ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS Discussion Biological Diversity and Conservation Value of ICOLLs There have been several studies that have aimed to compare either the productivity or diversity of ICOLLs with those of permanently open estuaries (Pollard 1994b; Valesini et al. 1997; Sarre, Platell & Potter 2000). Significantly, many of these studies have concluded that despite their productivity, ICOLLs do not support as diverse invertebrate and fish assemblages as comparable permanently open estuaries (Pollard 1994b; Gray & Kennelly 2003). Despite these reports, we found remarkable diversity in invertebrate and fish taxa sampled across the five ICOLLs assessed in this study. Whilst no single ICOLL exhibited diversity like that found in large open estuaries, a significant and broad range of taxa was collected. Significantly, this combined biodiversity highlights the substantial conservation importance of ICOLLs in providing habitat for a taxonomically wide range of organisms (Watts & Johnson 2004). We recommend that a greater understanding of the role of ICOLLs in supporting and maintaining biological diversity throughout the coastal zone is required before management plans and objectives, which typically only focus on single systems, are implemented. For example, although diversity is low in some ICOLLs, they do provide important habitat for species that may not be found in neighbouring systems (Watts & Johnson 2004). We also provide, in this study, evidence that suggests the diversity of ICOLLs is highly variable through time, with opening regimes being the key driving process in influencing species composition (see below). Stable Isotope Signatures of Biota in ICOLLs The stable carbon and nitrogen isotope signatures measured in this study provide support of our proposed MPC. The less depleted δ13C signatures in consumer tissues from systems that are open to the ocean (in comparison to closed systems) supports our hypothesis that marine sources of carbon are being used by consumers in ICOLLs. In addition, with the exception of Tallows Creek, which has a strong sewage nitrogen signature (see next Chapter), there was also a tendency for consumers in open ICOLLs to have higher δ 15 N signatures than those from closed ICOLLs. As numerous researchers have shown that marine nitrogen isotope signatures are generally higher than terrestrial and freshwater nitrogen signatures (Thornton & McManus 1994), this finding offers an additional line of evidence supporting the MPC. Opening Regimes and Carbon Flow in ICOLLs On the basis of the stable isotope data presented in this chapter, we hypothesise that opening regimes play a strong structural and functional role in influencing food web patterns. For example, we found that even in closed ICOLLs, there are strong isotopic patterns that reveal significant marine carbon resource use by invertebrate and fish taxa. We suggest this finding is probably a consequence of the fact that marine carbon sources are more labile and accessible to consumers than are terrestrial carbon sources with high carbon-nitrogen ratios (Thornton & McManus 1994). This research provides the first succinct evidence for applying existing and novel conceptual models of carbon flow to ICOLL environments. We have demonstrated that ICOLL food webs can be characterised by a combination of riverine models, although the degree to which any model is relevant will depend largely on system entrance status at the time of assessment. Conclusions and Implications The consequences of these research findings are two-fold. First, we have demonstrated the importance of marine sources of carbon in supporting consumers in ICOLLs (even those closed to the ocean for extended periods of time). This has implications for fisheries production, recreational use and management of ICOLLs. For example, ICOLLs with more frequent marine connectance are likely to support more estuarine and coastal species, many of which are important food resources (Pollard 1994b; Gray 2001; Gray & Kennelly 2003). Second, we provide evidence to suggest that ICOLLs need to be managed across the coastal landscape with a view to maintaining coastal biodiversity. It is highly likely that systems managed independently of this landscape-level approach will lead to increased entrainment of entrances and subsequent and perhaps irreversible changes in community composition and patterns of carbon flow in these systems. Whilst managers may find opening ICOLL entrances mitigates flooding risks and flushes out algal blooms (Griffiths 1999), the long-term sustainable use of ICOLLs is more likely to be enhanced via a landscape scale rationalisation of entrance modifications. We recommend that if ICOLLs with important recreational and commercial fisheries interests are to be managed to sustain and enhance catches, then neighbouring systems should be retained in pristine 24
ECOLOGY, THREATS AND MANAGEMENT OPTIONS FOR SMALL ESTUARIES AND ICOLLS conditions to facilitate maintenance of biodiversity and provision of recruits to the system targeted for fish and crustacean production. 25
- Page 1 and 2: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 3 and 4: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 5 and 6: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 7 and 8: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 9 and 10: Chapter 1 ECOLOGY, THREATS AND MANA
- Page 11 and 12: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 13 and 14: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 15 and 16: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 17 and 18: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 19 and 20: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 21 and 22: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 23 and 24: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 25 and 26: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 27 and 28: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 29 and 30: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 31: Hypseleotris spp. Pseudomugil signi
- Page 35 and 36: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 37 and 38: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 39 and 40: δ15 δ N (‰) 15N (‰) δ15 δ N
- Page 41 and 42: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 43 and 44: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 45 and 46: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 47 and 48: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 49 and 50: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 51 and 52: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 53 and 54: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 55 and 56: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 57 and 58: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 59 and 60: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 61 and 62: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 63 and 64: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 65 and 66: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 67 and 68: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 69 and 70: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 71 and 72: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 73 and 74: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 75 and 76: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 77 and 78: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 79 and 80: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 81 and 82: ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 83 and 84:
ECOLOGY, THREATS AND MANAGEMENT OPT
- Page 85 and 86:
Research Programs The Sustainable T