Marine ecosystems and their attributes, including species composition, ecosystem functions and resilience, are constantly changing. These changes can be biotic (e.g. species invasion) or abiotic (e.g. climate change), and can occur across evolutionary timescales or much shorter timescales of months to years. Given this continuous and ongoing change, definitions of the terms ‘natural’, ‘historical’ and ‘altered’ become blurred, and our ability to compare the current state of ecosystems with some potentially unknown historical ideal becomes ambiguous and somewhat arbitrary (Hobbs et al. 2009). Additionally, the concept of preserving components of marine ecosystems in a condition that was (hopefully) measured at an arbitrary point in time loses meaning. The reduction or removal of a single sector’s pressure may be insufficient to return a species or habitat to its prior condition across reasonable timescales (e.g. Williams et al. 2010b). This complicates the identification and selection of management goals and objectives (and how to measure these), because reference to condition at an arbitrary point becomes less important than reference to the potential environmental conditions that could be maintained, restored or even created in the changed social and physical environment we find ourselves in. It is therefore important to monitor changes in the environment, understand the drivers of change, identify thresholds below which the environment becomes compromised and identify measures required for continuing ecosystem functioning.
In the case of ecosystems that have undergone substantial change, ecosystem restoration may be required to ensure that ecosystem functioning and provision of ecosystem services are maintained. Ecosystem restoration can involve 4 key components:
- natural recovery of an ecosystem from a natural or anthropogenically induced change (e.g. recovery from a cyclone or the grounding of a vessel)
- anthropogenic interventions in response to a degraded or anthropogenically stressed environment (e.g. removal of crown-of-thorns starfish)
- anthropogenic responses to a single pressure (e.g. closure of an overfished area to fisheries)
- habitat enhancement or creation (e.g. re-establishment of lost shellfish reefs or development of an artificial reef; Elliott et al. 2007, Creighton et al. 2015).
Many restoration efforts focus on maintaining or restoring particular species to particular locations to an agreed ‘threshold’ level. For example, recovery of fisheries species from past overexploitation focuses predominantly on rebuilding the species to an agreed level at which the species can be considered as not overfished (e.g. CCSBT 2014, Upston et al. 2014). Recovery targets for species listed under the EPBC Act are less clear, and, although removal from the list would be a clear indication of species recovery, this has yet to happen for any marine species. There has been steady progress in recovery of populations depleted by past exploitation in Australia, although some have been slow to recover (e.g. the eastern population of southern right whales), show no signs of recovery (e.g. eastern gemfish) or at least in some locations appear to be declining (e.g. Australian sea lions), despite protection and implementation of management actions.
Restoration of habitats or communities is typically more complicated than restoration of single species because it can be a challenge to identify, characterise and monitor marine communities that are not easy to access from the shore. Efforts where ecosystem restoration is focused consequently tend to be areas close to shore and subject to intensive change, large historical loss and obvious poor ecosystem health (e.g. shellfish reefs; Gillies et al. 2015; see also Box COA13 in the Coasts report).
One of the management approaches used to restore identified habitats or communities situated in marine areas that are out of easy access is to reduce or stop the major pressures affecting those habitats or communities. This can take the form of marine protected areas, which aim to limit a range of pressures within a region (e.g. Abelson et al. 2016), or closure of certain areas to a specific industry or a component of that industry. Examples include:
- protection of the South Tasman seamounts, initiated in 1995 by industry, codified under Australian Government legislation in 1997 and included in the South-east Commonwealth Marine Reserves Network in 2007 (Williams et al. 2010b)
- closure of all waters deeper than 700 metres to bottom trawling by AFMA in 2007, to aid the recovery of orange roughy and reduce impacts on slow-growing and unassessed deepwater sharks (some areas have since been reopened following some recovery and specific risk assessments).
Artificial habitats, such as artificial reefs, are starting to be introduced at specific locations, to enhance growth of encrusting and attached habitats, and support particular invertebrate and vertebrate species (e.g. rock lobster off Tasmania; S Frusher, Institute for Marine and Antarctic Studies, University of Tasmania, pers. comm., 9 April 2016). A purpose-built offshore artificial reef to improve recreational fishing was introduced off the New South Wales coast in 2011 (NSW DPI 2015b). It was rapidly colonised, with 49 fish species present after 2 years, and, in response, recreational fishing effort increased across the site. The number of artificial reefs has expanded since this deployment, with the building of a fifth offshore artificial reef off New South Wales announced in June 2015. The reefs are designed to be nonpolluting and have a maximum life of about 30 years. Other examples include scuttling of old ships to provide new dive sites that will also aggregate marine life, and potentially deploying used oil rigs as artificial reefs in Bass Strait, where oil and gas infrastructure is already used by Australian fur seals (Arnould et al. 2015).