2016 SoE Marine Chapter - State and Trends - Water column, abyss (>700 m)

Brief description

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 habitats and communities - water column, abyss (>700 m)". 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.

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DESCRIPTION OF HABITAT/COMMUNITY FOR EXPERT ASSESSMENT
The water column is home to a diversity of communities. The relative biomass of the major communities is estimated to be 300:75:10:1 for phytoplankton, bacteria, zooplankton and higher predators in the southern ocean (Marchant 2002). For these dominant communities the major determinants of habitat quality is considered to be temperature (T), salinity (S), light, nutrients, dissolved oxygen (DO), pH, and food availability. SOE assessments for fish, EBPC listed species, marine mammals and benthic communities are found at elsewhere in this chapter. The phytoplankton community dominates the water column in terms of biomass and is the basis of all food for the other communities. Phytoplankton are all produced in the illuminated upper ~ 100m of the water column with light, phytoplankton biomass and food for other organisms generally declining exponentially with depth (Rex et al., 2006). At intermediate depths there is typically an oxygen and salinity minimum plus a nutrient maximum while deeper waters are progressively colder.
The major potential threats to the water column as habitat can be considered to be: warming of ocean, declining nutrients in the surface mixed layer (SLM), reductions in primary production, declining DO (Talley et al., 2016), decreasing pH and over fishing. The SLM from Port Hedland to Cape Howe has risen ~ 1°C from 1993 to 2013 (Foster et al., 2014), and portions of the SW region were 3°C hotter during February 2011 than normal (Pearce and Feng 2013). Open ocean phytoplankton biomass and primary production have generally declined at mid latitudes (Siegel et al., 2013, Signorini et al., 2015) although they have increased in the SE region (Matear et al., 2013; Kelly et al., 2015). There is very little evidence available of any other biotic responses from the water column to these climatic pressures although concerns over acidification continue to grow (e.g. Mongin et al., 2016) especially for deep sea corals (Thresher et al., 2011; Thresher et al., 2015).

DATA STREAM(S) USED IN EXPERT ASSESSMENT
Chlorophyll a data are computed from the level 3 (L3) daily global products using one merging method following Maritorena and Siegel (2005). Details can be found at http://www.globcolour.info/products_description.html
Zooplankton data are from Australia’s National Reference Stations operated by the Integrated Marine Observing System.

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2016 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details]

• 2016 •
Assessment grade: Good
Assessment trend: Unclear
Confidence grade: Limited evidence or limited consensus
Confidence trend: Limited evidence or limited consensus
Comparability: Grade and trend are somewhat comparable to the 2011 assessment
• 2011 •
Assessment grade: Very good
Assessment trend: Stable
Confidence grade: Limited evidence or limited consensus
Confidence trend: Limited evidence or limited consensus

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CHANGES SINCE 2011 SOE ASSESSMENT
This assessment uses observations from a greater range of spatial and temporal scales allowing a better assessment of current state and trends to be made. The time series of observations is becoming long enough to distinguish temporal variability associated with shorter term climate cycles (e.g. ENSO) from the longer term but relatively gradual impacts of climate change. These longer term trends are more apparent today than ever before. Consequently the SOE grade applicable to an increasing portion of these waters should be downgraded from ‘very good’ to ‘good’.

Lineage

Statement: QUALITY OF DATA USED IN THE ASSESSMENT
Spatial and temporal coverage are excellent. Conversion of ocean colour to chlorophyll a introduces a source of potential error. Data could be extracted for each region to allow improved regional assessments of state and trend.

Notes

Purpose
To describe the state and trends in the quality of the water column community, abyssal depth (>700 m) for use in the Marine chapter of the 2016 State of the Environment report.