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Anthropogenic Ecological Change and Impacts on Mosquito Breeding and Control Strategies in Salt-Marshes, Northern Territory, Australia
Abstract and Figures
Darwin, in the tropical north of Australia, is subject to high numbers of mosquitoes and several mosquito-borne diseases. Many of Darwin's residential areas were built in close proximity to tidally influenced swamps, where long-term storm-water run-off from nearby residences into these swamps has led to anthropogenic induced ecological change. When natural wet-dry cycles were disrupted, bare mud-flats and mangroves were transformed into perennial fresh to brackish-water reed swamps. Reed swamps provided year-round breeding habitat for many mosquito species, such that mosquito abundance was less predictable and seasonally dependent, but constant and often occurring in plague proportions. Drainage channels were constructed throughout the wetlands to reduce pooled water during dry-season months. This study assesses the impact of drainage interventions on vegetation and mosquito ecology in three salt-marshes in the Darwin area. Findings revealed a universal decline in dry-season mosquito abundance in each wetland system. However, some mosquito species increased in abundance during wet-season months. Due to the high expense and potentially detrimental environmental impacts of ecosystem and non-target species disturbance, large-scale modifications such as these are sparingly undertaken. However, our results indicate that some large scale environmental modification can assist the process of wetland restoration, as appears to be the case for these salt marsh systems. Drainage in all three systems has been restored to closer to their original salt-marsh ecosystems, while reducing mosquito abundances, thereby potentially lowering the risk of vector-borne disease transmission and mosquito pest biting problems.
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... Modifying or restoring vegetation in the environment where mosquitoes reside can also impact mosquito spread because vegetation is a source of nutrition and shelter for adult and immature mosquitoes [33]. Changes in vegetative cover can occur naturally, but they are often the outcome of landscape disturbance brought about by land clearance, urbanisation and vector-control initiatives [3,33]. ...
... Modifying or restoring vegetation in the environment where mosquitoes reside can also impact mosquito spread because vegetation is a source of nutrition and shelter for adult and immature mosquitoes [33]. Changes in vegetative cover can occur naturally, but they are often the outcome of landscape disturbance brought about by land clearance, urbanisation and vector-control initiatives [3,33]. In Australia, there are four broad categories of vegetation community type: (i) forest; (ii) rainforest; (iii) grassland; and (iv) desert. ...
... Most species of endemic mosquito traditionally occupy areas with the first three types of vegetation because these areas are inundated with vegetative cover (e.g. trees, shrubs, grasses) which they can use as food and energy sources, resting, breeding and oviposition sites [3,33]. However, the diversity of habitats within each of these categories can be significant and for individual mosquito species, there will be a suite of environmental factors that provide ideal conditions conducive for abundant mosquito populations; these can include freshwater, brackishwater or saline environments, as well as those predominantly permanent, semi-permanent, or ephemeral. ...
Changes to Australia's climate and land-use patterns could result in expanded spatial and temporal distributions of endemic mosquito vectors including Aedes and Culex species that transmit medically important arboviruses. Climate and land-use changes greatly influence the suitability of habitats for mosquitoes and their behaviors such as mating, feeding and oviposition. Changes in these behaviors in turn determine future species-specific mosquito diversity, distribution and abundance. In this review, we discuss climate and land-use change factors that influence shifts in mosquito distribution ranges. We also discuss the predictive and epidemiological merits of incorporating these factors into a novel integrated statistical (SSDM) and mechanistic species distribution modelling (MSDM) framework. One potentially significant merit of integrated modelling is an improvement in the future surveillance and control of medically relevant endemic mosquito vectors such as Aedes vigilax and Culex annulirostris, implicated in the transmission of many arboviruses such as Ross River virus and Barmah Forest virus, and exotic mosquito vectors such as Aedes aegypti and Aedes albopictus. We conducted a focused literature search to explore the merits of integrating SSDMs and MSDMs with biotic and environmental variables to better predict the future range of endemic mosquito vectors. We show that an integrated framework utilising both SSDMs and MSDMs can improve future mosquito-vector species distribution projections in Australia. We recommend consideration of climate and environmental change projections in the process of developing land-use plans as this directly impacts mosquito-vector distribution and larvae abundance. We also urge laboratory, field-based researchers and modellers to combine these modelling approaches. Having many different variations of integrated (SDM) modelling frameworks could help to enhance the management of endemic mosquitoes in Australia. Enhanced mosquito management measures could in turn lead to lower arbovirus spread and disease notification rates.
... Similarly, mosquitoes that serve as vectors for malaria and other diseases are endemic in many places where changes to mangrove ecosystems are occurring. Attributing changes in vector abundance to changes in mangrove structure requires comparison against a baseline level of vector abundance given natural wet-dry cycles (Jacups et al. 2012). ...
... Mangrove destruction can lead to a decline in fish production, ultimately affecting nutrition in associated communities (Naylor et al. 2000). Disease transmission is an example of a regulating service: within mangrove swamps, the natural wet-dry cycle that creates and limits mosquito habitat, and thus affects disease transmission, can be disrupted by increased waste-and storm-water run-off from nearby residential or commercial development (Jacups et al. 2012). Protection from storm surges is an example of a different type of regulating service: in the absence of intact coastal mangroves to attenuate waves, loss of life from coastal flooding may be significantly increased (Das and Vincent 2009). ...
... Similarly, mosquitoes that serve as vectors for malaria and other diseases are endemic in many places where changes to mangrove ecosystems are occurring. Attributing changes in vector abundance to changes in mangrove structure requires comparison against a baseline level of vector abundance given natural wet-dry cycles (Jacups et al. 2012). ...
... Mangrove destruction can lead to a decline in fish production, ultimately affecting nutrition in associated communities (Naylor et al. 2000). Disease transmission is an example of a regulating service: within mangrove swamps, the natural wet-dry cycle that creates and limits mosquito habitat, and thus affects disease transmission, can be disrupted by increased waste-and storm-water run-off from nearby residential or commercial development (Jacups et al. 2012). Protection from storm surges is an example of a different type of regulating service: in the absence of intact coastal mangroves to attenuate waves, loss of life from coastal flooding may be significantly increased (Das and Vincent 2009). ...
Background/Question/Methods
Changes in ecosystems have the potential to exert significant pressures on human health. Attributing morbidity and mortality impacts to specific ecological processes and functions, however, has proven difficult. Research efforts in both the ecological and health sciences have provided evidence for many elements linking ecosystem change and human health. Here, we connect these often disconnected, but intrinsically interrelated, research efforts into a comprehensive framework that allows us to assign human health impacts to specific ecosystem changes. There is a strong desire to link health effects of ecosystem change into ecosystem service assessments, but this has seldom been done. Our framework allows health impacts to be integrated into ecosystem service assessments. This work is a product of a multi-disciplinary working group sponsored by the National Academies Keck Futures Initiative.
Results/Conclusions
Our framework connects empirical research across diverse fields in the health sciences using an ecosystem services framework. This allows us to identify multiple causal pathways between ecosystem change and specific health outcomes. Here, we address the interdisciplinary aspects of susceptibility and risk that mediate the influences of human-land use on health-related ecosystem services. We present a template for aligning multiple human health categories, including both communicable and non-communicable diseases, with proximate and distally connected ecosystem changes. In support of this, we devise an interdisciplinary lexicon to improve communication across fields and guide future research efforts. By developing a set of common assessment metrics, we define how ecosystem services can be used as a framework to describe ecosystem influences on human health.
... However, rodents infected with Bartonella can also be found in these restored areas (Beckmann et al., 2020) which can increase disease risk if their populations achieve high abundances. Restoration impacts in temperate regions extend beyond terrestrial environments and are seen in salt marsh waterscapes, where restoration techniques that alter tidal channels and ponds to minimize flooding and encouraging habitation of vector predators have decreased the abundance of vectors resulting in potential health benefits (Jacups et al., 2012;Rochlin et al., 2009Rochlin et al., , 2012. ...
Zoonotic diseases represent 75% of emerging infectious diseases worldwide, and their emergence is mainly attributed to human‐driven changes in landscapes. Land use change, especially the conversion of natural areas to agricultural use, has the potential to impact hosts and vector dynamics, affecting pathogen transmission risk. While these links are becoming better understood, very few studies have investigated the opposite question—how native vegetation restoration affects zoonotic disease outbreaks.
We reviewed the existing evidence linking native vegetation restoration with zoonotic transmission risk, identified knowledge gaps, and, by focusing on tropical areas, proposed forest restoration strategies that could help in limiting the spread of zoonotic diseases.
We identified a large gap in information on the effects of native vegetation restoration on zoonotic diseases, especially within tropical regions. In addition, the few studies that exist do not consider environmental aspects that can affect the outcomes of restoration on disease risk, such as the land use history and landscape structural characteristics (as composition and configuration of native habitats). Our conceptual framework raises two important points: (1) the effects of forest restoration may depend on the context of the existing landscape, especially the percentage of native vegetation existing at the beginning of the restoration; and (2) these effects will also be dependent on the spatial arrangement of the restored area within the existing landscape. Furthermore, we propose important topics to be studied in the coming years to integrate zoonotic disease risk as a criterion in restoration planning.
Synthesis and application. Our results contribute to a more comprehensive forest restoration planning, comprising multiple ecosystem services and resulting in healthier landscapes for both people and nature. Our framework could be integrated into the post‐2020 global biodiversity framework targets.
... Generally, wetland restoration aims at reestablishing the original hydrology and expanding wetlands (Wagner et al. 2007). In inland wetlands, this could be done by artificial flooding of wetlands (Batzer and Resh 1992) to restore a natural flooding regime (Jacups et al. 2012). In coastal areas, the aim is to reconnect the marsh to the sea and intensify tidal flooding by digging tidal channels, or by OMWM, RIM or runneling (Turner and Streever 1999;Rochlin et al. 2009). ...
To stop the worldwide decline of wetlands, conservation measures like restoration, protection and construction of these ecosystems are indispensable. However, wetland conservation could influence mosquito populations. We analysed how conservation measures affect the species composition and abundance of mosquitoes by conducting a systematic literature review and generated results from 113 selected articles. Thereby, we separately assessed conservation measures in constructed, for example polders, and natural, non-constructed, wetlands. An increase in overall mosquito abundance was more prevalent in constructed wetlands, but not in studies conducted in non-constructed wetlands. Besides assessing overall mosquito abundance, we developed a scheme to rank mosquito species-specific nuisance after conservation measures. Mosquito species can differ in their nuisance potential according to their biting and host-seeking behaviors. We further assessed the effects of mosquito management practices on specific mosquito species and discussed different practices between constructed and non-constructed wetlands. Whereas in constructed wetlands more management practices could be applied, practices in non-constructed wetlands were limited. In conclusion, we were not able to reject entirely the hypothesis that mosquito populations change after conservation measures in wetlands.
... To reduce the burden of mosquito borne disease, the NT has active mosquito monitoring and control programs that service the major residential centers [3], with the highest control efforts concentrated around Darwin, due to the denser population and location adjacent to localised and extensive coastal wetlands, and due to the direct sea and air transport links with Asia [4]. Darwin also has a unique combined Mosquito Engineering Program between the NT Government, Top End Health Service Medical Entomology Section, and the City of Darwin (CoD) local council [3,4], which was created in 1982 to rectify the widespread mosquito problems caused by stormwater discharge along the coastal fringes of urban Darwin [5]. ...
The Northern Territory Top End Health Service, Medical Entomology Section and the City of Darwin council carry out a joint Mosquito Engineering Program targeting the rectification of mosquito breeding sites in the City of Darwin, Northern Territory, Australia. In 2005, an investigation into potential subterranean stormwater breeding sites in the City of Darwin commenced, specifically targeting roadside stormwater side entry pits. There were 79 side entry pits randomly investigated for mosquito breeding in the Darwin suburbs of Nightcliff and Rapid Creek, with 69.6% of the pits containing water holding sumps, and 45.6% of those water holding sumps breeding endemic mosquitoes. Culex quinquefasciatus was the most common mosquito collected, accounting for 73% of all mosquito identifications, with the potential vector mosquito Aedes notoscriptus also recovered from a small number of sumps. The sumps were also considered potential dry season maintenance breeding sites for important exotic Aedes mosquitoes such as Aedes aegypti and Aedes albopictus, which are potential vectors of dengue, chickungunya and Zika virus. Overall, 1229 side entry pits were inspected in ten Darwin suburbs from 2005 to 2008, with 180 water holding sumps identified and rectified by concrete filling.
... Source reduction is the removal or permanent destruction of mosquito breeding sites, or modification of sites that eliminate them as a potential breeding source. 170 It can also involve the removal of aquatic plants that are required for the lifecycle of specific mosquito vectors. Mosquito producing habitats that are appropriate for source reduction include the following: containers (e.g. ...
... The soil salinity not only was a key factor which decided natural vegetation distribution in coastal wetlands 28,35 , but also increased rates of net N and P mineralization fluxes and turnover in tidal wetland soils 55,56 , resulting in alteration of the soil nutrient content and distribution. In order to improve the soil quality to be suitable for farming, the techniques of salt leaching and salt reducing were applied in cropland of the YRD like other saline land in some countries [57][58][59][60] . Therefore, the soil salinity in croplands and paddy fields were much higher than those in natural wetlands (Fig. 4F) and soil salinity tend to increase with decreasing land formation age from 1855 to present (Fig. 5). ...
The delivery and distribution of nutrients in coastal wetland ecosystems is much related to the land use. The spatial variations of TOC, TN, NH4+-N, NO3−-N and TP and associated soil salinity with depth in 9 kinds land uses in coastal zone of the modern Yellow River Delta (YRD) was evaluated based on monitoring data in field from 2009 to 2015. The results showed that the average contents of soil TOC, TN, NO3−-N, NH4+-N and TP were 4.21 ± 2.40 g kg−1, 375.91 ± 213.44, 5.36 ± 9.59 and 7.20 ± 5.58 and 591.27 ± 91.16 mg kg−1, respectively. The high N and C contents were found in cropland in southern part and low values in natural wetland, while TP was relatively stable both in profiles and in different land uses. The land use, land formation age and salinity were important factors influencing distributions of TOC and N. Higher contents of TOC and N were observed in older formation age lands in whole study region, while the opposite regulation were found in new-born natural wetland, indicating that the anthropogenic activities could greatly alter the original distribution regulations of nutrients in coastal natural wetlands by changing the regional land use.
In northern Australia the northern salt marsh mosquito Aedes vigilax is a vector of Ross River virus and is an appreciable pest. A coastal wetland adjacent to Darwin's residential suburbs offers a favorable habitat for Ae. vigilax, and despite vigilant mosquito control efforts, peaks of Ae. vigilax occur in excess of 500/trap/night some months. To improve mosquito control for disease and nuisance biting to nearby residential areas, we sought to investigate meteorological drivers associated with these Ae. vigilax peaks. We fitted a cross-sectional logistic regression model to weekly counts of female Ae. vigilax mosquitoes collected between July, 1998 and June, 2009 against variables, tide, rainfall, month, year, and larval control. Aedes vigilax peaks were associated with rainfall during the months September to November compared with January, when adjusted for larval control and tide. To maximize mosquito control efficiency, larval control should continue to be implemented after high tides and with increased emphasis on extensive larval hatches triggered by rainfall between September and November each year. This study reiterates the importance of monitoring and evaluating service delivery programs. Using statistical modelling, service providers can obtain solutions to operational problems using routinely collected data. These methods may be applicable in mosquito surveillance or control programs in other areas.
The swamp area bordering the northern Darwin suburbs is an important breeding site for Ae. vigilax (Whelan 2007). Its eggs are laid in non-draining areas on salt affected damp soil with both bare soil or associated vegetation of relatively low height and density. This allows the female mosquitoes access to the soil or plant base for oviposition (Reynolds 1961, Sinclair 1976, Strickman 1982, Dale et al. 1986). The eggs can remain drought resistant for up to 12 months (Hamlyn-Harris 1933), and hatching occurs when the eggs are inundated by either tides or rain (Dale et al. 1986, Whelan 1989).
Our results show that in the Darwin coastal wetlands, most larval control for Ae. vigilax was carried out in the late dry and early wet season between October and January, with the highest Ae. vigilax larval densities occurring between October to December. Wet season flooded areas progressively recede after each wet season until most of the area is dry in the mid dry season (July). The various vegetation categories are determined by the length of time of fresh water flooding, both during and after the wet season, and the increasing extent of tides in the dry season. For the various reed categories, there is a vegetation progression from the lower tidal areas to the maximum extent of tidal flooding. The Schoenoplectus/mangroves (i) experience the shortest period of fresh water influence, with the Eleocharis (f) having longer fresh water flooding and with the Typha (g) having the longest period of fresh water influence.
Control of the vector is usually a crucial factor in control programs for tropical diseases spread by insect vectors. Successful control programs aim at vulnerable points in the interactions between the vector, the reservoir host, the pathogen, the human host, and the environment. The objective is to prevent potential transmission, or interrupt actual transmission, by reducing the abundance, longevity, or host contact of the vector--whichever is most appropriate to the particular pathogen or disease and the local situation. The importance of individual assessment in the light of local conditions and a knowledge of the biology of the local vector is stressed. The vector-borne diseases discussed here are malaria, filariasis, arbovirus diseases, trypanosomiasis, leishmaniasis, plague and rickettsiosis.
Abstract Will warming climate increase the risk or prevalence of mosquito-borne disease in Australia, as has been projected in a number of scientific publications and governmental reports? Unfortunately, most of these ‘predictions’ do not adequately consider the current and historical distribution of the vectors and diseases, their local ecology and epidemiology and the impact of societal features and the capacity for public health interventions in Australia. Overall, a strong case can be made that we are unlikely to see significant changes in the distribution of transmission of the exotic pathogens causing malaria and dengue, and while activity of endemic arboviruses such as Murray Valley encephalitis and Ross River viruses may possibly increase in some areas, it is likely to decrease in others. The ecologies of mosquito-borne diseases can be complex and difficult to predict, and any evaluation of potential effects of changes in climate will need a detailed examination of site-specific vector, host and other factors likely to influence the outcomes on human health. Of itself, climate change as currently projected, is not likely to provide great cause for public health concern with mosquito-borne disease in Australia.
The distribution of eggs and larvae of Aedes vigilax was studied on part of a coastal salt-marsh in south-east Queensland. At the macro-scale (8 ha area), the largest numbers of larvae hatched were from samples taken in areas with relatively low open vegetation adjacent to drainage channels. Such areas are likely to be suitable for egg conditioning and hatching and are also accessible to adult mosquitoes. At the micro-scale (the environs of two small pools), most hatching occurred in narrow bands at specific elevations from the pool bottom but the relationship with vegetation was variable. Failure to hatch larvae from samples taken at the start of, or during, the cooler months was thought to be associated with egg diapause. At the macro-scale whilst the marsh was flooded, most larvae were found in two habitat types: the tall dense Sporobolus virginicus in relatively elevated locations and in depressions dominated by Sarcocornia quinqueflora. At the meso-scale (on a 1.4 ha grid) the distribution of larvae was found to be further related to water movement. Most larvae were in areas of slower water movement and appeared also to be redistributed by tides.