Our coastal wetlands are made up of a variety of different habitats, including saltmarsh-claypans, mangroves, and seagrasses. Tidal wetlands are afforded specific protection through the provisions of fisheries legislation. All marine plants (including mangroves, seagrasses and saltmarsh species) are protected by this legislation. In addition, important fish habitats may be given increased protection through declaration as Fish Habitat Areas (formerly Fish Habitat and Wetland Reserves).

Occurrence of saltmarsh mosquitoes

Upper regions of intertidal zones may consist of saltwater couch in which saltmarsh mosquitoes are capable of completing their life cycle. The saltmarsh mosquito (Aedes vigilax) may lay eggs in saltmarsh vegetation within the upper reaches of the tidal zone. Isolated pools may occur as a result of inundation of shallow depressions which lie throughout the saltmarsh. These pools may evaporate naturally or persist as brackish pools after heavy rainfall, usually in summer. Saltmarsh mosquito larvae are capable of developing to adults, usually over a period of six days, if the pools persist.

Control of saltmarsh mosquitoes

Local governments have the responsibility of mosquito control, including control of saltmarsh mosquitoes. The adult form of this mosquito is a major pest in coastal residential areas, and is one of several species which are capable of transmitting the debilitating Ross River virus. Methods of control to reduce the occurrence of Aedes vigilax , include the following:

Chemical control

Local governments administer aerial and backpack spraying programs in known saltmarsh mosquito breeding areas. Controlled application of registered pesticides to the upper limits of the intertidal zone involves use of recommended dilutions of effective agents which specifically target the early stages of saltmarsh mosquito larvae (mosquito wrigglers). Products used include organophosphorus based pesticides, biocides or insect growth regulators. Local government authorities monitor the effectiveness of each application on resident mosquito populations and relate the required level of control to the reported pest and health problems in the area.

The use of pesticides, to control aquatic stages of the mosquito life cycle, has limitations in terms of requiring favourable conditions for aerial application, the expense of chemical supply and application costs, the possibility of inducing pesticide resistance in mosquito populations, and potential for effects on non-target organisms.

Biological control

The availability of biological agents for control of saltmarsh mosquitoes in shallow transient pools is limited. One promising agent is Bacillus thuringiensis var. israelensis (Bti), a bacterium producing active protein crystals, selectively toxic to mosquito larvae. Increased specificity of products used for mosquito control reduces the likelihood of deleterious impacts on non-target organisms. When ingested, the crystals rupture the digestive tract resulting in rapid mortality of the larvae.

Physical control - runnelling

A number of programs are presently in place which involve minor landform modifications to saltmarsh areas with minimal disturbance to associated vegetation. Approvals have been granted by the Department of Primary Industries to allow creation of shallow, spoon shaped drains or ‘runnels’ to enhance tidal flushing of ponds isolated from main tributaries

Suitability of a site for runnelling is determined by the general topography including the tidal profile, the proximity of natural waterways, and the density of intertidal vegetation. Wetlands vegetation may restrict the ease of construction of runnels. For example the occurrence of mangrove pneumatophores (shallow root systems at the base of mangroves) may influence the chosen path of disturbance. Post runnel construction may also be affected through regrowth of pneumatophores or colonisation by mangrove seedlings which may impede flushing of the runnel.

Specifications for the construction of runnels within saltmarsh zones include:

runnels may be hand-dug or constructed using specialised mechanical equipment where impacts on the surrounding vegetation or terrain are minimised;
runnels should be less than 30 cm deep with a width to depth ration of 3:1;
runnels should follow and be confluent with existing natural drainage lines; and
spoil from runnel excavation may be used as fill for very deep depressions or for isolated pools; spoil not be placed in such a position as to form a levee; spoil may be broadcast if dispersed to an undetectable level.
The effectiveness of runnelling in the control of saltmarsh mosquito larvae has been demonstrated at several sites. For example, Coomera Island, southern Broadwater. The increased tidal flushing of saltmarsh zones allows greater movement of larvivorous fish resulting in a reduction of mosquito larvae through both predation and downstream displacement. Runnelling programs which have recently been undertaken in Queensland are being monitored by researchers of Griffith University, to determine long term effects on vegetation patterns and effects on the local water table.

A Permit to undertake a runnelling program within coastal wetlands is required from Queensland Fisheries Service, Department of Primary Industries, in order to comply with the Fisheries Act 1994. Works performed within Fish Habitat Areas also require approval under the Fisheries Act 1994 . Authorisation for works may be considered when the proposed works are necessary in the interests of public health.

If granted, Permits are not transferable or renewable and are subject to restrictions and conditions appropriate to the proposal and the marine fish habitat at the time. Assessment of applications may involve consultation with other government agencies in areas where joint management exists.

In submitting an application for a permit to disturb mangroves, saltmarsh or other marine plants, an application assessment fee applies (please contact your nearest Fisheries Centre for information about application forms and current fees).

A Permit is necessary for any individual or organisation to undertake disturbance or collection of marine plants of any kind. All Government departments, local and semi-governments must also comply with these provisions.

In Queensland, mangroves and all other marine plants are completely protected under the Fisheries Act 1994.