2016 SoE Marine Chapter - State and Trends - Marine microbial community composition

The Marine chapter of the 2016 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Expert Assessment "The state and trends of marine microbial community composition". The full Expert Assessment, including figures and tables (where provided), is attached to this record. Where available, the Data Stream(s) used to generate this Expert Assessment are accessible through the "On-line Resources" section of this record.----------------------------------------DESCRIPTION OF ECOLOGICAL PROCESS FOR EXPERT ASSESSMENTThe microbial community composition is a sensitive indicator of ecosystem status and health. Marine waters typically contain 104-106 microbial (bacteria, archaea and unicellular algae) cells per milliliter, belonging to hundreds to thousands of different species. This highly diverse and abundant community has an intimate connection with its environment, the marine water. Marine microbial assemblages are the first responders to changes in the chemistry and physical properties of the surrounding water. At the same time, microbes also shape the marine environment by driving most of the biogeochemical cycles, supporting phytoplankton and primary productivity, contributing to the ocean carbon pump and the sequestration of carbon in recalcitrant forms, and removing a wide range of organics and pollutants. Photoautrophic microorganisms both form the base of the marine food-web and are responsible for ocean CO2 draw-down, while nitrogen fixing bacteria are often essential for fueling the food-web with bioavailable nitrogen.To this end, marine microbial assemblages display systematic and predictable change over seasons, across temperature climates, with distance to shore, with depth in association with different water masses and in response to nutrient enrichment, eutrophication and pollution, and the traits of marine microorganisms accurately reflect their niche adaptation.Many of the most abundant clades of marine bacteria, including the Prochlorococcus, Synechococcus, Pelagibacter, Roseobacter and the SAR86 cluster of the gammaproteobacteria have a very broad, if not a cosmopolitan distribution. However this is not reflected in an underlying genetic identity. Rather, widespread distribution in these organisms is achieved by the existence of closely related but discrete ecotypes that display niche adaptations. Closely related ecotypes display specific nutritional or energy generating mechanisms and are adapted to different physical parameters including temperature, salinity, and hydrostatic pressure.There is a global trend for rising incidence of disease in marine habitats. Within Australia there have recently been a number of significant disease outbreaks in organisms including corals, starfish, oysters and fin-fish. While pathogenic microbes constitute a very small minority of the marine microbial communities, their presence is of particular importance and interest.DATA STREAM(S) USED IN EXPERT ASSESSMENTThis assessment is based on peer-review papers and reports. Data on state and trends and associated spatial and temporal coverage are detailed in the publications provided in the reference list.----------------------------------------2016 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details]• 2016 •Assessment grade: UnclearAssessment trend: UnclearConfidence grade: Evidence and consensus too low to make an assessmentConfidence trend: Evidence and consensus too low to make an assessmentComparability: Grade and trend are not comparable to the 2011 assessment• 2011 •Assessment grade: Very goodAssessment trend: StableConfidence grade: Limited evidence or limited consensusConfidence trend: Limited evidence or limited consensus----------------------------------------CHANGES SINCE 2011 SOE ASSESSMENTThe 2016 assessment is similar to the 2011 assessment. With very little information on marine microbial communities with which clear trends could be determined it was considered appropriate to alter the state assignment to ‘unclear’ rather than ‘very good’ and trend assignment to ‘unclear’ rather than ‘stable’ to avoid assumptions on the current state and recent trends.