Fine-Scale Natural Variability of Community Distribution on a Low Temperature Discharge Outcrop of a Ridge Flank Hydrothermal System

Fine-scale mapping of macrofaunal communities on low-temperature vent-systems is unknown, yet critical for exploring how environmental parameters shape community distributions. A second comparable discharge outcrop lacks the fine-scale mapping data that enables assessment of the natural variability in community structure, however many others likely exist in the deep sea, setting the paramount need to assess the community distribution on a discharge outcrop of a Ridge Flank Hydrothermal System (RFHS). This study focuses on two mapping and reconnaissance expeditions on Dorado Outcrop. The R/V Atlantis in 2013 and 2014 deployed ROV Jason, AUV Sentry, and HOV Alvin to collect a uniquely diverse and voluminous set of video and environmental data used to determine faunal communities and relate environmental parameters to their distribution on this RFHS. In this study, environmental and observational data from Dorado, an elongated 1-km², 0.15-km tall, 3-km deep outcrop, 177-km from Costa Rica, are used to characterize biodiversity and identify trends in community distribution with respect to environmental parameters: depth, discharge sites, substrate type, and temperature. Intermittent fluid discharge from three sites on Dorado has a maximum-recorded temperature of 12°C and depleted dissolved oxygen concentrations, but is otherwise chemically indistinguishable from background bottom water. Preliminary results indicate that in areas directly associated with fluid discharge, community presence is sparse. Eight phylum types present on the outcrop are Annelida, Arthropoda, Chordata, Cnidaria, Echinodermata, Mollusca, Nematoda, and Porifera. This study fills our knowledge gap about the diversity and distribution of communities and their associated environmental parameters. Furthermore, results from this study will aid in predicting the presence of similar communities where only environmental data is available and in predicting the effect of warming on the occurrence of fauna.