Abstract
Sea urchins and sea cucumbers are mutually beneficial organisms in kelp ecosystem. As herbivores, sea urchins process kelp through feeding and egestion, providing inaccessible food for benthic consumers such as sea cucumbers. Sea urchins in turn profit from the sediment cleaned by sea cucumbers. However, behavioral interactions between them remain poorly understood, which greatly hampers our understanding on the relationship between ecologically important benthic species in marine ecosystems and the regulating mechanism. The present study investigated behavioral interactions between sea urchins Strongylocentrotus intermedius and sea cucumbers Apostichopus japonicus in laboratory conditions. We revealed that the presence of sea urchins caused significant higher speed movement of A. japonicus. Interestingly, the negative effects of S. intermedius on A. japonicus were significantly reduced in the shared macroalgal area. For the first time, we found the interspecific responses to alarm cues between sea cucumbers and sea urchins. Conspecific responses were significantly larger than the interspecific responses in both sea urchins and sea cucumbers. This indicates that interspecific response to alarm cues is an efficient approach to anti-predation and coexistence in mutually beneficial organisms. The present study shed light on the interspecific relationships and coexistence between sea urchins and sea cucumbers in kelp ecosystem.
Highlights
Sea urchins and sea cucumbers are mutually beneficial organisms in kelp ecosystem
The main purposes of the present study are to investigate: (1) whether behavioral interactions exist between sea urchins and sea cucumbers; (2) whether macroalgae regulate the interactions between sea urchins and sea cucumbers; (3) whether sea cucumbers respond to the conspecific alarm cues; (4) whether there are interspecific responses to alarm cues between sea urchins and sea cucumbers
Behavioral interactions exist between sea urchins and sea cucumbers
Summary
Sea urchins and sea cucumbers are mutually beneficial organisms in kelp ecosystem. As herbivores, sea urchins process kelp through feeding and egestion, providing inaccessible food for benthic consumers such as sea cucumbers. Conspecific responses were significantly larger than the interspecific responses in both sea urchins and sea cucumbers This indicates that interspecific response to alarm cues is an efficient approach to anti-predation and coexistence in mutually beneficial organisms. The mutual benefits between sea urchins and sea cucumbers enhance the nutrient cycling in benthic communities and improve the productivity of kelp e cosystems[3,5]. Despites their mutually beneficial relationship in kelp ecosystems, the two species are not highly compatible. We hypothesized that interspecific alarm cues exist as mutual benefits between sea urchins and sea cucumbers, because of their coexistence and the exposure to similar predators in kelp ecosystem. The main purposes of the present study are to investigate: (1) whether behavioral interactions exist between sea urchins and sea cucumbers; (2) whether macroalgae regulate the interactions between sea urchins and sea cucumbers; (3) whether sea cucumbers respond to the conspecific alarm cues; (4) whether there are interspecific responses to alarm cues between sea urchins and sea cucumbers
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