Prevalence of the parasites Sacculina carcini on Liocarcinus

Prevalence o f the parasites Sacculina c a rc in i on Liocarcinus holsatus
and P eltogaster p a g u ri on P agurus b e rn h a rd u s in the Belgian part o f
the North Sea
Breine Naomi T., Sofie Vandendriessche and Kris Hostens
Institute fo r A g ricu ltu ra l and Fisheries Research (ILVO), A quatic Environm ent and Quality, Bioenvironm ental Research, A nkerstraat 1, 8400 Oostende, Belgium
E-mail: naom i.breine@ ilvo.vlaanderen.be
Sacculina c a rc in i and Peltogaster p a g u ri are rhizocephalan parasites on com m on sw im m ing crab
Liocarcinus holsatus and com m on herm it crab Pagurus bernhardus, respectively. The order
Rhizocephala consists o f parasitic barnacles w ith an extrem ely reduced m orphology. Hosts are
attacked by female cyprid larvae, which fo rm an internal root-system (the interna), th a t eventually
can evaginate an external reproductive body (the externa) on which male cyprid larvae may settle.
A fte r male settlem ent, the externa m atures and several batches o f parasitic nauplii larvae are
released. The externa occupies the same place as em bryos in ovigerous females, and thus m im ic a
brood o f eggs, fo r which both male and female hosts w ill tend to as if it was th e ir own. The effects
o f infection on the host include cessation o f m oulting, m odifications o f the secondary sexual
characteristics and in fe rtility.
Seven years o f epibenthos traw ling data fro m various stations in the Belgian part o f the North Sea
(BPNS) were used to evaluate the prevalence o f both parasites on th e ir respective hosts. Differences
in infection rates were exam ined between years (2006 to 2012), seasons (spring vs. autumn),
distance from the shore, and three human pressures (im pact vs. reference sites fo r sand extraction,
dredge disposal and offshore w ind energy developm ent). For Sacculina c a rc in i also gender and size
preference were analyzed.
Over the seven years sam pling period, a to ta l o f 20,158 L. holsatus and 4 3,114 P. bernhardus
individuals were exam ined fo r the presence o f externae. Sacculina c a rc in i externae were fo un d on
676 crab individuals (or 3.35% o f the flying crab population). Peltogaster p a g u ri externae were
found on 161 herm it crab individuals (i.e. 0.37% o f the herm it crab population in the BPNS). A
higher percentage m ig ht have been infected w ith internae, but th is was not exam ined as only quick
visual screenings o f parasites were made. For both host species there was a sign ifican t difference in
infection percentage between the consecutive years and between the seasons, w ith higher infection
rates in 2006-2007, and in spring. Sacculina c a rc in i showed no preference fo r specific crab sizes,
but a sign ifican t preference fo r female crabs was found. No sign ifican t difference was observed
between near-shore, m id-shore and off-shore samples. Also, no sig n ifica n t differences were noted in
infection percentages between im pact and reference samples fo r the three human pressures.
In summary, we found substantial variation in infection rates, which seemed m ostly determ ined by
natural interannual and seasonal differences, and by host-specific preferences o f the parasites. We
found no evidence th a t human activities have an influence on the infection rates.
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