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Food selection of Antarctic sea star Odontaster validus (Koehler) : laboratory experiments with food quality and size

Kidawa A.

Polish Journal of Ecology

2009

Vol. 57, nr 1

139-147

According to Optimal Foraging Theory a consumer should select its diet in order to maximise net energy intake per unit of foraging time. Therefore, the Antarctic scavenging sea star Odontaster validus can be expected to choose food items of high profitability and ignore those of low profitability. Laboratory experiments with agar models of food items were performed to investigate the foraging behaviour and food selectivity of O. validus. Freshly caught sea stars were first fed with fish meat to minimize differences in their feeding status and then starved for 2 and 4 weeks. Sea stars were divided into three size groups (small - radius 1-3 cm, medium - radius 3-4 cm, large - radius 4-5.5 cm). Agar food items of different quality (low - 1.2 kJ, medium - 2.5 kJ, high - 4.1 kJ) and size (small - 8 cm[^3] and large - 64 cm[^3]) were utilized in the experiments. Sea stars were individually presented with food items placed on the aquarium bottom, and their behaviour (number and type of ivestigated food items, time needed for final choice) was observed for 30 minutes. Starved individuals preferentially selected more profitable food items as is predicted by Optimal Foraging Theory. Choice of food item was probably mediated by contact chemoreception. Starvation time and sea star size had significant impact on selectivity. Mean number of food items of different quality investigated by sea stars starved for 2 weeks was higher then in sea stars starved for 4 weeks. Low quality food items were mostly chosen by small sea stars, and never by large individuals starved for 2 weeks. Sea stars O. validus were also capable of distinguishing between small and large food items. Final choice made by sea stars presented with food items of differing size depended on their size with large and medium individuals choosing mostly large food items. Sea stars starved for 2 weeks chose higher proportion of large food items than individuals starved for 4 weeks. Such strategy in accordance with Optimal Foraging Theory allows for flexibility in O. validus feeding behaviour and enables this species to survive in harsh marine environment, where food resources accessible during the Antarctic winter are scarce and unpredictable in space and time.