Fabián Alberto Vanella

Temperature influence on post-prandial metabolic rate of sub-Antarctic teleost fish.

The influence of temperature on the aerobic metabolism and the energetic cost of food intake (Specific Dynamic Action; SDA) have been investigated in four species of Sub-Antarctic teleosts. The species were the notothenioids Paranotothenia magellanica, Patagonotothen sima and Harpagifer bispinis and the zoarcid Austrolycus depressiceps. Individuals were captured in the vicinity of Ushuaia Bay. Experimental temperatures were 10, 4 and 2 degrees C, which correspond to summer, winter and extreme winter respectively. Individual respirometry chambers and calorimetric techniques were used. Different food items were provided: crustaceans (isopods and amphipods) and Argentinean hake muscle. Interspecific analysis was done on species fed with isopods. A rapid increase in oxygen consumption was registered after meals, indicating a typical SDA response. The Duration of the SDA was longer at low temperatures. The extra energy spent during the process itself, and when expressed as a percentage of consumed food energy, decreased with decreasing temperature. The SDA Coefficient was higher for H. bispinis that were fed with isopods. We suggest that decreases in temperature diminish the metabolic cost and extend SDA. Energy-saving mechanisms could be an evolutionary advantage to minimize the energetic cost of living at low sub-Antarctic temperatures. A general model of exponential decay is suggested for the duration of SDA and Temperature, based on the present study and compiled from literature data.

Thermal ecology of Galaxias platei (Pisces, Galaxiidae) in South Patagonia: perspectives under a climate change scenario

The native freshwater fish Galaxias platei shows a wide latitudinal distribution in Patagonia, being found on both sides of the Andes. Currently, climate change poses one of the main threats to native fish, and its effects are appearing faster in high southern latitudes. The aim of this work was to analyse the possible effects of climate change in G. platei through its thermal responses. We hypothesized that juveniles of this species would be affected by indirect rather than by direct consequences of climate change. We determined the thermal tolerance polygon using Critical Thermal Methodology and preferred temperatures using a thermal gradient. Additionally, we evaluated routine metabolic rate using stop-flow respirometry. Results showed an intermediate to large polygon, with a non-negligible portion acquired through acclimation. Preferred temperatures and routine metabolic rates were positively related to acclimation temperature. Results suggest that G. platei thermal tolerance is dependent on its prior thermal history, have a eurythermal nature but maintain high levels of cold tolerance. Moreover, G. platei would be better suited at maintaining homeostasis at highest temperatures where more energy could be available for growth. This is the first time that thermal ecology data are registered for this species at its southernmost distribution.

Spatial patterns of summer demersal fish assemblages around the Antarctic Peninsula and South Shetland Islands

Abstract During the research programme conducted on the OV Puerto Deseado in the summers of 2011 and 2013, 36 stations were sampled using a demersal net at depths between 53–590 m in the Antarctic Peninsula and South Shetland Islands. A total 3378 fish specimens belonging to 36 species were recorded. Notothenidae was the best-represented family in species number, with Lepidonotothen nudifrons, L. larseni and Trematomus scotti being the most numerous species. Of the fish assemblages, 20% of the species were considered as dominant, 10% as common, 13% as occasional and 57% as rare. Six groups (and two sub-groups) were obtained by the ordination diagram based on geographical location: group 1=Gerlache Strait, group 2=Deception Islands, group 3=Biscoe Island, group 4=between Elephant and King George islands, group 5=northern Antarctic Peninsula, and group 6=South Shetland Islands, with sub-groups 6a shallower South Shetland Islands and 6b deeper South Shetland Islands. Sampling depth and water temperature significantly explained the spatial pattern. A latitudinal pattern of decreasing abundance from north-east to south-west was found in L. larseni and the opposite in T. scotti. The predictability of fish composition in the assemblages’ areas could be a useful tool for ecosystem-based management.

Palaeogeographic changes drove prehistoric fishing practices in the Cambaceres Bay (Tierra del Fuego, Argentina) during the middle and late Holocene

Fishing intensification is evidenced in the archaeological record of the Beagle Channel region (Tierra del Fuego, Argentina) during the late Holocene by significant diachronic increases in both the representation of coastal taxa and the diversity of pelagic fish species taken. Faunal evidence from the Imiwaia I site, however, shows a different pattern in temporal variation in the exploitation of coastal fish in contrast to that of the regional trend. By comparing data from palaeogeography and archaeoichthyology, we have been able to evaluate how changes in Holocene coastal geomorphology near the Imiwaia I site influenced hunter–gatherer subsistence. The results show that the abundance and taxonomic diversity recorded in ichthyofaunal assemblages at the Imiwaia I site coincide with the environmental expectations arising from palaeogeographic reconstructions of the Cambaceres Bay during the middle and late Holocene.

Thermal responses of three native fishes from estuarine areas of the Beagle Channel, and their implications for climate change

The aim of this work was to analyze the thermal responses of Odontesthes nigricans, Eleginops maclovinus and diadromous Galaxias maculatus, key species in estuarine areas of the Beagle Channel (Tierra del Fuego, Argentina), under a climate change scenario. We hypothesized that in the southernmost limit of the species’ distribution, individuals are more likely to be affected by indirect consequences of climate change rather than direct temperature mortality. Their thermal tolerance limits were assessed using the Critical Thermal Methodology and their preferred temperatures, using a thermal gradient. Additionally, the Fulton’s condition factor and the energy density of individuals were analyzed as a proxy of the condition of fishes acclimated to different temperatures. Results showed that species analyzed have the ability to acclimate to the different temperatures, intermediate to large tolerance polygons and positive relationships between preferred and acclimation temperatures, indicating their eurythermic nature. Thus, O. nigricans, E. maclovinus and diadromous G. maculatus populations from Tierra del Fuego could experience enhanced performances because of moderate warming being and, as it was hypothesized, be influenced by indirect consequences of climate change (habitat degradation or changes in trophic structure) since they are living in environments that are widely cooler than their maximum tolerance.