Assemblages of species associated with open-coast salt-wedge estuaries of western and central Victoria ecological community

Status: Endangered on the EPBC Act list

This ecological community is the assemblage of native plants, animals and micro-organisms associated with the dynamic salt-wedge estuary systems that occur within the temperate climate, microtidal regime, high wave energy coastline of western and central Victoria. The ecological community currently encompasses 25 estuaries in the region defined by the border between South Australia and Victoria and the most southerly point of Wilsons Promontory.

Government evidence of impact of climate change:

Expand all Close all
  • Approved Conservation Advice (including Listing Advice) for the Assemblages of species associated with open-coast salt-wedge estuaries of western and central Victoria ecological community

    Climate change The effects of human induced climate change; including reduced rainfall; rising temperature; sea level rise; increased storm activity and ocean acidification; are anticipated to significantly threaten the ecological community.

    Given the occurrence of other stressors; the ecological community is likely to be particularly sensitive to the added impacts of climate change.

    All estuaries in the ecological community are considered to be threatened by climate change. 4.2.

    Criterion 5 Rate of continuing detrimental change The ecological community is susceptible to a variety of significant threats; with the impacts from climate change being the most consistent and demonstrable threat across all 25 estuaries.

    Sea level rise and increasing air and water temperature; as a consequence of climate change; are key drivers for many of the other environmental threats; such as reduced freshwater inflows; water quality and pathogens; that continue to disrupt ecological processes.

    In light of the substantial rate of continuing detrimental change of the two key climate change impacts; rising sea level and rising temperature; and their projected continuing change; the ecological community is eligible for listing as Vulnerable under this criterion.

    Protect Climate Change Enhance the resilience of the ecological community to the impacts of climate change by reducing other pressures.

    Continue to build an understanding of the risks associated with climate change; including sea level rise; increasing temperature; ocean acidification and future flood risk.

    Regular cyclic variations; such as semidiurnal tides and spring tides; coupled with daily; seasonal and annual climatic variations in temperature and rainfall (and therefore freshwater flow); create a dynamic vertical and longitudinal salinity stratification.

    D1 Climate change and related impacts Climate modelling and projections by CSIRO (2015) indicate that the region of the ecological community will continue to experience a decrease in cool season rainfall; an increase in air and sea surface temperature; mean sea level rise; frequency of extreme weather events and ocean acidification; and a harsher fire weather climate.

    It is likely that salt wedge estuaries are extremely vulnerable to climate change; given their reliance on salinity stratification from marine and freshwater inputs; and the associated risk of becoming marinised (Sherwood 1988 Hirst 2004).

    Due to other threatening processes; many estuaries within the ecological community are considered stressed systems and are less likely to be resilient to the added impacts of climate change (Mondon et al. 2003 Barton et al. 2008 Pope et al. 2015 EPA 2011).

    The likely impacts of climate change on the ecological community are outlined in Table D1.

    Table D1 Likely impacts of climate change on the ecological community (modified from Newton 2007; OzCoasts 2008; Sherwood 1988; Voice et al. 2006; EPA 2011; CSIRO BoM 2015; Glamore et al. 2016 and DPI 2016).

    Climate Driver Potential Impacts Increased Increased evaporation rates of shallow water bodies. temperature Decreased dissolved oxygen; with increased risk of hypoxia and fish kills.

    An analysis of Table D3 indicates that climate change is currently an identified threat to all estuaries within the ecological community.

    Climate change threatening approximately 100 percent of estuaries. 2.

    Decline in See Criterion 5 (climate Can alter physical; chemical and Bayly (1965) water quality change impact). biological properties in estuaries.

    Seagrass beds are generally shallow by nature and sensitive to the main drivers of climate change (Short Neckles 1999 Bjork et al. 2008 Jones et al. 2011 in Mieszkowska et al. 2013).

    These findings imply that a marked reduction in flows such as through drought; abstraction of water; or future climate change; is likely to reduce the stratified area of the estuaries within the ecological community.

    These combined impacts (see Table E5) demonstrate that threats to the ecological community related to reduced discharge (from climate change and increased water extraction; see Appendix D) and rising temperature are impacting spawning habitat; prey availability and recruitment; of fish species.

    This is even more concerning given the identified relationship of the spread of infection and morbidity of the copepods with increased temperature; and the projected climate change derived increase in temperature in the region of the ecological community.

    Conclusion The combined impact of multiple and cumulative threats (in particular climate change; agricultural urban development; water extraction; and pathogens refer Appendix D and Table E5) have reduced the integrity of the ecological community through Disruption and attrition of natural salt wedge dynamics; including loss or decline in the typical hydrological cycle of salt wedge flushing; emplacement and presence loss reduction or projected reduction in salinity stratification and the threat of marinisation loss reduction or projected reduction in area of functional halocline loss of flushing floods or flash floods occurring in a normal season.

    There are several major consequences of climate change that threaten critical components of the ecological community; namely rising sea level increasing temperature increasing ocean coastal acidification and declining and changed seasonality of rainfall.

    Importantly; Church et al. (2013a) suggest that the increased rate of rise since 1990 is not part of a natural cycle but a direct response to increased radiative forcing (both anthropogenic and natural); which will continue to grow with ongoing greenhouse gas emissions.

    After accounting for and removing the effects of vertical land movements; natural climate variability; and changes in atmospheric pressure; sea levels have risen around the Australian coastline at an average rate of 2.1 mm year over 1966 2009 and 3.1 mm year over 1993 (Grose et al. 2015).

    The location of the estuary mouths directly on the Representative Concentration Pathway (RCPs) are used by the Intergovernmental Panel on Climate Change (IPCC) as the full range of emissions scenarios used for the global climate model (GCM) simulations.

    A greater marine influence in estuaries will reduce the present variability experienced in estuarine salinity regimes within the ecological community; with salinities remaining near 30 35 ppt for longer periods. 2) Increasing rate of rising temperature CSIRO BoM (2015) have developed climate projections for Australia s NRM regions.

    The rate of warming strongly follows the increase in global greenhouse concentrations (Grose et al. 2015).

    By 2030 Australian annual average temperature is projected to increase by 0.6 1.3 C above the climate of 1986 2005.

    Changes to temperature extremes often lead to greater impacts than changes to the mean climate (Grose et al. 2015).

    The likely impacts of an increasing rate of increasing water temperatures from climate change are highlighted in Tables D1.

    Increased fire Increased frequency and or intensity of aeolian dust and fire born particulates and wind can affect estuarine productivity and promote algal blooms.

    Hydrology River dominated Net flow seaward River dominance may wane during extended drought and periods of extreme low freshwater flow.

    Extreme weather Increased frequency of storm events; higher reach from storm surge and flash events flooding may alter salinity distribution; affecting salt wedge stability or lead to abrupt decreases in salinity.

    Increased Increased CO2 concentration in seawater is resulting in more acidic oceans; acidification affecting calcitic organisms; coastal food webs and productivity; with flow on effects (physical and biological) to estuaries.

    The reasons for the complete disappearance of these species is unclear; but hypothesised to be caused by a combination of pressure from the Millennium Drought followed by drought breaking floods in early 2011; combined with increasing pressure from catchment development leading to dieback (Dr D.

    Modelling has also demonstrated that over southern Australia; including the region of the ecological community; extreme sea level changes will be dominated by changes in mean sea level due to thermal expansion and ice sheet and glacier melt; rather than by changes in weather patterns (i.e. including wind waves and storm surges) (Colberg McInnes 2012 Hemer et al. 2013).