icolls - Sustainable Tourism CRC

More documents

Recommendations

Info

ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS information about the variability in source and consumer isotopic signatures in the proximity of the mouth of both systems. The primary sources of carbon sampled were riparian vegetation, mangroves, BFPOM, BCPOM, attached and free-floating algae and seston (suspended particulate organic matter). Riparian vegetation and mangroves were hand collected, 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. Using a scalpel blade and brush, attached algae were carefully scraped from all available surfaces, including mangrove pneumatophores, rocks and woody debris. Aquatic insects, crustaceans and small fish were collected using a dip net and a small purse seine net. Fish were also collected in a larger seine net (measurements required) and unbaited fish traps. Sediment-dwelling organisms, including bivalve molluscs and polychaete worms, were collected using a yabby pump. Mobile consumers such as crabs were opportunistically hand collected wherever possible. Upon collection, all samples were immediately placed in individually labelled zip-lock bags and stored on ice. For the smaller organisms collected, this approach has been shown to enable them time to void their guts to expedite processing in the laboratory (Bunn & Boon 1993; Beaudoin et al. 2001). Samples were frozen for transportation back to the laboratory. Laboratory Sample Processing In the laboratory, samples of riparian vegetation, BFPOM, BCPOM, attached algae 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 that 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 et al. 1999; Beaudoin et al. 2001). Analytical Methods Samples were analysed using a continuous flow-isotope ratio mass spectrometer (Micromass Isoprime EuroVector EA300, Manchester, UK) at Griffith University. Isotope ratios are expressed as either δ13C or δ 15 N and relate to the ratio of 13C:12C and 14N:15N, respectively. Values were calculated according to the following equation: δ 13 C or δ 15 N = [(Rsample / Rstandard) - 1] x 1000 where Rsample is the isotopic ratio for the sample and Rstandard is the isotopic ratio of the standard (PeeDee belemnite carbonate for δ13C and atmospheric N for δ 15 N). For abundant taxa, nitrogen isotope signatures were statistically compared between samples from Tallows and Belongil Creeks using one way ANOVAs (Sokal & Rohlf 1999). Food web analyses were conducted using IsoSource mixing model software (Phillips & Gregg 2003). Trophic fractionations of carbon and nitrogen signatures were set at 0.2‰ and 1.5‰ respectively, based on values reported in the stable isotope literature (Peterson & Fry 1987; McCutchan, Lewis, Kendall & McGrath 2003; Hadwen & Bunn 2004). Results Community Composition The composition of the Tallows Creek food web was distinctly different from that of Belongil Creek. There were generally more species collected from Tallows Creek, although some of these additional taxa reflected the status of Tallows Creek at the time of sampling (closed) more so than the influence of the STP inputs. For example, numerous freshwater macroinvertebrates were collected from Tallows Creek, highlighting the low salinity and absence of tidal fluctuations in the system. In contrast, moderate tidal exchange in Belongil Creek ensured that only estuarine/marine taxa were present at the time when collections were made. 28
ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS In both creeks there were seven major primary food sources collected, namely riparian vegetation, BCPOM, BFPOM, seston (particulate matter from the water column), mangroves (Avicennia marina), epilithon and filamentous algae. Aquatic macroinvertebrates sampled from both systems included polychaete worms (Marphysa spp.), bivalve molluscs, greasyback prawns (Metapeneaus bennettae) and false spider crabs (Halicarcinus sp.) (Table 5). In addition, freshwater bugs (Corixidae, Hemiptera) were collected from Tallows Creek. Fish diversity also differed between the two systems, with more taxa collected from Tallows Creek than Belongil Creek (Table 5). Five fish species were collected from both sites, namely Sillago ciliata, Mugil cephalus, Gerres subfasciatus, Ambassis marianus and Rhabdosargus sarba. Only one additional fish species was collected from Belongil Creek (Philypnodon grandiceps), whereas seven additional fish species were collected from Tallows Creek (Table 5). Table 5: Macroinvertebrate and fish taxa collected from Tallows Creek and Belongil Creek in May 2003 Stable Isotopes Taxa Tallows Creek Belongil Creek Invertebrates Fish Bivalvia Bivalvia Corixidae Marphysa sp. Marphysa sp. Metapenaeus bennettae Halicarcinus spp. Metapenaeus bennettae Centropogon australis Gerres subfasciatus Mugil cephalus Sillago ciliata Anguilla anguilla Mugil cephalus Rhabdosargus sarba Rhabdosargus sarba Ambassis marianus Ambassis marianus Pelates sexlineatus Philypnodon grandiceps Gerres subfasciatus Sillago ciliata Platycephalus fuscus Gobiomorphus sp. Achlyopa nigra Acanthopagrus australis Common names for these taxa are reported in Appendix B. As expected, all components of the Tallows Creek food web were enriched in nitrogen relative to those sampled in Belongil Creek (Figure 4). The degree of enrichment was substantial at all trophic levels, with a mean enrichment of 9.1 δ 15 N ‰ between primary carbon sources and 11.6 δ 15 N ‰ between consumers. Elevated BCPOM δ 15 N values (relative to riparian vegetation) reflect contributions from seston (dominated by the sewage effluent) and Avicennia marina, both of which have enriched δ 15 N signatures relative to samples collected from Belongil Creek. In contrast to BCPOM, BFPOM isotope signatures tended to be intermediate between riparian and algal sources, reflecting the mixed nature of this size class of benthic organic matter. 29
Page 1 and 2: ECOLOGY, THREATS AND MANAGEMENT OPT
Page 9 and 10: Chapter 1 ECOLOGY, THREATS AND MANA
Page 31 and 32: Hypseleotris spp. Pseudomugil signi
Page 35: ECOLOGY, THREATS AND MANAGEMENT OPT
Page 39 and 40: δ15 δ N (‰) 15N (‰) δ15 δ N
Page 85 and 86: Research Programs The Sustainable T

icolls - Sustainable Tourism CRC

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?