Trophic interactions among the macrofauna of the deep-sea hydrothermal vents of Alarcón Rise, Southern Gulf of California

Abstract

The Alarcón Rise (AR) hydrothermal system recently discovered in the Southern Gulf of California is characterized by the presence of black smokers, fluids with temperatures up to 360 °C, high concentrations of metal-sulfides and H2S. The trophic structure and the energy flow in the vent community were determined through the carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) isotopic signatures of 19 macrofaunal species. The δ13C values had an ample range from −36 and −8‰, reflecting a wide variety of carbon sources and the predominance of organic carbon fixed through the reductive tricarboxylic acid cycle (rTCA). The δ15N values varied from −7.9 and 18‰, corresponding to primary and secondary consumers, and the most enriched value (18‰) to a non-vent organism. Dominant organisms included primary consumers such as symbiont-bearing, and bacterivores, which revealed the importance of the bacterial consortium in the energy transfer. Secondary consumers comprised scavengers/detritivores, the most diverse guild, and predators, rather scarce. The δ34S values were between −14.5 and 15.6‰, indicating the assimilation of magmatic sulfur in the vent-fauna, and the complementary assimilation of photosynthetically derived organic matter in the non-vent organisms, hinted by their highest value (15.6‰). Interestingly, an unidentified Actiniaria anemone displayed anomalously depleted δ13C values (−30.4‰), reflecting a potential symbiotic relationship with sulfur-oxidizing endobacteria.