Resistance to change

2016

For ecological habitats, species and processes, strong resistance to change is often related to high biodiversity and healthy ecosystem function. High biodiversity leads to ecological redundancy, which is when multiple ecological components play a similar role in maintaining the ecosystem. This means that when one component fails, another can compensate, and the system is maintained. Because of the complexity of most ecosystems, it is often not practical to manage redundancy directly, and it is more common to manage biodiversity with the knowledge that this will act to maintain ecological redundancy and therefore resilience.

Resistance can also result from keystone or habitat-forming species that have a high tolerance for disturbances, harsh environmental conditions or diseases. Resistance can be increased through breeding programs that bolster tolerant genotypes, or by maximising genetic diversity to allow adaptation to the widest range of environmental conditions (see Box COA12). Ecological community- and species-level resistance to one pressure can also be increased if other pressures are moderated. For example, temperature tolerance may be higher if an organism is in good health.

Box COA12 Engineering climate-proof oyster reefs

The eastern seaboard of Australia is experiencing among the highest rates of climate warming on the planet. This is threatening the loss of endemic species, which comprise 80 per cent of temperate Australian coastal biodiversity. Intertidal plants and animals are particularly susceptible to climate warming because many already live close to their thermal limits. On rocky shores, these organisms may experience temperatures exceeding 50 °C when low tides coincide with maximum midday air temperatures. The ability of these animals and plants to adapt to warming conditions will be contingent on the availability of natural refuges that provide cooler conditions.

Sydney rock oysters (Saccostrea glomerata) could provide natural refuges for intertidal biodiversity from the effects of climate warming by providing shade and trapping moisture at low tide. On New South Wales rocky shores, maximum temperatures are, on average, 4.5 °C cooler inside oyster beds than on bare rock. Consequently, oyster beds contain species that are unable to tolerate temperature extremes on bare rock. Oysters once formed extensive reefs in estuaries of eastern Australia, but perhaps as few as 1 per cent of these remain because of historical overharvest. Rebuilding oyster reefs that are resilient to climate warming may help to curb the loss of Australia’s coastal biodiversity.

On the hot black tiles, more wild (left) than selectively bred (right) oysters survived to form habitat. In the right panel, only shells of dead selectively bred oysters remain

On the hot black tiles, more wild (left) than selectively bred (right) oysters survived to form habitat. In the right panel, only shells of dead selectively bred oysters remain

On the hot black tiles, more wild (left) than selectively bred (right) oysters survived to form habitat. In the right panel, only shells of dead selectively bred oysters remain

Photo by Dominic McAfee

Sydney rock oysters are the focus of a sizeable aquaculture industry in New South Wales and southern Queensland. The management strategy of the industry includes a selective breeding program to produce fast-growing and disease-resistant oysters. Researchers at Macquarie University are assessing the ability of Sydney rock oysters to persist and form habitat under warmer conditions, and whether there are particular oyster breeding lines that display greater thermal tolerance and could therefore benefit restoration projects targeting climate change adaptation of coastal ecosystems.

The researchers manipulated temperature conditions in the field by growing oysters on tiles that are white, grey or black in colour and differ in their thermal properties. The white tiles, which reflect heat, reach 36 °C; the grey tiles reach 47 °C; and the black tiles, which absorb heat, reach 60 °C. The experiments show that there are large differences in the ability of oyster breeding lines to continue to grow and form habitat on the hotter tiles. Whereas oysters selectively bred for fast growth and disease resistance grew faster than wild oysters on the cooler white plates, on the hotter grey and black plates they lost this growth advantage, and instead experienced higher mortality than the wild oysters. The net effect was that, on the hot black tiles, wild oysters provided more habitat and facilitated cooler temperatures and greater biodiversity than the selectively bred oysters. Nevertheless, the presence of either type of oyster on tiles reduced temperature, and increased biodiversity.

The results suggest that shading provided by the complex 3D structure of oysters will enhance the adaptive capacity of intertidal biodiversity to climate warming. The magnitude of this effect will, however, vary between oyster breeding lines.

Temperatures are hotter in the absence (left) than the presence (right) of oysters

Temperatures are hotter in the absence (left) than the presence (right) of oysters

Temperatures are higher in the absence (left) than the presence (right) of oysters

Photo by Dominic McAfee

Source: Associate Professor Melanie Bishop, Macquarie University

Resistance of the physical environment to change is largely dependent on engineering coasts to withstand changes such as rising sea level, or conserving natural ecosystem components that are able to buffer change. Mangroves, for example, accrete soil and can grow vertically in response to rising sea level (Krauss et al. 2014), although there may still be issues with the environment immediately landwards of the mangroves. So far, the need for coastal engineering to counter the effects of climate change has been patchy, but will increase and become widespread in the coming decades.

In 2015, the Australian Government released a National Climate Resilience and Adaptation Strategy, which outlines how Australia is building resilience against future climate risks. It identified principles to guide effective adaptation practices and management, much of which applies to the coastal zone. The strategy recognised the primary role of climate in shaping the coast, both historically and in the future. It outlined the risks to the coastal zone associated with changing climate, how Australia is preparing and what we need to do in the future.

Some recent initiatives relating to coastal resilience include:

  • the Reef 2050 Plan, which aims to build the resilience of the Great Barrier Reef
  • coastal management reforms in New South Wales
  • managing climate risks to Defence land and property holdings.

In another initiative, the National Climate Change Adaptation Research Facility is working with stakeholders around Australia to create an online coastal risk management framework, CoastAdapt. Due in 2017, this will help users to understand and manage the risks associated with sea level rise, storm surges and other hazards. It will be a practical, hands-on tool and information guide to help governments, businesses and communities manage climate risks in the coastal zone. CoastAdapt will make use of national datasets and research outputs developed during the past 5 years by Australian research organisations. Informed by extensive consultation with potential users, CoastAdapt aims to provide guidance on all aspects of adaptation planning in the coastal zone, including community engagement, risk assessment and adaptation options.

Clark GF, Johnston EL (2016). Coasts: Resistance to change. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/coasts/topic/2016/resistance-change, DOI 10.4226/94/58b659bdc758b