icolls - Sustainable Tourism CRC

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ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS Materials and Methods Site Selection Given the presumed influence of opening and closing regimes on the structure of food webs, we selected ICOLLs that spanned the range of opening frequencies typical for these systems in northern New South Wales (Figure 2.). We chose five ICOLLs for this study; three in Byron Bay (Belongil Creek, Tallows Creek and Taylors Lagoon), one in the Bundjalung National Park (Jerusalem Creek) and another in Woolgoolga (Lake Woolgoolga) a small coastal town 15 km north of Coffs Harbour. 16 NSW A B C C Woolgoolga Headland Figure 2: Maps of study ICOLLs in northern New South Wales A. Cape Byron region – Belongil Creek, Tallows Creek and Taylors Lagoon; B. Bundjalung National Park region – Jerusalem Creek; C. Woolgoolga Region – Lake Woolgoolga The features of the selected ICOLLs were highly variable and representative of the diversity of systems along the north coast of New South Wales. Both Belongil Creek and Tallows Creek have received large amounts of nutrients over the past 50 years, principally from STPs that discharge directly into their waters (McAlister, Richardson, Agnew, Rowlands & Longmore 2000). In contrast, Jerusalem Creek is a relatively pristine ICOLL whose catchment lies entirely within the relatively undeveloped Bundjalung National Park (McAlister et al. 2000). Lake Woolgoolga has a history of variable opening and closing (including artificially forced opening) as well as contamination. Local residents do not eat fish caught in Lake Woolgoolga, although anecdotal evidence suggests that visitors to the region often do (W. Hadwen personal observation). A Belongil Creek Tallows Creek Taylor’s Lagoon Jerusalem Creek B Cape Byron
ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS Sampling Methods The relative proportion of naturally occurring carbon and nitrogen isotopes have been used to describe feeding relationships and the relative importance of different carbon sources to aquatic food webs for the past 20 years (Kitting, Fry & Morgan 1984; Peterson & Fry 1987; France 1995; Post 2002). This method has been particularly useful in discriminating the relative importance of carbon sources from terrestrial, freshwater and marine sources, as the carbon isotope signatures for these different environments are generally distinct (Peterson 1999; Post 2002). In these instances, mixing models have been developed to quantitatively ascertain the role of the dominant carbon sources to consumer diets (Post 2002). In all ICOLLs, samples for stable isotope analyses of food web structure were collected at least once between January and May 2003 and November 2004. In order to get a handle on variability within ICOLLs, samples were collected from more than one site, depending on the geomorphology of the ICOLL and logistical constraints. An effort was made to collect samples from marine-, estuarine- and freshwater-dominated sites within each system wherever possible. Samples for stable isotope analyses involved collection of all sources of organic matter likely to support consumers at each sampling site, including sediment, detritus, algae and terrestrial vegetation. Invertebrate and vertebrate consumers were also collected, to enable construction of food webs on the basis of biota and food sources from each sample site. The primary sources of carbon sampled at all sites were riparian vegetation, mangroves, BFPOM(BFPOM), BCPOM (BCPOM), attached algae and epilithon, seston (phytoplankton + suspended organic matter) and macrophytes. Macrophytes, riparian vegetation and mangroves were collected by hand, while BFPOM and BCPOM samples were collected by sifting benthic sediments through a series of graded sieves (250 µm – 500 µm – 1 cm). BFPOM samples were obtained from the 250 µm sieve and BCPOM samples were collected from the 500 µm sieve. Attached algae and epilithon were carefully scraped from surfaces, including mangrove pneumatophores, rocks and woody debris using a scalpel blade and brush. Seston (phytoplankton, zooplankton and suspended organic matter) were collected using a 65 µm plankton tow net. Freshwater aquatic insects, crustaceans and small fish were collected using either a dip net or a small purse seine net. Fish were also collected in a larger seine net. Sediment-dwelling organisms, including bivalve molluscs, marine yabbies and bloodworms were collected using a yabby pump. Mobile consumers, including crabs, were opportunistically collected by hand whenever possible. Upon collection, all samples were immediately placed in individually labeled zip-lock bags and stored on ice. For animals, this approach has been shown to enable them time to void their guts, thereby expediting their processing in the laboratory (Bunn & Boon 1993; Beaudoin, Prepas, Tonn, Wassenaar & Kotak 2001; Hadwen & Bunn 2005). Samples were frozen for transportation back to the laboratory. Laboratory Sample Processing In the laboratory, samples of riparian vegetation, BFPOM, BCPOM, attached algae/epilithon, macrophytes and mangroves were rinsed with distilled water to wash away dirt and debris. All samples were dried in an oven at 60°C for at least 48 hours. Dried samples were pulverised in a puck and ring grinding mill for approximately 3 minutes, or until the sample had been reduced to a fine powder. Ground samples were subsequently stored in 5 ml vials and frozen prior to analysis. Trichopteran larvae were removed from their cases upon collection. All aquatic macroinvertebrates were rinsed and dried before being ground using a mortar and pestle. Individuals were ground whole, but ground individuals were often subsequently pooled to ensure sample size was sufficient to enable isotopic analyses. The exoskeletons of all aquatic crustaceans were removed to ensure that accumulated calcium carbonate did not influence carbon isotopic values (Mihuc & Toetz 1994; Leggett, Servos, Hesslein, Johannsson, Millard & Dixon 1999; Beaudoin et al. 2001). For zooplankton, samples were split in two, with half acid washed in 10% HCl to remove exoskeletons and the remainder processed as normal for accurate quantification of nitrogen isotope signatures (Bunn, Loneragan & Kempster 1995). 17
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