Ocean-scale connectivity and life cycle reconstruction in a deep-sea fish

Abstract

As human exploration and harvesting moves to the high seas, ecological understanding of the deep sea has become a priority, especially in those commercially exploited species whose life cycle, habitat use, and demographic structure remain poorly understood. Here we combine otolith trace element and stable isotope analyses with microsatellite data to investigate population structure and connectivity in the migratory deep-sea black scabbardfish (Aphanopus carbo), sampled along a latitudinal gradient spanning much of the known species range in the Northeast Atlantic. In each sampled life stage, otolith trace element and oxygen isotope compositions are similar among fish from different capture locations, but otolith compositions vary greatly between life stages. Oxygen isotope compositions indicate ontogenetic migrations from relatively warm water conditions during larval growth to cooler waters with increasing age. Analysis of microsatellite DNA also suggests lack of genetic structure among the areas sampled. The multidisciplinary approach employed collectively suggests that A. carbo individuals undergo an ocean-scale ontogenetic migration, beginning with spawning in southern, warm-water Macaronesian areas (potentially dominated by Madeira), followed by a large proportion of immature fish moving to and feeding on the continental slope in northern areas. The results lend the first conclusive evidence for defining the life-history circuit of this species and the perception of its stock structure across the North Atlantic.

Ecogeochemistry potential in deep time biodiversity illustrated using a modern deep-water case study

“…In A. carbo, for all life stages, a strong overlap in otolith elemental composition is evident across locations, suggesting overall panmixia in this highly mobile deep-sea species. This was supported by microsatellite DNA analyses, indicating a lack of substructure and absence of distinct biological populations, with divergence statistics implying that putative populations are effectively exchanging several hundred or more individuals per generation [23]. By contrast, separate populations of C. rupestris display chemically distinct trace element compositions [24], implying a lack of connectivity between populations.…”

“…C. rupestris grows to greater than 100 cm and feeds predominantly on amphipods and copepods as a juvenile, becoming increasingly piscivorous with size [29,30]. Trace element compositions have been determined across otoliths from A. carbo and C. rupestris sampled from multiple areas across the northeast Atlantic ( [23,24], figure 2c). In A. carbo, for all life stages, a strong overlap in otolith elemental composition is evident across locations, suggesting overall panmixia in this highly mobile deep-sea species.…”

“…Additional otolith isotope profiles are reported for the orange roughy (Hoplostethus atlanticus) [46] and the black scabbard (Aphanopus carbo) [23]. Among the six species sampled, only A. rostrata has no relatively shallow larval phase.…”

The Pillars of Hercules as a bathymetric barrier to gene flow promoting isolation in a global deep‐sea shark (Centroscymnus coelolepis)

“…; Longmore et al . ). However, there are a few notable exceptions of genetic differentiation, as in the roundnose grenadier (Knutsen et al .…”

Pelagic early life stages promote connectivity in the demersal labrid Choerodon rubescens

“…This assumption has, however, rarely been tested, partly because it is very difficult to disentangle the relative contributions of the different life-cycle stages to dispersal (Selkoe and Toonen, 2011). Some recent studies have, however, used data from complementary methods to assess these contributions (e.g., Berry et al, 2012aBerry et al, , 2012bLongmore et al, 2014;Schmidt et al, 2011), and have provided support for the above assumption. For example, the combined results of genetic, otolith microchemistry and particle modelling analyses indicate that the pelagic ELS of the West Australian Dhufish Glaucosoma hebraicum disperse relatively widely, while the adults and juveniles are fairly sedentary (Berry et al, 2012a;Fairclough et al, 2013).…”