Janua brasiliensis
Date of introduction and origin
Janua brasiliensis is suggested to have been
introduced into Portsmouth Harbour, the Solent, in 1974
(Knight-Jones et al. 1975), possibly from Brazil
(Zibrowius & Thorp 1989). This species is widespread in
tropical areas, including Brazil.
Method of introduction
One possible method of transport was on ships' hulls
(Zibrowius & Thorp 1989) from the Round the World Yacht Race -
the previous stop of the race was Brazil. Another possible method
of introduction was as epiphytes on Sargassum muticum
(Critchley et al. 1990).
Reasons for success
Unknown.
Rate of spread and methods involved
No spread has been recorded in British waters. While marginal
dispersal is unlikely through the brief, motile, larval stage
(Knight-Jones & Knight-Jones 1980), remote dispersal could be
expected by adults attached to drifting Sargassum muticum.
Spread is also conceivable as a fouling organism on ships' hulls,
however, its isolated location in Britain suggests this has not
occurred in British waters.
Distribution
This species, although widespread in tropical areas, has a
very limited distribution in Europe; in the UK it is limited to
Portsmouth Harbour; and elsewhere in Europe it is reported from the
Oosterschelde, The Netherlands (Critchley & Thorp 1985), and
St. Helier, Jersey (C.H. Thorp pers. comm.).
Factors likely to influence spread and distribution
This species' epiphytic association with the invasive brown
alga Sargassum muticum provides it with a convenient
vehicle for dispersal. Sargassum muticum is noted for its
habit of casting off lateral branches in late summer and early
autumn which, buoyed up with air bladders, are free to drift in
surface currents over long distances. Such drifting plants could
transport an 'innoculum' of attached Janua brasiliensis.
Elsewhere in Europe, in both the Goes Canal (Eastern Scheldt) and
Havre des Pas (Jersey), records of Janua brasiliensis are
from sites where Sargassum muticum had already been
recorded (Critchley, Farnham & Morrell 1983). Janua
brasiliensis reaches maturity within a single season and,
additionally, has a reduced brooding period for its embryos in
higher temperatures (Gray 1978). It would appear that while the
means are available for J. brasiliensis to be as widely
distributed as its Sargassum host, its limited occurrence
within temperate waters may be determined by the availability of
waters of suitable temperature. Elevated water temperatures in
enclosed or semi-enclosed systems, such as Portsmouth Harbour, are
likely to be a significant factor contributing to its success. In
Portsmouth Harbour Janua brasiliensis exhibits a marked
settlement preference for S. muticum in contrast to the
submerged pontoon surfaces. It is notable that elsewhere in Europe,
J. brasiliensis has become more successful on native host
plants, in the form of Zostera at Goes (Critchley &
Thorp 1985), and Fucus serratus at Havre des Pas (C.H.
Thorp pers. comm.).
Effects on the environment
In the Goes Canal the density of the settlement of J.
brasiliensis on the eel grass Zostera was great
enough to have weighed down leaves such that lay on the canal
sediment. This considerably impaired the eel grass' photosynthetic
efficiency (Critchley & Thorp 1985).
Effects on commercial interests
It is a fouling organism but has negligible effect in British
waters.
Control methods used and effectiveness
Not applicable to such a small animal.
Beneficial effects
None known.
Comments
All three records of J. brasiliensis from European
waters have come about as a consequence of monitoring the spread of
S. muticum, in the case of the Goes record in particular.
It is possible that there are other sites with isolated populations
on Channel coasts, both French and English, which have not been
visited by competent 'spirorbidologists'. Such sites would be
situated in the vicinity of warmed water, coastal power plants
etc.
References
Critchley, A.T., Farnham, W.F., & Morrell, S.L. 1983. A
chronology of European sites of attachment for the invasive brown
alga, Sargassum muticum, 1973-81. Journal of the
Marine Biological Association of the United
Kingdom,63: 799-811.
Critchley, A.T., Farnham, W.F., Yoshida, T., & Norton,
T.A. 1990. A bibliography of the invasive alga Sargassum
muticum (Yendo) Fensholt (Fucales; Sargassaceae). Botanica
Marina, 33: 551-562.
Critchley, A.T., & Thorp, C.H. 1985. Janua
(Dexiospira)brasiliensis (Grube) (Polychaeta:
Spirorbidae): a new record from the south-west Netherlands.
Zoologische Bijdragen, 31: 1-8. (Delta Institute
Communication, No. 304.)
Gray, P.W.G. 1978. An investigation of the fauna
associated with Sargassum muticum. Ph.D. Thesis, Council for
National Academic Awards, Portsmouth Polytechnic.
Knight-Jones, P., & Knight-Jones, E.W. 1980. Pacific
spirorbids in the east Atlantic. Journal of the Marine
Biological Association of the United Kingdom, 60:
461-464.
Knight-Jones, P., Knight-Jones, E.W., Thorp, C.H., & Gray,
P.W.G. 1975. Immigrant spirorbids (Polychaeta: Sedentaria) on the
Japanese Sargassum at Portsmouth, England. Zoologica
Scripta 4(4): 145-149.
Zibrowius, H., & Thorp, C.H. 1989. A review of the alien
serpulid and spirorbid polychaetes in the British Isles.
Cahiers de Biologie Marine, 30: 271-285
Acknowledgements (contributions from questionnaire)
Dr C.H. Thorp, University of Portsmouth.