Long-term change in the parasite burden of shore crabs ( Hemigrapsus oregonensis and Hemigrapsus nudus ) on the northwestern Pacific coast of North America

Abstract

The abundances of free-living species have changed dramatically in recent decades, but little is known about change in the abundance of parasitic species. We investigated whether populations of several parasites have shifted over time in two shore crab hosts, Hemigrapsus oregonensis and Hemigrapsus nudus, by comparing the prevalence and abundance of three parasite taxa in a historical dataset (1969–1970) to contemporary parasite abundance (2018–2020) for hosts collected from 11 intertidal sites located from Oregon, USA, to British Columbia, Canada. Our data suggest that the abundance of the parasitic isopod Portunion conformis has varied around a stable mean for the past 50 years. No change over time was observed for larval acanthocephalans. However, larval microphallid trematodes increased in prevalence over time among H. oregonensis hosts, from a mean of 8.4–61.8% between the historical and contemporary time points. The substantial increase in the prevalence of larval microphallid trematodes could be owing to increased abundances of their bird final hosts, increased production of parasite infective stages by snail intermediate hosts or both. Our study highlights the variability among parasite species in their temporal trajectories of change.

Worms of change: anthropogenic disturbance changes the ectoparasite community structure of Lake Victoria cichlids

“…Parasite populations are declining in Lake Victoria and elsewhere (Russell et al 2015, MacKenzie and Pert 2018, Wood et al 2023). However, this trend cannot be generalized, as the direction of change (if any) can vary between parasite taxa even within the same study (Howard et al 2019, Fiorenza et al 2020b, Quinn et al 2021, Welicky et al 2021). A decline in abundance is mostly observed in ectoparasites and in parasites with more than one host than endoparasites and parasites with one host (Carlson et al 2017, Vanhove et al 2022, Wood et al 2023).…”

Opening a can of worms: Archived canned fish fillets reveal 40 years of change in parasite burden for four Alaskan salmon species

“…For marine parasites, there are few data sources that can be used to reconstruct information about past abundances (Harmon et al., 2019 ; Wood & Vanhove, 2023 ). Comparing contemporary ecosystems to well‐studied ecosystems of the past by sampling the same sites with the same methodology has been effective (e.g., Quinn et al., 2021 ), but is constrained by the available data, which is contingent upon the interests of past researchers, sufficient documentation, and data retention. Local and Indigenous ecological knowledge can extend historical baselines farther back in time (e.g., Jessen et al., 2022 ), and in some cases can provide insights into changes in parasite abundance (Tomaselli et al., 2018 ), but to our knowledge such methodology has yet to be successfully applied to parasites in marine systems, and so associated limitations are not well‐understood.…”

How to use natural history collections to resurrect information on historical parasite abundances

“…Datasets that reproducibly document parasite abundances in the recent past are rare, and the few that exist pertain to just a handful of species (e.g. Cort et al , 1960; Keas & Blankespoor, 1997; Byers et al , 2016; Howard et al , 2019; Quinn et al , 2021). This handful represents just a tiny fraction of the total number of parasite species on Earth; the helminth endoparasites of vertebrates alone number between 100,000 and 350,000 species (Carlson et al , 2020b).…”