icolls - Sustainable Tourism CRC

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.
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