395 
Abstract — Distribution and preva- 
lence of the phoretic barnacle Xenobal- 
anus on cetacean species are reported 
for 22 cetaceans in the eastern tropical 
Pacific Ocean (21 million km 2 ). Four 
cetacean species are newly reported 
hosts for Xenobalanus: Bryde’s whale 
( Balaenoptera edeni), long-beaked 
common dolphin ( Delphinus capen- 
sis), humpback whale ( Megaptera 
novaeangliae), and spinner dolphin 
( Stenella longirostris). Sightings of 
Xenobalanus in pelagic waters are 
reported for the first time, and con- 
centrations were located within three 
productive zones: near the Baja Cali- 
fornia peninsula, the Costa Rica Dome 
and waters extending west along the 
10°N Thermocline Ridge, and near 
Peru and the Galapagos Archipelago. 
Greatest prevalence was observed on 
blue whales (Balaenoptera musculus ) 
indicating that slow swim speeds are 
not necessary for effective barnacle 
settlement. Overall, prevalence and 
prevalence per sighting were gener- 
ally lower than previously reported. 
The number of barnacles present 
on an individual whale was great- 
est for killer whales, indicating that 
Xenobalanus larvae may be patchily 
distributed. The broad geographic 
distribution and large number of 
cetacean hosts, indicate an extremely 
cosmopolitan distribution. A better 
understanding of the biology of Xeno- 
balanus is needed before this species 
can be used as a biological tag. 
Manuscript submitted 28 January 2008. 
Manuscript accepted 17 June 2008. 
Fish. Bull 106:395-404 (2008). 
The views and opinions expressed 
or implied in this article are those of 
the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Prevalence of the commensal barnacle 
Xenobalanus globicipitis on cetacean species 
in the eastern tropical Pacific Ocean, 
and a review of global occurrence 
Emily A. Kane (contact author) 1 ' 2 
Paula A. Olson 2 
Tim Gerrodette 2 
Paul C. Fiedler 2 
Email address for E A. Kane: ekane@tamu.edu 
1 Southampton College 
239 Montauk Highway 
Southampton, New York 11968 
2 National Marine Fisheries Service, NOAA 
Southwest Fisheries Science Center 
8604 La Jolla Shores Dr. 
La Jolla, California 92037 
Present address for contact author (E. A. Kane): Texas A&M University at Galveston 
5007 Avenue U 
Galveston, Texas 77551 
Barnacles of the superfamily Coronu- 
loidea live as obligate commensals on 
sea turtles, cetaceans, sirenians, sea 
snakes, and crustaceans (Newman 
and Ross, 1976). The monotypic Xeno- 
balanus globicipitis Steenstrup, 1851 
(herein referred to by genus) is spe- 
cialized for living as a commensal on 
whales and dolphins (Darwin, 1854). 
The typical six-plate balanomorph 
shell is small and is imbedded into 
the skin of the cetacean host. The 
membrane supporting the operculum 
is greatly elongated, so that externally 
Xenobalanus resembles a pedunculate 
barnacle. This species is most com- 
monly observed on the trailing edges 
of the dorsal fin, pectoral flippers, and 
tail fluke of the host, although it has 
been reported in areas such as the ros- 
trum and the area between the teeth 
(Samaras, 1989). Xenobalanus does 
not receive nutrition from its cetacean 
host and therefore is not considered 
a parasite. Instead, as a suspension- 
feeding cirriped, it uses the water flow 
around swimming cetaceans and ben- 
efits from being transported by its host 
(phoresis). This species is highly spe- 
cialized to live on cetaceans (Seilacher, 
2005) and it has been suggested that 
its hermaphroditic reproduction may 
be synchronized with that of its host 
(Dollfus, 1968; Fertl, 2002). A five- 
to six-month reoccurrence cycle has 
been reported for Xenobalanus (Van 
Waerebeek et al., 1993; Orams and 
Schuetze, 1998), which may indicate 
that its life span may be of similar 
length or that occurrence is correlated 
with seasonal environmental condi- 
tions. Xenobalanus has been reported 
on 30 cetacean species worldwide and 
has a prevalence ranging from 0.5% to 
55% of individuals in each sighting. 
However, intensity is highly variable, 
and there are some reports of greater 
than 100 barnacles on a single host 
(Aznar et al., 2005). 
We examined the presence of Xeno- 
balanus on cetaceans in the eastern 
tropical Pacific Ocean (ETP). Based 
on photographs taken during research 
cruises from 1977 through 2003, 
mean prevalence, mean intensity, and 
geographic distribution are described 
for Xenobalanus on 22 host cetacean 
species. In addition, peer-reviewed lit- 
erature on this subject is examined, 
updating a previous summary of the 
cetacean hosts of this barnacle (Raja- 
guru and Shantha, 1992). 
