Functional and life-history traits in deep-sea fishes

Abstract

The deep sea is one of the largest ecosystems on the earth and fishes play an important role of transporting energy and structuring communities in the deep-sea ecosystem. However, the evaluation of functional and life-history traits (behaviours) in deep-sea fishes is challenging and problematic to directly study at sea. Therefore, this research investigates sensory capabilities from functional tissues in deep-sea fishes to identify functional groups and reconstruct vertical migration patterns and ontogenetic metabolic histories of representative species.
Visual fields and resolving power, indicated by the ganglion cells density and topography on the retina provide the information of diet preferences, habitats and space usage. Otolith morphology, i.e. the outline, the weight and sensory epithelium areas, displays acoustic and vestibular demands in feeding behaviours. These sensory abilities differ between pelagic- and benthic-foraging species or active and passive feeders, and show that depth exerts a stronger pressure on sensory adaptation in pelagic-foraging species. Pelagic foragers with visual-based hunting respond sensitively to the decrease of light intensity with increasing depth through enhanced visual acuity but are also released from the selective pressure of rapid swimming.
Ontogenetic growth, vertical migration and metabolism in four representative deep-water fishes (Alepocephalus bairdii, Antimora rostrata, Coryphaenoides rupestris and Spectrunculus grandis) are reconstructed by the otolith microstructure and stable oxygen and carbon isotopes, respectively. C. rupestris, S. grandis and other passive/benthic foraging fishes, have evolved interspecific consistency in life history traits, with common large-scale ontogenetic vertical migration, transformations of feeding behaviours between life stages and a dramatic decrease of mass-specific metabolism in the early life. In contrast, A.bairdii, A. rostrata and active/pelagic foraging species, develop diverse and inconsistent patterns. This study is first to combine morphological and geochemical data to identify functional and life-history traits, and the diverse datasets greatly aids classification where direct observation is difficult.

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ORCID for Clive Trueman: orcid.org/0000-0002-4995-736X

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