Trophic ecology, habitat, and migratory behaviour of the viperfish Chauliodus sloani reveal a key mesopelagic player

Abstract

Mesopelagic fishes are numerically the most important vertebrate group of all world’s oceans. While these species are increasingly threatened by anthropogenic activities, basic biological knowledge is still lacking. For instance, major uncertainties remain on the behaviour, ecology, and thus functional roles of mesopelagic micronektivores, particularly regarding their interactions with physicochemical features. Here, we examine the trophic ecology, habitat, and migratory behaviour of the viperfish (Chauliodus sloani)—a poorly known and abundant deep-sea species—to further understand the ecology and thus functional role of mesopelagic micronektivores. Moreover, we explore how physical drivers may affect these features and how these relationships are likely to change over large oceanic areas. The viperfish heavily preys on epipelagic migrant species, especially myctophids, and presents spatial and trophic ontogenetic shifts. Temperature restricts its vertical distribution. Therefore, its trophodynamics, migratory behaviour, and functional roles are expected to be modulated by the latitudinal change in temperature. For instance, in most tropical regions the viperfish stay full-time feeding, excreting, and serving as prey (e.g. for bathypelagic predators) at deep layers. On the contrary, in temperate regions, the viperfish ascend to superficial waters where they trophically interact with epipelagic predators and may release carbon where its remineralization is the greatest.

Distribution and diel vertical migration of mesopelagic fishes in the Southern Sargasso Sea — observations through hydroacoustics and stratified catches

“…The here presented catches of stomiids reflected their known distribution and migration pattern as previously reported by Kenaley (2008) species. This corroborates accumulating evidence from oligotrophic, but also productive regions, that these species, despite remaining likely invisible in hydroacoustic recordings, contribute considerably to vertical energy fluxes (Cook et al 2013;Eduardo et al 2020a;Czudaj et al submitted). Sternoptychidae in general are considered limited or only partial migrants (Kinzer and Schulz 1988) and usually occur preferentially in deeper layers, although some shallower occurrences can be observed during night hauls, especially in oligotrophic regions as shown for the south western Atlantic (Olivar et al 2017;Eduardo et al 2020b).…”

Trophic indices for micronektonic fishes reveal their dependence on the microbial system in the North Atlantic

“…In our study, migrant fishes had higher trophic position values than non-migrants, but both migrant and non-migrant species distributed in the bathypelagic layer had also higher TP than those in the upper layer. Other studies also noted this increase in TP with migration and depth distribution which was attributed to the access to a larger variety of prey and the predominance of piscivory in deep layers 24 , 25 , 28 , 30 . Correspondingly, our metazoan TP estimates for species distributed in the bathypelagic layer were always above 2.5, indicating they were secondary consumers, although the values for the gonostomatid Cyclothone microdon (mean ± s.d.…”

“…This study shows that niche separation in micronektonic fishes is due to the vertical habitat range rather than to migration. The large niche overlap of migrant and non-migrant species can be expected because the feeding strategies of the species take advantage of different resources in each depth layer 24 , 30 , 31 . In turn, differences in stable isotopes between depth layers can be attributed to the vertical separation of resources, as δ 15 N and δ 13 C increase with depth consistently with a major reworking of the settling organic matter 43 .…”

“…They dominate the biomass of consumers 19 and the transfer of energy from zooplankton to higher trophic levels 20 , 21 . While their abundance is higher in the mesopelagic domain (200–1000 m depth), the distribution of the different species, including those performing diel vertical migrations also covers the epipelagic (0–200 m), bathypelagic (1000–4000 m) and even abyssopelagic (> 4000 m) layers 22 – 24 . Therefore, they provide a privileged opportunity to study trophic connections across the ocean.…”

“…Their trophic position varies within relatively narrow limits as some species are mostly planktivores 20 , 25 – 28 or piscivores 20 , 25 , 29 , 30 , while increasing significantly with individual size 20 , 25 , 27 . In addition, there is evidence of different feeding strategies for active migrants vs. opportunistic, non-migrant species 24 , 30 , 31 .…”