icolls - Sustainable Tourism CRC

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).
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