2021 State of the Environment Report Marine Chapter – Expert Assessment – State and Trend – Seamounts

Researchers: Althaus, Franzis (Author) ,  Althaus, Franziska (Author) ,  Emma Flukes (Point of contact) ,  Williams, Alan (Author)

Brief description The Marine chapter of the 2021 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Expert Assessment "State and Trend of seamounts". ***A PDF of the full Expert Assessment, including figures and tables (where provided) is downloadable in the "On-line Resources" section of this record as "EXPERT ASSESSMENT 2021 - Seamounts"*** ---------------------------------------- DESCRIPTION OF HABITAT/COMMUNITY/PROCESS FOR EXPERT ASSESSMENT Australia’s marine realm encompasses many seamounts (undersea mountains, often with volcanic origin); the best known are the Tasmanian seamounts and the Tasmantid seamount chain (Figure 1). Additional seamounts continue to be discovered and mapped – particularly in the Coral Sea. Seamounts provide ‘oasis’ habitats of hard substratum in the deep sea that often support elevated biomass and productivity — including dense aggregations of corals with high associated biodiversity (Clark et al. 2010; Rowden et al. 2010). These often contain vulnerable marine ecosystems (VME) (e.g. UNGA 2006; Clark et al. 2011; Williams et al. 2020a). An ecological definition for seamounts (Pitcher et al. 2007) is preferred to geological (elevation of >1,000 m) because small seamounts frequently support high biodiversity. A rich variety of seamount benthic fauna in Australia’s south-east and south-west regions is associated with biogenic habitats formed by live and dead stony coral, mostly Solenosmilia variabilis, to ~1500 m depth (Thresher et al. 2014; Williams et al. 2020a). Communities and habitats on deeper seamounts (>1500 m) are usually less diverse and abundant, but see Thresher et al. (2014). Tasmantid Chain seamounts are mapped and used for commercial fishing (e.g. Williams et al. 2016), but their epifaunal communities remain poorly documented compared to Tasmania’s seamounts (Williams et al. 2012). DATA STREAM(S) USED IN EXPERT ASSESSMENT RV Southern Surveyor and RV Investigator survey data, held in CSIRO MarLIN. ---------------------------------------- 2021 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details] • 2021 • Assessment grade: Very good-Poor Assessment trend: Stable- Improving Confidence grade: Adequate high quality evidence or high level of consensus Confidence trend: Adequate high quality evidence or high level of consensus Comparability: Grade and trends are somewhat comparable to the 2016 assessment, but confidence is improved based on additional data collection • 2016 • Assessment grade: Very good-Poor Assessment trend: Stable- Improving Confidence grade: Adequate high quality evidence or high level of consensus Confidence trend: Adequate high quality evidence or high level of consensus Comparability: Grade and trends are somewhat comparable to the 2011 assessment • 2011 • Assessment grade: Good Assessment trend: Stable Confidence grade: Limited evidence or limited consensus Confidence trend: Limited evidence or limited consensus ---------------------------------------- CHANGES SINCE 2016 SOE ASSESSMENT not supplied

Lineage Statement: QUALITY OF DATA USED IN THE ASSESSMENT no info supplied

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Notes Credit
Peer reviews of this assessment was provided by: Nic Bax (CSIRO, UTAS)

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