Environmental factors and body size effects on helminth transmission in mole crabs

Infections from helminths, also known as parasitic worms, can result in a health burden on the host species and pose significant ecological consequences. Understanding the dynamics behind parasite transmission, including possible environmental conditions that may play a role, is vital to understanding disease transmission more broadly.

Mole crabs are affected by three types of helminths: Profilicollis altmani, Maritrema trematodes and Proleptus nematodes. While these worms have the ultimate goal of infecting seagulls that occupy the same beaches as the crabs, mole crabs become infected as well when they come in contact with the feces of the birds. 

The research team, including CEID researcher Jeb Byers, tasked themselves with determining whether helminth abundance in mole crabs varied based on the size and density of the mole crabs as well as the environmental factors of their beaches. To investigate this, they took cores of sand at eight different beach sites and counted the number of crabs in each core to estimate the density of mole crabs. They also recorded the density of seagulls, characteristics and size of the beach, the distance from the beach to the nearest port and the distance to the nearest freshwater outlet. The crabs from the sand cores were taken back to the lab to be measured and dissected to determine the presence and abundance of the worms in each individual.

The researchers found that the body size of the mole crabs had the most prominent effect on Profilicollis altmani infection levels, with larger individuals having higher parasite prevalence and abundance. They also found that mole crabs were often infected with more than just one species of helminth. 

Additionally, they discovered that as crab density increased, Profilicollis altmani parasite prevalence decreased. The research team believes this could be due to an encounter-dilution effect, meaning that large groups of crabs are more protected from parasites because it lowers the chance of an individual mole crab coming in contact with a worm.

While environmental effects may be able to influence parasite prevalence in some cases, researchers did not find any evidence that was the case for helminth prevalence in mole crabs within their study. The results of this study shed more light on the role of environmental factors in the dynamics of helminth transmission from seagulls to mole crabs and provide insight on disease transmission more broadly. Future research may be able to tease out environmental factors that do demonstrate a significant impact on helminth abundance.

For more information on this study, click here.

By Amanda Budd