Claudia C. Boy

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.

Reproductive biology and energy allocation of the sea star Cosmasterias lurida (Echinodermata: Asteroidea) from the Beagle Channel, Tierra del Fuego, Argentina

Abstract Seasonal fluctuations in environmental factors at high-latitude marine regions have a strong influence on the reproductive cycles of echinoderms. The purposes of this study on a population of Cosmasterias lurida in the Beagle Channel are to describe the reproductive cycle through histological analyses, to characterize the pattern of gonad and somatic indices, to determine the energy content of different organs and their temporal variation and to establish the pattern of energy allocation. During the study period, from August 2010 to June 2011, four seasonal samplings were performed in the subtidal zone of Ushuaia Bay. Indices (gonad, pyloric caeca and stomach), gonadal histology, organic matter and calorimetric measurements were determined. Gametogenesis begins in February and continues until June when oocyte size increases. The gonadal maximum development and gamete releasing take place between August and December. Temporal variation of energetic reserves in gonads occurs through the variation in gonad mass, with a GI major peak and energy content during August. Stomach and pyloric caeca show their maximum energy accumulation during June, while decrease of organic matter of the body wall takes place from August to December. The population of C. lurida from Beagle Channel suggests an annual reproductive cycle with two maturation events and the influence of water temperature on maturation and releasing of gametes. Different patterns of energy allocation to gonads between sexes were observed, with a greater energy investment in females than in males. Pyloric caeca, stomach and body wall were proposed as energy reservoirs for gonadal maturation and spawning.

Relationship between energy allocation and gametogenesis in Aulacomya atra (Bivalvia: Mytilidae) in a sub-Antarctic environment

Resumen es: Se analizo la gametogenesis y la variacion temporal en la asignacion de energia a diferentes organos de Aulacomya atra del Canal Beagle (Tierra del Fuego...

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.

Age and growth of diadromous Galaxias maculatus (Jenyns, 1842) in southernmost South America (54° S) including contribution of age classes to reproduction

The population of Galaxias maculatus studied here, Arroyo Negro (54° S), is located at the southern extreme of the species distribution. This is the first work on growth and other life history traits of a Fueguian diadromous population based on otoliths study. This species is part of the native fish fauna of Patagonia. Furthermore, studies on the growth and reproduction of G. maculatus in South America mostly refer to freshwater populations of Andean-Patagonian lakes and rivers (about 41° S). Size cohorts were studied; age and growth parameters were estimated, the latter using the VBGM. Four size cohorts were established, and 3+ was determined as maximum age class. No differences were found in growth curves between males and females. The 1+ age class was by far not only the most numerous in the population but also the most represented in the reproductive population. The relation between mean TL and latitude was positive (r = 0.62) for South American populations; however, further studies are needed to determine whether it is this population’s life strategy, the local adaptation of a peripheral population or countergradient growth. The results are interpreted in the context of the information available for other populations, and provide important information about the plasticity in life history traits of this species.