Managing mosquitoes without destroying wetlands: an eastern Australian approach
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- Dale, P.E.R. & Knight, J.M. Wetlands Ecol Manage (2012) 20: 233. doi:10.1007/s11273-012-9262-6
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Recognising both the importance of intertidal wetlands and their role in mosquito-borne disease we discuss wise management to conserve wetland values and to reduce vector borne disease health risks. First we summarise the mosquito-borne diseases associated with intertidal wetlands in sub-tropical and tropical Australia. We consider the Ramsar Strategic Plan, its reflection in some key Australian statutes and the relationship between environment-focussed legislation and health legislation. This is followed by a brief overview of mosquito control and its impact on human health. Using a salt marsh example of an integrated process, we describe the development of what was, in the 1980s in Australia, a novel method of habitat modification (runnelling) for mosquito control. Runnelling modifies the tidal water flow on salt marshes, reducing mosquito larval numbers and minimising environmental impacts. The approach is related to two of the Ramsar goals (wise use and institutional capacity and effectiveness). We then describe the extension of its rationale to a complex mangrove system. Finally, with a concept model, we consider the convergence between minimal habitat modification for wetland conservation and human health protection using an interdisicplinary approach involving multiple stakeholders.
KeywordsAustraliaRamsarSaltwater mosquitoSalt marshMangrovesMosquito-borne diseaseHuman health
Wetlands are important ecosystems, as evidenced by the international Ramsar Convention held in 1971 and its on-going role in the wise use of wetlands. There are 160 contracting parties (countries that are member states) in 2012, protecting almost 193 million hectares of wetlands (Ramsar 2012a). Australia was one of the first countries to sign as a contracting party to the Convention on 21st December, 1975. Wetlands provide a range of values, covering both intrinsic existence values and instrumental ones. The latter are often the focus of management, conserving those values that are important to humans, such as support of commercially important species, protecting water quality and shorelines as well as providing opportunities for recreation and research. Historically the recognised threats to wetland have focussed on development pressures and now to these must be added pressures from climate change and related sea level change (IPCC 2007). Coastal wetlands are increasingly coming under pressure from these threats (Millenium Ecosystem Assessment 2005).
With many stakeholders, such as land developers, conservation agencies and mosquito control agencies, there is a need to balance potentially competing interests, as was noted in the Changwon Declaration (Ramsar 2008) and the Millenium Ecosysten Assessment (2005, p. 48) and this extends also to undisturbed wetlands. There is a need to both conserve wetland values and maintain the health benefits that wetlands provide. However there can be negative health impacts from wetlands and both the Changwon Declaration and the Millenium Ecosystem Assessment noted the human health problems that can result, especially from degraded wetlands. These include waterborne diseases and vectors such as the mosquitoes that transmit pathogens that cause diseases. With climate and sea level changes, areas with vector-borne diseases are likely to expand (Hughes and McMichael 2011, pp. 19–20). For more detail, the relationship between wetlands and mosquitoes and management was reviewed in Dale and Knight (2008).
The Ramsar Convention in 1971 adopted a mission for “the conservation and wise use of all wetlands through local and national actions and international cooperation, as a contribution towards achieving sustainable development throughout the world” (Ramsar 2012b). Since then there have been on-going committments to the wise management of wetlands by, for example, the Millenium Ecosystem Assessment (2005) synthesis of human well-being and wetlands.
Addressing such issues, Horwitz and Finlayson (2011) recently stressed the importance of wetland ecosystem services and, recognising the interaction with human health, proposed an integrated approach to management. Balancing wetland conservation against the need to protect human health is a challenge (Pittock et al. 2010; Lynch 2011) and one that is considered here, mainly in the context of intertidal wetlands in eastern Australia, as they are often very close to human settlement and are particularly threatened by climate and sea level change (Millenium Ecosystem Assessment 2005).
This paper considers the question: “Can wetland management and mosquito control be integrated to meet two of the Ramsar goals: of wise use and of institutional capacity and effectiveness?” To address this we take, as an Australian example, a long-term project in an intertidal wetland in Queensland and follow this with the recent extension of the approach to a mangrove project in northern New South Wales.
We first outline mosquito-borne diseases associated with intertidal wetlands in sub-tropical and tropical Australia, establishing the need for management for human health. Second, we consider the Ramsar Strategic Plan as a high level guide for wise management (wise use) of wetlands. We consider its reflection in some key Australian statutes and the relationship between environment-focussed legislation and health legislation. Third, we consider saltwater mosquito management, outlining control methods that directly affect wetlands and the effect of these on environment and on disease. Fourth, in order to ground the discussion in a real situation, we refer to a long-term salt marsh project which took an environment-focussed approach while also solving a mosquito management problem. Its success led to the extension of the concept to a mangrove system resulting in a trial project. This example has been well-documented in the refereed literature and key references are provided should a reader wish to delve more deeply. Fifth, we reflect on the process and how it relates to the two selected Ramsar Goals (wise management and institutional capacity and effectivness) and describe the extension of the rationale to a complex mangrove system. Sixth we synthesise the process in a concept model and relate it to the selected Ramsar Goals. We conclude that it is possible to wisely use and manage an intertidal system for mosquito control, particularly if it is facilitated by an interdisciplinary and collegiate approach.
Mosquito-borne disease in Australia related to intertidal wetlands
The most common mosquito-borne diseases in Australia are Ross River virus infection (RRV) and Barmah Forest virus infection (BFV). These are transmitted by several species but Aedes vigilax (Skuse) is the most important RRV vector and is associated with intertidal wetlands (Hu et al. 2010). The ecology of RRV is reported inter alia in Russell (2002) and, of the vector, was more recently reviewed by Knight (2011). RRV and BFV are polyarthritic diseases which, while debilitating, are not fatal. The most common is RRV with around 5,000 cases reported each year, 50 % of which are in Queensland, a sub-tropical to tropical state. The population of Queensland is growing rapidly, especially in the south-east Moreton Region, which includes the state capital city (Brisbane) and a Ramsar site (Moreton Bay Marine Park). There are extensive salt marshes and mangroves which provide Ae. vigilax habitats (e.g., Dale et al. 1986, 2008a, b), and are protected by state law.
The Ramsar strategic plan and Australian statutes and guidelines
The latest Ramsar Strategic Plan 2009–2015 (The strategic plan) provides an overview of the major issues and approaches advocated by the convention (Ramsar 2012c). There are five main goals. These are to: (1) work towards the wise use of all wetlands; (2) develop and maintain an international wetland network; (3) use international co-operation to enhance wise use of wetlands; (4) ensure institutional capacity and effectivness, and (5) move towards universal membership of the Convention. Of these, Goal 1 (wise use) and Goal 4 (institutional capacity and effectiveness) are of paramount importance at a regional level, especially where the primary management aims may be focussed, not only on wetland conservation but also on, for example, mosquito control. For a perceptive and in depth analysis and critique of the Ramsar Convention committments and the Australian government actions, especially in the context of climate change the reader is referred to Pittock et al. (2010).
In signing the Ramsar Convention Australia agreed to pursue the goals of the convention and in 2012 has 81 Ramsar sites covering 8.1 million ha. Thus there are Acts at the national (Commonwealth) level that are consistent with Ramsar. Of particular importance is the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) which, in its objects (in Section 3) mirrors the goals of the Ramsar strategic plan. Objects of particular relevance to management include: Section 3 (1) (a) “to provide for the protection of the environment”….; (c) “to promote the conservation of biodiversity”; (d) “to promote a co-operative approach to the protection and management of the environment involving governments, the community, land-holders and indigenous peoples” and (e) “to assist in the co-operative implementation of Australia’s international environmental responsibilities”, the latter acknowledging Ramsar and bringing the strategic plan into the management arena. Indeed, in the context of achieving the objects of the EPBC Act, Sect. (2) (f) “includes provisions to enhance the protection, conservation and presentation of world heritage properties and the conservation and wise use of Ramsar wetlands of international importance”.
At a state level it follows that wise management should be the focus in Queensland. However the statutory system that governs wetlands in the state of Queensland is fragmented, with the different perspectives of various agencies potentially not fully supporting the wise use concept (Dale et al. 2010). The main statutes with direct relevance to intertidal wetlands include the Fisheries Act (1994) and the Marine Parks Act (2004), the latter applying to, for example, the Moreton Bay Marine Park (a Ramsar site). The Environmental Protection Act (1994) applies generally. These statutes are all environment-focussed and do not specifically mention human health. This is the subject of the Queensland Public Health Act (2005).
Progress towards achieving a more integrated and adaptive outcome would be to adopt a standardized approach such as the one proposed for Queensland wetlands by Lynch (2011), addressing the monitoring needs for Ramsar (and other) wetlands. Recently Horwitz and Finlayson (2011) also proposed an integrated approach to wetland management and stressed the need for dialogue between the various players (p. 2). This is referred to later.
Mosquito control in Queensland is mandatory for local governments by powers delegated under the Public Health Act (2005). The object of that act is “to protect and promote the health of the Queensland public” (Section 6). Chapter 2 Part 1 of the Public Health Act deals with Environmental Health. It only focusses on human health risks related to environment, not to the health of the environment per se and Section 11 (i) refers to “a designated pest“ which includes mosquitoes (Schedule 2 of the Act). The Public Health Regulation (2005) provides for mosquito management (in the section that also includes dealing with asbestos, a serious pollutant). Thus Part 1A Division 2, Section 2 N refers to the “Requirement to ensure place is not a breeding ground for mosquitos”. It further provides in Section (1) that it must be ensured that “an accumulation of water or another liquid at the place is not a breeding ground for mosquitos”; in Section (2) that “it is irrelevant whether the accumulation of water is artificial, natural, permanent or temporary” and, finally, in Section (4) defines a breeding ground for mosquitoes as “a place where mosquito eggs, larvae or pupae are present” and examples of these places include ponds and tidal pools. This could mean that wetlands may be seriously impacted by mosquito control, as a consequence of physical modification or by the effects of insecticide application. However, drainage of wetlands is not specifically required, as it was with the Health Regulation 1996, under the earlier 1937 Health Act.
As well as legislation there are guidelines available for mosquito control at state and national level. At the state level a mosquito code of practice was published in 2002 (Local Government Association of Queensland 2002). It was developed by local and state government agencies (mosquito managers and environment protection agencies respectively) as well as involving university researchers. It provided some detail on the various forms of mosquito control and how to prepare a mosquito control program.
A mosquito control program relies on integrated biological, physical, chemical and behavioural control measures. Programs are aimed at preventing new mosquito breeding sites, eliminating established breeding sites and reducing the contact between mosquitoes and humans. A well balanced program will ensure maximum long-term control at lowest overall cost. (Italics added)
At a national level, the Australian Mosquito Control Association prepared a manual for mosquito control, edited by researchers and mosquito control agency personnel, now in its third edition (Durre et al. 2009).
Saltwater mosquito management in eastern Australia
Wise management of mosquito problems emanating from saltwater wetlands, generally those near human settlement, requires institutional capacity and effectiveness so as to develop integrated management programs. Mosquito management tools may be indirect such as public education, or involve direct actions, such as adulticiding in or near human settlements, larviciding of wetlands (and containers), habitat modification (often referred to as source reduction) and biological control. Biological methods alone are generally not sufficient to reduce mosquito populations to an acceptable level. Adulticiding of dispersed adult mosquitoes in Queensland is recommended only when other control measures have failed (Local Government Association of Queensland 2002). Thus the preferred method of control in Australia is to manage larvae in their relatively contained wetland habitats generally by larviciding or, the focus here, by habitat modification.
The major forms of mosquito control were reviewed for intertidal salt marsh habitats in Dale and Hulsman (1990) and remain timely. They identified gaps in knowledge, especially for long-term and chronic effects of pesticides. Resistance is also a potentially ongoing issue with larviciding. This is not a problem with habitat modification, but there is a risk of serious environmental consequences, unless the modification is carefully designed, implemented and monitored. Thus there is a need for wise management and for capacity building for those involved in the management process. This requires integration between science and management activities at all levels both for managing the wetlands and their mosquito populations.
Here we are interested in direct mosquito control by modifying the environment for long-term and effective reduction in mosquito larval numbers, but not by ‘eliminating’ breeding sites in natural systems (as in the Queensland Strategic Framework noted above).
Mosquito management should have positive health impacts, but there is not a great deal of information on this aspect. In theory, reducing mosquito populations should lead to a lower risk of contact between people and possibly infected mosquitoes and hence to reduced incidence of diseases such as RRV. In practice, it is well recognized that mosquito management does reduce mosquito populations, for example see Rochlin et al. (2009) but the link to the impact on disease is not generally made. Ghosh and Guha (2011) reviewed and then modeled risk factors for mosquito-borne disease but, although mosquito control was noted in the concept model, it was not used in the analyses. One study examines the relationship between adulticiding of urban areas and disease (West Nile virus) but adulticides do not directly affect wetlands. The only other research that addresses the link between mosquito management in wetlands (mainly intertidal ones) and disease outcomes is that of Tomerini (2007). She showed, for Queensland, that the more integrated programs (with surveillance, and a range of methods including larviciding, and habitat modification) had lower rates of RRV than those programs that had simpler programs or none at all (Tomerini 2007; Tomerini et al. 2011).
Grounding the discussion a real world example
The following section exemplifies an Australian approach to habitat modification in intertidal wetlands with the dual goals of conserving wetlands and protecting human health. In hindsight it appears to have followed, in essence, the model in Fig. 3 in Horwitz and Finlayson (2011, p. 12). Thus the aim was to move the system from the status quo of healthy ecosystem services (+) but poor health outcomes (−) to one of maintained or enhanced ecosystem services (+) and improved health outcomes (+). In short it aimed at a win–win result.
The increasing concerns in the 1980s about the environmental impacts of pesticides used in intertidal salt marshes and the costs of mosquito management provided the impetus for a change in approach to mosquito management, starting in New South Wales and Queensland. The Gold Coast City Council (a local government body) was the institutional driver in Queensland. It had a triple agenda: to reduce costs of mosquito management, to manage the pest in the light of increasing population pressure and to do this by finding new management tools. The first step was to engage an interdisciplinary team to research the problem. It included people with entomological, geomorphological, fisheries, environmental and mosquito management expertise, representing local and state governments and universities (Dale 2000). That team had an additional agenda: to also reduce impacts on non-target aspects of the environment.
Basic to developing a new method was an understanding of Ae. vigilax requirements and specifically its water-related needs. This species requires a sequence of events in order to successfully develop from egg stage to adult emergence (and biting). This information is well established in the literature and it has been reviewed in Knight (2008, 2011). The habitat needs are specific but the habitats themselves are based on a diversity of land form and tidal flooding patterns so that at some time there is bare exposed substrate (for oviposition and egg conditioning), then flooding (for egg hatch) and finally water remaining long enough for larvae to develop through their four instar stages, pupation and adult emergence. These stages may be completed in less than a week in sub-tropical and tropical climates, especially in summer.
The saltmarsh runnelling project
From this a new paradigm emerged for mosquito management, to do as little as possible to modify the environment while also reducing the chance of mosquito survival to the adult (and biting) stage.
Reflecting on the process
In hindsight the Coomera case study mapped an evolution from fragmented management focused originally on the mosquito to one that has moved towards the type of integration recently envisaged by Lynch (2011) and by Horwitz and Finlayson (2011). In the early 1980s, when the first project started, the mosquito-borne disease aspect of health and its management was the mandate of local government. The environent per se was not seriously considered, and when it was, in the early 1980s, it was not by government mandate but through the actions of individuals. These individuals included the initial driver, the Gold Coast Senior Health Surveyor who directed mosquito control, and the co-opted research personnel (Dale et al. 2008a, b) (The Queensland Environment Protection Agency did not exist until 1994). The underlying rationale of an integrated interdisicplinary approach was reflected in the conceptual model developed post hoc that focussed on human health in its environmental context (Sipe and Dale 2003).
Extension to a mangrove system
Runnelling has only been recommended for suitable salt marsh systems where the detailed survey that is essential for careful design and wise management is relatively easy. However, Ae. vigilax does not confine itself to salt marshes: it can be prolific in mangrove systems (Knight et al. 2012). After the success of runnelling in salt marsh environments, there were requests from managers to develop a similar method for managing mosquitoes in mangrove systems. The need to manage mosquito populations was becoming urgent, as human settlement came closer to mosquito mangrove habitats in south-east Queensland.
The involvement of both scientists and managers at state and local government level also met the Ramsar Goal 4 of developing institutional capacity and effectiveness. The strategies for achieving this that are relevant here, as shown in Fig. 3, include communication and awareness (with participation) and working with international partners (see Dale et al. 2008a, b for collaboration with Florida mosquito management). Developing financial capacity for management is generally beyond the scope of researchers but the methods described in this paper do lead to cost savings and hence contribute to financial capacity (see below). Capacity was developed in an adaptive manner, as local governments in the region learned how runnelling was done (and its rationale), learned how to do it for themselves and finally, in adopting the innovation, developed a suitable technology: a machine specifically designed to create runnels, referred to in the Code of Practice (Local Government Association of Queensland 2002). Effectiveness was demonstrated not only by cost savings, but also by the adoption of the method in the region (and later interstate). For one local government area there was a 50 % reduction in chemical usage after 50 % of the wetland had been modified (Mulder, personal communication); in another, over 50 km of runnels were created over several years (Doyle, personal communication).
It is expected that a similar development of institutional capacity and effectiveness will follow from the mangrove project. With careful monitoring the wetland health should be safeguarded, while also reducing the risk of RRV transmission to the nearby human population.
Our key question was “Can wetland management and mosquito control be integrated to meet the two Ramsar goals of wise use and institutional capacity and effectiveness?” Interpreting wise use, satisfying the dual management objectives of sustaining wetland health and effective mosquito control, is achievable as exemplified by our projects. The interdisciplinary and integrated approach balanced potentially competing interests so that no one perspective dominated and the wetlands were conserved. Further, based on the experience in our projects we find that broad participation by all players at all stages and levels leads to institutional capacity and effectiveness and this is applicable to other complex management issues.
We thank the anonymous reviewers for their constructive comments. In developing this paper we have relied on the many years of collaboration with: state governments (Department of Primary Industries, Fisheries; Department of Environment and Resource Management; Department of Health) and local governments, especially the Gold Coast City Council who also provided vital in-kind support and Tweed Shire Council for valuable advice. For the New South Wales (NSW) project we especially thank Tweed Shire council mosquito managers Clive Easton and Brian Falkner for sharing their knowledge and for field assistance, NSW Recreational Fishing Trusts, Fisheries Ecosystems Branch, Industry and Investment NSW, NSW Land and Property Management Authority. We thank too our many university colleagues and Dale family and student assistants who have provided inputs to the project dating back to the 1980 s. Over several decades funding has been provided from diverse sources. The main ones have been the Australian Research Council (Grants: C19906833; C00001962; LP0211583), Gold Coast City Council, the Queensland Department of Health and the Mosquito and Arbovirus Research Committee.