Behavioral plasticity of nocturnal marine organisms under interspecific competitive pressure

Abstract

Pacific abalone (Haliotis discus hannai) are typical nocturnal organisms in the marine benthic ecosystem. However, whether their rhythmic behavior is related to the avoidance of interspecific competition for food resources is unknown. In this study, abalone and sea urchins (Anthocidaris crassispina) with the same feeding habit were placed in the same experimental area, and the effects of food abundance on movement, feeding, spacing between individuals (cohesion), and group polarity (coordination) of H. discus hannai and A. crassispina were studied using infrared video monitoring. The cumulative distance moved, time moved, and cumulative feeding duration of abalone and sea urchins exhibited significant cosine rhythms regardless of food abundance under both monoculture and polyculture. With sufficient food available in polyculture, the cumulative distance moved and time moved by abalone and sea urchins were significantly higher than when food was insufficient. After polyculture with abalone, the cumulative feeding duration of sea urchins under the food insufficient condition was significantly lower than that in the sufficient food group. Under the food sufficient condition, the cohesion of abalone and sea urchins in polyculture did not differ significantly but the coordination of sea urchins was significantly higher compared to that of the insufficient food group. Once the food abundance decreased, the cohesion among individuals in the monoculture sea urchin group decreased; although the group coordination in the abalone group was the lowest at this time, the group coordination of abalone was significantly higher after polyculture with sea urchins. Comparison of the diurnal movement behavior characteristics of abalone and sea urchins revealed that these two species with similar ecological niches coexist through competitive interactions under the abundance and scarcity of food resources. These results provide new insights into how the nocturnal rhythmic behavior of marine organisms occurs, and they also provide important explanatory evidence for the formation and maintenance of marine benthic biodiversity.

Keywords

• Haliotis discus hannai
• Anthocidaris crassispina
• Food abundance
• Interspecific competition
• Behavioral rhythms