Comportamento do mexilhão-dourado (Limnoperna fortunei) na presença de peixes e coespecíficos fragmentados: efeitos sobre a produção de bissos, agregação e locomoção

Abstract

Sessile and semi-sessile organisms are not capable of undertaking long-distance movements to avoid a risky zone. Therefore, such organisms have developed alternative defense strategies. Bivalves are unable to escape but can increase their chances of survival in the presence of predators by allocating more energy towards substrate fixation and/or selecting safer locations. It can be expected that these organisms are capable of perceiving the presence of predators and, consequently, responding through these anti-predatory defense mechanisms. This phenomenon is commonly mediated by chemical signals, and previous studies suggest that these signals are alarm cues originating from the injury of conspecific prey that have passed through the predator's digestive tract. The golden mussel, Limnoperna fortunei, is an invasive bivalve species native to Southeast Asia that has become a significant part of invaded ecosystems in South America, competing with other organisms for food and space, as well as occupying an important role in trophic networks. However, physiological and behavioral alterations related to byssus production, aggregation, and displacement of this species in the presence of predators have not yet been investigated. The objective of this study was to experimentally evaluate the behavior of L. fortunei in the presence of fishes with different feeding habits and fragmented conspecifics. Individuals of L. fortunei were collected from the reservoir of the UHE Volta Grande and transferred to the laboratory, where they were kept in aquariums and subjected to three experiments. In the first experiment, L. fortunei was exposed to the following treatments: C - Control, T1 - Prochilodus lineatus, T2 - Piaractus mesopotamicus, and T3 - fragmented conspecifics. The fishes were separated from L. fortunei by a 1mm-thick mesh, allowing the fishes to move throughout the aquarium but preventing direct contact with the mussels. At the end of the assays, we measured the percentage of individuals forming aggregations, and then the mussels were fixed for subsequent byssus counting. In the second and third experiments, individuals of L. fortunei were exposed to effluents from the same fishes and diluted fragmented conspecifics in the water, with the aim of evaluating changes in the horizontal and vertical movement patterns of these organisms. The experimental arrangements assumed that the prey can detect the presence of a potential predator through chemical signals and/or through water currents generated by the fish movements. Differences in byssus emission, aggregation, and movement were tested using mixed-effects generalized linear models. It was observed that L. fortunei individuals of different sizes produced more byssal filaments when exposed to P. mesopotamicus, P. lineatus, and fragmented conspecifics, but only small and large individuals showed this response. No significant changes in aggregation behavior were observed. Regarding movement, a significant decrease in horizontal movement was observed in mussels exposed to these fishes. The findings of this study represent an advancement in understanding the ecological relationships of the invader L. fortunei in the new environment, suggesting the occurrence of adaptive responses mediated through chemical interactions with different species.