Benthic Communities on Lo'ihi Submarine Volcano Reflect High-Disturbance Environment

Abstract

Bottom surveys and collections on Lo'ihi Seamount, Hawai'i, revealed two distinct and recurrent benthic communities. One comprises bacterial mats and is closely associated with hydrothermal vents. The other consists of dense aggregations of megabenthos-octocorals, sponges, hydroids, and black corals-all normal inhabitants of nonvolcanic hard-bottom habitats at comparable depths in the Hawaiian Islands. The bacterial mats are devoid of specialized megafauna and are found in summit areas or rift peaks where diffuse low-temperature hydrothermal vents are common. The absence of megafauna there may be due to extreme environmental conditions produced by vent waters that contain no oxygen and extraordinarily high concentrations ofCO2 (pH = 5.5) and trace metals. At greater depths, from 200-300 to 1,000m below the summit, dense aggregations of gorgonians and other megafauna exist but are uncommon. Aggregations are restricted to stable outcrops of pillow basalts (kipukas). Surrounding areas are covered by talus and are virtually devoid of benthic organisms. Their rarity may be due to instability of the substratum caused by frequent slumping and debris avalanching (mass wasting). Both bacterial mat and deep flank megabenthic communities reflect a high-disturbance environment.