River Murray - Darling to Sea Ecological Community: Criteria/Condition Thresholds Workshop Report
An expert Technical Workshop was held by the Threatened Species Scientific Committee (TSSC) in July 2009 to deliberate on the Lower Murray River and associated wetlands, floodplains and groundwater systems from the junction of the Darling River to the Sea (here after River Murray - Darling to Sea). This nomination, placed on the 2008 Final Priority Assessment List, is being assessed under the Environment Protection and Biodiversity Conservation Act (EPBC Act) as a potentially threatened ecological community. Outcomes from the Technical Workshop provided information and guidance on the description, boundaries, key characteristics, and suitability of listing criteria for this complex aquatic ecosystem.
The Technical Workshop was unable to focus on the consideration of thresholds for both the listing criteria used to assess ecological communities under the EPBC Act and potential ecological community condition states (or classes). Criteria thresholds enable the assignment of conservation status (i.e. vulnerable, endangered, critically endangered). Condition thresholds enable determination of degraded components of the ecological community (previously, for some terrestrial ECs, severely degraded parts have been excluded from listing protection under the Act). The Criteria/Condition Thresholds Workshop addressed this important gap and examined the suitability and applicability of these two types of thresholds for aquatic ecosystems using the River Murray - Darling to Sea ecological community as a test case. Information gained from this workshop will be used to guide the assessment process for this priority aquatic ecological community.
A vital aspect of the assessment process of an ecological community is the assessment and interpretation of 'listing criteria' as set out in the EPBC Regulations, which each specify indicative thresholds against the various conservation categories (i.e. vulnerable, endangered, critically endangered). The TSSC have adapted the criteria and provided additional interpretive explanation for their application to ecological communities (see Guidelines). Outcomes of the Thresholds Workshop highlighted the challenges associated with assessing aquatic ecological communities when applying the regulated criteria and their thresholds. While there were no recommendations to amend the criteria thresholds, it was clear that the interpretation of the criteria thresholds should be undertaken on a 'case-by-case' basis for aquatic ecological communities. In some cases they apply, in others they do not, and in yet others additional considerations need taking into account, such as meaningful timeframes, connectivity factors, etc.
The importance of ecological function appears more relevant than physical area for aquatic ecological communities, and therefore Criteria 4 seems the most effective for assessment for the River Murray - Darling to Sea, with Criteria 3 and 5 also highly relevant. The possibility for unpredictable and sudden or 'step' change in aquatic systems, rather than gradual or linear change also needs consideration when interpreting the criteria thresholds. Regarding probability of extinction, for ecological communities the concept of 'functional extinction' is more relevant (i.e. as compared to species extinction).
The River Murray - Darling to Sea ecological community is a highly dynamic and highly connected system. The workshop agreed that a number of states (or conditions) and associated indicators could be identified for the system as a whole and for its various sub-units — with 'state' often forming a series of continua. However, the consensus view was that condition thresholds were in general not practical for this type of aquatic ecological community. The inherent resilience and capacity for 'functional' recovery added further weight to the approach of not excluding degraded components of the ecological community. However, it was acknowledged that there is the potential for the ecological community to irreversibly change state so that it becomes compositionally, and even functionally, different but would still constitute the 'ecological community'.