Abstract
Hadal trenches are isolated habitats that cover the greatest ocean depths (6,500–11,000m) and are believed to host high levels of endemism across multiple taxa. A group of apparent hadal endemics is within the snailfishes (Liparidae), found in at least five geographically separated trenches. Little is known about their biology, let alone the reasons for their success at hadal depths around the world. This study investigated the life history of hadal liparids using sagittal otoliths of two species from the Kermadec (Notoliparis kermadecensis) and Mariana (Pseudoliparis swirei) trenches in comparison to successful abyssal macrourids found at the abyssal-hadal transition zone. Otoliths for each species revealed alternating opaque and translucent growth zones that could be quantified in medial sections. Assuming these annuli represent annual growth, ages were estimated for the two hadal liparid species to be from five to 16 years old. These estimates were compared to the shallower-living snailfish Careproctus melanurus, which were older than described in previous studies, expanding the potential maximum age for the liparid family to near 25 years. Age estimates for abyssal macrourids ranged from eight to 29 years for Coryphaenoides armatus and six to 16 years for C. yaquinae. In addition, 18O/16O ratios (δ18O) were measured across the otolith using secondary ion mass spectrometry (SIMS) to investigate the thermal history of the three liparids, and two macrourids. Changes in δ18O values were observed across the otoliths of C. melanurus, C. armatus, and both hadal liparids, the latter of which may represent a change of >5°C in habitat temperature through ontogeny. The results would indicate there is a pelagic larval stage for the hadal liparids that rises to a depth above 1000m, followed by a return to the hadal environment as these liparids grow. This result was unexpected for the hadal liparids given their isolated environment and large eggs, and the biological implications and plausibility of interpretations of these data are discussed. This study presents a first look at the life history of some of the deepest-living fishes through otolith analyses.
Highlights
Hadal trenches cover the greatest ocean depths (6500–11,000 m) and have a distinct fauna from the surrounding deep-sea environment with high apparent levels of endemism (Wolff, 1959; Beliaev, 1989; Jamieson, 2015)
This study investigated the life history of hadal liparids using sagittal otoliths of two species from the Kermadec (Notoliparis kermadecensis) and Mariana (Pseudoliparis swirei) trenches in comparison to successful abyssal macrourids found at the abyssal-hadal transition zone
Age estimates based on opaque zones in otolith thin sections for Coryphaenoides armatus and C. yaquinae were lower than may have been expected from bathyal species, but growth rates may be slow (e.g. Andrews et al, 1999a; Drazen and Haedrich, 2012)
Summary
Hadal trenches cover the greatest ocean depths (6500–11,000 m) and have a distinct fauna from the surrounding deep-sea environment with high apparent levels of endemism (Wolff, 1959; Beliaev, 1989; Jamieson, 2015). A characteristic endemic group known as the snailfishes (Family Liparidae) are prominent members of the hadal community in at least five widely-distributed trenches (Japan, Kermadec, Kurile-Kamchatka, Mariana, and Peru-Chile; Nielsen, 1964; Jamieson et al, 2009; Fujii et al, 2010; Linley et al, 2016). These hadal fishes are notably different from common abyssal species that border the hadal zone in both form and functional role. Observations of large aggregations of these snailfishes that are similar in form, at similar depths, and yet widely dispersed geographically in the seemingly isolated hadal systems, frames the question—why are liparids so successful in the hadal zone?
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