Crabs, leeches and trypanosomes: an unholy trinity?

Area of Science:

• Marine Biology
• Parasitology
• Invasive Species Ecology

Background:

• The red king crab (Paralithodes camtschaticus) was introduced to the Barents Sea from the North Pacific.
• The crab's carapace serves as an egg-laying substrate for the leech Johanssonia arctica.
• This leech acts as a vector for trypanosome blood parasites affecting marine fish, including cod.

Purpose of the Study:

• To investigate the relationship between red king crab density and trypanosome infections in cod.
• To assess the geographical distribution and prevalence of trypanosome infections in cod along the Finnmark coast.

Main Methods:

• Conducted annual surveys of cod populations along a 1000 km stretch of the Finnmark coast over three years.
• Examined cod for trypanosome infections.
• Correlated infection levels with the density of red king crabs in different areas.

Main Results:

• Cod exhibited significantly higher trypanosome infection levels in areas with the highest red king crab populations.
• This pattern was consistent across all three years of the study.
• A positive correlation was observed between king crab density and trypanosome prevalence in cod.

Conclusions:

• The study hypothesizes that increased red king crab populations indirectly enhance trypanosome transmission to cod.
• This indirect effect is mediated by an increase in the population of the leech vector, Johanssonia arctica.
• The invasive red king crab may play a role in the epizootiology of marine fish blood parasites.