- Title
- Trophic associations involving temperate estuarine fish and crustaceans in coastal saltmarsh habitat
- Creator
- Alderson, Brendan Dean
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2014
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- It is well regarded that coastal saltmarshes provide nursery habitat, food and refuge to many species of fish and invertebrates that utilise estuarine environments and can often supply vast quantities of organic material to nearby aquatic habitats. As with many vegetated estuarine areas, the loss of saltmarsh habitat from various pressures can have a deleterious effect on organisms that utilise them. One of the primary causes of saltmarsh loss comes from the movement or transgression of mangroves into saltmarsh habitat. Due to the possible threat of sea-level rise, which may enhance the effects of mangrove transgression into saltmarsh habitat, an important question to be asking at the present time is ‘how would the loss of saltmarsh habitat, especially from the transgression of mangroves, affect estuarine fish assemblages that utilise these areas’. The overall aims of this thesis, therefore, were to examine the trophic importance of saltmarsh habitat to estuarine fish and shore crab assemblages within a typical temperate Australian estuary (Brisbane Water, NSW), and to investigate how these assemblages that utilise saltmarsh areas interact with nearby estuarine habitats, such as mangroves. Sampling was done at a number of spatial scales throughout the estuary to compare these spatial patterns over time, where applicable. The results of this research suggest that fish and nektonic invertebrate assemblages sampled from saltmarsh habitat within Brisbane Water were quite diverse compared with other temperate Australian saltmarsh areas within the same region, and as with other similar studies, were dominated by a few small species such as Macrobrachium intermedium, Pseudomugil signifer and Ambassis marianus as well as numerous juveniles of commercial species such as Liza argentea, Myxus elongatus and Acanthopagrus australis. The large abundance of these juveniles further provides evidence to the hypothesis that saltmarsh habitat provides an important nursery function for fish and mobile invertebrates that utilise estuarine ecosystems. In terms of functional guilds, the results of this research are similar to those found for saltmarsh areas in other parts of the world, where estuarine residents and marine migrants often dominate saltmarsh fish assemblages. In addition, the low proportions of the fishes from the piscivorous feeding guild suggests lower predation pressures for the smaller fish that inhabit saltmarsh areas and again highlights the provision of refuge that saltmarsh offers within the estuarine environment. The unique feeding opportunities that present themselves to fish that visit inundated saltmarsh areas (such as the mass export of crab larvae during spring tidal phases) do not appear to influence fish assemblage structure in other nearby habitats such as mangroves. Although fish assemblage structure in adjacent mangrove areas did not appear to be influenced by the presence of saltmarsh habitat, the abundance of the common estuarine species, Ambassis jacksoniensis, was found to be greater within mangrove areas associated with saltmarsh habitat during spring tidal cycles when saltmarsh was inundated by tidal water. This finding suggests that this species may be a key vector in the trophic relay of secondary production from saltmarsh habitat to the greater estuary in coastal saltmarsh areas of Australia. Although the presence of saltmarsh habitat appeared to influence the abundance of Ambassis jacksoniensis within neighbouring mangrove areas, the diets of this species sampled from saltmarsh and mangrove habitat were not significantly different despite their apparent preference for crab larvae within saltmarsh patches and larval insects within mangrove forests. This infers that if saltmarsh habitat were to be replaced by mangroves due to factors such as sea-level rise and subsequent transgression, the ecological consequences to estuarine fish assemblages, at least in terms of dietary requirements, may not be as severe as first thought. With respect to shore crab diet, the results of this research suggest that in temperate Australian locations, crabs feed primarily on fine benthic organic matter and microphytobenthos rather than fresh plant material such as Sporobolus virginicus, although this vegetation type could influence the isotope signature of microphytobenthos on the marsh surface by contributing to the local pool of dissolved inorganic carbon. The results also suggest a patch size threshold may exist before the enriched dissolved inorganic carbon can be distinguished in microphytobenthos from background levels. The large amount of variability in fish and crab data observed both within and among different saltmarsh patches within Brisbane Water throughout the research indicates not all saltmarsh areas within a particular estuary function the same as a fisheries resource. This could have important implications for conservation management with respect to saltmarsh habitat, with the application of an adaptive management strategy. This may aid in the setting of realistic restoration and rehabilitation targets that may vary between settings and may also help to select areas for priority conservation and restoration. More research is required to fully understand the function and processes that are evident within this vegetated estuarine habitat and to provide a more general basis to the knowledge already known in regards to the ecology of these areas.
- Subject
- saltmarsh; fish; diet; shore crab
- Identifier
- http://hdl.handle.net/1959.13/1051193
- Identifier
- uon:15256
- Rights
- Copyright 2014 Brendan Dean Alderson
- Language
- eng
- Full Text
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