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Fisheries
INTRODUCTION
How parasites affect fisheries is of immediate and significant economic and social relevance. The converse, how fisheries affect parasites, receives less attention. Here, we present the results of a meta-analysis that suggests fishing can alter aquatic parasite assemblages, and we argue that these changes can indirectly alter ecosystem function and its associated services.
Why should we care whether fishing alters parasite communities? In certain circumstances, parasites can regulate host populations (e.g. Hudson et al. 1998) and mediate the species composition of free-living communities (e.g. Mouritsen and Poulin, 2005; Wood et al. 2007). There is also an increasing awareness that parasites can shape entire aquatic food webs (e.g. Lafferty et al. 2008a ). Parasites are extremely diverse: at least 40% of animal species are parasitic (Dobson et al. 2008), as are the majority of species in 27 of the 42 recognized animal phyla (Poulin and Morand, 2000; deMeeus and Renaud, 2002). In some aquatic ecosystems, parasites can comprise a large proportion of total biomass, surpassing the biomass even of top predators in estuarine salt marshes (Kuris et al. 2008) and insects in freshwater ponds (Preston et al. 2013). In addition to representing a large proportion of food web nodes and of the biomass within those nodes, parasites can also account for a large proportion of the linkages between nodes: in an analysis of four food webs, parasite-host links outnumbered predator-prey links (Lafferty et al. 2006), and parasites increased food web connectance (Lafferty et al. 2006), with implications for overall food web stability (Dunne et al. 2002). Parasites might also influence the strength of linkages between their hosts and other species by affecting host growth, survival, behaviour, reproductive investment and competitive ability (Lafferty, 2008). A common adaptation of many parasites is to manipulate host behaviour to facilitate transmission, particularly by inducing behaviours in an intermediate host that make it susceptible to predation by a definitive host (Moore, 2002). Because such trophically transmitted parasites are common in aquatic ecosystems (Marcogliese, 2002b ), it is possible that this manipulation is widespread; if so, parasites might broadly increase the interaction strength of predator-prey relationships that would otherwise be weak, with implications for the abundance, biomass and population dynamics of...