Obligate hydrothermal vent fauna at East Diamante submarine volcano (Mariana Arc) exploit photosynthetic and chemosynthetic carbon sources

Two volcanic cones in the degraded caldera of East Diamante submarine volcano (Mariana Arc) were surveyed and sampled in April 2004 as part of the ‘Submarine Ring of Fire 2004’ expedition. The first images revealed hydrothermal venting within the photic zone and a striking overlap between chemosynthetic and photosynthetic communities. We used fatty acid biomarkers and bulk stable isotopes to determine the relative importance of chemosynthetic and photosynthetic material in the diets of invertebrates at 6 vent sites (Eastern Cone: Barnacle Beach and Black Forest; Central Cone: Floc Storm, Boulder Vent, Mid-cone, and Fe-Mn Crust) and 1 non-vent site (Central Cone: Aquarium). Principal components analysis revealed depth-related dietary differences: vent-obligate invertebrates at Barnacle Beach (~460 m) belonged to a purely chemosynthetic food web, non-vent organisms at Aquarium (179 m) had diets based on the products of photosynthesis, and most of the invertebrates at Black Forest (349 m) and Central Cone vent sites (247-288 m) had mixed chemosynthetic/photosynthetic diets. Carbon stable isotope ratios corroborated the photosynthetic input in the diets of the vent-obligate invertebrates. Long-chain polyunsaturated fatty acids were found in overlying waters and in detritus. We suggest that photosynthetic material arrives at East Diamante in the form of marine snow. Photic zone hydrothermal venting has now been found on several arc volcanoes in the western Pacific Ocean. Our study underscores the potential influence of benthic-pelagic coupling on trophic interactions and community structure for vent-obligate species in such settings.