Blackfordia virginica Mayer, 1910

Figure 2

Blackfordia virginica Mayer 1910: 277 –278, pl. 36, figs. 3–5, pl. 37, fig. 6; Kramp 1959: 156, fig. 210; Kramp 1961: 181; Kramp 1968: 85, fig. 228; Naumov 1969: 348 –350, figs. 211–214; Moore 1987: 287 –289, figs. 1–2; Bouillon 1999: 423, fig. 3.83; Mills & Rees 2000: 153, fig. 1; Álvares-Silva et al. 2003: 409 –412, fig.1; Bouillon et al. 2004: 129, figs. 67N and 68A–B; Genzano et al. 2006: 257 –259, fig. 2; Nogueira Jr. & Oliveira 2006: 38 –39, figs. 6–9. Blackfordia virginiana — Cowles 1930: 331 [incorrect subsequent spelling]

Examined material. Brazil: State of São Paulo: Cananéia: Cananéia Channel: 25º00.129' S, 47º54.276' W: 1 medusa, sex undetermined, salinity 10, 24.i.2008, 4% formalin, coll. J. Bardi (MZUSP 006851); 1 male medusa, salinity 10, 03.i.2008, 90% ethanol, coll. J. Bardi (MZUSP 006852); State of Paraná: Pontal do Paraná: Paranaguá Bay: 25º34.578’ S, 48º26.226’ W: 2 female medusae, salinity 10, 31.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006853); 25º33.710’ S, 48º26.151’ W: 1 female medusa, salinity 15, 31.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006854); 25º32.453’ S, 48º31.430’ W: 1 female medusa, salinity 15, 01.ii.2007, 4% formalin, coll. J. Bardi (MZUSP 006855); Guaratuba: Guaratuba Bay: 25º48.731’ S, 48º36.450’ W: 1 female medusa, salinity 10, 17.iii.2008, 4% formalin, coll. J. Bardi (MZUSP 006856); 1 male medusa, salinity 10, 17.iii.2008, 90% ethanol, coll. J. Bardi (MZUSP 006857); State of Santa Catarina: São Francisco do Sul: Babitonga Bay: 26º22.458’ S, 48º44.049’ W: 64 medusae (female and male), salinity 15, 03.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006858); 8 medusae (female and male), salinity 15, 03.i.2007, 90% ethanol, coll. J. Bardi (MZUSP 006859); 26º22.104’ S, 48º43.446’ W: 132 medusae (female and male), salinity 20, 03.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006860); 10 medusae (female and male), salinity 20, 03.i.2007, 90% ethanol, coll. J. Bardi (MZUSP 006861); 26º22.104’ S, 48º43.446’ W: 5 medusae (female and male), salinity 25, 03.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006862); 26º16.040’ S, 48º41.513’ W: 51 medusae (female and male), salinity 30, 0 3.i.2007, 4% formalin, coll. J. Bardi (MZUSP 006863); 26º22.440' S, 48º44.483' W: 6 medusae (female and male), salinity 15, 21.ix.2007, 4% formalin, coll. J. Bardi (MZUSP 006864).

Description. Medusa—Umbrella hemispherical, diameter 4.1– 14 mm, height 2.7–7.3 mm, with rounded apex. Mesoglea thick at apex, mesoglea height 0.8–2.8 mm, becoming thinner at umbrellar margin. Height of subumbrellar cavity almost half of umbrellar height. Velum thin, maximum opening 3/4 of diameter of umbrellar margin. Umbrellar margin with 50–142 filiform tentacles, each tentacular base with rounded bulb and finger-shaped projection towards mesoglea. One marginal vesicular statocyst between adjacent tentacles. Manubrium quadratic in cross section, length 0.4–1.4 mm. Mouth with four perradial, elongated, curved and crenulated lips. Four radial canals, one circular canal. Gonads beginning close to manubrium and extending ca. 2/3 of length of radial canals. Mature female gonads linear and granulated, with visible eggs. Proximal part (close to manubrium) of male gonads linear, medium and distal part sinuous and homogeneous.

Polyp—description of polyp stages can be found in Naumov (1969).

Distribution. Medusa—USA: Chesapeake Bay and San Francisco Bay (Calder 1971; Mills & Sommer 1995; Mills & Rees 2000, 2007); Mexico: coastal lagoons in Chiapas and in Gulf of Mexico (Álvarez & Silva 1999; Segura-Puertas et al. 2003); Brazil: Pernambuco, estuary of the Jaboatão River (Paranaguá 1963); São Paulo, Cananéia, Cananéia channel (this study); Paraná, Paranaguá Bay (Nogueira Jr. & Oliveira 2006) and Guaratuba Bay (this study); Santa Catarina, Babitonga Bay (this study); Argentina: estuary of the La Plata River (Genzano et al. 2006); Portugal: estuary of the Mira River (Moore 1987); France: Loire estuary (Denayer 1973) Bulgaria: swamp in Mandra at the Black Sea (Valkanov 1935); Russia: Caspian Sea and brackish water regions (Logvinenco 1959; Naumov 1969); India: estuary of Ganges River and Fairway Bay (Kramp 1958; Vannucci et al. 1970; Santhakumari et al. 1999); China: Fujian coast (Chen-tsu & Chin 1962).

Polyp—Bulgaria: swamps in Mandra by the Black Sea (Valkanov 1935); Russia: in brackish water regions (Naumov 1969); USA: estuary of San Francisco River (Mills & Rees 2000, 2007; Mills et al. 2007).

Remarks. According to the original description in Mayer (1910: 278), Blackfordia virginica is distinguished from B. manhattensis “by the dense-black entodermal pigment-granules adjacent to the lithocysts”. However, some specimens nominally considered to be B. virginica may not have pigments in the vesicles of the medusae (cf. Kramp, 1958: 343; 1961: 181; 1968: 85 for materials from the Ganges estuary, India; Norfolk Harbour, USA; Black Sea, Bulgaria). Moore (1987: 290) observed that only some of the specimens of B. virginica from the Mira estuary in Portugal had black pigment in these vesicles, which suggests that this feature could be polymorphic and unreliable as a taxonomic character. The 284 medusae that we studied did not have black pigment in their vesicles. Variation of the character may be related to its ontogeny, because in smaller medusae there is “…no black pigment in the entoderm of the bell-rim. This black pigment begins to develop when the medusa has 16 tentacles and the bell is hemispherical and 1.7 mm in diameter” (Mayer 1910: 277). We conclude that either (a) this character is polymorphic (although not present in Brazilian populations) and therefore the two nominal species are conspecific, or (b) many records attributed to B. virginica actually represent B. manhattensis.

Other characters used to separate the species, including number of statocysts and gonadal morphology, are also polymorphic or variable (Table 2) and of no taxonomic significance. The number of statocysts between adjacent tentacles may range from 1 to 3 (B. virginica, after Mayer 1910; Moore 1987; one in our specimens), 2 to 3 (B. manhattensis), and only 1 (B. polytentaculata). Another incorrect generalization used to separate species of Blackfordia is gonad shape and its relation to the sex of the specimen. Mayer (1910: 277) described the morphology of the gonads of B. virginica as “linear, extending from radial corners of stomach over somewhat more than half the length of the radial-canals” and differentiated the sexes by noting that “the eggs of the female protrude from the surface of the ectoderm and are cast off one by one” (see also Mayer 1910, pl. 36, figs. 3–5, pl. 37 fig. 6). We believe that Mayer was not precise in interpreting the different gonadal morphologies between the sexes. Female specimens of B. virginica from Brazil have linear and granulated gonads, while male specimens have only the proximal portion of the gonad linear, and the medial and distal portion sinuous. In this respect, it is possible that Mayer’s (1910) description is representative of fertile (Mayer’s illustration at pl. 36, fig. 5) and infertile (Mayer’s illustration at pl. 36, fig. 3) female gonads. Still concerning gonadal morphology, Mayer (1910: 27, pl. 36, fig. 2) noted that the gonads of B. manhattensis were “found in the middle parts of the radial-canals and are irregularly flexed, sinusoidally, from one side to the other of the canal”, again not differentiating the sex of the specimens. We conclude that this morphology likely corresponds to the male gonads of B. virginica. The gonads of the third species of the genus, B. polytentaculata, are described as long and linear, similar to the female gonads of B. virginica, but again there is no information on the sexes of the specimens described.

In addition to the morphological similarity between B. manhattensis and B. virginica, their geographic distributions also suggest the need for taxonomic caution (Figure 3). The two species have geographically proximate distributions on the northeastern coast of the USA (type localities of the species are in the state of New Jersey for B. manhattensis and the state of Virginia for B. virginica). Although the two species inhabit the same biogeographic area, records of B. manhattensis are mainly restricted to its type locality. There are only two studies reporting B. manhattensis from China, although they include no description, illustrations, or designations of voucher specimens (Zhang 1979; Yanyu et al. 1991). Blackfordia virginica by contrast is widely distributed and considered an invasive species.

1961), Moore (1987), and this study. *— refers to the original description.

The validity of both Blackfordia manhattensis and B. virginica has been questioned by some authors (e.g., Kramp 1959, 1961; Calder 1971; Moore 1987). Recent studies including both of the names relied on Mayer’s (1910) account for records of B. manhattensis (e.g., Bouillon et al. 1988; Bouillon & Boero 2000). Taxonomic uncertainty about whether the two are conspecific raises nomenclatural issues. Notably, B. manhattensis is the type species of Blackfordia (Mayer 1910: 277), yet the name is far less well-known than B. virginica. Moore (1987: 290) assumed the synonymy of both species, and acting as First Reviser assigned precedence to the more widely known name B. virginica. The type species of the genus remains B. manhattensis (a junior subjective synonym of B. virginica). Another taxonomic issue needing attention is that no type material apparently exists for either species.

Abiotic factors and the distribution of Blackfordia virginica. While Blackfordia virginica has been reported over a wide geographic area, it is mainly restricted to scattered records within estuarine areas of temperate and tropical regions (Figure 3). Indeed, in spite of extensive plankton surveys in neritic waters of southern Brazil, the species was never recorded there (Tronolone 2008; in a review of the distribution of Brazilian Medusozoa see Migotto et al. 2002 and Marques et al. 2003). We found the species only in estuaries and especially those with ports. The species has never been recorded in much-surveyed São Sebastião harbor (cf. Tronolone 2001), where salinities are always above 32 (e.g., Migotto et al. 2001).

Although Blackfordia virginica is apparently an estuarine endemic, it is reportedly euryhaline, occurring in salinities from 3 to 35 (Moore 1987; Bouillon et al. 1988). We found this hydromedusa over a salinity range from 10 to 30 in our samples, being most abundant in waters of 20 (10.6 individuals/m3), 15 (3.9) and 30 (2.6; Table 3).

In theory, hydroids of Blackfordia virginica may be transported by ships, and production of medusae might be stimulated in low-salinity conditions (Moore 1987). The scattered geographical distribution pattern would be the result of repeated introductions (Kramp 1961; Mills & Sommer 1995; Mills & Rees 2000; Genzano et al. 2006), with medusae having limited dispersive capacity. Yet the asexual form of the life cycle is a reduced polyp stage not exceeding 0.5 mm in height, with a presumably short benthic life, which makes its records rather rare (Moore 1987; Mills & Sommer 1995; Mills & Rees 2000). Dormant stages may play an important role in the dispersal of the species. However, they are unknown.

The occurrence and distribution of B. virginica also seem to be associated with episodes of abundance peaks (see Table 3). Monitoring of the four estuaries in southern Brazil where the species was found has been underway since 2007, and only three episodic events of abundance peaks occurred, always during summer. After these episodes, abundances decline drastically but, at least in São Francisco do Sul harbor (Babitonga Bay), the population seems to be well established (we collected males, females, and juveniles during summer and winter). The same pattern was observed in the Paranaguá Bay, a port region in which B. virginica also seems to be well established (Nogueira Jr. & Oliveira 2006). The presence of a small number of B. virginica in the Cananéia-Iguape estuarine complex and in Guaratuba Bay may indicate recent dispersal from adjacent regions. Indeed, in southern South America, B. virginica was recorded in the La Plata estuary in a plankton study based on a long series of samples from 1983 to 2000 (Genzano et al. 2006). The species was first recorded in February 2000 in large numbers (more than 5.000 specimens, almost 30 ind/m3).

Additional taxonomic study of this invasive medusa species is warranted, as well as investigations to improve understanding of its population dynamics and ecophysiological tolerances.