Year: 2014
Type: dissertation
Abstract: Climate change has been affecting the Southern Ocean, particularly in the Antarctic Peninsula where the rate of temperature increase is around 3.5 ºC per century. This warming is affecting the duration and extent of the formation of sea ice, and ice shelves, which are known to play an important role in the recruitment and replenishment of stock of Antarctic krill (Euphausia superba). Antarctic krill is the keystone species of the food web in the Southern Ocean, and its low availability may have a negative impact in the reproductive output of Antarctic top predators such as penguins, fur seals and albatrosses. Antarctic krill is caught by fisheries that are managed by the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR), who define precautionary catch limits taking into account the food requirements of top predators such as penguins. One of the species used to monitor changes in the Antarctic is the Gentoo penguins Pygoscelis papua, due to their ecological relevance in the Southern Ocean. P. papua are distributed in a broad range of areas that include islands in the sub-Antarctic and Antarctic regions whose feeding habits in the Antarctic localities consist mainly of Antarctic krill. Furthermore, being a year round resident and having a limited foraging range, P. papua is considered a key species to the CCAMLR program regarding the monitoring of fluctuations in the local availability of Antarctic krill. Furthermore, there is a need to develop CCAMLR methods to reduce handling penguins while assessing their diet. The aims of this study are to characterize the diet of P. papua in Hannah Point, Livingston Island (South Shetland Islands, Antarctic Peninsula) using fresh dead chicks (that died from natural causes), using their body tissues (feathers, nails, flesh) and stomach contents, in order to assess their trophic level and habitat (using the stable isotope signatures of 15N and 13C respectively) and test the reliability of using dead chicks to determine the diets of P. papua in the breeding season. The different tissues and stomach contents were analysed from individuals retrieved near the colony of P. papua in Hannah Point in December 2011. The individuals were chosen based on the condition of the corpse giving priority to those that had little or no sign of predation or decomposition (i.e. recently dead). Then, all taxa found in the stomach contents were quantified, measured, weighted and a frequency analysis made. Also, feathers, nails and flesh were also obtained from the dead chick bodies for stable isotopic analyses. In the case of Antarctic krill, carapaces from individuals were measured to estimate their total length. Also Antarctic krill was randomly collected from a nearby beach (that occurred stranded in excellent condition) close to the Bulgarian Base (BB; approximately 11km from Hannah Point) to compare to the results obtained from the stomach contents of P. papua to assess if P. papua was feeding on Antarctic krill from nearby the colony. Crustaceans comprised 100% by mass of the diet of P. papua. The most represent species in the stomach contents was the Antarctic krill with a 96.77% by mass (100% by frequency of occurrence and 96.77% by number) with a mean length of 40.64mm. Other crustaceans in the diet were Themisto gaudichaudii (0.07% by mass) and members of the orders Mysidacea (0.06% by mass) and Amphipoda (0.02% by mass). The mass of the stomach contents ranged from 12g to 145.5g. The analysis of the isotopic values of 15N and 13C of both Antarctic krill retrieved from stomach contents (5.58 ± 0.73; -25.89 ± 1.07, respectively) and from the BB beach (5.03 ± 0.59; -24.62 ± 0.82, respectively) and for all tissues collected as well (feathers: 9.03 ± 0.77; -23.88 ± 0.42, nails: 8.37 ± 0.55; -24.35 ± 0.39 and flesh: 8.24 ± 0.53; -25.38 ± 0.40) showed that there were significant differences on the 13C values between Antarctic krill retrieved from the stomach contents and from those collected from the BB beach. The correlations obtained between feathers vs. nails and nails vs. flesh for the 15N values suggest that the female progenitor could have been feeding on the same type of prey during the formation of the egg as during the chick rearing period, while the correlations obtained between all tissues analysed for the 13C values suggest that the foraging range could have been the same for both periods. The ratios of isotopes 15N values expressed a significant difference between feathers and all other tissues which can be explained through the fact that different tissues accumulate the same isotope at different ratios as the significant differences found on the 13C values for all tissues further corroborate. In this study I had the possibility to calculate the discriminant factors for the ratio of 13C and 15N for the 3 different chick tissues when they were being fed Antarctic krill and obtained enrichment values similar to the literature. This study concludes that using recently dead chicks it is possible to describe the diet of P. papua that in this case was mainly based on Antarctic kill. By using 13C and 15N values I showed that it is possible the use of dead chick tissues (feathers and flesh preferably) to reconstruct the diet of that population for at least the breeding season, and assess the habitat and trophic levels of Antarctic krill in the Livingston Island region. This study also demonstrates the viability of using recently dead chicks in order to reduce the necessity of handling live penguins thus lessening the impact on penguin populations, relevant to CCAMLR monitoring programs.
Author: Tiago Valente
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2610883810