Predation Structures Communities at Deep-Sea Hydrothermal Vents

Abstract

The structure and dynamics of natural communities result from the interplay of abiotic and biotic factors. We used manipulative field experiments to determine the relative roles of abiotic conditions and biotic interactions in structuring deep-sea (2500 m depth) communities along environmental gradients around hydrothermal vents of the eastern tropical Pacific Ocean (East Pacific Rise, at 9Њ50Ј N). We tested (1) whether predation by crabs and fishes affects the recruitment of benthic species and subsequent community structure and (2) whether the effects of predation vary along the steep gradients of temperature, oxygen, sulfide, and metal concentrations near vents. Recruitment substrates (basalt cubic blocks, roughly 10 cm on a side), both uncaged and caged to exclude predators (crabs, fishes, whelks, and octopi), were deployed along a decreasing vent fluid-flux gradient. The exclusion of predators for 8 mo increased the abundance of small mobile gastropods and amphipod crustaceans but decreased the abundance of sessile invertebrates, including juvenile vestimentiferan worms, tubiculous polychaetes, and mussels. Effects of predation were strongest nearest to hydrothermal vents, where abiotic environmental conditions were most extreme but productivity and the overall abundances of benthic invertebrates and mobile predators were the greatest. Additional 5-mo experiments conducted at three different locations showed similar trends at all sites, indicating that these effects of predation on benthic community structure are repeatable. Stomach-content analyses of the most abundant predators found at vents indicated that the zoarcid fish (Thermarces cerberus) primarily feeds on the vent snail Cyathermia naticoides, the limpet Lepetodrilus elevatus, and the amphipod crustacean Ventiella sulfuris, the very species that showed the greatest increase following predator exclusion. In contrast, brachyuran (Bythograea thermydron) and galatheid (Munidopsis subsquamosa) crab stomachs did not contain small mobile grazers, and crabs presented with arrays of the most common vent invertebrate species preferred mussels and vestimentiferans over limpets. Our results indicate that predation by large mobile predators influences the structure of hydrothermal vent communities, directly by reducing the abundance of gastropod prey species, and indirectly by reducing gastropod grazing and by bulldozing of recruits of sessile invertebrates.

Imprint of past environmental regimes on structure and succession of a deep-sea hydrothermal vent community

“…Just one species, the protist Abyssotherma paciWca Brönnimann, Van Dover and Whittaker, colonized the end-interval blocks in cool habitat (C2). This is surprising because other blocks in this habitat type, from the C1 and C1C2 treatments, supported many more taxa (11 each), and the community of species settling in this habitat is typically more diverse, even after short intervals (e.g., Micheli et al 2002). Temperatures recorded at the bases of the C2 blocks on deployment and recovery were no diVerent from the ambient deep-sea temperature (1.8°C).…”

“…All but one, an unidentiWed kinorhynch, had been observed previously as colonists on blocks deployed at the East Wall site (e.g., Micheli et al 2002;Mullineaux et al 2003;Lenihan et al 2008). Most of the taxa (9 of 11) that settled in the cool habitat (C1) appeared capable of surviving the transition to warm conditions (C1W2); the only taxa that did not persist were the polychaetes Nicomache sp.…”

“…The hydrothermal Xuid venting at the site extended over tens of square meters, reached temperature anomalies of 30°C above ambient (1.8°C), and extended from the Xoor of the axial valley, up the 15 m high wall and onto the ridge crest. Two distinct environmental and faunal zones (Micheli et al 2002) were identiWed for the experiments: the vestimentiferan zone where vent Xuids exited the seaXoor at temperatures ranging from 4 to 30°C above ambient, and the suspension-feeder zone, where vent Xuid temperatures were <2°C above ambient. When the experiments were initiated in December 1995, the vestimentiferan zone was characterized by dense clumps of large vestimentiferan tubeworms (Riftia pachyptila Jones, Siboglinidae).…”

“…This observation, however, raises the question of why these species are not typically found in the established communities in warm conditions. We suggest they may be excluded by species that grow more quickly, are more eVective at using the enhanced productivity, or disturb or prey upon (Micheli et al 2002) their propagules. On a longer time scale, it is possible that species interactions would eliminate these 'cool' species or their longevity would be exceeded and, without replacement by new recruits, cause the transitional community to gradually resemble the warm community.…”

Picturing thermal niches and biomass of hydrothermal vent species

“…Fewer studies have simultaneously estimated the biomass and the link between density distributions and food-web structure (Bergquist et al, 2007). Due to the restrictions of working in an isolated and extreme environment, competition, territoriality and predatory behaviour are more recent topics in deep-sea research which require setting up manipulative field experiments (Levesque et al, 2003;Micheli et al, 2002) or analysing imagery (Grelon et al, 2006;Matabos et al, 2015;Podowski et al, 2009;Sen et al, 2013). Species assemblage distribution and composition also rely on the succession of species that occurs during the colonising processes after disturbance (e.g.…”