Biogeographic distribution of the eel Anguilla luzonensis: dependence upon larval duration and oceanic currents

Abstract

Anguilla luzonensis, a recently identified tropical Anguilla species, was categorized as 'Near Threatened' in the International Union for Conservation of Nature (IUCN) Red List in 2014. However, its biogeographic distribution and dispersal mechanism remain unconfirmed. This study aimed to clarify the biotic and abiotic factors that may shape the eel's dispersal range, which could help to establish suitable conservation strategies. Glass eel distribution was investigated in Taiwan, Luzon, Mindanao, and Sulawesi. A. marmorata was used as a reference eel species for comparison. Although both species were found year-round, A. marmorata was found in all locations and was abundant at most sites. However, A. luzonensis was concentrated only on Luzon Island, mainly between June and October. It was rarely observed in Taiwan and Mindanao, and was not found in Sulawesi. The spawning site of A. luzonensis is probably located more northward in the North Equatorial Current (NEC), whereby the eel larvae avoid entering the Mindanao Current (MC). In addition, A. luzonensis typically spawns between February and May, and is preferentially transported into the Kuroshio from May to August, when the NEC bifurcation latitude reaches its southernmost position and the Kuroshio transport volume peaks. Furthermore, A. luzonensis has a shorter/narrower range of larval duration than A. marmorata, and its dispersal distance is therefore restricted. The life history traits of A. luzonensis, together with the oceanic current regime, may act together to concentrate its biogeographic distribution on Luzon Island.

The ecology of oceanic dispersal and survival of anguillid leptocephali

“…If true, this species has a unique larval 0°20°W 40°W 60°W 80°W 10°E 0°20°W 40°W 60°W 80°W dispersal and recruitment pattern compared with both A. japonica and A. marmorata because it appears to have a very narrow species range centered on the northern Philippines according the lack of its detection in other areas in studies using genetic identification of specimens (e.g., Kuroki et al 2014;Han et al 2016). The sampling surveys conducted in the northern Indonesian Seas region have indicated that anguillid leptocephali are usually present but not at high abundances.…”

Location, size and age at onset of metamorphosis in the Japanese eel Anguilla japonica

“…Therefore, metamorphosis at a younger age results in migration to lower latitudinal growth habitats. This mechanism could also explain the difference in biogeographic distribution between the A. japonica and Anguilla luzonensis Watanabe, Aoyama & Tsukamoto 2009, individuals of which are spawned in the vicinity of A. japonica and are also transported with the NEC and Kuroshio Current (Han et al, ). Unlike A. japonica , which is distributed widely across East Asia, A. luzonensis tends to be concentrated in the southernmost part of East Asia around Luzon Island due to its short and narrow range of larval duration (Han et al, ).…”

“…This mechanism could also explain the difference in biogeographic distribution between the A. japonica and Anguilla luzonensis Watanabe, Aoyama & Tsukamoto 2009, individuals of which are spawned in the vicinity of A. japonica and are also transported with the NEC and Kuroshio Current (Han et al, ). Unlike A. japonica , which is distributed widely across East Asia, A. luzonensis tends to be concentrated in the southernmost part of East Asia around Luzon Island due to its short and narrow range of larval duration (Han et al, ). Similarly, although the leptocephalus distribution and spawning area of Anguilla marmorata Quoy & Gaimard 1824 overlap with those of the A. japonica (Miller et al, ; Kuroki et al, ), there are latitudinal differences in their growth habitats, probably due to differences in their larval durations (Leander et al ., ).…”

Ecology and evolution of migration in the freshwater eels of the genus Anguilla Schrank, 1798

“…The spawning occurred through the whole year in several tropical eel species ( Arai et al., 2001 ; Shiao et al., 2002 ; Arai et al., 2016 ; Arai and Abdul Kadir, 2017a ). The year-round spawning together with constant early growth during the oceanic period throughout the year, expand the recruitment period to continental habitats throughout the entire year for tropical anguillid eels ( Beumer and Sloane, 1990 ; Arai et al., 1999b ; Sugeha et al., 2001 ; Han et al., 2012b , 2016a ; Leander et al., 2012 ; Aoyama et al., 2015 ; Hewavitharane et al., 2018 ). The continuous spawning migration may stimulate breeding with different cohorts (year classes) or divergent habitats within the population.…”

“…The lengthy duration of the larval stage might lead to global dispersion and their consequent speciation. The durations of leptocephalus stages span from several months to approximately two years (e.g., Tsukamoto, 1990 ; Lecomte-Finiger, 1992 ; Cheng and Tzeng, 1996 ; Arai et al., 1999a , 2001 ; 2003a ; Wang and Tzeng, 2000 ; Marui et al., 2001 ; Robinet et al., 2003a ; Robinet et al., 2008 ; Réveillac et al., 2008 , 2009 ; Bonhommeau et al., 2010 ; Han et al., 2016a , 2019 ; Hewavitharane et al., 2020 ). Many marine organisms have a planktonic larval stage during their early life and larvae are passively transported by oceanic currents.…”