Crustaceans as Intermediate Hosts in the Life Cycles of Parasites

Abstract Many parasitic worms, or helminths, have evolved complex life cycles in which juvenile stages infecting an intermediate host must be transferred trophically to a definitive vertebrate host. The generally small-to-medium body sizes of crustaceans favor their role as primary or secondary consumers in food webs, making them ideal intermediate hosts for helminths and perfect vehicles for their prey-to-predator transmission. This chapter reviews the life cycles and biology of the four major taxa of helminths using crustaceans as intermediate hosts: acanthocephalans, nematodes, trematodes, and cestodes. The zoonotic helminth taxa that parasitize crustaceans before infecting humans are highlighted, followed by a summary of the most frequently studied helminth-crustacean associations. The many impacts of helminth parasites on crustacean biology range from effects on individual behavior and fitness, to potentially major influences on population dynamics and community structure and composition, especially when acting in combination with other stressors such as rising temperatures. There is currently little information available on biogeographic patterns in helminth infections of crustaceans, and there are glaring gaps in our knowledge of, and research on, helminth parasitism of crustaceans; brief suggestions for promising research directions to address these issues are given. The take-home message of this chapter is that parasites matter; they can affect multiple aspects of the physiology, behavior, survival, population biology, and community ecology of their crustacean hosts. All crustacean biologists should be strongly encouraged to take them into account in their future research.