Case study 2: Trampling through the intertidal

Exploring management thresholds for Victoria’s Marine National Parks 

In order to adaptively manage protected areas, conservation managers need to know when to implement management actions to prevent ecosystems trending towards an unfavourable condition.

Figure 1: The current condition of Hormosira (blue line: mean % cover ± standard error) at Point Lonsdale intertidal reef (Port Phillip Heads Marine National Park) from 2004 – 2013. Through the SDM process, participants were asked to consider the current condition of Hormosira (Scenario 1) and three future scenarios of reduced condition of Hormosira (Scenario 2-4), when estimating the consequences of management alternatives on management objectives.

Figure 1: The current condition of Hormosira (blue line: mean % cover ± standard error) at Point Lonsdale intertidal reef (Port Phillip Heads Marine National Park) from 2004 – 2013. Through the SDM process, participants were asked to consider the current condition of Hormosira (Scenario 1) and three future scenarios of reduced condition of Hormosira (Scenario 2-4), when estimating the consequences of management alternatives on management objectives.

Whilst ecological research and monitoring can help define unfavourable ecosystem conditions; the question of when to implement a management action requires value judgements by decision-makers. Such judgements require decision-makers to subjectively trade-off competing objectives. For example, if visitors to a reserve are having an impact, there is a trade-off between environmental (eg, biodiversity benefits), social (eg, visitor satisfaction) and economic (eg, the cost of management actions) objectives.

We worked with Parks Victoria to trial a SDM process to explore where to set management thresholds for the intertidal brown alga, Hormosira banksii, at Port Phillip Heads Marine National Park*. Hormosira (commonly referred to as Neptune’s necklace) is an indicator of the condition of invertebrate and algal communities on Victoria’s rocky intertidal reefs. Parks Victoria has identified that a key threat to intertidal reef communities is trampling by humans.

 “At what point should a more intensive management strategy be implemented to minimise the impact of trampling?”

While the condition of Hormosira has remained relatively stable since 2004 (Fig 1), Parks Victoria are concerned that human trampling may increase in the future and is likely to result in declining condition of intertidal reef communities.

Figure 2. Example decision scores presented to Parks Victoria decision-makers. Decision scores are based on the consequences and trade-offs elicited through the SDM process.

Figure 2. Example decision scores presented to Parks Victoria decision-makers. Decision scores are based on the consequences and trade-offs elicited through the SDM process.

Pictured on the left is a survey of the
intertidal zone. (Photo by Museum Victoria)

The challenge for Parks Victoria is this: If the condition of Hormosira starts to decline in the future, at what point should a more intensive management strategy be implemented to minimise the impact of trampling?

We involved Parks Victoria staff (decision-makers and on-the-ground rangers) and marine scientists with expertise in intertidal ecology in the SDM process. All participants had valuable experience and knowledge of the management of marine national parks and the effectiveness of biodiversity protection which they could contribute.

By building on work already done by Parks Victoria, participants developed a series of management objectives and alternative management actions relevant to the decision context. The management objectives (step 2) represented environmental factors (eg, to improve the condition of Hormosira), social factors (eg, to improve visitor satisfaction) and economic factors (eg, to minimise resources spent), all of which were considered fundamentally important to the decision context by participants.

The management alternatives (step 3) represented increasing levels of investment to address the impact of trampling (eg, from ranger patrols to ensure visitor awareness, through to restricting

Hormosira banksii (aobove) is one of the most distinct seaweeds in Australia. The common name for this species (Neptune’s necklace) is derived from its pearl necklace shape. Parks Victoria use Hormosira as an indicator of the condition of invertebrate and algal communities on Victoria’s rocky intertidal reefs.

Hormosira banksii (aobove) is one of the most
distinct seaweeds in Australia. The common name
for this species (Neptune’s necklace) is derived
from its pearl necklace shape. Parks Victoria use
Hormosira as an indicator of the condition of
invertebrate and algal communities on Victoria’s
rocky intertidal reefs.

visitor access to reducing the impacts of trampling).

Pictured on the left is a survey of the intertidal zone (Photo by Museum Victoria).

Pictured on the left is a survey of the
intertidal zone (Photo by Museum Victoria).

Participants were asked to consider the current condition of Hormosira (Scenario 1; Fig 1) and three future scenarios of reduced condition of

Hormosira (Scenario 2-4; Fig 1). Under each of these scenarios, we elicited participants’ estimates of the consequences of management alternatives on the management objectives (step 4). The SDM process is particularly useful at this stage, as we can incorporate participants’ uncertainty in scientific knowledge, particularly when it comes to predicting the effectiveness of management alternatives under future scenarios.

We also guided the decision-makers through an exploration of their value judgements relating to the trade-offs involved under different scenarios of decline in the condition of Hormosira (step 5).

By combining the consequences and trade-offs elicited in our workshop, we were able to present decision scores for each management alternative under each scenario of reduced condition of Hormosira (eg, Fig 2). These decision scores represent the management alternatives that best perform under the different scenarios of decline of Hormosira.

The SDM outputs can be used to help Parks Victoria decision-makers decide where to set management thresholds for Hormosira at Port Phillip Heads Marine National Park (step 6).

More info: Prue Addison p.addison@student.unimelb.edu.au

*This project is part of Prue Addison’s research. It is being supported by Parks Victoria’s Research Partners Panel program. The results of this case study are being considered by Parks Victoria in relation to how well the SDM process can assist them in developing management thresholds for the MNP Adaptive Management program.

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