The trophic structure of fauna and photosynthetic influence at two distinct hydrothermal vent fields on the Mid-Cayman Rise

The two known deep-sea hydrothermal vent fields along the Mid-Cayman Rise are separated by a distance of only 21 km, yet their chemistry and faunal diversity are distinct. The deeper of the two vent fields, Piccard (with active venting from Beebe Vents, Beebe Woods and Beebe Sea), at 4960 m is the deepest known vent field on Earth and is basalt hosted. The shallower vent field, at 2300 m appears to have an ultramafic influence. The diversity of the fauna at Von Damm is greater than that at Piccard, though there is still an overlap in certain species. The two vent fields have been selected as analogues to systems that may exist elsewhere in our solar system due to their potential lack of influence from photosynthetic carbon (Piccard) and their potential for abiotic carbon synthesis (Von Damm). In this study we have examined the bulk carbon, nitrogen and sulfur isotope composition of fauna at each vent field and carried out compound specific carbon isotope analysis on select species. With these data we have deduced the trophic structure of the communities and potential influence of photosynthetic carbon. The diversity of the Von Damm fauna, including the unexpected presence of tubeworms, shows distinct variations in sulfur isotope composition and we will discuss the potential for source variation and fractionation during sulfur assimilation. As analogues, the Piccard vent field provides the most photosynthetically detached system currently known on Earth and the distinct sulfur isotope signatures as well as compound specific isotopes may provide important biomarkers for detection of current or previous hydrothermal activity elsewhere in our solar system.