Despite prior studies showing good agreement between fin and muscle isotope ratios in temperate fishes, the non-lethal method of fin sampling has yet to become a standard technique in isotopic food-web studies, and the relationship between the two tissues has never been tested in the tropics. We hypothesised that fin and muscle δ13C and δ15N would be strongly correlated in tropical fishes, thus allowing non-lethal sampling of these species. To test this hypothesis, we analysed fin and muscle tissues from 174 tropical fishes representing 27 species from the Mitchell River, Queensland, Australia. Fin tissue was a strong predictor of muscle-tissue δ13C (r2 = 0.91 for all species) and was slightly enriched in 13C (0.9‰), consistent with the results of studies on temperate species. Fin tissue was a poorer predictor of muscle-tissue δ15N (r2 = 0.56 for all species) although the mean difference between the tissues was small (<0.1‰). Differences were smallest in the largest fish, possibly because the elemental composition (%N) of fin more closely resembled that of muscle. These measurements provide more impetus for increased use of fin tissue as a non-destructive means of testing hypotheses about fish food webs in the tropics and elsewhere.

Early Tertiary sediments of the Antarctic Peninsula region continue to yield a rich assemblage of well-preserved fossil dicotyledonous angiosperm wood. The wood ¯ora under consideration is from the Collins Glacier region on Fildes Peninsula, King George Island and is derived from tuaceous sediments of the Middle Unit of the Fildes Formation. These deposits accumulated in a volcanic setting adjacent to a basic-intermediate stratocone. The fossil assemblage provides further evidence for the existence of cool temperate forests, similar in composition to those found today in New Zealand, Australia and, in particular, southern South America. This paper describes two conifer and ®ve angiosperm morphotypes, four of which are new additions to the Antarctica palaeo¯ora records. Cupressinoxylon Goeppert, which is the dominant conifer in terms of numbers, and Podocarpoxylon Gothan represent the conifers. The angiosperm component includes two species of Nothofagoxylon and two previously undescribed wood morphotypes that exhibit greatest anatomical similarity to woods of Luma A. Gray (Myrtaceae) and Eucryphia Cav. (Cunoniaceae). These morphotypes are described and assigned to the organ genera Myrceugenelloxylon Nishida, and Weinmannioxylon Petriella, respectively. A model based on the extant cool temperate Valdivian rainforests is proposed and ecological reconstructions based on palaeobotanical and geological evidence suggest that changes in the palaeovegetation re¯ect natural dynamics following volcanic disturbances.

1. High light availability and stable base flow during the dry season promote primary production in perennial rivers of the wet-dry tropics, in contrast to production during the wet season which is often limited by turbidity and scouring. The Mitchell River of northern Queensland (Australia) was studied to understand controls on aquatic production and respiration in the dry season in relation to spatial and temporal gradients of light and temperature. 2. At three sites along the river, whole-ecosystem gross primary production (GPP) and respiration (ER) were measured from diel changes of dissolved oxygen using the open-channel single station method. Using stable carbon and nitrogen isotope analysis, aquatic consumers and their potential basal food resources were also assessed to determine food web relationships at the beginning and end of the dry season. 3. Nutrient limitation of aquatic net primary production was implied from the oligotrophic conditions and high algal C:N ratios. Rates of GPP were comparable with other tropical and temperate rivers and were regulated by light availability. 4. Respiration rates were high and similar to other tropical and subtropical rivers. Up to 52% of temporal variation of ER was explained by temperature, while P ⁄ R was lowest at the downstream site. 5. Benthic algae were the major carbon source for primary and secondary benthic consumers (insects) in the dry season but not for higher consumers (fish and crustaceans). Despite high rates of ER, which were probably supported by decaying terrestrial C3 plant material, this carbon source was not identified as contributing to animal consumer biomass. 6. While benthic algal production in the dry season sustained benthic invertebrates, the importance of external subsidies of carbon along the river, probably from the floodplain, was emphasised for fish and large invertebrates, which evidently were feeding on carbon sources not present in channel waterholes during the dry season.

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The identification of the dominant sources of carbon supporting consumer biomass in aquatic food webs is often difficult but essential to understanding the limits to aquatic secondary production. Stable isotope analysis (SIA) is a powerful tool to estimate the contribution of different sources to consumers, but most food web studies using this approach limit analyses to a few key consumer taxa rather than measuring biomass-weighted contribution of sources to the entire community. Here we combined stable isotope analysis with standardized measurements of abundance and biomass of fishes and invertebrates in seven waterholes of a wet-dry tropical river sampled early and late in the dry season. We showed that periphyton (as opposed to phytoplankton and terrestrial C3 plant detritus) was responsible for most standing fish biomass (range 42%-97%), whereas benthic invertebrates were reliant on a mixture of the three sources (range 26%-100%). Furthermore, larger, older fishes at high trophic levels (catfish Neoarius spp., sleepy cod Oxyeleotris lineaolatus and barramundi Lates calcarifer) were supported almost exclusively by periphyton. Phytoplankton and detritus supported a considerable biomass of benthic and pelagic invertebrates, but only in taxa that occupied low trophic levels (e.g. snails). These measurements provide further evidence that although periphyton is relatively inconspicuous relative to other sources, it contributes disproportionately to metazoan biomass in wet-dry tropical rivers.