Marine ecosystem health

2011

 

The health of marine ecosystems has been assessed by examining the status and trends of the major physical and chemical processes that maintain the quality of the biodiversity and habitats in each region. Outbreaks of diseases, non-natural algal blooms and infestations by pests have been assessed as symptoms of an unhealthy marine ecosystem. The assessments of marine ecosystem health (available on the SoE websitee) are summarised for each region, and aggregated into a single national assessment and summary.

The overall assessment of ecosystem health found that all the regions are in very good condition except for the south-east, which is in good condition (Figure 6.11).

Physical and chemical processes

This section reports on our best understanding at the national level of the status and trends of the 14 major national-scale physical and chemical processes that operate in the regions and their interaction with human activities.

South-west region

The physical and chemical processes in the south-west region are considered to be in very good condition, with little human-induced impact. Ocean currents have broadly maintained their natural structure and dynamics; nutrient cycling (the movement and exchange of organic and inorganic matter back into the production of living matter) has been maintained at natural levels and extent in ocean waters (although it has been severely affected in estuaries and some coastal waters); and salinity and oxygen conditions remain in natural condition. However, near to the shore, the light, sediment, freshwater and nutrient regimes have been severely altered in a number of the estuaries and bays in the region, and several estuaries have a significant number of recurrent dead-zone (low oxygen) episodes. These nearshore pressures are continuing to increase, most notably the land-based sources of nutrients, and increasing changes are noted for sea level rise, frequency of storms and changes to ocean current patterns, associated with gradually changing global climatic conditions.

North-west region

Like the south-west region, the physical and chemical processes across most of the north-west region are considered to be in very good condition, with little human-induced impact. Ocean currents have broadly maintained their natural structure and dynamics; and nutrient cycling has been maintained at natural levels and extent in ocean waters. The most important process in this region that has been affected by human activities is the coastal sediment supply regime, which is considered to be in poor condition in some places. The sediment supply and dynamics of the coastal region have been heavily affected by structural developments on beaches and dunes in the southern part of this region (particularly port development and shipping channels), and by broadscale agricultural practices and mining in the central parts of the region.

North region

The physical and chemical processes in the north region are also considered to be in very good condition, approaching pristine in most places. Although there have been extensive agricultural changes in a number of catchments, and mining has had a major impact in some localised areas, these are not regional-scale effects. The most affected process is the flow and hydrological regime, which has been affected by major modification to some of the significant rivers of the region (such as the Macarthur River).

East region

Physical and chemical processes overall are considered to be in very good condition in the east region. However, a number of processes have been degraded at a regionwide scale. These include the sediment input regime, and the freshwater inputs and hydrological cycles—these are considered to be good overall, but very poor in some areas; and the changes in sea temperatures, which are in poor condition across the region (because of increasing ocean temperature across the region). Other issues include the prevalence of pesticides in waters across the region, which may be affecting biodiversity.

South-east region

Physical and chemical processes overall are considered to be in good condition in the south-east region. However, there have been substantial changes to sediment input, the dynamics of freshwater inputs and hydrological cycles, the land-based nutrient inputs, the turbidity and light regime of inshore waters, and the dynamics of the East Australian Current that affect this region. In some areas in the region, these changes are extreme, and there have also been substantial inputs of toxicants, resulting in serious impacts on ecosystems. Taken together, this region has experienced changes in physical and chemical processes that are significantly affecting ecosystem functions. Examples include the Coorong, the Derwent River and estuary, and the Gippsland Lakes.

Pests, introduced species, diseases and algal blooms

This section reports on our best understanding for each region of the status and trends of outbreaks of diseases, pests and introduced species (including pests listed in the National Introduced Marine Pest Information System—NIMPIS), and algal blooms in the region and their relationship with human activities. These are summarised at the national level in the assessment summary.

South-west region

The south-west region is overall in very good condition in relation to pests, introduced species, algal blooms and outbreaks of disease that can cause ecological imbalances. However, pest species have been documented from a number of the ports across the region, and have caused significant ecological impacts in their local areas. A large number of introduced species are recognised across the region whose ecological significance is unknown. The herpes-like virus that has seriously affected the region in past decades (see Box 6.8) appears to have now declined, and there are no obvious ongoing impacts on pilchard populations. However, there is only limited knowledge of the impact of the previous virus outbreaks on bird populations and other species that may be ecologically dependent on the pilchards. Blooms of toxic and nuisance algae continue to be a problem in a number of the estuaries and inshore waters across the region, creating substantial changes, fish kills (deaths of a large number of fish over a short period) and associated ecological impacts. When they occur, algal blooms in this region can cover large areas (see Box 6.1).

North-west region

The north-west region is also in very good condition overall in relation to pests, introduced species, algal blooms and outbreaks of disease. Only two pest species are known to have been established in this region, although many (likely hundreds) of species are introduced to the region as fouling on ship hulls. The intense level of shipping activity associated with the oil and gas sector in the region has probably made a big contribution to this problem. However, few data are available on the ecological impacts of such introductions and, for now, these effects are assumed to be neutral in terms of ecological function. There are natural algal blooms in this region, but only low levels of coastal and related development that are likely to be the source of nutrients for human-induced algal blooms of any significance. Poor catchment management in many parts of the region influences sediment and nutrient input (such as in floods), but there are no data on the relationship between catchment management and algal blooms in coastal waters. Issues associated with Lyngbya (a toxic alga) are noted near Broome, possibly associated with local groundwater, urban run-off and sewage management.

North region

The north region is also in very good condition overall in relation to pests, introduced species, algal blooms and outbreaks of disease. One pest species (striped mussel) has been recorded in the region, but is now thought to have been largely eliminated. Monitoring of the high-risk areas (Darwin Harbour) has not detected further pest incursions. The region is also likely to have many introduced species, as in other areas of Australia, and for the same reasons (including shipping activity, the aquarium trade, tourism and petroleum industry infrastructure) There are few ecological data on impacts.

East region

The east region overall is considered to be in good condition in relation to pests, introduced species, algal blooms and outbreaks of disease. Four species of pest have been recorded in the region, in and around the ports, shallow bays and estuaries. However, the region suffers from periodic outbreaks of crown-of-thorns starfish, and there are extensive algal bloom issues in Moreton Bay and other bays and shallow coastal northern waters, including outbreaks of Lyngbya. These shallow and inshore waters of the region are considered to be heavily impacted at times by algal blooms, and their condition is considered overall to be poor in this respect. When they occur, algal blooms in this region can cover large areas. The Pacific oyster (Crassostrea gigas, endemic to Japan) has been introduced to the region for oyster farming and has spread, with a significant ecological impact in the estuaries of the southern part of the region.

South-east region

Pests and outbreaks of disease have had major impacts in the south-east region and, overall, the regionwide condition is poor with respect to pests, diseases, introduced species and algal blooms. The pests noted in the region (some of which are widespread and have major ecological impacts at times) include starfish (Asterias), sea urchins(Centrostephanus rodgersii), plankton (toxic dinoflagellates), algae (Undaria, Caulerpa), molluscs (Maoriocolpus), crustaceans (Carcinus) and worms (Sabella). Port Phillip Bay has been described as one of the most invaded marine ecosystems in the Southern Hemisphere, but there are others of equal note, including the Derwent estuary. Outbreaks of harmful native species are also pervasive, mainly toxic algal blooms. The zooplankton Noctiluca (a red form of ‘sea sparkle’, often responsible for ‘red tides’) has recently become very widespread and is dominant in many parts of the region, probably displacing other forms of native species. The drivers and consequences of this phenomenon are unknown, but are of ecological concern across the region. A severe outbreak of abalone viral ganglioneuritis has affected abalone in several parts of the region, with serious ecological consequences (Box 6.8, p. 428).

Box 6.1 Surface phytoplankton blooms and phytoplankton biomass in coastal waters

Timeseries from satellite data at five coastal sites (monthly data from 2003 to 2010) have compared chlorophyll-a concentrations in the upper water column (a proxy for phytoplankton biomass) with the occurrence and extent of surface phytoplankton (or algal) blooms. The information retrieved from satellite ocean-colour remote sensing is based on the cloud-free portions of the images. Therefore some sites, such as Storm Bay or Broome, may have a more restricted spatial and temporal representation due to more frequent cloud cover.

Site 1, Darwin

The phytoplankton biomass peaks in January and then progressively declines through the rest of the year, before increasing again at the start of spring (September). The biomass level here is the highest of all the sites, and shows the greatest decline of all the sites over the period reported. There is a peak in surface phytoplankton blooms during September and October, covering a limited spatial extent (

Site 2, Burdekin River, Townsville

The Burdekin River catchment is located in the Great Barrier Reef region, and generates significant river plumes during wet-season flood events (see Box 6.10). The phytoplankton biomass peaks during the early wet season, between February and March. The biomass shows a general decline during the reporting period, although there was high phytoplankton biomass during the 2007 and 2008 wet seasons, following the large flood events in those years. Surface phytoplankton blooms, likely Trichodesmium spp.,occur mainly between June and October, and may cover large areas (≥30% of the site).

Site 3, Storm Bay, Hobart

The phytoplankton biomass data from this site were affected by cloudy conditions (annual cloud cover 70–80%). The phytoplankton biomass peaks annually in September–October, the ‘spring bloom’. However, the available satellite data and field studies confirm a decline in phytoplankton biomass during the reporting period. Surface phytoplankton blooms occur mainly in June and may cover up to 10% of the site.

Site 4, Geographe Bay, Perth

The phytoplankton biomass is localised close to the coast and is highest during winter. Nutrients supporting this biomass probably come from local river run-off and storm disturbance of sediments. Compared with the other sites, this is the only site with an apparent increasing (although not statistically significant) trend in phytoplankton biomass. Surface phytoplankton blooms were found to occur mainly in early autumn, sometimes covering large areas (>30% of the site).

Site 5, Broome, South Kimberley

There is a peak of phytoplankton biomass in May, with high variability in August. The biomass shows a significant decline over the reported period. Surface phytoplankton blooms occur mainly in March and September. They appear to be more limited in extent than those at the Geographe Bay site, covering

A detailed description of the methodology and additional data can be found in Blondeau-Patissier et al. (2011).38

NIMPIS = National Introduced Marine Pest Information System

Ward T (2011). Marine environment: Marine ecosystem health. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/6-marine/2-state-and-trends/2-2-marine-ecosystem-health, DOI 10.4226/94/58b657ea7c296