Freshwater eels: A symbol of the effects of global change

Abstract

Temperate eels Anguilla anguilla (European eel), A. rostrata (American eel) and A. japonica (Japanese eel) are three catadromous species which have been declining since the 1970s/1980s despite their remarkable adaptive capacity. Because of their specific life cycles, which share distant oceanic spawning grounds and continental growth stage, eels are affected by five components of the global change: (a) climate change affecting larval survival and drift, (b) an increase in pollution leading to high levels of contamination exacerbated by their high lipid levels, (c) increasing fragmentation and habitat loss that reduce dramatically the amount of available habitats and induce increased spawner mortality, (d) the appearance of Anguillicola crassus a parasitic alien nematode that impairs spawning success, and (e) the impact of commercial and recreational fisheries for all life stages of eel. In this context, the rapid increases of pressures during the “Great Acceleration” have surpassed the adaptive capacity of eels. This illustrates that cumulative effects of global change can lead to the collapse of species, even in species that have amazingly high adaptive capacities.

Gene expression response to a nematode parasite in novel and native eel hosts

“…The European eel is undergoing catastrophic population declines, and infection with A. crassus could be one of the contributing factors (Drouineau et al, ). Based on comparison of the number and diversity of differentially expressed genes with the Japanese eel, we conclude that the European eel has not adapted to A. crassus .…”

“…Infection intensities measured in natural populations (Audenaert et al, ; Gérard et al, ; Heitlinger et al, ; Knopf, ; Münderle et al, ) and in experimental individuals several weeks after an infection was established (Knopf & Lucius, ; Knopf & Mahnke, ) indicate greater susceptibility by the novel host, the European eel. The population of the European eel has undergone catastrophic declines (Bornarel et al, ; Diekmann et al, ; ICES, ), and A. crassus infections have been implicated (Drouineau et al, ; Sures & Knopf, ). We found similar infection intensities in the two eel species 23 days after experimental infection, at which time larval parasites had finished migrating to the swim bladder, and we did not find any dead larvae.…”

“…A number of species of eels are threatened (Jacoby et al, 2015), and nonnative parasites in their freshwater habitat have been proposed as a contributing factor in their decline (Drouineau et al, 2018;Miller, Feunteun, & Tsukamoto, 2016;Sures & Knopf, 2004). The parasitic swim bladder nematode Anguillicola crassus Kuwahara, Niimi & Hagaki, 1974 was introduced into Europe from Southeast Asia where it is native to the Japanese eel (Anguilla japonica Temminck & Schlegel, 1846; Figure 1).…”

Age of European silver eels during a period of declining abundance in Norway

“…Recruitment to freshwater habitats decreased by more than 90% in the early 1980s, and since 2008, the European eel has been listed as critically endangered on the International Union for Conservation of Nature (IUCN) red list (Jacoby & Gollock, 2014). Causes for the decline are related to habitat loss, hydropower, overfishing, climate change, pollution, parasites, and diseases (Aschonitis et al, 2017; Castonguay & Durif, 2016; Drouineau et al, 2018).…”

Genetic variability and demographic history of Anguilla mossambica (Peters, 1852) from continental Africa and Madagascar

“…Habitat loss (Bevacqua et al ., ) as well as oceanic changes (Drouineau et al ., ) are considered to potentially influence population size of A. anguilla . Also comparable demographic histories of Atlantic A. anguilla and A. rostrata (Jacobsen et al ., ) and western South Pacific A. marmorata , Anguilla megastoma Kaup 1856, Anguilla obscura Günther 1972 and Anguilla reinhardtii Steindacher 1867 (Gubili et al ., ) have been described, albeit at time scales of 100–3000 kBP.…”