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Many species of tilapia (a collection of fish species from the cichlidae family) have biological traits that make them successful invaders. Widespread herbivory has been observed across tilapia species, however knowledge on habitat preferences and tilapia interactions with native fish food webs is limited. This study was conducted three years after spotted (Pelmatolapia mariae) and Mozambique (Oreochromis mossambicus) tilapia were detected in the Mitchell River catchment, northern Australia. Tilapia diet and habitat preferences and their trophic position in native fish food webs was determined using a combination of stomach content, stable isotope, and habitat assessment analyses. Plant material was the most abundant item in tilapia stomachs, and some stomachs also contained other items in small quantities, such as fish eggs, small shrimp, and bivalves. Some niche overlap occurred between P. mariae and native omnivore or herbivore fish species. Macrohabitat type (in-channel (no tilapia), floodplain (no tilapia), weir (tilapia present)) was related to native fish food web structure, with weir food webs showing similarities to floodplain food webs. Floodplain habitats including creeks and wetlands were also most similar to weir habitats and may therefore be most at risk of colonization as tilapia spread throughout the catchment. This study clearly demonstrated that the successful rapid invasion of these two tilapia species is linked to suitable habitat with abundant food that fuels growth and reproduction. These findings increase understanding of diet related habitat use during new tilapia invasions and trophic interactions with native species. [ABSTRACT FROM AUTHOR]

Metabolomic and genomic markers in plants have helped diagnose evolutionary pressures and resulting modern-day floristic diversification. Here we use a different set of metrics, 17 biochemical measures made at the whole tissue or bulk tissue level, to study diversification in resource use and productivity among Pacific mangroves. Three mangrove species Bruguiera gynmorhiza (BRGY), Rhizphora apiculata (RHAP), and Sonneratia alba (SOAL) were studied across 5 sites on the island of Kosrae, Federated States of Micronesia with measurements of the following chemical metrics: C, N, P, K, Na, Mg, Ca, B, S, Mn, Fe, Cu, Zn elements and isotope values δ2H, δ13C, δ15N, and δ34S. Species were remarkably distinct in chemical profiles, showing significant differences across all metrics. This indicated long-term resource use partitioning and optimization, with metrics showing physiology and patch-related differences. The patch-related differences meant that metrics were not really fixed in species, but represented flexible traits (“flexitraits”) in fingerprinting mangrove ecology. Effects of tree harvesting could be fingerprinted with the metrics at one of the Kosrae sites. Modeling showed two results. (1) Conservation efforts to preserve low-nutrient specialists like BRGY probably should involve removal of competing SOAL and RHAP rather than nutrient reductions. (2) Although mangrove growth rates were most limited by P, water was a strongly co-limiting factor. This study introduces a new physiological parameter to plant ecology, a water-to-phosphorus ratio, “normalized δ13C/P” or “f13C/P”, that should generally help diagnose how plant N and P nutrient use can be co-limited by water. [ABSTRACT FROM AUTHOR]

Polyunsaturated fatty acids (PUFA) are essential components of cell membranes and reproductive and sensory organs in vertebrates and are largely acquired through their diets. Accordingly, identification of the dietary sources of PUFA is an important consideration in food web studies.We collected fish, macroinvertebrates (aquatic and terrestrial), and plants (aquatic and terrestrial) from floodplain and river channel habitats in a tropical river catchment in northern Australia, to identify food sources and habitats that provided lipid and PUFA rich food that sustain fish populations.The composition of most FA in fish was similar to that reported from other freshwater tropical environments, with the exception of their higher arachidonic acid content. Fish were found to derive their fatty acids primarily from aquatic sources of food and had similar FA composition to aquatic macroinvertebrates. Aquatic macroinvertebrates fed on aquatic plants (algae) and had higher total lipids and FA contents than plants and fish, providing a more concentrated source of PUFA for fish. Fish obtained most of their FA from their diet except for docosahexaenoic acid (DHA), which they must synthesize due to low DHA in algae and macroinvertebrates.There was no overall difference in basal dietary FA composition between floodplain and river channel habitats. However, macroinvertebrate taxa varied in their lipid and PUFA content.Food quality for fish may therefore vary between habitats as a consequence of differences in macroinvertebrate community composition. Given the high algal production on floodplains compared to the river channels, these habitats are likely to represent the major source of high quality food for fish and other aquatic consumers, and conserving habitats that are rich in lipids and PUFA is important for maintaining healthy fish communities. [ABSTRACT FROM AUTHOR]

Floods are extreme weather events that can rapidly change water quality in receiving estuaries. The delivery of nutrients to the coastal zone via floods may stimulate productivity; however, in urban areas, the degradation of water quality and influx of contaminants can negatively affect inhabiting biota. Determining flood effects on inhabiting biota is important for informing catchment management practices. We investigated the body condition response of a commercially important prawn species, the brown tiger prawn Penaeus esculentus, to a large cyclone-driven flood in an urbanized subtropical coastal bay. Prawns were caught 10 days before the flood, 11 days after the flood, and 53 days after the flood in bare substrate areas of central Moreton Bay in Australia. Stable isotopes (δ15N and δ13C) were determined for prawn muscle tissue, and lipid content and a length-weight (Fulton's K) index were used to assess prawn body condition. There were two distinct isotope signatures of tiger prawns living in either riverine or marine influenced areas, suggesting different residency areas within the bay. A flood signal (lower δ13C values post-flood) was detected in prawns in the southern area closest to the Logan River. Condition indices showed a short-term increase in condition of prawns in these southern sites, with no apparent condition change in prawns at other sites. A concurrent pulse in benthic primary productivity (chlorophyll a biomass) was measured in this southern area. Our results suggest that nutrients from the flood stimulated benthic primary production that was transferred through the food web, with positive impacts on prawn nutrition at southern sites. With an expected increase in unpredictable weather, including floods, under a changing climate, understanding short- and long-term ecosystem responses in modified catchments is important for mitigating sediment erosion and estuarine and coastal infilling effects, while maintaining productivity benefits to fisheries in receiving estuaries. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is expected to result in dramatic shifts in the abiotic conditions within estuaries, including an elevation of temperature and salinity levels. Even so, few studies have addressed the impacts of multiple abiotic stressors on the behaviour and life history of key estuarine species, such as those of biological and commercial importance. Here we used a cross-factored experimental design to tease apart the effects of temperature and salinity on intraspecific aggression and growth rates of a native estuarine fish species, the Australian bass ( Macquaria novemaculeata). Juvenile bass were exposed to one of four treatment conditions: 1) baseline temperature and salinity, 2) elevated temperature, 3) elevated salinity, and 4) elevated temperature and salinity. Elevated salinity increased rates of aggression, and elevated temperature decreased rates of growth, although the effects of both factors were mediated by the body size of individual bass. These results therefore highlight complex and variable effects of abiotic stressors and body size, emphasising the importance of considering individual-level attributes when evaluating the impacts of climate change on estuarine fishes. [ABSTRACT FROM AUTHOR]