The energy–diversity relationship of complex bacterial communities in Arctic deep-sea sediments

Several explanations have been proposed for the relationship between diversity and bio available energy, for example, effects of population size, competition and evolutionary, environmental or resource heterogeneity. However, scientists have only just begun to understand the relationship between abundance, diversity and biomass in complex microbial communities. With the advancement of technology, the fingerprinting methods needed to determine the relationships in complex bacterial communities have been discovered. Unscrambling the relationships between environmental conditions, organism diversity and ecosystem functions will help us understand the effects of global change.

Continental slopes are one of the best places to study productivity-diversity relationships as there are relatively defined variations in energy availability with water depth. Communities living in the benthic zone depend on the sedimentation of phytodetritus from the productive surface waters; however the detritus flux decreases with increasing water depth. Phytodetritus flux to the deep sea affects the abundance, biomass and biodiversity of benthic organisms. The input of phytodetritus to deep-sea sediments influences bacterial biomass and activity, though it has not been shown that energy availability at the seafloor and bacterial diversity patterns have been linked.

This is first study that has tested the bacterial energy-diversity relationships for complex natural communities in the Arctic seafloor on a defined, regional scale. Depths were chosen to cover a range of phytodetritus fluxes, and representing mesotrophic to olgiotrophic deep-sea setting.

Community structure and functions were shown to be highly related to each other and with energy availability. These structures and functions include enzymatic activity, oxygen consumption and carbon remineralisation rates. In oligotrophic regions, bacterial richness increased with an increasing sediment pigment content, which means a positive energy-diversity relationship is present. However, richness plateaued when mesotrophic sites were included; meaning that bacterial communities and other benthic fauna may be structured by similar mechanisms. Dominant bacterial taxa showed positive or negative relationships with phtodetritus input. Individual taxa had very different responses to changes in pytodetritus input. This also suggests that various ecological strategies among bacterial groups along the energy gradient. With regards to the environment, it was found that any environmental changes affecting primary productivity and particle export will cause changes in the bacterial community structure and function in the Arctic. This could affect key processes such as carbon cycling.  

The authors in this report have successfully identified an energy-diversity relationship of complex bacterial communities in Arctic deep-sea sediment. This study also offers an ecological baseline against which ecosystem shifts can be assessed in the future.

Christina Bienhold, Antje Boetius and Alban Ramette

The ISME Journal (2012) 6, 724–732; doi:10.1038/ismej.2011.140; published online 10 November 2011

http://www.nature.com/ismej/journal/v6/n4/full/ismej2011140a.html