Reef Research: Volume 8 No. 1 March 1998

GREAT BARRIER REEF WATER QUALITY MONITORING AND DUGONG PROTECTION AREAS

David Haynes, Janet Slater, Michelle Devlin and Leane Makey

Introduction

erial surveys of dugong (Dugong dugon) within the Great Barrier World Heritage Area (GBRWHA) have indicated that there has been a dramatic decline in dugong numbers in southern Great Barrier Reef waters between 1984 and 1994 (Marsh and Corkeron 1997). It is estimated that the population decline is in the order of 50 per cent over the 10-year survey (Marsh and Corkeron 1997). This is of particular concern as the dugong has been endangered or exterminated over much of its range and the species is considered to be vulnerable to extinction (IUCN 1990). Definitive reasons for the reported decline are unclear, but are certain to include indigenous hunting and accidental capture in fishing nets, as well as loss of seagrass habitat and water quality degradation caused by coastal and hinterland development (The condition of river catchments in Queensland: a broad overview of catchment management issues 1993; Marsh et al. 1995; Marsh 1992; Preen et al. 1995). Current management initiatives for dugong in the GBRWHA are designed to contribute to maintenance of dugong populations at current or higher levels throughout their range (Great Barrier Reef Marine Park Authority 1994). This is to be achieved via establishment of dugong protection areas, tighter controls and bans on fish netting, and tighter controls on indigenous hunting. Research on dugong biology is being extended with scoping studies of environmental factors which may impact on dugong and their habitat such as water quality.

Dugong Protection Areas

Figure 1. Dugong Protection Areas

Click on thumbnail to view this map

In August 1997, the Commonwealth and Queensland Governments agreed to the establishment of a coastal sanctuary system to protect dugongs in the southern Great Barrier Reef and the Hervey Bay region (figure 1). Sanctuary establishment was seen as the most effective immediate measure to address the rapid decline of the southern Great Barrier Reef dugong population.

Dugongs are threatened by both direct (e.g. entanglement in fishing nets, indigenous hunting) and indirect impacts (e.g. degradation of water quality and seagrass beds). Sanctuaries provide a focus for implementing both immediate and longer-term management measures to protect dugong populations from these types of impacts. Ultimately, a combination of these measures will promote the long-term recovery of the species.

Criteria for selecting sanctuary locations and boundaries

The location and size of the sanctuaries is based on past and current distribution of dugong populations and their seagrass habitats, as well as the recommended geographical spacing to ensure adequate genetic interchange within the species. They have also been designed to encompass areas large enough to protect a significant percentage of a typical home range.

It is essential to restore historically important habitat (even though they may not currently support large dugong numbers) in order to provide viable and protected refuges for anticipated increased populations, as well as protect existing dugong populations. For example, dugongs were historically abundant in the Newry region (figure 1), with populations large enough to support two dugong fisheries in the 1900s. In recent times, the population has been severely reduced even though the area supports substantial seagrass meadows. If managed effectively, the Newry sanctuary should be a valuable recovery area for the species.

Two tiered system of protection

A two-tiered system of 'A' and 'B' type sanctuaries has been established (figure 1). In 'A' sanctuaries, the use of offshore set nets, foreshore set nets and drift nets are prohibited. The use of river set nets will be allowed with modification in all sanctuaries except Shoalwater Bay and Hinchinbrook where they are banned. Other netting practices such as ring, seine and tunnel netting are not considered to pose a serious threat to dugong and will continue to be permitted with some modifications. In 'B' sanctuaries, mesh nets are permitted, but with more rigorous safeguards and restrictions than before (e.g. compulsory net attendance). These measures will be kept under review and strengthened if necessary.

Implementation

Sixteen dugong sanctuaries between Hinchinbrook and Hervey Bay will be implemented under the Queensland Nature Conservation Act 1994 (figure 1). New regulations are now in place to implement netting changes in these sanctuaries under the Queensland Fisheries Act 1995. Additional steps to protect dugong populations completely are currently being considered and include reductions in boat speeds, traditional hunting agreements and increased enforcement and surveillance of new conservation measures.

Impacts from outside the sanctuaries

The dugong sanctuaries should provide protection from the direct human impacts of accidental death from fishing and boating but it is also important to consider indirect impacts arising from pollution.

Agriculture, public health, urban expansion and industrial activities around the world have contributed to the widespread contamination of aquatic ecosystems with organochlorine compounds, heavy metals, polycyclic aromatic hydrocarbons (PAHs) and excess nutrients (Fowler 1990; Tatsukawa et al. 1990; Brodie 1995; Connell 1995). Organochlorines and heavy metals are conservative and essentially permanent additions to the environment (Clark 1992) and are often highly toxic to biota (Richardson 1995). Polycyclic aromatic hydrocarbons and excess nutrients can also have profound environmental impacts (Grimmer 1983; Brodie 1995).

Organochlorines

Organochlorines are organic (carbon-based) chemicals which contain bound chlorine. Many of these compounds are 'man-made' and enter the environment through human activities. Chlorinated organic compounds have a wide range of industrial and agricultural applications. They include pesticides and herbicides such as DDT, lindane, diuron and 2,4-D; and polychlorinated biphenyls (PCBs) which were, and are still used in a range of industrial applications including dielectrics in electrical transformers. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are also chlorinated organic compounds. PCDDs and PCDFs are not produced intentionally, and have no known use. They form as unwanted bi-products of processes such as waste incineration, coal burning, metal smelting, car exhausts, cigarette smoke, pulp and paper manufacture and sugarcane and trash burning (Dioxins in the environment: report of an interdepartmental working group on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans 1989; Müller et al. 1996a, b). They also occur as contaminants in a range of herbicides and in PCB mixtures (Safe and Hutzinger 1989).

Pesticides and herbicides are transported to the aquatic environment as aerosols and in overland flows and ground leachate following rainfalls (Clendening et al. 1990). Organochlorine compounds can also enter the environment as contaminants contained in effluent discharges and in urban storm water run-off. Organochlorine compounds are highly hydrophobic, and once in the water column, tend to adsorb to fine particulates or be bioaccumulated in lipids in aquatic biota (Olsen et al. 1982). Tissue accumulation of organochlorine pesticides and PCBs have been implicated in reproductive and immunological abnormalities observed in terrestrial bird populations and in marine mammal populations (Boon et al. 1992). Many of these compounds are also suspected carcinogens (Richardson 1995), and herbicides, in particular, have the potential to adversely impact seagrasses.

Heavy metals

In contrast, heavy metals are natural constituents of rocks and soils and enter the environment through atmospheric transport of dust and through sediment movement caused by overland flows (Bryan 1971; Förstner 1989). Many metals are biologically essential, but all have the potential to be toxic to biota above certain threshold concentrations. Following industrialisation, unnaturally high quantities of metals such as arsenic, cadmium, copper, mercury, lead, nickel and zinc have been released, and continue to be released into the aquatic environment in many urban, industrial and agriculture storm-water and wastewater discharges (Förstner 1989).

Once solubilised in the water column, metals may be accumulated by marine organisms from solution via passive uptake across permeable surfaces such as gills and from food in the digestive tract (Chester and Murphy 1990; Rainbow 1990). Metal toxicity is primarily a consequence of the chemical inactivation of cellular enzymes (Förstner 1989), with organism growth, reproduction and behaviour all being potentially affected by elevated environmental metal concentrations (Langston 1990).

Polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons are derived from petroleum products and their use and enter the marine environment bound to particulates in wastewater spills and discharges, urban run-off, and during the emission of combustion exhausts. They are known carcinogens and mutagens (Clark 1992; Benlahcen et al. 1997), and have strong bio-accumulation capacities in aquatic organisms (Broman et al. 1990; Connell 1995). Polycyclic aromatic hydrocarbons have been implicated in a wide range of human health effects and disease problems in aquatic organisms (Grimmer 1983; Plesha et al. 1988).

Nutrients and sediments

Nutrients and sediments are exported to the marine environment in wind-blown dust and in water and sediments contained in overland flows and river discharges. Soil erosion and loss of nutrients is generally elevated from agricultural lands. Almost all of the catchments draining into Great Barrier Reef waters are used for agricultural purposes and have been extensively modified since European settlement (The condition of river catchments in Queensland: a broad overview of catchment management issues 1993). It is estimated that sediment loads discharged to the Great Barrier Reef region are now two to five times higher than loads discharged prior to settlement. As a consequence, total nutrient input into the Great Barrier Reef is estimated to have risen by about 30 per cent in the last 140 years (Moss et al. 1992; Furnas et al. 1994; Brodie 1995; Furnas and Brodie 1996; Neil and Yu 1996). A majority of land sourced sediments and nutrients are transported to reef waters during flood events (Brodie and Mitchell 1992; Brodie et al. 1996).

The modern increase in nutrient and sediment load discharge into reef waters has created a potential long-term threat to seagrasses (Preen et al. 1995; Short et al. 1996). Increased turbidity from discharged sediments may result in a shade induced reduction in seagrass photosynthesis (Shepherd et al. 1989; Walker and McComb 1992; Abal and Dennison 1996) or in extreme conditions, result in smothering of plants (Walker and McComb 1992). Increased nutrient concentrations also have the potential to cause epiphyte growth on seagrasses which reduces seagrass photosynthetic rates (Walker and McComb 1992). High nutrient concentrations may also weaken the structural integrity of seagrasses (Burkholder et al. 1992).

Figure 2. Pollutant transfer through the dugong food chain

Great Barrier Reef water quality research and monitoring

Water quality monitoring associated with DPAs and dugong management and conservation is based around measurement of the transfer of pollutants from the land to the nearshore marine environment and their subsequent incorporation into the dugong/seagrass food chain (figure 2). This water quality monitoring program can be divided into five broad areas of research.

a. Marine Park pollutant concentrations

Figure 3. Intertidal sediment and seagrass sampling sites, 1997

click on thumbnail to view this map

In 1997, sediment and seagrass samples were collected from the intertidal zone of 15 sites between Torres Strait and Moreton Bay (figure 3). These sampling sites are under a range of urban and agricultural influences and include many of the DPAs and other critical dugong habitat. Collected sediments and seagrasses have been analysed for the presence of heavy metals, PCBs, pesticides, herbicides and polycyclic aromatic hydrocarbons (PAHs). Samples of sediments and seagrasses from selected sites have also been analysed for polychlorinated-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Additional sampling of sediments from river mouths and sites further offshore will be carried out during May 1998. Atrazine and diuron (herbicides), PCBs, PAHs and PCDD/Fs have all been detected in sampled sediments and seagrasses. Detailed analysis of the data will be used to establish pollutant concentration baselines in DPAs and elsewhere, and correlations for environmental pollutant concentrations and human activity will be derived. The data will also be used to develop pollutant-partitioning models to investigate the movement of pollutants between sediments, seagrass and biota (including dugong).

b. Dugong pollutant concentrations

Tissue samples are being collected opportunistically from dugong reported stranded along the Queensland coast. Carcass recovery is being carried out in conjunction with the Department of Environment (DoE), James Cook University and the Department of Primary Industries (Queensland Boating and Fisheries Patrol). Three dugong carcasses recovered from Magnetic Island, Bowen and Mackay in late 1996 have been sampled in a pilot study. All animals were drowned or suspected to have been drowned in fishing nets. Arsenic, chromium and nickel were found to be elevated in collected tissue. Total dioxin concentrations were also elevated and dioxins were found in an unusual congener pattern compared with other marine mammals (Haynes et al. 1998). Pollutant data will continue to be collected from further animals stranded along the Queensland coast. As this occurs analyses will allow temporal and spatial variation in dugong pollutant body burdens to be examined and correlated with animal sex, age, condition and home range.

c. Seagrass herbicide impacts

Contamination of nearshore environments by pollutants may be an additional stress on seagrass meadows and their potential role in seagrass decline in Queensland water is essentially unknown (Walker and McComb 1992; Ralph 1998). The herbicides atrazine and diuron are used extensively by the agricultural industry in Queensland (Hamilton and Haydon 1996). They are highly water-soluble and have relatively long environmental half-lives. Preliminary investigations of the toxicity of atrazine and diuron to Halophila ovalis have been completed (Ralph 1997, 1998). This study determined that short-term herbicide exposure resulted in reduced photosynthesis and leaf loss in this seagrass species. Toxicity trials will be continued, with the toxicity of diuron to additional species of seagrasses (Halodule sp., Zostera sp. and Cymodocea sp.) assessed in 1998. The exposure concentrations of the herbicide will be based on existing literature and Great Barrier Reef Marine Park Authority survey data. This information will then be combined with catchment monitoring data of herbicide concentrations to assess potential risk to seagrass meadows from current and predicted agricultural herbicide applications.

d. Chlorophyll a monitoring

Dissolved nutrients have a relatively short life span in reef waters as they are actively acquired by phytoplankton and benthic plants. As a consequence, chlorophyll concentration acts as a sensitive, direct integrator of phytoplankton biomass and hence, nutrient status of sampled water masses (Bell and Elmetri 1995; Brodie et al. 1996). The key objectives of the chlorophyll monitoring program are the detection and quantification of long-term trends and regional differences in the nutrient status of Great Barrier Reef waters (Brodie et al. 1996). Forty-eight stations situated along nine inshore-offshore transects are currently sampled monthly in the monitoring program (Haynes et al. 1997). The time-scale over which the monitoring program has been carried out (1992-1998) is, as yet, too short to determine whether there is evidence of eutrophication in Great Barrier Reef waters. However, data collected has confirmed that chlorophyll concentrations (and therefore nutrient concentrations) recorded from nearshore waters are significantly higher and more variable than samples collected further from the coast (Haynes et al. 1997). This chlorophyll monitoring program is complemented by a second program which collects quantitative information on the composition and spatial dynamics of flood plumes discharging to Great Barrier Reef waters. The flood monitoring program was initiated to map the distribution of phaeopigments, dissolved and particulate nutrients, suspended solids and herbicides as they are transported offshore into reef waters in river flood plumes (Devlin et al. 1997a, b).

e. Dugong habitat risk assessment

Environmental and predictive data collected during the dugong water quality monitoring program will be combined with other information to carry out a risk assessment for dugong habitat and stocks within Queensland waters. Partitioning models will be used to develop pollutant mass balances for Marine Park waters. An assessment of the health risks from consumption of contaminated dugong tissue will also be made.

Acknowledgments

Julie Bahr, Leon Jackson and Cyrilla Wellings (GBRMPA) are thanked for production of figures. Mike Short, David Savage, Cameron Mulvulle and Graham Byron (DoE) and Andy Dunstan (Undersea Explorer) are thanked for facilitating field collections. Tony Preen (James Cook University) and Lochy Markwell (DPI) are thanked for assistance with dugong tissue collection. Bill Dennison (University of Queensland) and Tony Stokes and Jon Brodie (GBRMPA) are thanked for their ongoing support for the program.

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