Effects of penguin guano on spatial behavior of Antarctic marine invertebrate species: an exploratory study

Abstract Antarctic penguins’ guano represents a complex mixture of nutrients and chemical compounds. A large amount of guano produced during the breeding season can flow into seawater, near the colonies, altering the chemical balance of coastal environments. However, information on how guano input may alter marine community structures and dynamics in Antarctic ecosystems remains scarce. This exploratory investigation assesses the influence of guano, as a chemical stressor, on habitat selection (spatial avoidance behavior) in three key Antarctic marine invertebrate species: the amphipods Cheirimedon femoratus and Oediceroides lahillei , and Antarctic krill Euphausia superba . We employed a linear non-forced exposure system simulating a chemically heterogeneous environment, combining: (i) model organisms; (ii) two exposure scenarios, a linear guano gradient and guano as chemical barrier; (iii) guano from two penguin species, Chinstrap and Gentoo; (iv) two light conditions (outdoor and darkness); and (v) two exposure times (5 and 8 h). After 5 h, both amphipod species exhibited significant avoidance responses to guano under the conditions tested. Krill did not show a response related to guano; they consistently aggregated at the system’s extremes, reflecting krill’s complex spatial dynamics. These findings indicate that guano can alter amphipod distribution by triggering avoidance responses, potentially affecting distribution patterns and leading to localized population declines. As a pilot assessment, this study highlights the need to integrate behavior-based endpoints and non-forced exposure approaches to understand the ecological effects of chemically complex inputs in Antarctic marine ecosystems. Graphical abstract