Effects of Parasitic Crustacea on Hosts

This chapter summarises our understanding of the direct effects that parasiticcrustaceans have on their invertebrate and vertebrate hosts. At the individual hostlevel, the effects of infection with parasitic Crustacea with respect to host pathologicalchanges 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 arisingfrom studies of sea lice (caligid copepods) infections of salmonids. Quantifyingsublethal impacts of parasitic Crustacea infection on the biology and ecology of hostsis especially challenging even under controlled laboratory conditions. This is due to thecomplex and poorly understood interactions between parasite, host and environmentaldeterminants, which ultimately influence the outcome and magnitude of the effect.There is very limited information on the effects that parasitic Crustacea have on theirhosts at a population level, as well as on the indirect effects that they may have onspecies that interact with their hosts (community level effects). Our relatively goodunderstanding of effects of sea lice on salmonids has been brought about due to thelarge economic impact that these parasites have on farmed salmonids and the necessityto develop new methods for their control. Unfortunately, the progress for other parasitesand hosts is much slower which is in part due to the lack of experimental systems,research tools and funding