Spatial variations of ascidian diets in a glacial retreated fjord of the West Antarctic Peninsula.

Abstract

The impacts of glacial retreat on diets of ascidians, one of the filter feeders and a major component of the benthic-pelagic energy pathway, remain unclear. We analyzed carbon and nitrogen stable isotopes of four dominant ascidian species and five potential food sources in Marian Cove, a deglaciating fjord in West Antarctica. Microphytobenthos was a major food source for ascidians regardless of proximity to the glacier, but phytoplankton contribution decreased closer to the glacier. Particularly near the glacier, microphytobenthos formed visible bushes on the surface of ascidians providing an easily accessible potential food source. The diet of Molgula pedunculata changed with spatial variations in food sources influenced by glaciers, whereas Cnemidocarpa verrucosa, which exhibits a squirting behavior, showed a consistent diet primarily contributed by microphytobenthos regardless of glacial impact. These results provide necessary information for understanding the impact of climate change-induced glacial retreat on the diet of ascidians, a dominant taxon in the Antarctic coast.