Scavenging amphipods of the Angolan deep-sea habitat, with a focus on Abyssorchomene distinctus (Birstein and Vinogradov, 1960) (Amphipoda: Lysianassoidea)

Abstract

Owing to its vast natural resources and the influence of the Congo River and associated submarine canyon, the Angolan continental margin is of both socioeconomic and ecological interest. The deep-sea ecosystems of the region are nevertheless understudied, and much of the deep-sea fauna remains undescribed. Here, we document the scavenging amphipods of the Angolan deep-sea habitat, which provides valuable new insights into the ecology of Angolan deep-sea scavengers. This can be used as an ecological baseline, against which resource-extraction impacts can be measured. A total of 7996 scavenging amphipods, representing 10 species, were identified. At least four species were new to science. The relatively low scavenger diversity of the region, combined with the large sample sizes, may be indicative of abundant food falls in the region due to the presence of the submarine canyon system. The dominant species across all samples, Abyssorchomene distinctus (Birstein and Vinogradov, 1960), was the focus of a population-level study, which was used to describe the population structure of this species and identify species traits. Of the 826 individuals of A. distinctus dissected and measured, 533 were unsexed juveniles, 149 were male, and 144 were female. Females were significantly larger than males, which is indicative of non-mate-guarding pre-copulatory behaviour, but had significantly shorter antennae, which may indicate that males use chemical cues during mate searching. Two, three, and five discrete size-based cohorts were identified for juveniles, males, and females respectively. No ovigerous females were caught but brood size of A. distinctus was estimated to be 10-38 offspring based on ovary contents.

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