Feeding ecology of the anchialine caridean shrimp Halocaridinides trigonophthalma (Fujino & Shokita, 1975) (Decapoda: Caridea: Atyidae) on Ishigaki Island, Japan

Abstract

Anchialine ecosystems are brackish environments formed through subsurface connections between marine and freshwater inputs that are influenced by tidal fluctuations. These ecosystems encompass two habitat zones: an epigeal habitat at the surface and a hypogeal habitat underground. Organisms inhabiting aphotic hypogeal habitats often exhibit distinctive physiological adaptations. We examined the feeding ecology of Halocaridinides trigonophthalma (Fujino & Shokita, 1975), an atyid shrimp inhabiting hypogeal anchialine habitats in Japan, by integrating gut-content DNA metabarcoding with stable isotope analysis. DNA metabarcoding revealed that more than 50% of gut-content reads were assigned to terrestrial plants. At the study site, however, sediment was identified as a potential source of organic matter in addition to terrestrial plant fragments. We evaluated three candidate food sources (surface sediment, wood chips, and leaf litter) using stable isotope analysis. The isotope-based mixing results showed that H. trigonophthalma primarily assimilated sediment rather than terrestrial plant-derived material. Given that closely related atyid shrimps in photic environments rely on algal resources, this sediment-centered assimilation pattern likely reflects an adaptive trophic strategy for persistence in aphotic anchialine habitats.