icolls - Sustainable Tourism CRC

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ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS open/closed estuaries’ (Froneman 2002; Perissinotto, Nozais, Kibirige & Anandraj 2003; Teske & Wooldridge 2003) in South Africa. This diverse range of names reflects the complexity and uncertainty surrounding ICOLL form and connection to the sea. We propose that the term ICOLLs best describes many of the intermittently opening systems in Australia, as they behave more like large lakes during times of closure than they do as estuaries. However, we acknowledge that systems within this subset of waterbodies may, at least seasonally or occasionally, behave like estuaries. Although many researchers consider ICOLLs to be a subset of estuaries (e.g. Day 1981; Roy et al. 2001), ICOLLs differ from estuaries in that they do not always experience the tidal ranges and salinity gradients typical of the large macrotidal rivers upon which much of our understanding of estuaries is based (Neira & Potter 1992, Balls, Macdonald, Pugh & Edwards 1995; Young, Potter, Hyndes & de Lestang 1997). In addition to these periods of reduced tidal flux, ICOLLs tend to have comparatively low surface and catchment areas. In Australia, freshwater discharge into ICOLLs is generally low and, subsequently, their connection to the sea is usually infrequent (Young et al. 1997; Roy et al. 2001). Thus for extended periods they may function more like saline lakes, but with unique biogeochemical characteristics and limnological processes. The role of ICOLLs in coastal zone conservation and fisheries production has long been overshadowed by the high productivity and fisheries catches that typify large estuaries (Pease 1999; Roy et al. 2001; Saintilan 2004). Nevertheless, ICOLLs provide nursery and breeding habitats for a wide range of commercially and recreationally valuable fish, mollusc and crustacean species (Pollard 1994b; Bell 1997; Roy et al. 2001). In addition, ICOLLs can provide habitat and resources to rare and threatened species that do not occur in large macrotidal estuaries (Arthington & Marshall 1999; Hughes, Ponniah, Hurwood, Chenoweth & Arthington 1999; Bilton, Paula & Bishop 2002; Watts & Johnson 2004). Although water quality changes and fisheries production responses to changes in catchment management practices are reasonably well understood in large estuaries (Edgar & Barrett 2000; Josefson & Rasmussen 2000; Bowen & Valiela 2001; Morrisey, Turner, Mills, Williamson & Wise 2003), the response of ICOLLs to natural and artificial (human) perturbations are largely unknown. We believe that whilst much of the literature on estuaries is likely to be useful in the conceptualisation of ICOLL ecological processes, only dedicated research in these systems will ensure that their unique characteristics are understood, and consequently, coastal conservation and fisheries production goals met in the future. In light of increasing developmental pressures in coastal regions of Australia and the absence of reliable ecological information on ICOLLs, the identification of key knowledge gaps is essential to prioritise research that will enable ecologically sustainable management of these systems (Blaber et al. 2000; Jones, Tyler & Wither 2002; Wilson 2002). We identify high priority research themes in this Chapter. At present, the major processes threatening the ecological health of coastal waterways (including ICOLLs) are (see Table 1): • Eutrophication and contamination – excessive nutrient and contaminant inputs from agricultural, industrial and urban sources; • Fisheries – impacts of excessive harvesting of fish and macroinvertebrates by commercial and recreational fishers; • Modification of flow regimes, including water allocation to industry, urban settlements and agriculture, and specifically for ICOLLs, the artificial breaching of berms; • Tourism – increasing tourist and resident recreational demand and use of ICOLLs; and • Coastal development – increasing land clearing for urban, industrial and agricultural land uses, and habitat loss through in-system modifications. This report presents a review of current understanding of the effects of each of the listed threatening processes, with emphasis on our knowledge or lack thereof with respect to ICOLLs. We draw heavily on estuarine data and resources from the scientific literature, but also refer to lake and river literature to aid understanding of systems that experience long periods without surface water connection to the ocean. 2

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS Table 1: Processes threatening the ecological health of ICOLLs Process Causes Ecological Effects Required Research Required Management Eutrophication and Contamination Changes in land use – especially increases in percent land cover of agriculture, industry and urban developments. In addition, land clearing can lead to increased runoff and groundwater inputs. Fisheries Unsustainable management of extractive industries. Commercial fisheries and recreational fishing practices are unsustainable in many coastal regions. Modification of Flow Regimes and Artificial Berm Breaching Flow Regimes: Irrigation water extractions and the establishment of weirs and dams upstream can markedly alter flow regimes. Berm Breaching: Local councils often open ICOLLs in response to resident concerns regarding flood abatement and/or water quality / algal bloom issues. ICOLLs can act as nutrient sinks – internal processing and cycling can subsequently lead to algal blooms, even after inputs cease. Contaminant bioaccumulation is highly likely in consumer organisms in ICOLLs (including humans) due to the capacity of these systems to trap heavy metals and organic toxins and their accumulation in the tissues of aquatic biota. Excessive removal of top order consumers and filter feeders can have deleterious effects on population dynamics and genetic diversity. In addition, water quality can suffer if filter feeders and consumers are removed, thus leading to undesirable algal blooms. Hydrodynamic modifications can lead to changes in physical and chemical characteristics of the waterbody. Changes to flow characteristics can influence the nature and abundance of useable sources of nutrients and organic matter. Artificial breaching can lead to drastic changes in species composition through immigration and emigration of consumers. Exotic invasions can be enhanced through artificial modification of opening regimes. Research is required to assess how ICOLLs process nutrients and organic matter and whether or not they do act as sinks for these inputs. Can food web processes reduce the impact of nutrient inputs? Do toxicants and contaminants accumulate in ICOLL food webs? More information on the catches of commercial and recreational fishers is required to assess the sustainability of fishing practices in ICOLLs. More information is required to assess the repercussions of forced opening at different times of the year on species survival, population dynamics (e.g. effects on recruitment) and community composition. Sustainable management of STP outflows, e.g. further treatment by passage through constructed wetlands. Reduced industrial and agricultural inputs especially during periods of low or no flow/tidal flushing. Restoration of riparian buffer zones is likely to inhibit excessive inputs from agricultural runoff. The timing and periodicity of extractive fisheries might enhance sustainability through provisions for emigration, immigration and reproduction. Acknowledgement of environmental flow requirements in coastal waterways should enable the implementation of ecologically sustainable water use, flow management and entrance opening practices. 3

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