Effects of Parasitic Crustacea on Hosts

Abstract

This chapter summarises our understanding of the direct effects that parasitic crustaceans have on their invertebrate and vertebrate hosts. At the individual host level, the effects of infection with parasitic Crustacea with respect to host pathological changes and the development of disease states are reasonably well understood. However, we have a much poorer understanding of how infection affects the physiological, immunological and reproductive status of hosts, with much of what is known arising from studies of sea lice (caligid copepods) infections of salmonids. Quantifying sublethal impacts of parasitic Crustacea infection on the biology and ecology of hosts is especially challenging even under controlled laboratory conditions. This is due to the complex and poorly understood interactions between parasite, host and environmental determinants, which ultimately influence the outcome and magnitude of the effect. There is very limited information on the effects that parasitic Crustacea have on their hosts at a population level, as well as on the indirect effects that they may have on species that interact with their hosts (community level effects). Our relatively good understanding of effects of sea lice on salmonids has been brought about due to the large economic impact that these parasites have on farmed salmonids and the necessity to develop new methods for their control. Unfortunately, the progress for other parasites and hosts is much slower which is in part due to the lack of experimental systems, research tools and funding.