were goofing around and pretending to throw each other in the ocean, I felt something wrap around my ankles, which I originally thought was seaweed. When I looked down, I saw the characteristic bluish float nearby. We got out of the water fast, but I had already been stung. I was very lucky because although I had sharp pains immediately, and dull stinging for a few hours, there were no serious side effects. Per my inquisitive nature, I wanted to learn about the animal that had accosted me.

Despite being stung by a Portuguese man-of-war, I still have an affinity for the species. I have always felt the need to stand up for animals that get a bad reputation, usually with the help of Hollywood. I am a long-time fan of sharks and have defended them to the bitter end to people playing the “Jaws” card. Even though men-of-war pose a threat to humans and economic problems for the tourist industry, I still contend that Physalia physalis deserves to have its place. After all, with a 600 million year old fossil record, they were here first.

Plus, blue is my favorite color.

References

Bonnet, D. D. 1946. “The Portuguese man-of-war as a food source for the sand crab (Emerita pacifica).” Science. 103: 148-149.

Brusca, R. C. and G. J. Brusca. Invertebrates. Sinauer Associates, Inc., Publishers: Sunderland, Massachusettes, 2003.

Bullard, S. G. and M. E. Hay. 2002. “Palatability of marine macro-holoplankton: nematocysts, nutritional quality, and chemistry as defenses against consumers.” Limnology and Oceanography. 47 (5): 1456-1467.

Edwards, L. and D. A. Hessinger. 2000. “Portuguese man-of-war (Physalia physalis) venom induces calcium influx into cells by permeabilizing plasma membranes.” Toxicon. 38 (8): 1015-1028.

Edwards, L. P., E. Whitter, and D. A. Hessinger. 2002. “Apparent membrane pore formation by Portuguese man-of-war (Physalia physalis) venom in intact cultured cells.” Toxicon. 40 (9): 1299-1305.

Haddad, V. J., F. L. da Silveira, J. L. C. Cardoso, and A. C. Morandini. 2002. “A report of 49 cases of cnidarian envenoming from southeastern Brazilian coastal waters.” Toxicon 40: 1445-1450.

Jenkins, R. L. 1983. “Observations on the commensal relationship of Nomeus gronori with Physalia physalis.” Copeia. 1: 250-252.

Johnsen, S. 2000. “Transparent animals.” Scientific American. 282 (2).

Johnsen, S. 2001. “Hidden in plain sight: the ecology and physiology of organismal transparency.” Biological Bulletin. 201: 301-318.

Kirkpatrick, P.A. and P. R. Pugh. Siphonophores and Velellids. The Linnean Society of London and the Estuarine and Brackish-Water Sciences Association: London, 1984.

Kurlansky, M. 2004. “Physalia physalis.” (on-line), Animal Diversity Web. Accessed February 25, 2004 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Physalia_physalis.html

Lee, J.B. 2003. “Portuguese man-of-war.” (on-line), Dangerous and venomous--Hawaiian ocean organisms. Accessed February 25, 2004 at http://www.aloha.com/~lifeguards/portugue.html

Parks, Peter. 2000. “The Blues Brothers: Part I.” Ocean Realm. Winter: 76-89.

Purcell, J. E. 1989. “Predation on fish larvae by Physalia physalis.” Marine Ecology-Progress Series. 19: 189-191.

Stein, M. R., J. V. Marraccini, N. E. Rothschild, J. W. Burnett. 1989. “Fatal Portuguese man-o'-war (Physalia physalis) envenomation.” Annual Emergency Medicine. 18 (3): 312-315.

Sterrer, W. Bermuda’s Marine Life. Island Press: Bermuda, 1992.

Thompson, T. E., and I. Bennett. 1969. “Physalia nematocysts: utilized by mollusks for defense.” Science. 166 (3912): 1532-1533.

Links

University of Michigan Museum of Zoology: Animal Diversity Web, Physalia physalis
Dangerous and Venomous-- Hawaiian Ocean Organisms: Portuguese Man-of-War
eNature.com: Seashore Creatures: Portuguese Man-of-war