2016 SoE Marine Chapter - State and Trends - Trophic structures and relationships

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 ecological processes – trophic structures and relationships". 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 ASSESSMENT For this assessment, food web structure and function as defined by diet and modelling studies (which synthesis much of the available information) have been used to evaluate the status and trends for trophic structures and relationships. The status and outlook for the structure of Australian marine ecosystems is highly variable. Food webs are naturally dynamic, through time and space (e.g. Griffiths et al. 2009), and human pressure on them has varied around Australia over the past two centuries, altering trophic structures to differing degrees (Dell et al. 2013, GBRMPA 2014). Food webs studies have primarily focused on coastal and shelf waters (e.g. Salini et al 1998, Bulman et al. 2001, DofWWA 2009), with much less coverage of deep water food webs. Diet studies have only occurred intermittently and few studies have been subsequently repeated (e.g. recent resampling of fish diets on the shelf of SE Australia; CSIRO unpublished). Consequently, understanding the true magnitude of inter-annual variation in diets is low and there is little capacity to be sure of dietary changes through time. Modelling studies (Fulton et al. 2005, Klaer 2005) suggest there has been trophic restructuring of food webs in south-eastern Australia over the last century, particularly as a result of the intensification of commercial fisheries up to the 1990s. The reduction in fishing pressure, particularly over the last 5-10 years (Flood et al. 2014, Patterson et al. 2015) will likely, eventually, allow the recovery of trophic structures. However, a complete recovery is unlikely given the multitude of on-going pressures (e.g. remaining fishing pressure, both recreational and commercial, shipping, coastal habitat modification, pollution, etc.) and because some highly depleted species (e.g. eastern gemfish) have failed to recover from past overexploitation; which itself may be related to shifts in trophic connections with predators and prey (TSSC 2009). In addition, climate change is reshaping south eastern ecosystems, with shifts in species ranges (Sunday et al. 2015) and the realisation of new trophic interactions (e.g. shifts in octopus diets; Briceno et al. 2015), as omnivorous species appear to shift more rapidly than carnivores (Sunday et al. 2015). Eastern Australian ecosystems, including the Great Barrier Reef are highly modified (Butler and Jernakoff 1999, GBRMPA 2014). Amongst the most obviously shifted systems are around population centres and in the southern Great Barrier Reef (GBRMPA 2014). As elsewhere, fishing pressure has eased over the past 5 years, but other pressures (e.g. from increasing development) have increased (AIMS 2014). Overall trophic structures likely remain highly modified, both by past and present removal of predatory species and shifts in abundance of basal species, due to eutrophication or habitat removal (GBRMPA 2014, Fulton and Gorton 2014). The ecosystems of northern, western, southwestern and southern Australia see less direct, and spatially more variable, pressure than those in the east and south east. Over the past 3 decades, fishing pressure in the region has significantly declined, and has continued to do so (though at a reduced rate) over the past 5 years (Prince et al. 2008, Patterson et al. 2014, Fletcher and Santoro 2015). Development of other sectors (e.g. shipping) has grown, but largely concentrated on specific locations (AIMS 2014). Consequently, some locations will remain highly modified (e.g. where there is heavy cumulative pressure, due to the combined effects of catchment and urban outflow, shipping, tourism, fisheries, etc), while food webs in remote locations (or those primarily influenced only by sustainable fisheries, such as in the Great Australian Bight) may be stable and in good condition. Shifting climate drivers (e.g. marine heatwaves) are likely to be effecting trophic interactions (e.g. via declines in kelp shifts in fish communities; Wernberg et al. 2013), but there is too little data to be certain of the true status and trends. DATA STREAM(S) USED IN EXPERT ASSESSMENT Diet data from south east and western Australia as well as information published in peer reviewed publications and reports. Details of the specific data sets used to generate the assessment have not been provided. ---------------------------------------- 2016 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details] • 2016 • Assessment grade: Poor-Good Assessment trend: Unclear 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 trend are 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 2011 SOE ASSESSMENT Diet studies have only occurred intermittently and few studies have been subsequently repeated (e.g. recent resampling of fish diets on the shelf of SE Australia; CSIRO unpublished). Consequently, understanding the true magnitude of inter-annual variation in diets is low and there is little capacity to be sure of dietary changes through time. As a result trends cannot be considered to be stable and can only be regarded as unclear.

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Statement: QUALITY OF DATA USED IN THE ASSESSMENT Moderate quality due to low sample sizes and uneven design (as south east data collected by ships of opportunity).

Notes

Purpose
To describe the state and trends in trophic structures and relationships based on physical processes for use in the Marine chapter of the 2016 State of the Environment report.