Phyto-detritus feeding by early-stage larvae of Electrona antarctica(Myctophidae) off Wilkes Land in the Southern Ocean, austral summer 2017

摘要

Myctophid fish function as a significant trophic link between zooplankton and higher predators in the oceanic ecosystems of the Southern Ocean. Although Electrona antarctica is one of the most abundant myctophids in the Southern Ocean, its early life history remains unclear. We analysed the food composition and details of gut contents of larval E. antarctica (5.0-11.9 mm standard length) using both light microscopy and scanning electron microscopy. Larvae were collected in January 2017 off Wilkes Land, East Antarctica. Detailed observations showed that the larvae fed mainly on aggregated particles composed largely of diatom frustules and diatom fragments (phyto-detritus); however, the species feeds mainly on zooplankton after completion of the larval stage. We found, on average, 1.5 phyto-detrital particles per individual and 0.15 zooplankton particles per individual among early-stage larvae. Phyto-detritus was found in 47% of the larval guts analysed. Separated intact diatom frustules were rarely found, and the numbers were negligible. Twenty-nine percent of aggregates contained shreds of larvacean filters. Thus, larval E. antarctica feeds mainly on phyto-detritus, sinking particles containing larvacean houses and other aggregated particles. We also concluded that, unlike observations from previous studies, zooplankton were a less important food source for the early-stage larvae. This study provided fundamental knowledge about diet of biomass-dominant myctophid fish during the early larval stage, which contributes to our understanding of the life history of E. antarctica and also to oceanic food webs in the Southern Ocean.