Why do physalia cause beach closures

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 P. Siphonophores are a relatively understudied group of colonial hydrozoans. Colonies are composed of functionally specialized bodies termed zooids that are homologous to free living individuals.

Most species are planktonic and are found at most depths from the deep sea to the surface of the ocean 5 , 6 , 7. They are fragile and difficult to collect intact, and must be collected by submersible, remotely operated vehicle, by hand while blue-water diving, or in regions with localized upwellings 8 , 9. However, Physalia physalis is the most accessible, conspicuous, and robust siphonophore, and as such, much has been written about this species, including the chemical composition of its float, venom especially envenomations , occurrence, and distribution 4 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , Fewer studies, however, have taken a detailed look at P.

These studies provide an important foundation for understanding the morphology, cellular anatomy, and development of this pleustonic species. It can be difficult to understand the morphology, growth, and development of P. Here, we combine what is already known about morphology and development with new microscopical techniques, including the use of optical projection tomography, and recent phylogenetic and histological knowledge from related siphonophore species, to add new perspectives on the morphology and development of P.

As the colony organization is so distinct from other siphonophores, an important first step is to homologize the anatomical axes in developing and mature specimens with other siphonophores. It is then possible to describe the order, pattern, and directionality of budding, and place this within a broader phylogenetic context.

There are also still open questions about the homology and origin of some of the unique zooids in P. Additionally, understanding the complex 3D structure of P. Finally, we also review what is known about the ecology and lifecycle of this pleustonic species. Siphonophores consist of a number of functionally specialized zooids that are homologous to free living polyps or medusae 27 Fig.

Physalia physalis belongs to Cystonectae, a clade that is sister to all other siphonophores 8. In long-stemmed cystonects all cystonects except for Physalia physalis gastrozooids feeding polyps arise as buds in the anterior of the colony and are carried to the posterior by an elongating stem, while gonodendra reproductive structures appear independently along the stem In all cystonects, the gonodendra are compound structures, containing gonophores reduced medusae, bearing a gonad , palpons derived gastrozooids, that lack tentacles in cystonects , and nectophores Cystonects are dioecious, and all the gonodendra in a colony bear gonophores of only one sex.

Schematic showing the anatomy of a Physalia physalis colony, with descriptions of the function of each zooid. As compared to other siphonophore species, including other cystonects, Physalia physalis is peculiar with regards to its colony organization Figs 1 and 2.

The only exception is the protozooid the first gastrozooid to form during development , which is essentially a typical siphonophore gastrozooid, with a mouth, tentacle and small basigaster region 26 , Apart from the protozooid, in P. Other authors refer to either the zooid or the attached tentacle as a dactylozooid 10 , 13 , 21 , 30 - the term dactylozooid has historically been applied to palpons in other siphonophore species but is not currently used, and dactylozooids are specialized palpon-like defensive zooids in other hydrozoans 31 , 32 , To avoid confusion about the homology of this zooid, we suggest that the term dactylozooid should not be used, as we consider this zooid to have arisen de novo in P.

Additionally, the term ampulla is also commonly associated with the terminal vesicle of the tricornuate tentillum of agalmatids Colony orientation in siphonophores. A Schematic of a mature colony of the siphonophore Nanomia bijuga. B Schematic of a developing Physalia physalis larva.

Drawing based on photograph by Linda Ianniello. C Schematic of a mature Physalia physalis colony. Haeckel outlined two possible hypotheses for the origin of tentacular palpons - the first hypothesis, promoted by Huxley, is that they are not zooids, but are instead secondary diverticula at the base of the tentacle that function similarly to ampullae in echinoderm tube feet 34 , In the second hypothesis, modification and subfunctionalization of an ancestral gastrozooid gave rise to two separate zooids - a gastrozooid without a tentacle and a tentacular palpon with a tentacle.

However, we favor the second hypothesis, based on observations of the gastrozooid and tentacular palpon Figs 3 — 6 ; Supplementary videos 1 , 2.

The gastrozooid and tentacular palpon are borne on separate peduncles Figs 5A,B and 6A ; Supplementary video 2 , and develop from distinct, separate buds Figs 3A,B , 4 ; Supplementary video 1. Thus, the tentacular palpon is a derived gastrozooid, unique to Physalia physalis , that has an enlarged tentacle, no mouth, and is functionally specialized for nematocyst production.

The gastrozooids in P. The subfunctionalized gastrozooid hypothesis is also more parsimonious than the other hypotheses, as the modification and subfunctionalization of zooids is common in siphonophores - palpons, for example, are considered to be derived, modified gastrozooids that typically have a reduced tentacle Photographs of formalin fixed developing Physalia physalis.

Five different specimens are shown in A — E. Abbreviations: Tp: Tentacular palpon number indicates order of appearance ; G: Gastrozooid number indicates hypothesized order of appearance; G1 and G2 likely appear at the same time P: Protozooid; PrT - Tentacle of protozooid; TpT: tentacle of tentacular palpon number indicates order of appearance.

Images of formalin fixed larval Physalia physalis , images obtained by optical projection tomography. Images are different views of the same specimen. The 3D image was segmented and false-colored to highlight different morphological features. Green- gastrozooids; Red- Protozooid; Orange- tentacle associated with protozooid; Dark blue- Tentacular palpon; Light blue- tentacle associated with tentacular palpon. Gastrozooids and tentacular palpons forming at the base of the first set of gastrozooids and tentacular palpon are unlabelled and are light grey in color.

Photographs of live juvenile Physalia physalis. A Developing tripartite group, with gastrozooid, tentacular palpon and developing gonodendron. B Schematic of the tripartite group. C Developing gonodendron with mature gastrozooids and buds that will give rise to gonophores, nectophores, palpons. D Schematic of the developing gonodendron. E Close up of branchlet within the gonodendron, from proximal to distal: jelly polyp Jp , palpon P , nectophore N , palpon, with gonophores Go along the branchlet, additionally there is a nectophore, palpon and gonophores that are part of a new branchlet.

F Schematic of a close up of a branchlet within the gonodendron. Images of formalin fixed juvenile Physalia physalis zooids, images obtained by optical projection tomography. The 3D image was segmented and false-colored to highlight tripartite groups. The un-segmented image is shown below. Green- gastrozooid; Dark blue- tentacular palpon; Yellow- developing gonodendron.

A Tripartite group with developing tentacular palpon, gonodendron and gastrozooid. B Two sets of developing tripartite groups at different developmental stages are highlighted, while others are visible but not segmented. Historically, there was no consistent terminology to describe the axes of mature siphonophore colonies. A standardized scheme was developed to describe mature planktonic siphonophore colonies, with the anterior end of the colony as that with the pneumatophore or nectophores, and the posterior end of the colony as that with the oldest zooids zooids are carried towards the posterior end by the elongating stem 36 Fig.

The dorsal-ventral axis is perpendicular to this axis, with siphosomal zooids attached to the ventral side of the stem. Left and right are determined as perpendicular to the anterior-posterior and dorsal-ventral plane. The oral end of the larva corresponds to the posterior of the mature colony As Physalia physalis is a pleustonic species, with distinctive colony morphology and arrangement, it is important to homologize the axes with other siphonophores.

Totton does not use the terms anterior-posterior, and defines an oral-aboral axis that corresponds directly to the larval axis, with the protozooid, the first feeding zooid Fig. The oral end of the colony thus corresponds to the posterior end This corresponds directly with the anterior-posterior axis defined by other authors 25 , 35 , with the apical pore defined as the anterior of the colony. To keep terminology consistent across all siphonophores, we will follow this convention, with the anterior corresponding to the apical pore and the posterior corresponding to the protozooid Fig.

The dorsal-ventral axis is perpendicular to this plane, with the dorsal side towards the crest of the float and zooid attachment on the ventral side Fig. We will follow the same left-right and proximal-distal axis conventions. While zooid attachment is on the ventral side, there are very clear left-right asymmetries in the placement and growth of zooids in this species, and colonies are either left-handed or right-handed. Cormidia are typically defined as a group of zooids that are reiterated along the siphosomal stem in many siphonophore species 27 Fig.

Cystonectae, the clade to which P. Cystonects produce all zooids from single buds that arise along the stem, while probud subdivision all zooids in a cormidium arise from a single bud is a synapomorphy of Codonophora Probud subdivision is associated with the origin of cormidia along the branch that leads to Codonophora Due to this, and the fact that P. Larval development has not been observed directly, and development has been described by comparing the morphology of fixed specimens 23 , 24 , The pneumatophore forms in a manner similar to other siphonophores, with an invagination of the aboral end of planula forming the pneumatosaccus 24 , 29 , 37 Fig.

However, Mackie suggests that the pore is not completely closed even in mature colonies, but the pore is so tightly constricted that gas release is unlikely to occur naturally Other reports suggest that young Physalia may be able to release gas from the pore In the earliest stages, there is no separation between the gastric cavity of the protozooid and the main gastric cavity The pneumatosaccus, that is formed via the invagination, protrudes into the main gastric cavity and is connected at the site of invagination As the protozooid differentiates, a septum separates the gastric cavity of the protozooid from the main gastric cavity Schematic of the cell layers in the pneumatophore, showing the distinction between the codon, pneumatosaccus, and gas gland.

Orange - ectoderm; dark grey - chitin; red - endoderm; light grey - mesoglea. Anterior to the protozooid, three buds arise on the ventral side as three transverse folds Based on our observations of the budding order and the relative size of the zooids, the posterior most of these three buds is a gastrozooid G1, followed by a second gastrozooid G2 and tentacular palpon labelled Tp1 Figs 3A,B , 4.

The observation of the three transverse folds suggests that G1,G2, and Tp1 all arise at the same time The third gastrozooid G3 subsequently appears anterior to gastrozooids G1, G2, and tentacular palpon Tp1. Okada numbers the buds based on hypothesized order of appearance, which differs from ours only in that G2 is considered the first bud, perhaps based on size, and G1 is considered the second 23 , 24 Fig. The gastrozooid labelled G2 here is larger in older specimens Figs 3C,D , 4 , but not in the youngest developing specimen Fig.

Physalia physalis colonies can be either left or right handed, and the location of first tentacular palpon Tp1 and the attachment point of the tentacle is the first indicator of left-right asymmetry 24 , The tentacle of the tentacular palpon is placed either on the left or right side, depending on the handedness of the colony Figs 3 , 4 ; Supplementary video 1.

The secondary series of buds always appear on the same side as the tentacular palpon tentacle. The attachment point of the tentacle of the protozooid may even be an earlier indication of left-right asymmetry Figs 3 , 4 ; Supplementary video 1.

As live embryos are not available, it remains an open question as to whether left-right asymmetries are established via molecular mechanisms similar to those underlying left-right asymmetry in bilaterians As the organism grows and the pneumatosaccus expands anteriorly, new tentacular palpons grow at the base of the original gastrozooids Figs 3B2 and 4.

In larger specimens, new gastrozooid and tentacular palpon buds form anterior and posterior to the three gastrozooids G1, G2, G3 and tentacular palpon Tp1 Fig.

A secondary series of buds also form at the base of the gastrozooids in line with the first tentacular palpon either left or right, depending on the handedness of the colony 23 Figs 3D2 , 4. Additionally, in the expanding space between the protozooid and the primary series of gastrozooids, a series of buds form Fig.

This region of growth directly anterior to the protozooid Fig. Bernard, P. Journal of Oceanography, Research and Data, 4: Occurrence and public perception of jellyfish along the German Baltic coastline Journal of Coastal Conservation, Baumann, S.

Occurrence and public perception of jellyfish along the German Baltic coastline. Journal of Coastal Conservation, Identifying potentially harmful jellyfish blooms using shoreline surveys Aquaculture Environment Interactions, Fleming, N. Identifying potentially harmful jellyfish blooms using shoreline surveys.

Aquaculture Environment Interactions, 4: Digestion and predation rates of zooplankton by the pleustonic hydrozoan Velella velella and widespread blooms in and Journal of Plankton Research, Journal of Plankton Research, A physical context for gelatinous zooplankton aggregations: a review Hydrobiologia, Graham, W. A physical context for gelatinous zooplankton aggregations: a review. Mapstone, G. Global diversity and review of Siphonophorae Cnidaria: Hydrozoa. Plos One, 9: e Serious Physalia Portuguese man o'war stings: implications for scuba divers Journal of Wilderness Medicine, Burnett, J.

Serious Physalia Portuguese man o'war stings: implications for scuba divers. Journal of Wilderness Medicine, 5: Jellyfish stings and their management: a review Marine Drugs, Cegolon, L. Jellyfish stings and their management: a review.

Marine Drugs, Haddad Jr. An outbreak of Portuguese man-of-war Physalia physalis - Linnaeus, envenoming in Southeastern Brazil. Revista da Sociedade Brasileira de Medicina Tropical, Systematics of siphonophores Evolution of venomous animals and their toxins, Systematics of siphonophores. In: Gopalakrishnakone, P. Evolution of venomous animals and their toxins. Springer, Amsterdam, pp.

Portuguese Man-of-War Physalia physalis in the Mediterranean: a permanent invasion or a casual appearance? Scientific Reports, Prieto, L. Scientific Reports, 5: Predation on fish larvae by Physalia physalis, the Portuguese man of war. Marine Ecology Progress Series, Bingham, F. Observations on beach strandings of the Physalia Portuguese-Man-of-War community.

Veliger, Pontin et al. Pontin, D. Determining factors that influence the dispersal of a pelagic species: a comparison between artificial neural networks and evolutionary algorithms.

Ecological Modelling, Molecular phylogenetics of the genus Physalia Cnidaria: Siphonophora in New Zealand coastal waters reveals cryptic diversity Hydrobiologia, Molecular phylogenetics of the genus Physalia Cnidaria: Siphonophora in New Zealand coastal waters reveals cryptic diversity. Oliveira, O. Zootaxa, Nota sobre Physalia physalis L. Fagetti, E.

Molina, J. Saggio sulla storia naturale del Chili. Stamperia di S. Tommaso d'Aquino, Bologna. Leloup, E. Physalia physalis Linnaeus, Cnidaria, Hydrozoa, Siphonophora en la costa central de Chile, Brito, J.

Purcell et al. Temperature effects on asexual reproduction rates of scyphozoan polyps from the NW Mediterranean Sea. Araya, J. On the distribution of Physalia physalis Hydrozoa: Physaliidae in Chile. Marine Biodiversity, Table 1 Reports of colonies of Physalia physalis during spring and summer from the southeastern Pacific Ocean. R Core Team, R: a language and environment for statistical computing, The data were obtained by means of an intensive search procedure parallel to the tide line for counting P.

Sampling was conducted every fortnight, at weekends and at the flood tide, as these animals are more frequently found in this type of tide. The data were geoprocessed using the QGIS version Information concerning envenomations caused by Portuguese man-of-war was obtained through the application of a specific questionnaire.

These data were collected in lifeguard department posts on the two evaluated beaches, from August to December , on weekends and holidays, when the number of beachgoers was higher. Data on envenomation place of occurrence, month, year, and first-aid measures were obtained. From January to December , a total of 1, Portuguese man-of-war specimens were found on the two evaluated beaches, in and 1, in Portuguese man-of-war were most frequent in August 90 , September 89 , and October , and in August , September , and November Figure 2.

The months with the highest number of occurrences were January 11 cases , September 9 cases , and November 19 cases Figure 2. The highest occurrence of Portuguese man-of-war specimens coincided with the highest occurrence of human envenomations on Calhau beach, as both are close to the lifeguard station. The main response measures adopted after Portuguese man-of-war envenomations at the lifeguard stations were as follows: topical vinegar acetic acid application at the site 50 cases ; freshwater, silver sulphadiazine, and lidocaine 4 cases ; vinegar and silver sulphadiazine 2 cases ; freshwater and vinegar 2 cases ; vinegar, silver sulphadiazine, and lidocaine application 1 case ; freshwater, vinegar and sea water 1 case and vinegar and sea water 1 case.

Moreover, 5 cases did not receive first-aid measures. The bathers themselves carried out all the freshwater applications reported herein. The high number of P. The largest Portuguese man-of-war agglomerations generally occur during the dry season August to December , as reported previously by Haddad et al. Med J Aust. On the distribution of Physalia physalis Hydrozoa: Physaliidae in Chile.

Mar Biodivers. Some studies point out that the environmental conditions that surround the Portuguese man-of-war agglomerations are not yet well known 15 Ecol Modell. Purcell JE. Predation on fish larvae by Physalia physalis, the Portuguese man of War. Acta Bot Brasilica. Lat Am J Aquat Res. Climate effects on formation of jellyfish and ctenophore blooms.

A review. The higher density sites of Portuguese man-of-war organisms coincided with the sites where the greatest number of human envenomations occurred, while the months comprising the highest P.

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