Western rock lobster

Legal description

The Commonwealth marine area is a matter of national environmental significance under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). As such, actions that have, will have, or are likely to have, a significant impact on it require approval.

In February 2014, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) became the sole designated assessor of petroleum and greenhouse gas activities in Commonwealth waters in accordance with the Minister for the Environment’s endorsement of NOPSEMA’s environmental authorisation process under Part 10, section 146 of the EPBC Act. Under the streamlined arrangements, impacts on the Commonwealth marine area by petroleum and greenhouse gas activities will be assessed solely through NOPSEMA.

Key ecological features are not matters of national environmental significance and have no legal status in their own right. However, they may be considered as components of the Commonwealth marine area.

This KEF was identified in the South-west Marine Bioregional Plan. Under section 176 of the EPBC Act, once a bioregional plan has been made the minister responsible for the environment must have regard to it when making any decision under the Act to which the plan is relevant.

Values

Western rock lobster (Panulirus cygnus) is the dominant large benthic invertebrate in this bioregion. It is also an important part of the food web on the inner shelf, particularly as a juvenile, when it is preyed upon by octopus, cuttlefish, baldchin groper, blue groper, dhufish, pink snapper, wirrah cod and breaksea cod. Western rock lobsters are also particularly vulnerable to predation during seasonal moults in November–December and to a lesser extent during April–May. The high biomass of western rock lobsters and their vulnerability to predation suggest that they are an important trophic pathway for a range of inshore species that prey upon juvenile lobsters.

National and/or regional importance

The Western rock lobster is defined as a key ecological feature due to its presumed ecological role on the west coast continental shelf.

Location

Within the South-west Marine Region, western rock lobsters can be found north of Cape Leeuwin to a depth of 150 m. As an abundant and wide-ranging consumer, the western rock lobster is likely to play an important role in ecosystem processes on the shelf waters in the region (MacArthur et al. 2007).

The spatial boundary of this KEF, as defined on the Conservation Values Atlas, includes Commonwealth waters in the South-west Marine Region, to a depth of 150 m, north of Cape Leeuwin.

Description

The ecological role of western rock lobster is best understood in shallow waters (less than 10 m) where it can significantly reduce the densities of invertebrate prey, such as epifaunal gastropods, through its varied and highly adaptable diet (MacArthur et al. 2007). However, there is a lack of similar studies in deep water (greater than 20 m) in the region. The little information available for deepwater populations suggests that, in contrast to shallow water, lobsters forage primarily on animal prey, which is dominated by crustaceans such as decapod crabs and amphipods (MacArthur et al. 2007). However, there are no quantitative data to indicate the significance of their foraging behaviour on deepwater ecosystems in the region.

Despite the limited information currently available about the ecological role of western rock lobster, the presumption that it has a significant ecological role is supported by research elsewhere (e.g. Tasmania, New Zealand, South Africa and North America), where studies in marine reserves have helped identify significant interactions between lobster and prey species (MacArthur et al. 2007).

The species plays an important trophic role in many of the inshore ecosystems on the inner shelf, particularly during the post-larval puerulus phase. The life-cycle of the western rock lobster is complex. Spawning and egg hatching occur in late spring to summer, typically in water depths of 40 m or more. The summer hatching and night-time aggregation of phyllosoma in surface water coincides with maximal wind-generated offshore surface transport vectors, resulting in offshore larval dispersal into the Indian Ocean and beyond the influence of the Leeuwin Current. The phyllosoma life stage lasts 9–11 months during which time the larvae become widely distributed throughout the south-eastern Indian Ocean, at distances greater than 1500 km from the Western Australian coast (Hayes et al. 2008 and references therein). Late larval stages are known to aggregate at depths of 50–120 m, particularly during the day, and are therefore subject to subsurface circulation features resulting in a net transport of late phyllosoma larvae back to the Australian coast. Late phyllosoma larvae metamorphose into a post-larval puerulus beyond, or just on, the edge of the continental shelf. During this life stage, the puerulus, or juvenile lobsters, actively swim across the shelf waters to settle in shallow inshore reefs where they remain for three to four years before migrating to deeper waters in summer to spawn and complete the life-cycle (Hayes et al. 2008 and references therein). While on the inshore reefs, they become important prey for a range of species, including octopus, cuttlefish, baldchin groper, blue groper, dhufish, pink snapper, wirrah cod, breaksea cod and Australian sea lions (Hayes et al. 2008). The high biomass of rock lobster, combined with its vulnerability to predation, suggests it is an important trophic pathway for a range of inshore species, many of which also inhabit the Commonwealth marine environment. These large invertebrates figure prominently in food webs of other key ecological features, such as the Commonwealth marine environment surrounding the Houtman Abrolhos Islands.

Puerulus settlement peaks between September and January and strongly correlates with the strength of the Leeuwin Current (Caputi et al. 1996 in Hayes et al. 2008). The strength of the Leeuwin Current therefore has a strong influence on the commercial catch of western rock lobster, and is used as an indicator of the likely state of the fishery in three to four years’ time.

Western rock lobster is the basis of one of Australia’s most valuable commercial fisheries. The Western Rock Lobster Fishery was the first Australian fishery to be accredited with Marine Stewardship Council certification. In recent years, larval settlement, which predicts catch levels 3–4 years in advance, has undergone substantial decline. Recent environmental conditions have not been conducive to high puerulus settlement, with water temperature and westerly winds both below average. The past two years have seen the lowest catches on record (WA DoF 2010).

Pressure

During the development of marine bioregional plans, a regional pressure analysis was conducted to assess present and emerging pressures affecting conservation values in the Marine Regions and the effectiveness of mitigation and management arrangements that are currently in place to address these pressures. The analysis enabled pressures to be categorised in terms of their relative importance or concern and has informed the identification of regional conservation priorities. For the purpose of the plans, pressures are defined broadly as human-driven processes and events that do or can detrimentally affect the region's conservation values.

Pressures assessed as of concern for the Western rock lobster are changes in sea temperature and change in oceanography as a result of climate change.

Pressures assessed as of potential concern are sea level rise and ocean acidification as a result of climate change; changes in turbidity; physical habitat modification; extraction of living resources; and oil pollution. These pressures are described in more detail below.

Sea level rise (climate change)
Global sea levels have risen by 20 cm between 1870 and 2004 and predictions estimate a further rise of 5–15 cm by 2030, relative to 1990 levels (Church et al. 2009). Longer term predictions estimate increases of 0.5 m to 1 m by 2100, relative to 2000 levels (Climate Commission 2011). One of the anticipated effects of sea level rise is the increase in coastal erosion processes, which might be accompanied by an increase in sediment loads in the water column, particularly in inshore environments, and a possible loss of seagrass beds (Hobday et al. 2006).

Changes in sea temperature (climate change)
Sea temperatures have warmed by 0.7 °C between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 °C warmer by 2030 (Lough 2009). The south-west of Western Australia in particular is one of three hotspots in the Indian Ocean where rising temperature trends exceed the Indian Ocean basin average (Feng et al. 2009). All key ecological features considered important for the region’s primary productivity and biological production are at risk from climate change. Changes in sea temperature and oceanographic processes have been implicated in the region in shifts in distribution of marine species, changes to prey variability (including positive changes for some species, such as bridled tern) and effects on reproductive time and success (Dunlop 2009; Gaughan et al. 2002; Surman & Nicholson 2009). The overall implications for ecosystem processes in the region are not known.

Change in oceanography (climate change)
The strength of the Leeuwin Current has decreased slightly since the 1970s. This weakening is expected to continue, although this prediction currently has low confidence (Feng et al. 2009). The Leeuwin Current is the basis of much of the region’s biological productivity, and its strength and seasonal/climatic variability are a primary driver for the intensity, timing and locations of productivity events in the region, from the waters off Geraldton to the Great Australian Bight (Pattiaratchi 2007). The long-term implications for the region’s ecosystems and its key ecological features are uncertain. This pressure is considered of concern for those key ecological features important for the region’s productivity and for which the Leeuwin Current is considered a primary ecological driver.

Ocean acidification (climate change)
Driven by increasing levels of atmospheric CO₂ and subsequent chemical changes in the ocean, acidification is already underway and detectible. Since pre-industrial times, acidification has lowered ocean pH by 0.1 units (Howard et al. 2009). Furthermore, climate models predict this trend will continue, with a further 0.2–0.3 unit decline by 2100 (Howard et al. 2009). Projected changes in Australian waters by 2070 include a decline in pH of 0.2 units (Lawrence et al. 2007). There is a high level of uncertainty about the effects of ocean acidification on marine life. While some organisms might be able to adapt (Orr et al. 2009), anticipated changes to phytoplankton and zooplankton have the potential to detrimentally affect ecosystem processes and the structure of ecological communities. Research on the impact of ocean acidification on Antarctic krill has found that increased levels of CO₂ kill their embryos (Kawaguchi et al. 2011). Krill are an important part of the food chain because they feed on phytoplankton and zooplankton, and are a key food source for many species that occur in Australian waters. Consequently, acidification impacts have the potential to affect species further up the food chain. The potential effects of increased acidity on the region’s biodiversity also include changes to growth and population dynamics of some shell-forming organisms, impacts on the reproductive and metabolic functions of a number of fish and invertebrate species, and sensitivity of some early-life stages to acidification (Orr et al. 2009).

Changes in turbidity
Changes in turbidity in the region can be associated primarily with increased coastal erosion (due to sea level rise). Increased run-off, which is the cause of turbidity changes in other parts of Australia, is not likely to be a significant source of pressure in the south-west due to the absence of large rivers and the anticipated dramatic decrease in rainfall predicted for the south-west corner of Australia (Hennessy et al. 2006). Key ecological features that are particularly vulnerable to increased turbidity are those that have extensive and important seagrass beds or that have an ecological reliance on this type of habitat (western rock lobster).

Physical habitat modification
Coastal, urban and industrial development and port activities can result in loss or significant degradation of areas of important habitat. Of potential concern are those features occurring on the west-coast continental shelf, where the rate of development is higher (Clifton et al. 2007). Inshore habitats, such as the seagrass beds and limestone reefs of the west coast and Geographe Bay, are important breeding and nursing areas for a range of fish and shark species and for western rock lobster. In the region, disturbance and physical changes to benthic habitats result from bottom trawling, although the extent of trawling varies broadly among the fisheries in the region. Sponges, bryozoans and sea squirts are particularly vulnerable to trawling impacts (Currie et al. 2009). Bottom trawling occurs on the west-coast shelf edge and slope, and loss or modification of the benthic community is likely; 20 out of 48 habitat types occurring within the fishery area are at risk (Wayte et al. 2007). Effects of benthic habitat loss on demersal communities and associated ecosystems are not certain. Other sources of benthic habitat loss or modification at more localised scales are dredging, construction of infrastructure, and laying of underwater pipelines and cables. The implications of benthic habitat loss on the region’s species and ecosystems are not adequately understood.

Extraction of living resources
Understanding of ecosystem effects of fishing is very limited. Evidence of reliance of species on targeted stocks include research on the feeding ecology of seabirds foraging around the Houtman Abrolhos Islands, which indicates that a number of species, including the threatened Australian lesser noddy, are reliant on the availability of specific species of small pelagic fish (Gaughan et al. 2002). Some seabird species that inhabit the region are also known to depend on large pelagic predators, such as tunas, for driving prey fish to the surface, and some species, such as sooty tern, are thought to be totally reliant on this method of feeding (Dunlop 2009; Jaquemet et al. 2007).

Based on the latest fisheries status reports from the Australian Government, Western Australia and South Australia (respectively, considering the 2009, 2008–09 and 2006 stock status reports), 10 stocks in the region are assessed as ‘overfished.’ 16 stocks have an uncertain status, including dhufish, for which substantial declines have been reported (Fletcher & Santoro 2009; Linnane et al. 2010, 2010a; Wilson et al. 2010). Recent management changes have been implemented to facilitate stock recovery for dhufish and other west coast demersal finfish (DoF 2011, 2011a). In light of limited understanding about the ecosystem effects of extraction of living resources for the key ecological features of the region, the pressure is considered of potential concern.

Oil pollution
A number of the key ecological features, including western rock lobster, have characteristics that make their ecosystems and communities vulnerable to the effects of an oil spill, for example, features that include localised areas of high productivity, which attract large aggregations of marine life.

The intensity and distribution of activities implicated in oil spills, such as oil production and transport, are likely to increase in the region.

Australia has a strong system for regulating industry activity that is the potential source of oil spills and this system has been strengthened further in response to the Montara oil spill. While oil spills are unpredictable events and their likelihood is low based on past experience, their consequences, especially for threatened species at important areas, could be severe.